A COMPARATIVE STUDY OF DIFFERENT PV TECHNOLOGIES FOR LARGE SCALE APPLICATIONS IN IRELAND

A COMPARATIVE STUDY OF DIFFERENT PV TECHNOLOGIES
FOR LARGE SCALE APPLICATIONS IN IRELAND
Department of Electrical Engineering Systems
COLLEGE OF ENGINEERING & BUILT ENVIRONMENT
Due Date: 7th
September 2012

MSc Energy Management 2012 Page i
Declaration
I hereby certify that the material, which is submitted in this assignment, is entirely my own
work and has not been submitted for any academic assessment other than as part fulfilment of
the assessment procedures for the program Master of Science in Energy Management (MSc)
(DT 711).
Signed............................................... Date................................................

MSc Energy Management 2012 Page ii
Acknowledgements
• I would firstly like to thank my supervisor Kevin O’ Farrell who provided all the recorded
data which made this study possible.
• I would also like to thank Dr Sarah Mc Cormack who provided me with measured data
from Dublin Airport which benefited my thesis greatly.
• I would also like to thank BNRG Renewables who offered to answer any questions I had
regarding the design and economics of PV systems as well as providing insights into the
operation of the large scale PV industry itself
• Finally I would like to thank anyone else that gave me assistance during the course of
this study.

MSc Energy Management 2012 Page iii
Abstract
The purpose of this study was to determine the potential for installing multi megawatt ground
mounted PV systems in Ireland. Firstly a study was conducted to determine the best performing
PV technology type for Irish Climate conditions which was found to be a Sanyo HIT module.
Using PV design software in conjunction with recorded data it was then determined a 1MW
large scale PV system would produce 1012MWh annually and generate electricity at a price of
31.5c/kWh. Based on these findings it was concluded that a substantial support mechanism
would need to be put in place in order to make large scale PV generation viable in Ireland.

MSc Energy Management 2012 Page iv
Table of Contents
Chapter 1- Introduction ......................................................................................... 1
1.1 Introduction to area of research ....................................................................................................1
1.2 Rational behind selected research topic.........................................................................................2
1.3 Aims ..............................................................................................................................................3
1.4 Objectives......................................................................................................................................3
1.5 Ethics.............................................................................................................................................3
Chapter 2 -Literature Review................................................................................. 4
2.1 PV technology types......................................................................................... 4
2.1.1 Crystalline Silicon PV (C-Si)..........................................................................................................4
2.1.2 Amorphous silicon (a-Si)..............................................................................................................6
2.1.2.1Benefits of using a-Si modules in Irish climate .......................................................................7
2.1.3 Triple junction a-Si ......................................................................................................................7
2.1.4 Cadmium Telluride PV technology (CdTe)....................................................................................8
2.1.4.1Recycling solution and cost of CdTe.......................................................................................9
2.1.4.2 Future of CdTe ...................................................................................................................10
2.2 Recorded module data................................................................................... 10
2.2.1 HIT PV module ..........................................................................................................................10
2.2.1.1 Temperature performance.................................................................................................11
2.2.1.2 Spectral response...............................................................................................................12
2.2.3 Kaneka a-Si module...................................................................................................................13
2.2.4 c-Si modules .............................................................................................................................13
2.3 Solar resource in Ireland ................................................................................ 14
2.3.1 The link between radiation and electrical power ...................................................................14
2.3.2 Calculating the solar resource in Ireland................................................................................15
2.3.4 Collection of data..................................................................................................................16
2.3.5 Comparison of data sources..................................................................................................17

MSc Energy Management 2012 Page v
2.3.6 Diffuse radiation ...................................................................................................................19
2.3.7Diffuse radiation estimation...................................................................................................20
2.4 Economic Viability.......................................................................................... 22
2.4.1 PV economic parameters ..........................................................................................................22
2.4.2 Government support for large scale PV generation in Ireland....................................................23
2.4.3 UK PV support mechanisms ......................................................................................................24
2.4.4 ROC’s system ........................................................................................................................25
2.5 Design consideration for large scale PV.......................................................... 26
2.5.1 Inverter design......................................................................................................................26
2.5.2 Reactive power and voltage stability .....................................................................................27
2.3.3 MPPT ....................................................................................................................................28
2.5.4 Harmonic Content at inverter output ....................................................................................29
2.5.5 Inverter Layout in large scale plant............................................................................................30
2.5.6 Centralized inverter layout........................................................................................................31
2.5.7 Sting inverter layout..................................................................................................................32
2.2.8 Single phase inverter layout ..................................................................................................33
2.5.8 Three phase inverter approach .............................................................................................34
3.5.9 PV blocks within large scale layout............................................................................................35
3.5.10 Wiring losses and cost.............................................................................................................36
Chapter 3- Methodology...................................................................................... 39
3.1 Solar Resource assessment............................................................................ 39
3.2 Software used to model performance ........................................................... 40
3.2.1 PVSYST..................................................................................................................................40
3.2.2 Validation of PVSYST model ......................................................................................................40
3.2.3 PVSYST 3-D shading tool........................................................................................................41
3.2.4 Climate data base used for PVSYST study ..............................................................................41
3.3 Models used in Comparative study................................................................ 42
3.3.1 Recorded DIT data ....................................................................................................................42
3.3.2 PVSYST Comparative model ......................................................................................................43
3.3.3 Large scale system performance ...............................................................................................43

MSc Energy Management 2012 Page vi
3.4 Economic methodology ................................................................................. 43
Chapter 4-Results................................................................................................. 44
4.1 Initial assumptions within the PVSYST model ...............................................................................44
4.2 PVSYST 1kWP comparative study..................................................................................................46
4.2.1 Sanyo modeled performance ................................................................................................48
4.2.2Kaneka modeled performance ...............................................................................................49
4.2.4 Sharp modeled performance.................................................................................................50
4.2.5 Sunpower modeled performance..........................................................................................51
4.2.6 Sunteck modeled performance ............................................................................................52
4.3 PVSYST results for 1KW system....................................................................................................53
4.3.1 Irradiance loss.......................................................................................................................54
4.4 Recorded data results .................................................................................... 56
4.5 Economic consideration................................................................................. 57
4.5.1 Retail price comparison.............................................................................................................58
4.6 Large scale system PVSYST model.................................................................. 60
4.6.1 String shading diagram..............................................................................................................62
4.6.2 Wiring size calculation ..............................................................................................................63
4.6.3 System performance.................................................................................................................64
4.6.4 Economic calculation ................................................................................................................65
Chapter 5 Conclusions ......................................................................................... 69
5.1Further research...........................................................................................................................70
References........................................................................................................... 70
6.1 Standards ....................................................................................................................................78
Appendix A ............................................................................................................ A
Kaneka PVsyst data..........................................................................................................................A
Appendix B............................................................................................................. B
Sanyo PVsyst data............................................................................................................................B
Appendix C............................................................................................................. C
Sunpower PVsyst data .....................................................................................................................C

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Appendix D ............................................................................................................D
Sunteck PVsyst data.........................................................................................................................D
Appendix E............................................................................................................. E
Sharp PVsyst data............................................................................................................................E
Appendix E..............................................................................................................F
PVsyst W/m2
VS irradiance .............................................................................................................. F
Appendix F.............................................................................................................H
PVsyst efficiency VS irradiance........................................................................................................ H
Appendix G ............................................................................................................. J
A-Si triple data..................................................................................................................................J
Appendix H ............................................................................................................ K
Recorded data .................................................................................................................................K

MSc Energy Management 2012 Page viii
Table of figures
Table 1 Module manufacture data ............................................................................................... 13
Table 2: Reference prices for renewable generators ................................................................... 23
Table 3 Sanyo results .................................................................................................................... 48
Table 4 Kaneka modelled results.................................................................................................. 49
Table 5: Sharp modelled results ................................................................................................... 50
Table 6 Sunpower modelled results ............................................................................................. 51
Table 7: Sunteck modelled results................................................................................................ 52
Table 8: Module comparison table............................................................................................... 53
Table 9: Results from DIT recorded data...................................................................................... 56
Table 10: Retail price comparison between technologies, 2012) ................................................ 59
Table 11: Voltage drop calculations for large scale system.......................................................... 64
Table 12: Total cost of 1MW plant. .............................................................................................. 66
Table 13: NPV analysis of large scale system................................................................................ 68

MSc Energy Management 2012 Page 1
Chapter 1- Introduction
This chapter will introduce the main area of research for this project and the relevance of the
research question chosen. Firstly a brief overview of the political and economic factors which
have contributed to the growth of PV generation in recent years will be given. The potential for
installing large scale ground mounted PV systems in Ireland as a means of reaching our
renewable generation goals will then be discussed.
1.1 Introduction to area of research
In recent years the use of renewable technologies such as wind and solar PV has grown
dramatically in line with European and global directives to reduce CO2 production. The 20 20 20
targets are one such initiative which aims to cut emissions by 20%, increase efficiency by 20%
and increase the use of renewable by 20% by 2020 (European Environment Agency 2010). As a
result of these targets many countries have been expanding the use of PV for large grid
connected systems in order to reduce C02 production. Germany is an excellent example of how
a country with a somewhat limited PV resource can produce large amounts of PV electricity
through introducing a structured feed in tariff for ground mounted PV systems (Suri et al,
2007).Germanys current installed capacity has now reached 25gigawatts (clean technica, 2012)
.As a result of the success of the German system similar policies have also been introduced in
other countries such as Spain, Italy Greece, Czech Republic and the UK (Marcel Suri et al, 2007).
Despite major growth in large scale PV generation in the UK with 366MW of PV capacity
registered with the DECC since they initiated a structured PV tariff in 2010 Ireland have yet to
recognize the potential of PV especially for large scale ground mounted systems and PV
generation as a whole is not included in any of the 3 REFIT schemes currently used by the
Department of Communications, Energy & Natural Resources to support new renewable
installations (EPIA 2012).
In spite of significant differences in government policy towards PV generation in the UK and
Ireland in terms of energy resource both locations offer similar potential with Ireland receiving
between 910-1100kWh/m2
as reported in (Dykes, 2011) and the UK receiving an average of

950kWh/m2
as seen in figure 1 (Sullivan, 2012). This result indicates that if Ireland’s policy
towards PV changes at government level PV generation could potentially become a significant
player in Ireland renewable generation portfolio.
Figure 1: UK and Ireland average radiation (Sullivan 2012)
1.2 Rational behind selected research topic
At present very little data is available regarding the potential of installing large scale multi
megawatt PV systems in Ireland. As described in (SEAI , 2012) natural gas currently accounts for
61% of all fuel used in electricity generation in Ireland, this dependency on foreign imports
reduces Irelands security of supply and also means that electricity prices are highly influenced
by price volatility in the gas market (SEAI , 2012) . As large scale PV generation could potentially
increase Ireland’s security of supply and help achieve our target of 40% renewable generation
by 2020 a detailed studied of the potential of this technology in terms of cost and performance
is required.

1.3 Aims
• The first aim of this study is to determine the performance of thin film and c-Si modules
under Irish Climate conditions.
• The second aim consists of determining which module type is best suited for use in large
scale ground mounted PV systems in Ireland in terms of both performance and cost.
• The 3rd
aim is to estimate the performance of a large scale PV system in Ireland.
• The final aim is to determine the economic viability of large scale PV in Ireland and
determine the magnitude of support mechanism needed to make the system viable if a
subsidy is required.
1.4 Objectives
• The first objective is to establish the level of solar resource in Ireland by analyzing a
combination of both ground measured data and satellite data.
• To establish which PV module type performs best under Irish climate conditions using
both recorded data from modules installed in DIT and modelled data from the PVsyst
software package (PVsyst, 2012).
• To study the performance of a large scale PV system by designing a 1MW theoretical
system in PVsyst.
• To determine the price of electricity (COE) the system would produce and the profit or
loss it would make over its lifetime by performing a Net Present Value (NPV) analysis.
1.5 Ethics
Good ethical behaviour was maintained throughout the completion of this study. All
paraphrased material was referenced using the Harvard referencing system, all recorded and
estimated data was obtained from reliable sources and this data was referenced accordingly.
All calculations were carried out using original data and the collected data was not modified in
order to present misleading results. Finally data was collected from as many sources as possible
to insure the information and results reported were not biased towards a particular outcome.

Chapter 2 -Literature Review
This chapter covers both the technical and economic consideration which must be made when designing
a large scale system. The chapter consists of 5 main topics which are outlined below.
• Overview of thin film and Crystalline PV.
• Overview of each of the 5 modules which were analyzed in this study.
• Solar resource in Ireland.
• Grid requirements and design of a large scale PV plant.
• Economics of large scale PV generation.
2.1 PV technology types
2.1.1 Crystalline Silicon PV (C-Si)
At present the dominant player in large scale PV generation has been Crystalline Silicon PV
which can be found in 2 main forms of technology. Mono-Crystalline PV cells are produced
when thin silicon wafers with a thickness of up to 200 microns are cut from a single crystal
ingot. Multi-Crystalline PV cells are produced when a large block of silicon is first cut into blocks
and then individual wafers are cut out. Although mono crystalline offers slightly more efficient
results in terms of electricity production the industry as a whole has seen a slight divergence
away from mono-crystalline because the manufacturing processes involved in mono crystalline
PV production are more complex and therefore more expensive. The breakdown of PV
generation as a whole can be seen in figure 2 where it can be seen that thin film PV only holds a
small percentage of overall market share (Willeke et al, 2008).

Figure 2: Market share of c-Si and thin film (Willeke et al, 2008).
Crystalline PV is often viewed as a mature technology as this industry has been developed
extensively over the last 30 years however recent reports have suggested that the technology is
still maturing which is highlighted by the fact that the payback period for multi-crystalline PV
has been dropping significantly since 2005 through major advancements in the manufacturing
processes involved in producing PV cells, these processes range from using thinner sawing wire
and producing thinner wafers which still operate at high efficiencies of around 18%.One of the
most important advancements was reported by the REC (Renewable Energy Convention) in
2005 where they suggested that switching from the costly manufacturing processes established
by Siemens to using fluidized bed reactors to produce high quality crystalline PV material could
dramatically decrease costs (Saurer, 2008). One report by the REC estimates potential savings

of 60% and the energy payback period for crystalline PV modules to drop from 2 to 1 year as
seen in Fig 4 (Saurer, 2008), (Moro, 2010).
Figure 3: Energy Payback Period with advancements in production (Saurer, 2008).
2.1.2 Amorphous silicon (a-Si)
Amorphous silicon has been investigated as a PV material since the 1970s and differs from
crystalline silicon in that some of the atoms within the material remain unbounded (Sturm, J.C
2011). The main advantage of this technology is that it requires a very small quantity of active
material when compared to other mono and multi crystalline silicon PV cells. This means the
cost of manufacturing these panels is not directly related to the cost of silicon as in crystalline
PV which reduces the overall cost of this material greatly. It has been estimated that with
current manufacturing processes the cost for these cells can be as little as 1€/WP with further
improvements obtainable if more efficient manufacturing processes are established. For large
scale use and durability issues the thin film PV array is mounted between glass panels (Doni,
2010). In terms of efficiency these types of cells still cannot compete with crystalline PV cells
which means for large scale developments a larger area is required to produce the same power

output as crystalline panels. The typical efficiency for an amorphous silicon panel is 7% (Sturm,
J.C, 2011).
2.1.2.1Benefits of using a-Si modules in Irish climate
One of the main advantages of a-Si modules in an Irish climate is the performance of these cells
under cloudy conditions and low irradiance levels. In (Jansen, 2006) it was estimated that for
UK climate conditions a-Si modules would see a 15-20% energy cost advantage over c-Si grid
connected systems. This result was again reinforced in (Krauter & Preiss, 2011) where the
energy yield of a-Si modules was found to be 2% higher than c-Si modules for Berlin local
conditions for the year of 2009.
2.1.3 Triple junction a-Si
Although single junction a-Si modules suffer from poor efficiency compared with c-Si modules
significant improvements in terms of performance can be achieved depositing a number of
layers of a a-Si material on top of each other to form double and triple junction devices. The
main benefit from this type of configuration is that each a-Si layer can extract energy from a
different portion of the electromagnetic spectrum increasing the ability of the module in terms
of radiation capture. An example of a typical a-Si triple junction cell is shown in figure 4, the
first section in the system is a-Si material with a band gap of approximately 1.8eV which is ideal
for extracting low wavelength blue light. The second section consists of an a-SiGe alloy made up
of approximately 85% a-Si and 15% Germanium which has a band gap of approximately 1.6eV
making it suitable for absorbing photons from the green spectrum. Finally the last layer also
consists of a-SiGe however in this case the Ge material makes up 50% of the material which
gives a band gap of 1.4eV allowing absorption of red light. The introduction of the oxide coating
on the bottom of the module also means that photons that are not absorbed as they initially
pass through the module are reflected back up through each layer which allows for additional
power output (SolarFocus, 2005). It was reported in (Wang, 2002) that an efficiency of 12.71%
was obtained using an a-Si triple junction module arrangement.

Figure 4: Triple junction module layout (SolarFocus, 2005)
2.1.4 Cadmium Telluride PV technology (CdTe)
Cadmium Telluride thin film panels have developed significantly in recent years and have
greater efficiency in terms of solar to electricity generation than A-SI PV panels and also cost
less to produce than typical silicon cells. Cadmium Telluride cells also provide a longer
operating life than A-Si cells and from a power production standpoint It can also be noted that
CdTe cells also handle cell temperature variations better than standard crystalline cells (Doni,
2010) . It has been reported that for crystalline PV panels if the cell temperature goes beyond
250
/C there can be a significant drop in DC output power from the unit (Suri et al,
2007).Although this technology has many advantages over a-SI thin film it must also be noted
that Cadmium is a toxic element and therefore additional costs such as the disposal of the
material itself must also be considered when estimating the cost savings from switching from
silicon based PV to CdTe cells. Another issue that must also be considered is the availability of
Tellurium which is limited and therefore could prevent this type of technology from having a
significant impact on large scale PV electricity production. Many study’s have been carried out
to establish the cost of disposal and whether recycling the PV units could offer an economically
viable solution in dealing with PV cells which have reached the end of their operating life. In
terms of disposal it was determined that the cost was highly dependent on state and local

regulations on what is considered a “hazardous material”. Based on the Resource Conservation
and Recovery Act (RCRA) and the Hazardous Waste Control Law (HWCL) which are the two
main acts which control the recovery of waste in the United States it was found that most CdTe
PV panels exceeded the allowable limits of cadmium which means end of life disposal could be
extremely costly (Eberspacher et al, 2008).
2.1.4.1Recycling solution and cost of CdTe
As a result the recycling of these CdTe modules could offer an economical viable alternative to
direct disposal. The recycling process for CdTe cells at present is based on using chemical
compounds to separate the CdTe and Cds semiconductor films from the surrounding glass and
metal back plate in a process known as etching. The individual sections of the PV module can be
seen in figure 5 (Bohland et al., 1997).
Figure 5: CdTe module layers (Bohland et al., 1997)
Based on information from a pilot recycling plant set up by US Company Solar Cells Inc. it was
found that this method of recycling produces 4 usable materials which include saleable glass,
Cadmium carbonate, tellurium and ethylene-vinyl acetate at a cost of just 0.04$/watt. In
comparison the cost of disposal was estimated between $0.2/watt and $0.4/watt (Bohland et al
1997). Another advantage of recycling is that the process itself is not hugely energy intensive
and produces no hazardous byproducts as a result it was also suggested in this report that the
PV plant and recycling plant could be co-located reducing costs even further.

2.1.4.2 Future of CdTe
In order to determine if the CdTe PV is likely to become a major contributor in PV markets
Professor Stuart Irvine who is the chairman of the Director Centre for Solar Energy Research at
OpTIC Technium , Glyndwr University was contacted directly. He concluded that the market
share of CdTe has actually declined in the last 2 years due to continued expansion of c-SI
technologies however the annual output of CdTe has also continued to increase (Irvine, 2012).
“The annual output of CdTe PV modules has continued to grow year on year but the proportion
of the total market has declined over the past two years because of the very rapid growth in
crystalline silicon PV module production. The PV market remains very competitive with over
supply and is volatile but predicted trends are for expansion over all product types. Price
competition is fierce and will remain the key driver”
2.2 Recorded module data
Recorded time series data for a number of modules currently installed in DIT and was used to
analysis the performance of both thin film and crystalline modules under Irish Climate
conditions. The data corresponded to radiation data from a Kipp and Zonen CM6B pyrometer
and corresponding current and voltage readings from a datalogger located in the DIT Focus
building (McGlynn, 2010). The technical details of each module currently installed in DIT are
discussed below.
2.2.1 HIT PV module
The first module which will be examined in this report is the Sanyo HIP-215NHE5 module which
has a maximum power output of 215WP based on testing at standard testing conditions (STC).
In terms of structure the panel itself contains a very thin a-Si intrinsic layer inserted between
p+- type or n+- type a-Si and n-type c-Si . This structure has been made possible by using low
temperature plasma processes to grow extremely high quality a-Si large area thin films and
solar cells (Taguchi, et al, 2005). One of the most beneficial features of this design is the
mitigation of surface defects in the in the c-SI material by the introduction of the a-SI material

which results in improved overall efficiency and significantly a high VOC which is important for
improving the efficiency for large grid connected systems (Taguchi, et al, 2005).
Figure 6: HIT PV cell (Maruyama, et al., 2006)
From the cell layout above it can be seen that the front a-SI layer is p-type a-SI and back layer n
type material. A transparent conductive oxide coating is also placed on top of both doped layers
which act as an anti reflective coating. The finger structure for the electrodes also insures that
that all solar cells within the module are symmetrical resulting in reduced thermal and
mechanical stresses (Taguchi, et al., 2005)
2.2.1.1 Temperature performance
As mentioned before the HIT design allows for a higher VOC than standard c-SI modules due to
the mitigation of defects in the c-Si layer. This result also has the added benefit of improving
the temperature coefficient of the module as VOC and temperature performance are related.
This means that the HIT cells can operate more efficiently at higher cell temperatures than
typical c-SI modules. It has been found that with a VOC of 680mv a temperature coefficient of –
0.33 %/ºC can be achieved while it was also documented that –0.25 %/ºC was obtainable by
changing the deposition conditions on both sides of the a-Si silicon wafers with clean surfaces
before they were deposited onto the c-Si substrate (Maruyama, et al., 2006), (Taguchi, et al.,
2005).

Figure 7: Improvement of temperature performance with new process (Maruyama, et al., 2006).
2.2.1.2 Spectral response
HIT modules also can be more effective than typical c-Si modules due to the ability of the a-Si
layer to capture energy of from shorter wavelengths as shown in figure 8. For the most part
these wavelengths correspond to diffuse radiation which has been scattered by clouds or
aerosols in the atmosphere and are in the range of 400-500nm. This means the HIT panels
could offer improved energy yield in climates where a large proportion of the global irradiation
is comprised of diffuse radiation such as in Ireland (Krauter & Preiss, 2011).
Figure 8: Spectral performance of different types of modules (Krauter & Preiss, 2011).

2.2.3 Kaneka a-Si module
The 2nd
module which will be used for calculations in this study is the Kaneka G-A060 which has
an STC power rating of 60W. Interestingly the Kaneka module has a VOC value of 91 volts which
is 40 volts more than the Sanyo HIT module and 70 volts greater than any of the c-SI modules
studied in this project. Many reports such as (Taguchi et al., 2005) have shown a good
correlation between high VOC and low power temperature coefficients which is also
demonstrated in this case with a power temperature coefficient value of just -0.26%/°C making
this module also suitable to high temperature conditions.
2.2.4 c-Si modules
In conjunction with the a-Si module and HIT modules located in DIT the I-V characteristics for 3
c-Si based modules currently installed in the college were also available and allow for detailed
comparison of both c-Si and a-Si technology’s. The c-Si modules installed consist of a Sharp
NE80E2E polycrystalline 80WP module specifically designed for large scale applications, a
Sunpower SPR-90 mono crystalline 90WP module and finally a Sunteck STP080B12/BEA mono
crystalline module with an 80WP power rating. The manufacturer data for all 5 panels was
collected and can be seen in full in table 1 below.
Manufacturer Model
VMP
(Volts)
IMP
(Amps)
PMAX Temp. Coefficient of
Power
Efficiency
(%)(Watts)
Kaneka G-EA060 67 0.9 60 -0.26%/°C 6.3
Sharp NE-80E2E 17.1 4.67 80 - 0.485%/°C 12.6
Sunpower SPR-90 17.7 5.1 90 -0.38%/°C 16.5
Suntech
STP080B12/
BEA 17.5 4.58 80 -0.48 %/°C 12.4
Sanyo
HIP-
215NKHE5 42 5.13 215 -0.3%/°C 17.2
Table 1 Module manufacture data (McGlynn, 2010)

2.3 Solar resource in Ireland
2.3.1 The link between radiation and electrical power
The feasibility of a large scale PV system is largely dependent on the solar resource available at
the location the system is being installed. As described in (Fontana, 2012) solar irradiation is
essentially the fuel of a PV plant that allows the creation of DC current flow when it falls on a
semiconductor material that exhibits the photoelectric effect. This effect can be described as
the absorption of energy contained within the incident light by electrons within the metal itself,
when an electron receives a photon of light energy greater than the band gap energy which for
silicon is approximately 1.1eV electron hole pairs can be formed which results in the generation
of DC current (Würfel, 2009). The band gap of a material affects what portion of the
electromagnetic spectrum a PV cell absorbs which makes it a significant factor in calculation of
a PV modules possible efficiency. The link between band gap energy and efficiency was defined
fully in (Shockley& Queisser, 1961) where it was determined that the max obtainable efficiency for SI
cells was 33.7%. Figure 9 shows the band gap and corresponding efficiency’s for a number of materials
currently used in the PV industry.
Figure 9: Band gap VS efficiency (Peter,L.M, 2011)

The amount of energy available in each photon of light was also defined in Einstein’s equation
shown below where the energy in each photon is proportional to the frequency of the light
multiplied by Planks constant of 6.626×10-34
J/s. This in turn can be related to the wavelength of
the light source by describing the frequency as a function of the wavelength as seen in equation
1 and 2 (PhysicLAB, 2002).
ࡱ = ࢎࢌ Equation 1
ࢌ =
࡯
ࣅ
Equation 2
2.3.2 Calculating the solar resource in Ireland
As large scale PV projects require a significant long term financing sourced from both debt and
equity the initial resource assessment must be carried out using reliable data in order to insure
that the system operates successfully both from an economic and design point of view. A
methodology for carrying out an initial yield assessment was described in (FRV, 2012) where it
was suggested that the most optimal solution was the use on site data in conjunction with
other solar data basis. The structure of a typical solar resource assessment can be seen in figure
10 (FRV, 2012).

Figure 10: Resource estimation structure (FRV, 2012)
2.3.4 Collection of data
For this project 5 different sources were used to estimate the solar resource in the Dublin area.
3 software packages were used including Climate-SAF PVGIS which uses satellite images over a
period of 12 years to estimate results, PVGIS Classic which interpolates long term ground based
measurements taken from the closest weather stations to the requested location and
Meteonorm which also uses interpolated ground based measurements to estimate resource
(Meteonorm,2012),(PVGIS, 2012). Additional ground based hourly measurements from Dublin
Airport weather station from the years of 1977-2006 were supplied by Dr Sarah Mc Cormack
from the Dept of Civil, Structural and Environmental Engineering in Trinity College (Mc
Cormack, 2012). Data from the Focus building in DIT was also measured and analyzed in a
previous project using a Sunny SensorBox that measured global radiation on a horizontal plane
and provided the final data base for resource estimation (Duarte, 2011).

As the data from all software packages and Focus Building data was presented in kWh/m2
/day it
was necessary to convert the hourly met Eireann data from j/cm2
to kWh/m2
/day. This was
achieved by first converting cm2
to m2
and then converting joules to watts using the principle
that 1 watt is equal to 1 joule/second. The data was then analyzed using Excel and graphed as
seen below.
2.3.5 Comparison of data sources
Figure 11: Resource estimation results kWh/m2
/day
It can be seen that there is strong correlation between all data used to estimate resource
however it can be noted the all software programmes over estimate solar resource slightly in
the months of May, June, July and August. The data used from the focus building indicates that
0
1
2
3
4
5
6
Nov Dec Feb Apr May Jul Aug Oct Dec Jan
PVGIS-SAF
PVGIS-CLASSIC
Meteonorm
Met Eireann
Focus Building(Duarte, 2011)
Sommerset
KWh/m2/day
Time (months)

June has the highest energy resource on average with a value of 5.1kWh/m2
/day being
observed. All other software packages estimate June to provide the highest resource with
values ranging from 4.7kWh/m2
/day to 5.1kWh/m2
/day. Interesting the results from the Met
Eireann data indicate that May has the highest resource with an average value of
4.5kWh/m2
/day observed. Overall the results from all 3 software packages used correlate well
with what was observed in the Focus building and Met Eireann data with PVGIS Classic and
Meteonorm providing the best fit to this data. The results from the satellite based programme
PVGIS-SAF also correlate with what was seen at the Focus building and Met Eireann data
however estimate the solar radiation to be 2% higher than all other data sources on an annual
basis. The solar resource for a location corresponding to Sommerset in the UK was also
estimated using PVGIS. This specific location was chosen because BNRG renewable have
recently constructed a 2MW PV plant at this site and therefore by comparing resources
between this location and Ireland the potential for large scale PV in Ireland can be examined
(BNRG, 2012). As can be seen in figure 11 the solar resource in both locations are evenly
matched with the highest radiation level experienced in Sommerset only 0.44kWh/m2
/day
greater than the corresponding level of radiation in Dublin.
One of the most significant issues identified in figure 11 is the seasonal variations in solar
resource in Ireland where there is 4.4kWh/m2
/day difference in radiation levels between June
and December if the data from Meteonorm was used. This seasonal variation can be attributed
to the fact that the earth’s axis of rotation is tilted approximately 23.5o
compared to the plane
in which the sun is located. This causes the suns relative height above the horizon to change as
the earth orbits the sun. The relative sun heights for each month for a latitude of 53.1o
North
corresponding to Dublin were modelled using PVsyst in order to show this variation graphically.
It can be seen from the results that the highest sun height annually is 63.5 which occurs at the
June solstice on the 22nd
June and the lowest height of just 16.50
occurs on the December
solstice on the 22 December. This graph also shows the significant variation in available sun
hours between summer and winter months.

Figure 12: PVsyst modelled sun paths (PVsyst 2012)
This variation is an important factor to be considered when designing grid connected plants
over 2MW connected to the sub-transmission or transmission network as the ability of the
plant to offer operational security, stability and power quality to the whole grid network is of
key importance (Marinopoulos et al, 2011).
2.3.6 Diffuse radiation
Another important point to consider when estimating the solar resource for a location is the
ratio of diffuse to global radiation. Diffuse radiation can be described as the scattering of direct
beam radiation by molecules and particles in the atmosphere. There are 2 key processes which
cause this effect. Rayleigh scattering can be described as the scattering of light by air molecules
such as oxygen and nitrogen which are more effective at scattering shorter wavelengths in the
region of 400nm. Mie scattering relates to the scattering of light by cloud droplets with a
diameter of approximately 20 micrometers (PVEducation, 2012).

Figure 13: Diffuse radiation diagram (Lorenzo, 2005)
2.3.7Diffuse radiation estimation
In order to estimate the percentage of diffuse radiation under Dublin climate conditions PVGIS-
SAF, PVGIS Classic, Meteonorm and Met Eireann data from Dublin Airport were again the main
sources of data used. Importantly all models used consisted of 10 or more years of climate data
which allowed direct comparison between each model. The data was then formatted in order
to calculate the average ratio of global to diffuse radiation for each month. Interestingly all
software packages estimated the diffuse component to be at least 6.5% more then what was
seen in the Met Eireann data on an annual basis. Overall PVGIS-SAF offers the best fit to the
monthly trend found in the Met Eireann data. The Meteonorm model provides the least
accurate results especially during the months of June and December where it over estimates
what was observed in the Met Eireann data substantially. This being said all models calculate
the average diffuse component to be between 55-62% which correlates well with what was
reported in other reports (SEAI(b), 2012).

Figure 14: Diffuse VS global radiation calculation
These results are a clear indicator that when considering PV technology for an Irish climate the
selected system must be able to extract energy from low irradiance penetration with a high
diffuse component. This information in conjunction with the studies carried out in (Krauter &
Preiss, 2011) and (Jansen, 2006) mean that a-SI modules and HIT modules could offer
advantages in terms of energy yield over c-SI modules especially in months where the ratio of
diffuse to global irradiance is high.
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
Nov Dec Feb Apr May Jul Aug Oct Dec Jan
pvgis saf
pvgis classic
meteonorm
met eireann
Time(Months)
ratioofDiffuse/GlobalIradiation

2.4 Economic Viability
2.4.1 PV economic parameters
One of the most significant factors in determining the economic viability of any PV plant is the
cost at which electricity can be produced as this will determine if the technology can compete
with other renewable and non renewable generators in the electricity market. One approach to
estimating the price of electricity was identified in (Conlon, 2012) where the price of generated
electricity was defined as being dependent on 4 variables. These 4 parameters include CO&M
which is the annual expenditure on operation and maintenance, the FCR which is the fixed
charge rate and reflects interest rates, Ea which is the annual electricity production in kWh and
finally the total capital cost which is described by Cc. Equation 3 shows how these parameters
can be used to find the price of electricity in terms of €/kWh.
࡯ࡻࡱ࢑ࢃࢎ =
ሺࡲ࡯ࡾ×࡯࡯ሻା۹‫ࡹ&۽‬
ࡱࢇ
Equation 3
Another important factor which plays a role in weather a project is invested in or not is a
payback analysis which estimated the potential return on invested capital. In order to achieve
this a Net Present Value calculation must be carried out which can be described by a
summation of all present values of future income and expenditure. Equation 6 shows how the
present value of future income can be calculated where A is the annual revenue, r is the
discount rate and n is the project life time in years (Mukund R. Patel, 2010). The Net Present
Value (NPV) of the system can then be calculated by subtracting the initial capital investment
away from the present value of all future incomes, a positive NPV describes an overall profit on
initial investment however a negative NPV suggests that the system will make a loss on initial
investment.
ࢂ࢖ =
࡭
࢘
ሾሺ૚ − ሺ૚ + ࢘ሻି࢔ሿ Equation 4

2.4.2 Government support for large scale PV generation in Ireland
In order to find out if there are any support mechanisms in place for large scale PV generation
at government level the Department of Communications, Energy and Natural Resources was
contacted directly. This led to contact with Gerald McTiernan who works in the Renewable and
Sustainable Energy Division of the Department and who gave a detailed account of the current
REFIT tariff for renewable installations in Ireland.
The current Irish REFIT scheme works on the basis of a reference price system. Each renewable
system supported by the scheme is set a certain reference price which they are guaranteed to
receive for their energy regardless of what is happing in the whole sale market price. This
allows renewable generators to operate with reduced financial risk. Additionally a balancing
payment of up to €9.90/MWh may be paid to the supplier for exporting the energy to the grid.
This balancing payment is only made to the supplier if certain conditions are met, the full
€9.90/MWh is made if the market price is less than or equal to the reference price for the given
technology, if the wholesale price is greater than the reference price and the balancing
payment combined then no balancing payment is awarded, the final scenario occurs when the
market price is greater than the reference price but is less than the sum of the reference price
and balancing payment, in this case a portion of the €9.90/MWh payment is made which
reflects the payment needed to insure that the renewable generator receives a total payment
equal to the sum of the reference price and €9.90/MWh balancing payment (DCENR, 2012). The
reference prices for each renewable technology can be seen in table 2.
Table 2: Reference prices for renewable generators (DCENR, 2012)

It was identified that PV generation is not included in any of the 3 REFIT schemes currently in
use under Irish legislation and therefore would not have a chance to compete with other
renewable energy technologies including hydro wind and biomass for government support. The
main support mechanisms for PV systems in Ireland have been in the microgeneration sector
with ESB being the first company to introduce a tariff at 10c/kWh which was approved by the
CER. Interestingly although all other suppliers were authorised to introduce their own tariff
systems by the CER when the ESB first introduced this scheme and as of the 4th
of April 2011
are eligible to introduce new tariffs Electric Ireland are still the only company to avail of this
opportunity. Other support mechanisms have also been implied at government level for
microgeneration PV including the Accelerated Capital Allowance scheme (ACA) which is aimed
at improving energy efficiency in company’s and allows organisations to claim 100% of the
initial capital cost of installing energy efficient technologies back from corporation tax and
which was passed through the Finance Act 2008 (McTiernan, 2012).
From the above information it is clear that large scale PV generation has not been considered
as an economically viable solution to meeting Irelands future renewable generation deadlines.
The attitude towards large scale pv generation in the UK has been much different to the
approach taken in Ireland and will be discussed in the next section.
2.4.3 UK PV support mechanisms
The UK government has implemented a structured PV tariff where installations are segmented
into groups by nature of their size. The scheme was first implemented on the 1st
of April 2010
with installations between 500kw-5MW receiving a tariff of 30.7p/kWh (Ernst & Young 2011).
This scheme saw massive growth in PV installations with 366MW of PV capacity registered with
this scheme as of November 2011 resulting in the creation of an estimated 2,500 jobs within
the sector in 2010. Although the Department of Energy and Climate Change (DECC) decided to
reduce PV tariffs significantly in 2012 to just 8.5 p/KWh for installations in the 500Kw-5MW
range it still remains clear that PV generation will become a major part of the UK’s energy

portfolio with the climate change minister stating in 2011 that the original target of 2.7GW of
PV capacity by 2020 would now be increased to a new target of 22GW (EPIA 2012).
Figure 15: Growth in UK PV installed capacity (Ares,E, 2012)
2.4.4 ROC’s system
There is also a second option in place in order for PV generators to receive support in the UK,
the Renewable Obligation scheme was initially introduced in 2002 and puts an obligation on
suppliers to source a specified amount of electricity from renewable sources annually. As of
2011 each supplier must source 9.4% of electricity from renewable sources. The scheme is over
seen by Ofgem who issue renewable generators certificates on the basis of how much
renewable energy they generate. The current rate for PV generation is 2 ROC’s/MWh.
Generators can then sale these certificates to suppliers who in turn can use them to meet there
renewable obligation which mean the renewable generator receives both the wholesale price
for their electricity and an additional revenue from the sale of ROC’s (DECC, 2012). As the
current FIT does not fund projects over 5MW and has also been reduced to 8.5p/kWh for
systems over 500Kw ROC’s have become an attractive option to developers of large scale PV

plants in the UK with Lark energy announcing in June 2012 that they are currently designing a
30MW PV park which would be the biggest installation in the UK to date (Becky Beetz, 2012).
2.5 Design consideration for large scale PV
2.5.1 Inverter design
One of the most important components in a grid connected PV system is the inverter which is
used to convert the DC electricity produced by the panels into AC electricity which can be
utilized by the grid network. Grid tied inverters automatically synchronize the phase of the PV
system and grid, the frequency of the system with the frequency of the grid which in Ireland is
50hz and also insure the generated voltage from the system is the same as the voltage at the
designated connection point. A typical layout for PV grid tied inverter is shown in figure 15
which includes a disconnection switch on both the AC and DC side of the plant (NREL, 2010).
Figure 16: Typical DC/AC PV inverter (NREL, 2010)
In conjunction with meeting voltage, frequency and phase requirements large scale systems
connected to the medium voltage grid network may also be required to provide additional
services to insure network stability. These services may include the ability to remain connected
to the grid during low voltage levels or in the event of a fault and supply active power directly
after the fault in order to stabilize the system which is known as Low Voltage Ride Capability
(LVRC). In terms of large scale PV systems connected to the medium voltage and distribution
level the ability to supply reactive power to support voltage stability is becoming a key talking

point with countries such as France and Germany issuing strict requirements for reactive power
provision from large scale PV in 2008 and 2009 respectively (SMA, 2009).
2.5.2 Reactive power and voltage stability
In order to understand the importance of reactive power to grid stability the concept of
reactive power must be explained. In an electrical system when the voltage and current are out
of phase there are 2 components that make up the total apparent power(VA) in a system, the
first component consists of active or real power which is measured in watts and the second
component consists of reactive power which is measured in VARs. Although reactive power
does not provide energy it is vital to the operation of many loads that need to establish
magnetic fields in order to operate such as induction motors. Transformers and transmission
lines also produce inductance which opposes the flow of current and therefore to counteract
this reactive power is needed to maintain voltage levels and deliver active power. If the reactive
component isn’t large enough voltage sag and in extreme cases voltage collapse can occur due
to inability to supply loads with sufficient active power (Andersson et al 2005). Reactive power
can be explained graphically as shown in figure 17 where the angle ∅ corresponds to the
relative angle between the voltage and current. Changing this angle effectively changes the
ratio between active (W) and apparent power (VA) known as the power factor (PF) which
controls how much reactive power is being supplied to the grid as seen in figure 17 and
described in equation 5 (SMA, 2009). At present the majority of inverters do not have the
ability to change PF to suit grid requirements however some inverters including the SMA Sunny
Tripower 3 phase inverter have the ability to either supply or consume reactive power by
operating with a PF in the range of 0.8leading to 0.8lagging (SMA, 2009).
ࡼࡲ = ‫ܛܗ܋‬ሺ∅ሻ =
‫ܚ܍ܟܗܘ ܍ܞܑܜ܋ۯ‬ሺ‫܅‬ሻ
‫ܚ܍ܟܗܘ ܜܖ܍ܚ܉ܘܘۯ‬ሺ‫ۯ܄‬ሻ
Equation 5

Figure 17: Reactive Power Triangle (SMA, 2009)
2.3.3 MPPT
As the I-V characteristics of a solar cell are nonlinear and vary with both irradiation and
temperature there is a point on the I-V curve that a PV array produces its maximum possible
power under given operating conditions. This point is referred to as the Maximum Power Point
(MPP).Figure 18 shows graphically the Maximum Power point for a typical c-SI module where it
can be seen that there is an I-V relationship which results in the module producing its maximum
possible power (Solmetric, 2011).
When comparing PV modules the Fill factor (FF) is often used to model the non linearity of a PV
cells I-V curve. The fill factor measures the relationship between the maximum power
production and the product of VOC and ISC as seen equation graphically in figure 18. This
performance parameter becomes especially important when measuring different types of PV
materials as often cells that display similar ISC and VOC can operate at a different maximum
power point due to the nature of their I-V characteristics. In general c-SI modules have a higher
FF then a-SI modules due to the fact that these cells have a squarer I-V curve which is closer to
ideal conditions (Solmetric, 2011).

Figure 18: MPP for a c-Si module (Solmetric, 2011).
In large scale systems an important function of the GTI is to insure that at any given condition
the MPP is obtained from the PV array. This is achieved through a system called Maximum
Power Point Tracking (MPPT) which is an electronic system that varies the electrical operating
point within of the PV array to insure it is operating at its MPP at any given instant (IFC, 2012).
2.5.4 Harmonic Content at inverter output
In a typical PV inverter Pulse Width Modulation (PWM) is used to control IGBT switches which
in turn generate AC output. Although this method of AC generation allows for accurate control
of both magnitude and frequency which is important for grid synchronization high order
harmonics and noise which are detrimental to system performance can also be produced due
to the high frequency switching of the IGBT’s. To remove these unwanted harmonics a series
inductive filter and capacitive shunt filter are generally used to filter out harmonics due to
switching transients and also harmonics produced by the electronic control section of the
inverter as seen in the inverter layout described in figure 16 (Enslin, 2003). Clause 10 of the EU
standard IEEE Std 519-1992 is the main document which regulates harmonic content from the
output of PV systems. The requirement of PV inverters under this standard is that the total
harmonic current distortion should be less than 5% of the fundamental component. Although
this is generally achieved when using 1 inverter the problem of harmonics can become more

complex when designing large scale PV plants that contain a large number of inverters
connected to the network (Enslin, 2003). When a large number of inverters are connected at
distribution level harmonic resonance can occur between the PV system and the grid in 2
different ways. Parallel resonance occurs due to resonance between the network capacitance
and the supply inductance and where the PV inverter is seen as the source of harmonic
distortion as seen in fig 123. This results in high impedance at the point of resonance which can
cause high voltage distortion at the PCC. Series resonance on the other hand occurs due voltage
distortion in the supply voltage itself which results in low impedance at the point of resonance
and high current distortion. These factors must be considered when connecting large amounts
of PV to the LV and Distribution networks as THD could breach the 5% limit under certain
conditions (Benhabib et al, 2007),(Enslin, 2003).
Figure 19: Parallel and Series resonance circuits (Enslin, 2003).
2.5.5 Inverter Layout in large scale plant
For large scale applications modules are typically connected in strings of series connected
panels in order to insure a significantly high input voltage to the inverter is achieved which
allows for greater DC/AC conversion efficiency (Giral et al., 2010),(SMA, 2010). In terms of inverter
layout within a large scale system there are 2 main kinds of inverter configuration which can be
considered

2.5.6 Centralized inverter layout
The first type of inverter layout and traditionally the most used design is the centralized
inverter system. In this system strings of series connected modules are constructed as
described above, a number of strings can then be connected in parallel in order to meet the
specific power requirement of the plant. A single centralized inverter is then used to connect
the paralleled strings to the grid as seen in figure 20. One of the advantages of a centralized
approach is that only a small amount of inverters are needed for the whole system which mean
in terms of initial capital investment the cost per watt is often lower than other inverter
layouts. From a design point of view these inverters also enable a more simplistic overall
system design and easier on site install. This being said in terms of performance this simplicity
comes at a price, the first problem arises from the fact that as all strings are connected in
parallel designers need to ensure that all strings have the same power output as there is only 1
MPPT system for the whole array. This can be a major disadvantage for designers as strings
cannot be constructed using different module types or varying orientation in order to maximize
performance. Shadowing can also be a major problem in this type of system. As all strings are in
parallel the maximum MMP of each module is limited to the power in the weakest module in
the system, this can be a significant problem in a large plant as if a section of the site is
shadowed by cloud cover or external factors the overall power production of the entire plant
would be reduced. Shadowing can also cause heat damage to modules due to the shadowed
cell or module in a string acting as a load on the system which in turn leads to current flowing
into the showed cell resulting in I2
R losses in the form of heat (Giral et al, 2010).Another
disadvantage is that the warranty on large scale central inverters is typically only 5-10 years
which is much shorter than on small string inverters which often have 20 year warranty, this
results in the initial cost of the inverter being tripled over the lifetime of the plant (IFC, 2012).

Figure 20: Centralised layout (left), String layout (right),(IFC, 2012)
2.5.7 Sting inverter layout
The second configuration consists of using string inverters which convert each string of modules from
DC to AC individually rather than as a large group of parallel strings as seen in figure 20.Shadowing loss
and potential heat damage are both minimized in this case as MPPT is carried out on each string
allowing for optimum power production from each string. Another advantage of string inverter is due to
the size and cost compared to a central inverter it becomes economical to have 1 or more spare
inverters onsite which reduces down time in a fault situation. As mentioned before string inverters such
as the SMA Sunny Tripower series offer a 20 year warranty (SMA, 2010). One of the main advantages
of a string inverter system is that maximum power point tracking (MPPT) can be carried out for
each string of panels which means that if a section of the plant has reduced output power due
to shadowing effects only the power output of that group of panels will be effected and not the
efficiency of the entire system (Giral et al., 2010).The arrangement of strings becomes even more
significant in systems when strings are tilted and there is large seasonal variation in sun height
as is the case in Ireland. When there is shading between the strings themselves the efficiency of
the system can be improved greatly if all shaded areas have their own MPPT as seen in figure
21.

Figure 21: String shading and layout of MPPT area within string (Danfoss, 2009)
2.2.8 Single phase inverter layout
In terms of inverter choice designers can also choose between using 1 phase or 3 phase
inverters. One solution in large scale systems is to use single phase string inverters for each
string of modules. The single phase output of 3 inverters can then be connected through a
subfield junction box allowing for a 3 phase output for grid connection. In this type of system it
is imperative that the power is distributed between each phase evenly with no more than
4.6KVA difference between each phase. A power balancer may also be used to maintain even
power distribution however this requires extra cabling between each phase. Figure 22 shows a
layout of a 1.2MW large scale plant using a 1 phase inverter layout feeding into a 20Kv grid
network.

Figure 22: 1.2MW PV plant layout (SMA, 2010)
2.5.8 Three phase inverter approach
An alternative approach to the 1 phase layout is to use 3 phase inverters. By using 3 phase
inverters the inverter output can be fed directly to the main field junction point eliminating the
need for grouping inverters at sub field. This reduces the complexity and also the extra cabling
cost associated with a 1 phase approach. An example of a large scale PV plant using 3 phase
inverters is shown in figure 23 (SMA, 2010).

Figure 23: Example of a 3 phase PV plant design (SMA ,2010)
3.5.9 PV blocks within large scale layout
For multi megawatt installations a PV plant may be made up of individual blocks which can be
connected to the grid network using separate connection points for each block as shown in
figure 24. In order to get further information on the advantages and disadvantages of this
approach David Maguire from the solar development company BNRG Renewables with
headquarters based in the International Financial Service Centre (IFSC) in Dublin was contacted
directly. He explained that although using additional transformers increases system losses
slightly there are design benefits to building large scale PV plants in blocks. The first advantage
comes from the fact that if one block in a plant has a fault the other sections of the plant can
continue to produce power reducing the financial implications of a fault on the system. Another
advantage arises from the fact that each section of plant can be switched into the grid network
as soon as it is constructed and does not depend on the overall completion of the system. This
means that if the construction of the plant has to be completed under a strict deadline due to
changes in government FIT or other support mechanisms as seen in the UK in 2011 if the entire

plant cannot be completed the individual blocks that were complete within the deadline can
still be connected (Maguire, 2012)
Figure 24: PV system made up of blacks (Mitavachan, 2011)
3.5.10 Wiring losses and cost
Another important factor to consider when designing large scale plants is the length of the
cables needed on both the DC side of the plant between the modules and the inverter and on
the AC side of the plant between the inverter and transformer station (Danfoss, 2009). As all
cables have some internal resistance a certain amount of power is lost due to the fact that the
power in a circuit is proportional to I2
×R. There is also a corresponding voltage drop which can
be calculated using ohms law as seen in equation in conjunction with the cable resistance which
is usually provided by the cable manufacture in Ω/km (Wiles, 2001).

ࡼ = ࡵ૛
ࡾ Equation 6
ࢂ = ࡵ × ࡾ Equation 7
if the distance between major components on the AC or DC side of the system is significant a
larger diameter cable may be needed in order to reduce voltage drop which results in a
increase in overall cable cost, therefore when designing a large scale it is imperative that the
system is designed in a way that minimizes cable distance on both the AC and DC side of the
plant. This being said when designing a PV system there is a balance between cable cost and
efficiency, in must designs a certain amount of power loss is accepted as long as the overall
cable loss is kept less than 1% of system output. In order to reduce the diameter of cable
needed in large scale plants it is optimal to have a high DC voltage in the range of 600-700 volts
which allows for small diameter cable to be used (Danfoss, 2009). Another point to consider is
the fact that generally the DC voltage will be larger than the corresponding AC voltage which
means in order to reduce system losses it may be preferable to design the system such that all
long cable paths are on the DC side. For most designs 4mm2
solar cable will be sufficient to
keep losses under 1% up to a distance of 200m on the DC side of the system, for any distances
longer than this 6mm2
may be required. There are a number of design options in terms of
inverter and transformer placement, the first design option and most efficient in terms of cable
loss on both the AC and DC side of the plant is a quadratic layout where a compact transformer
station is placed centrally in the plant and all inverters are placed together at a central point
near the transformer connection as seen in figure 25 (Danfoss, 2009). The use of compact
transformer stations in this configuration is generally the preferred option for plants connected
to the LV or MV system as cable length is minimized both on the AC and DC of the plant. As
mentioned above this type of layout also allows for direct connection from inverter to the
transformer station if there is a significantly high DC voltage which means there is no need for
an additional combiner box on the AC side of the plant. The second approach is to place the
inverters close to each string of modules as seen in figure 26. Although this approach decreases

cable length on the DC side between modules and inverter it often leads to much longer AC
cable runs which can result in higher losses.
Figure 25: Quadratic PV plant layout, (Danfoss, 2009)
Figure 26: PV plant design with inverters decentralised (Danfoss, 2009).

Chapter 3- Methodology
This section highlights the main tools used in this study to accurately determine the potential for large
scale PV generation in Ireland. In terms of methodology the study was broken up into 4 individual
sections which include an initial resource assessment, a comparison of PV technologies, the construction
of a large scale PV system model and finally an economic analysis .A methodology schematic diagram
can be seen below which shows each of the 4 sections and the corresponding tools that were employed
at each point of the study in order to achieve the aims and objects of the overall project.
3.1 Solar Resource assessment
5 data sources consisting of ground based measurements and satellite data were used to
complete the initial resource assessment as seen in section 2.3.2. The first parameter which
was modeled using this data was the total irradiation on a horizontal surface which was
calculated on a kWh/m2
/day basis for every month of the year. The second parameter modeled
was the ratio of diffuse radiation to global radiation which was also modeled on a monthly
basis. All data analysis was carried out using Microsoft Excel and all relevant calculations can be
found on the data CD attached with this document.
Resource
Assessment
Climate-SAF
PVGIS
PVGIS Classic
Met Eireann
Focus
building DIT
Meteonorm
Technology
Comparison
PVSYST
DIT
Recorded
Module Data
Large Scale
Model
PVSYST
BNRG
Renewables
Economic
Study
NPD Solarbuzz
Module Price Index
BNRG Renewables

3.2 Software used to model performance
3.2.1 PVSYST
In order to estimate the potential yield of each technology type the PVSYST software package
which was developed at the University of Geneva and is currently the most used PV estimation
software in Europe was used. The model itself contains a wide range of input parameters
including temperature coefficients, tilt angle, solar cell type, shading, module degradation,
mismatch losses, I-V characteristics and many other specifications making it one of the most
accurate yield assessment tools available to PV developers (Mermoud, 1995). Importantly the
software also has a large database of models corresponding to known PV panels and inverters
which includes models for the Kaneka a-SI module, Sanyo HIT module, Sharp NE-80E2E p-SI
module, Sunpower Spr-90 m-SI module and Sunteck STP m-SI module.
3.2.2 Validation of PVSYST model
As PVSYST uses manufacture data to estimate a modules potential power generation it was
imperative that all data being used was measured using the same operating conditions and was
calculated in accordance with all relevant standards. The main standard which governs the
measurement of a PV modules performance is IEC 60904 which lays down a set of standard test
conditions (STC) that all modules must be measured under. These STC can be defined by a
module temperature of 25°C at an irradiance level of 1000 W.m-2
under a reference spectral
distribution of AM 1.5. PVSYST also uses Normal Operating Cell Temperature (NOCT) as a
performance indicator which must be calculated under an irradiance of 800W/m2
, ambient
temperature of 20o
C and wind speed of 1m/s and as specified in both IEC 61215 and IEC 1646
for c-SI and Thin film PV respectively. Another set of significant parameters used in the PVSYST
model are the temperature coefficients of short circuit current ISC (α), open circuit voltage VOC
(β) and maximum power PMAX (δ). Standards IEC 61215 and IEC 1646 define the procedure for
measuring temperature coeffcients which involves recording these values either during cooling
down or heating up of the module over a 30°C sweep of 5°C intervals. An important point to
consider when using temperature coefficients as a performance indicator is that they are only
valid for the irradiance level at which the measurements were made unless the linearity of the
module is specified in which case the values for each temperature coefficient are valid over

±30% of the irradiance value they were recorded at and not over all irradiance levels. All
module manufacture data used in this study is in compliance with the standards set out above.
3.2.3 PVSYST 3-D shading tool
Within the PVSYST software a 3-D layout of the PV system can also be constructed which
allows for a detailed analysis of shadow loss due to external objects. This tool can also estimate
shading between different strings within a large scale system which means the optimum
distance between each shed of PV panels can be estimated. For a more detailed shading loss
calculation the layout of PV strings within the PV area can also be specified which means when
estimating power output only the shaded group of strings will be effected and not the entire
system. In the case where a section of a string is shaded completely the electrical output of the
whole string is deemed to be 0 (Mermoud, 1995).
3.2.4 Climate data base used for PVSYST study
In order to estimate energy yield from a particular module climate time series data including
horizontal global radiation, ambient temperature and diffuse radiation data was imported into
the PVSYST software. The database that will be used for this project is the Meteonorm global
meteorological database which is specifically designed to provide accurate data for solar
planners and engineers. For the purpose of direct comparison of all PV modules the same
climate location were used corresponding to an area in Dublin with the coordinates 53.07,53,4
North,-6.02,-6, 1 West. As PVSYT uses internal models to convert horizontal radiation data to
radiation on an inclined surface it was important to consider which model would achieve the
most accurate results. The 3 main models considered were Hay’s model, Reindl’s model and the
Perez model which are all designed to estimate diffuse radiation on inclined surfaces. As it was
reported that the Perez model has the lowest route mean squared error out of the 3 models
the Perez model was used in PVSYST for all calculations (Soga, Akasaka & Nimiya, 2009).

3.3 Models used in Comparative study
3.3.1 Recorded DIT data
The recorded current and voltage from each panel in conjunction with the corresponding
irradiance data allowed for the calculation of module efficiency at any given time. This was
achieved by calculating the MPP for each time interval which was then divided by the area of
the module which allowed each module to be compared on a W/m2
power base. The efficiency
of each panel could then be obtained by dividing the electrical energy on the DC side of the
system by the corresponding irradiation falling on the PV panel as seen in equation 8 (Jiang &
Lim, 2010).
ࡱࢌࢌࢉ࢏ࢋ࢔ࢉ࢟ሺ%ሻ =
ࡱࡰ࡯
ࡱࡼࢂ
× ૚૙૙ Equation 8
As all panels consist of different sizes in terms of power output a second parameter was needed in order
compare performance. The PR ratio which shows the difference between the actual and
theoretical maximum power output for any given climate conditions was deemed the best way
to compare each module in this study and is widely regarded the best tool to compare different
types of PV systems. International standard IEC 61724 also considers the PR to be the most
effective tool to measure and compare PV performance from different systems. The 3 relevant
formulas needed for this calculation are shown below (Jiang & Lim, 2010).
ࡼࡾ =
ࡲ࢏࢔ࢇ࢒ ࡿ࢙࢚࢟ࢋ࢓ ࢅ࢏ࢋ࢒ࢊ ሺࢅࡲሻ
ࡾࢋࢌࢋ࢘ࢋ࢔ࢉࢋ ࢅ࢏ࢋ࢒ࢊ ሺࢅࡾሻ
Equation 9
ࢅࡲ =
ࡿ࢙࢚࢟ࢋ࢓ ࡱ࢔ࢋ࢘ࢍ࢟ ࡻ࢛࢚࢖࢛࢚
ࡵ࢔࢙࢚ࢇ࢒࢒ࢋࢊ ࡼ࢕࢝ࢋ࢘ ࡯ࢇ࢖ࢇࢉ࢏࢚࢟
Equation 10
ࢅࡾ =
ࡵ࢔ିࡼ࢒ࢇ࢔ࢋ ࡭ࢉ࢚࢛ࢇ࢒ ࡵ࢘࢘ࢇࢊ࢏ࢇ࢚࢏࢕࢔
ࡾࢋࢌࢋ࢘ࢋ࢔ࢉࢋ ࡵ࢘࢘ࢇࢊ࢏ࢇ࢚࢏࢕࢔
Equation 11

3.3.2 PVSYST Comparative model
As recorded data was only available for the months of June July and August from 2010 PVSYST
was used in conjunction with the recorded data in order to determine the seasonal variation in
module output over a full year. In order to estimate the area requirement for each technology a
theoretical 1kW system was created for each module type in PVSYST. The average PR and
efficiency was calculated for each 1KW system. This allowed direct comparison between all
modules tested. Additionally PVSYST allowed for the main losses in the system to be plotted
individually which resulted in a greater understanding of the performance of each module
under Irish Climate conditions. Using this function within PVSYST 2 addition plots were created
for each module. As module performance under low irradiance levels is a key factor for PV
installations in Ireland a graph showing module efficiency plotted against irradiance in W/m2
was created to show how irradiance level affects the efficiency of each module, in order to
isolate the loss due to irradiance level from other losses in the system a second graph was
created showing irradiance loss measured in watts plotted against irradiance level in W/m2
.
3.3.3 Large scale system performance
In order to examine the performance of a large scale ground mounted system in Ireland a 1MW
PV system was constructed in PVSYST using the same climate conditions used for the 1KW
comparative study. In order to improve the accuracy of this model BNRG renewable were
contacted who provided information regarding standard practices within the large scale PV
industry. This included information regarding specific limits on losses within the system,
appropriate plant layout, grid connection point and guidelines for the acceptable levels of
performance expected from large scale systems.
3.4 Economic methodology
As module price has dropped considerable since the 5 modules studied in this project were
installed the main source of data used to compare current module prices was the NPD
Solarbuzz Module Price Index which allowed mono-crystalline, multi-crystalline and thin film
modules to be compared in terms of €/WP based on 2012 retail prices.

For the large scale system 2 economic parameters were used to determine the economic
viability of the modelled 1MW PV plant. The cost of electricity (COE) produced was the first
parameter used in the study and was calculated using the equations shown in section 2.4.1 and
presented in both €/kWh and €/MWh. Secondly a NPV calculation was carried out in order to
determine the level of subsidy needed for the system to generate a profit over the estimated
25 year lifetime of the system. 2 separate NPV calculations were carried out using the
equations shown in 2.4.1 for discount rates of 8% and 10% respectively. BNRG Renewables also
provided prices for initial construction, operation and maintenance and external transformer
costs which allowed for greater accuracy in terms of capital cost estimation.
Chapter 4-Results
4.1 Initial assumptions within the PVSYST model
In order to compare each technology PVSYST was used to measure the performance of each
module under Irish climate conditions using a Dublin location with coordinates 53.07,53,4
North,-6.02,-6, 1 West as outlined in section 3.3.4.To insure all conditions were identical for all
modules initially the optimum tilt and azimuth angle of the panels for the location was chosen
based on maximizing irradiance capture throughout the year. From the optimization graph
below it can be seen that a tilt of 35o
and azimuth angle of 0o
corresponding to directly south
resulted in the greatest annual irradiance capture for the location studied.
Figure 27: PVsyst model for optimum tilt and azimuth angle

For the next part of the calculation shading loss due to the position of the sun with respect to
the tilt of the panels was calculated. To achieve this estimation a sun height diagram was
constructed for every day in the year in PVsyst as seen in figure 29. The blue lines in this
diagram correspond to the points at which the suns angle passes behind the plane of the tilted
arrays and therefore no direct beam radiation falls on the modules. As a typical PV grid
connected system contains a number of modules connected in series or parallel for the purpose
of these calculations each of the PV module types were constructed into arrays which have an
AC nominal power output of 1kW. The 3-D drawing tool was then used in PVSYST in order to
estimate shading loss due to the layout of the arrays themselves. For simplicity a perfectly flat
surface was chosen with no surrounding obstacles in the form of buildings or tress and
therefore the only near shadings were at low sun angles when the sun was passing behind the
plain of the array and therefore a section of the array was not receiving radiation. The shading
loss at these points are shown by a series of black lines corresponding to different shading loss
percentages in figure 29 for a 1kW array containing 5 Sanyo HIT-215NHE5 panels.
Figure 28: Sanyo array layout within PVsyst (PVsyst, 2012)

Figure 29: Shading loss diagram for Sanyo array (PVsyst 2012)
4.2 PVSYST 1kWP comparative study
Using the method described in above 5 1kW systems corresponding to each module type
currently installed in the Focus building in DIT were modeled in PVSYST, the technical
specifications including inverter type, number of panels and I-V characteristics for each array
are shown in Appendix A,B,C,D, and Erespectively. the PV array loss factors for each 1kW
system were also included in the simulation and can also be seen in appendix A,B,C,D and E,
theses loses included mismatch loses due to each module in the string having slightly different
I-V characteristics which were set at 2% of the MPP, quality loss which shows the difference
between manufacture performance data and actual performance which was set at 2.5% and
finally incident angle modifier (IAM) loss which can be defined by the weakening of the
irradiation really reaching the PV cells's surface, with respect to irradiation under normal
incidence and which is effected by transmission and reflection of radiation on the protective
material on the front of the panels. PVSYST uses the ASHRAE model shown below which was
originally identified in Souka & Safat (1966) and is shown in equation 12 to estimate this loss.
The value of b0 determines the significance of the overall loss factor and was set at 0.05 based

on the recommendations for crystalline PV within PVSYST. The value of ݅ corresponds to the
incident angle on the plane of the array.
ࡲࡵ࡭ࡹ = ૚ − ࢈࢕ × ቄ
૚
‫ ܛܗ܋‬ሺ࢏ሻ
− ૚ቅ Equation 12

4.2.1 Sanyo modeled performance
Figure 30: Sanyo modelled output, (PVsyst, 2012)
Table 3 Sanyo results
NormalizedarrayproductionKWh/KWP/day

4.2.2Kaneka modeled performance
Figure 31: Kaneka modelled results (PVsyst, 2012)
Table 4 Kaneka modelled results (PVsyst, 2012)

4.2.4 Sharp modeled performance
Figure 32: Sharp modelled results, (PVsyst, 2012)
Table 5: Sharp modelled results (PVsyst, 2012)

4.2.5 Sunpower modeled performance
Figure 33: Sunpower modelled results (PVsyst 2012)
Table 6 Sunpower modelled results (PVsyst)

4.2.6 Sunteck modeled performance
Figure 34: Sunteck modelled results (PVsyst 2012)
Table 7: Sunteck modelled results (PVsyst 2012)

4.3 PVSYST results for 1KW system
As the inverter chosen for each array was different the associated system losses were different
for each array. Therefore in order to directly compare each modelled system the inverter losses
were added back into the final system yield which meant that the only losses which contributed
to system output were the array losses. The normalised output of each array was compared on
a kWh/KWP/day basis as seen in table 8.In terms of energy yield and efficiency the Sanyo
module performs the best with a final yield of 2.64kWh/KWP/day and an average annual
efficiency of 14.83%. These simulated values correlate well with what was found in (Ayompe et
al 2007) where a yield of 2.62kWh/KWP/day and average module efficiency of 14.9% were
recorded for a 1.72KwP Sanyo array installed in DIT. The Sunpower m-Si module was the second
best performing module with an array yield of 2.57kWh/KWP/day and an average efficiency
of14.71%. In terms of array losses which are affected by module temperature and irradiance
level the Sanyo module also performs the best with average array loss of 13%. Interestingly the
a-Si simulated array does not perform well under Irish climate conditions and has the highest
array loss of all simulated modules especially during the months of December and January
where an array loss of 25% was estimated as seen in figure 31. In terms of the area requirement
for each 1KW array it can be seen that the a-Si array requires over twice the land area to
produce the same power as the other 4 module which is a major disadvantage for large scale
PV applications. Finally it can be noted that the array loss for both the Sharp and Sunteck
modules increases during the summer months of May June and July, this behaviour can be
attributed to the fact that both these module have a temperature power coefficient of -0.48
%/°C which is 1% higher than any of the other 3 modules and leads to greater power loss at high module
temperatures.
Model Type kWh/kWp/day Efficiency Array area requirement (m2
) PVSYST Array LC
Sanyo HIT 2.64 14.83 6.3 13
kaneka a-Si 2.41 5.03 17.1 20.3
Sharp poly 2.53 10.49 7.6 16.6
Sunpower m-Si 2.57 14.71 6.6 15.3
Sunteck m-Si 2.54 10.38 7.8 16.4
Table 8: Module comparison table

4.3.1 Irradiance loss
The performance of a PV module under low irradiance levels can significantly affect the final
energy yield from a system (Donovan et al, 2010). As a result of this when choosing a module
for an Irish system it is vital that the module used has the ability to extract energy at low
irradiance levels. In order to analyze the effect of irradiance level on module performance
PVSYST was used to isolate irradiance loss from other losses in the system. This allowed for the
creation of a graph showing incoming radiation measured in W/m2
plotted against irradiance
loss measured in watts. Loss due to irradiance level was estimated for all 5 modules currently
installed in DIT which meant each module could be compared in terms of low irradiance
performance. As the 1kW PVSYST study found that the Kaneka a-Si module performed the
worst of all modules under Irish Climate conditions a Biosol XXL 124 triple junction a-Si module
was also modelled in order to see if this type of module showed any significant performance
improvements compared to the single junction a-Si module. The results for all modules can be
seen in figure 35.As expected the Sanyo panel shows the best performance under low
irradiance and high irradiance conditions with a loss of just 12 watts at an irradiance level of
400W/m2
and a loss of just 2 watts at a level of 800W/m2
. The kaneka panel shows high losses
at all irradiance levels especially at levels between 300-600W/m2
where losses of 25-30 watts
are estimated. Interestingly the triple junction module shows the best performance out of all
modules at irradiance levels between 200-400W/m2
where losses are under 10 watts. All other
modules show similar losses over all irradiance levels.

PVLossduetoirradiance(Watts)PVLossduetoirradiance(Watts)
Figure 35: (A: Kaneka a-SI), (B: Sunteck), (C: Sunpower), (D: Sanyo), (E: Sharp), (G: Biosol a-SI H triple)
A. B.
C. C.
D. E.
W/m2
W/m2
PVLossduetoirradiance(Watts)
W/m2
W/m2
W/m2
W/m2

4.4 Recorded data results
The recorded I-V characteristics for the 5 panels were analyzed in Microsoft Excel. The data was
arranged to show power measured in W/m2
plotted against corresponding radiation measured
in kW/m2
for all 5 modules using the methodology outlined in section 3.3.1, the efficiency
graphs for all 5 modules are shown in appendix 6.The average efficiency for each panel was
then estimated by dividing the module power by the incoming radiation. The PR was also
calculated for each module by dividing the actual array power calculated in W/m2
by the power
achievable at STC. The results of all calculations are table 9.
Manufacture Model Efficiency PVSYST % Recorded Efficiency% Recorded PR
Kaneka G-EA060 5.03 2.9 46.1
Sharp NE-80E2E 10.49 7.4 54.36
Sunpower SPR-90 14.71 10.46 63.41
Suntech STP080B12/BEA 10.35 7.358 59.34
Sanyo HIP-215NKHE5 14.83 10.63 61.882
Table 9: Results from DIT recorded data
From the table of results presented above it can be seen that the recorded data suggests a
lower overall efficiency for all 5 modules compared to the PVSYST results however this may be
attributed to the fact that the PVSYST model represents module performance in ideal
conditions with no external shading at an optimum tilt angle of 350
, in contrast to this the
modules installed in DIT were monitored at a tilt angle of 530
and additionally are installed on
R² = 0.7679
0
10
20
30
40
50
60
70
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Watts/sq.m
kW/sq.m
Kaneka

the roof of a building and therefore external shading could be an issue in regards to power loss.
This being said in the recorded data shows the same trend as the PVSYST results with the Sanyo
module operating at the highest efficiency of 10.63% closely followed by the m-Si Sunpower
module with 10.46% efficiency. Both the p-Si Sharp module and the Sunteck module are also
equally matched with recorded efficiencies of 7.4% and 7.3% respectively. Interestingly The
Sunpower module has a slightly better recorded PR at 63.4% compared to a PR of 61.8% for the
Sanyo module indicating the m-Si Sunpower panel is operating closer to its maximum
theoretical output on average. As with the PVSYT results the Kaneka module recorded results
are the worst with a PR of just 46.1% and average efficiency of 2.9%.
4.5 Economic consideration
As there has been a significant decrease in PV module cost since early 2008 the prices that the
modules studied above were purchased for in 2007 do not reflect the current costs associated
with PV generation. The first factor which has contributed to the fall in module price is the
expansion in the number of PV module suppliers within in the industry which has meant that
the once dominant European, US and Japanese market has seen more competition from
Chinese and Taiwanese producers. This increase in supply also occurred in conjunction with
Spain announcing a 500MW limit on their PV FIT and a global recession which meant that there
was significant over supply in the market. With this in mind the cost associated with each
technology will compared based on the current market price in terms of €/WP as opposed to
using the original 2007 costs for each module. The main source data with regards to module
pricing used in this study was the NPD Solarbuzz Retail Module Price Index which tracks retail
pricing data for PV modules for both the US and European market. Figure 36 shows retail price
trend from 2001-2012 where it can be seen that between 2007 and 2012 the average market
price for PV modules has dropped from 4.5€/WP to 2.17€/WP.

Figure 36: Solarbuzz Retail Module Price Index (Solarbuzz, 2012)
The Solarbuzz data also shows that 34% of modules currently on their data base of over 900
modules are retailing for under 1.54€/WP. The data also shows that the lowest priced mono
crystalline module currently in the European market is 0.81€/WP, the cheapest multi crystalline
module is 0.78€/WP and the cheapest thin film module cost 0.62€/WP. as shown in figure 37.
Figure 37: Solarbuzz Retail Module Price Index, short term (Solarbuzz, 2012)
4.5.1 Retail price comparison
In order to see whether the data presented by Solarbuzz is a true representation of what is
happening in the PV retail market the prices for a number of PV modules currently available
were sourced from online suppliers. A number of different types of technologies were

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