project_final 6.1

Bachelor of Engineering in Mechanical Engineering and Renewable Energy, Year 3
Laboratory Analysis of a Flat-Plate Solar Thermal Collector
By
GROUP PLATINUM
Comprising of:
Antonio Escrivá Salvador
Alexander Ivanov
Alejandro Blay Orenga
Barry Beglan
DR. Niall Burke, Advisor
Bachelor of Engineering in Mechanical Engineering and Renewable
Energy, Year 3
Athlone Institute of Technology
June 2014

i
Acknowledgments
As a project team, we would like to thank all the people who helped us during
the project. Our supervisor, Niall Burke, was of great help throughout the project
and his help and guidance was greatly appreciated. The next group of people
that helped us a great deal during the course of the project were the technicians
in the trades building located in the east campus. The next group of people
whose help was greatly appreciated was the staff at Heavins Hardware Store.
The technicians here in the engineering building were also very helpful in
helping the group complete the project.
Abstract
This project has been focused on flat-plate collectors in the solar thermal sector.
The price of the electricity and fuels has been rising in the few last years and it
this will continue to happen. For example, the electricity price increased by 17%
in Ireland or by 56% in Spain since 2005 (Sustainable Energy Authority of
Ireland , 2013).
Figure 1 Household Electricity Price (Sustainable Energy Authority of Ireland , 2013)
The electricity or fuel needed to obtain hot water is relatively big so it is a good
idea to use the solar water heating systems to effectively obtain “free” hot water.
The project consists of the efficiency of the solar flat-plate panel in different
conditions. An auxiliary system simulating a real circuit used in homes has been
built. It consists of two different circuits, the first one will be heated by the solar
thermal collector and the second one will supply this heat to a copper cylinder

ii
which will heat the water inside. During the course of the project different
elements of flat-plate solar collectors will be studied. In the literature review
about this topic, the efficiency, the temperature in the different parts of the
circuit and the time needed for the tank to arrive at the required temperatures
will be obtained for the flat-plate collector and the results will be collected and
analyzed.
Contents
Acknowledgments........................................................................................................... i
Abstract............................................................................................................................. i
Nomenclature ................................................................................................................vii
Chapter 1: Introduction..................................................................................................1
1.1: European Solar Thermal Sector.......................................................................2
1.2: Irish Solar Thermal Sector: ...............................................................................2
1.3: Project Aims ........................................................................................................3
1.4: Project Objectives...............................................................................................3
1.5: Project scope.......................................................................................................3
1.6: Project budget .....................................................................................................4
1.7: Project methodology ..........................................................................................4
Chapter 2: Literature Review .......................................................................................5
2.1: Weather in Ireland..................................................................................................5
2.2: Strengths and weaknesses of solar systems .................................................8
2.2.1: Strengths.......................................................................................................8
2.2.2: Weaknesses .................................................................................................8
2.4: Feasibility of installing solar thermal panels in Ireland .................................9
2.8: Natural circulation and forced circulation......................................................10
2.5: Selection of the Solar Collector Type ............................................................10
2.5.1: Flat plate solar collectors..........................................................................10
2.5.2: Evacuated tube solar collectors: .............................................................13

iii
2.5.3: Cost:.............................................................................................................14
2.5.4: Size: .............................................................................................................14
2.5.5: Life Spam:...................................................................................................14
2.5.6: Payback Periods:.......................................................................................15
2.5.7: Installation:..................................................................................................15
2.5.8: Useful Climates..........................................................................................15
2.5.9: Orientation ..................................................................................................15
2.5.10: Efficiency:..................................................................................................16
2.5.11: Conclusion:...............................................................................................16
2.6: Calibration for the project ................................................................................16
2.6.1: Thermocouple ................................................................................................16
2.7.4: Flow meter......................................................................................................20
2.7.1: Circulating pump ...........................................................................................23
2.7.6: Radiometer.....................................................................................................26
Chapter 3: Materials & Methods:...............................................................................27
3.1.2: Circulating pump ........................................................................................28
3.1.3: Thermocouple ............................................................................................29
3.1.4: Hot water tank ............................................................................................30
3.1.5: Flow meter ..................................................................................................31
3.1.6: Copper and plastic pipes..........................................................................32
3.1.7: Valves..........................................................................................................33
3.1.8: Pressure Valves.........................................................................................33
3.1.9: Insulation.....................................................................................................34
3.1.10: Expansion tank vessel............................................................................34
3.1.11: Panel with the lights ................................................................................35
3.1.12: Radiometer ...............................................................................................36
3.2: Methods .............................................................................................................37
3.2.1: Procedure: for original system................................................................37
3.2.2: Analysis For the original system..............................................................37
3.2.3: Procedure: for the new system................................................................39
Chapter 4: Results .......................................................................................................40
4.2: Original system...............................................................................................41
4.2.1 Results..........................................................................................................41

iv
4.2.2 Calculation of thermal efficiency for the original system. .....................43
4.2.3: Conclusion for the Original System........................................................46
4.3 External System Built.....................................................................................46
4.3.1 Results..........................................................................................................46
4.2.2 Calculation of thermal efficiency for the External System Built...........49
4.2.3: Conclusion for the External System Built.. ............................................52
Chapter 5: Conclusion.................................................................................................52
5.1 Key findings: ....................................................Error! Bookmark not defined.
5.2 Conclusion...................................................Error! Bookmark not defined.
5.3 Future recommendations .................................................................................54
Chapter 6: Bibliography...............................................................................................55
Bibliography ..................................................................................................................55
4.3: Experimental results for the old system (Test 2) Error! Bookmark not
defined.
4.3.1 Calculation of efficiency for the second experiment (test 2) ..........Error!
Bookmark not defined.
4.3.2 Conclusion for the second experiment (Test 2) ..Error! Bookmark not
defined.
Table of figures
Figure 1 Household Electricity Price (Sustainable Energy Authority of Ireland ,
2013)................................................................................................................................. i
Figure 2 This is the total Primary Energy Requirement Ireland (Sustainable
Energy Authority of Ireland , 2013). ............................................................................1
Figure 3: Map of Ireland showing by the sunlight distribution of the sun during
the summer (Walsh S, 2012) .......................................................................................6
Figure 4: Map of Ireland showing the sunlight distribution of the sun during
winter (Walsh S, 2012) .................................................................................................6
Figure 5: Map of Ireland showing the sunlight distribution of the sun during in
spring (Walsh S, 2012) . ...............................................................................................7
Figure 6: Map of Ireland showing the sunlight distribution of the sun during
autumn (Walsh S, 2012) ..............................................................................................7
Figure 7: Graph showing the overall sunshine hours in Ireland along the year
(Weather and Climate, 2013) ......................................................................................7
Figure 8: Flat-Plate Collector (The Worlds of David Darling, 2009). ...................11

v
Figure 9: selective coatings applied to transparent covers on flat plate collectors
(Vettrivel H.V, Dr. Mathiaragan, 2013) . ..................................................................13
Figure 10: Schematic for Evacuated-Tube Collector (The Worlds of David
Darling, 2009). ..............................................................................................................14
Figure 11: Schematic showing thermocouple calibration (Facstaff, 2014) .........18
Figure 12: Tolerance classes for k type thermocouples (Omega, 2014) ............19
Figure 13: Tolerance classes for k type thermocouple (Uteco, 2014).................19
Figure 14: The above is thermocouple calibration (Marineinsight, 2014) ...........19
Figure 15: Thermo well diagram (blogspot, 2014) ..................................................20
Figure 16: Picture showing the acrylic flow meter (Inds, 2014) ............................21
Figure 17: the volumetric calibration method for variable area flow meter (ISA,
1961)..............................................................................................................................22
Figure 18: the gravimetric calibration method (ISA, 1961)....................................23
Figure 19: the comparison calibration method (ISA, 1961)...................................23
Figure 20: pressure calibration pump (Magnumpropumps, 2014) .......................24
Figure 21 Pump Wilo-Star-RS 25/4 (Valgroup, 2014)............................................24
Figure 22: Pump Wilo-Star-RS 25/4 impulse and power absorbed (Valgroup,
2014)..............................................................................................................................26
Figure 23: Original system to evaluate the efficiency of the solar thermal panel
........................................................................................................................................27
Figure 24: New system to evaluate the efficiency of the solar thermal panel ....28
Figure 25: Circulating Pump.......................................................................................29
Figure 26: Thermocouple............................................................................................30
Figure 27: Copper cylinder used in the external circuit..........................................31
Figure 28: Flow meter used in the external circuit..................................................32
Figure 29: Copper and plastic pipes .........................................................................32
Figure 30: Valve on the hot return in the primary circuit ........................................33
Figure 31: Pressure valves on the copper cylinder ................................................33
Figure 32: Insulation ....................................................................................................34
Figure 33: the expansion tank vessel .......................................................................35
Figure 34: the high intensity lamps used during the experiments........................36
Figure 35: Radiometer.................................................................................................36
Figure 36: Return reverse header design in evacuated tube panel.....................38
Figure 37: steady state diagram ................................................................................38
Figure 38: Variation of temperature along time in the Original System. .............43
Figure 39 System efficiency over the temperature difference in the Original
System...........................................................................................................................46
Figure 40: Temperatures measured at different parts of the circuit.....................49
Figure 41: System efficiency over the temperature difference in the External
System Built. .................................................................................................................52
Figure 42: Second experiment graph result (old system)........................................2
Figure 43: Temperatures measured at the closed circuit along the time with 10
litres of water inside the tank and no flow rate in the second circuit. ....................4

vi
Figure 44: Temperatures measured at the closed circuit along the time with no
water inside the tank and no flow rate in the second circuit. ..................................5
Table of tables
Table 1: Safe temperature ranges for solar thermal panels (Kalogirou, Soteris
A., 2004). .......................................................................................................................11
Table 2: Usefull pump information (Valgroup, 2014)..............................................25
Table 3: Radiation along the surface measured twice in the solar flat panel
during the experiments................................................................................................40
Table 4: Average irradiance at each part of the solar flat panel...........................41
Table 5: Temperatures measured in the original system the first 10 minutes. ..42
Table 6: Temperatures measured in the original system between first 10 and 20
minutes. .........................................................................................................................42
Table 7: Temperatures measured in the original system between first 20 and 30
minutes. .........................................................................................................................42
Table 8: Useful data for the original system. ...........................................................43
Table 9: experimental data .........................................................................................44
Table 10: experimental data.......................................................................................44
Table 11: Temperatures measured in the first experiment along the first 90 min.
........................................................................................................................................47
Table 12: Temperatures measured in the first experiment between min 100 and
180..................................................................................................................................48
280..................................................................................................................................48
340s................................................................................................................................49
Table 15: Useful data for the External System Built...............................................49
Table 18: Experimental data results (test 2)..............................................................2
Table 19 Temperatures measured in the second experiment along the first hour.
..........................................................................................................................................3
Table 20 Temperatures measured in the second experiment along the second
hour. .................................................................................................................................3
Table 21: Temperatures measured in the second experiment from the second
hour till the stabilization of T2. .....................................................................................3
Table 22: Temperatures measured in the third experiment along the first hour ..4
Table 23: Temperatures measured in the third experiment from the first hour till
the stabilization of T2. ...................................................................................................5
Table of equations

vii
Equation 1 Triple E eligibility criterion.......................................................................12
Equation 2: The equation used for liquid calibration volumetric method (ISA,
1961)..............................................................................................................................21
Equation 3: The equation used for liquid calibration gravimetric method (ISA,
1961)..............................................................................................................................22
Equation 4: Solar Thermal Effciency.........................................................................44
Equation 5: quantity of heat absorbed by the water ...............................................44
Equation 6: Incident light radiation ............................................................................45
Equation 7: Pump power.............................................................................................45
Equation 8: quantity of heat output out of the system due to the water flow ......45
Equation 9 Solar Thermal Effciency final calculation .............................................45
Equation 10: Mass flow rate .......................................................................................47
Equation 11: Solar Thermal Effciency ......................................................................50
Equation 12: quantity of heat absorbed by the water in the tank .........................50
Equation 13: Incident light radiation..........................................................................51
Equation 14: Pump power ..........................................................................................51
Equation 15: quantity of heat output out of the system due to the water flow....51
Equation 16: Solar Thermal Efficiency final calculation.........................................51
Nomenclature
ASHRAE American Society of
Heating Refrigerating
and Air Conditioning
-
EU European Union -
ESTIF European Solar
Thermal Industry
Federation
-
FPC Flat Plate Collector -
Sec Collection time in
seconds
[s]
SWG Standard Wire Gauge -

viii
SPRT Standard Platinum
Resistance
Thermometer
-
TC Thermocouple -
A Collector area
corresponding to the
performance
parameters
[𝑚2
]
𝐶 𝑃 Specific heat capacity
of water
[𝐽. 𝑘𝑔−1
. 𝐾−1
]
T Time [𝑠]
T Temperature [℃]
𝑉𝑐 Volume of calibrating
liquid collected in units
consistent with 𝑄 𝑚
𝜌𝑓 Density of liquid to be
metering float in
grams/cc
[𝑔/𝑐𝑐]
𝜌 𝑚 Density of liquid to be
metered in grams/cc
[𝑔/𝑐𝑐]
𝜌𝑐 Density of calibrating
liquid in grams/cc
[𝑔/𝑐𝑐]
Q̇ Heat [𝑊]
𝑄̇ 𝑅𝑎𝑑𝑙𝑖𝑔ℎ𝑡
̇ Incident radiation from
lamps
[𝑊]

ix
𝑄̇ 𝑤𝑎𝑡𝑒𝑟 Energy transferred to
the water
[𝑊]
𝑄̇ 𝑙𝑜𝑠𝑠 Losses in the system -
𝑄 𝑚
Volumetric flow rate of
liquid to be metered in
units per minute
-
𝑊𝑚 Mass flow rate of fluid
to be metered in
pounds per minute
-
𝑊𝑐 Weight of calibrating
fluid collected in
pounds
-
𝜌𝑓 Density of metering
float
[𝑔/𝑐𝑐]
𝜌 𝑚 Density of liquid to be
metered
[𝑔/𝑐𝑐]
𝜌𝑐 Density of calibrating
liquid
[𝑔/𝑐𝑐]
q Power output [𝑊]
G Solar irradiance on
collector plane
[𝑤/𝑚2
]
𝑎1 1st order heat loss
coefficient (heat loss
coefficient at collector
fluid temperature equal
to the ambient
temperature)
[𝑊/𝐾]
𝑎2 2nd order heat loss
coefficient(temperature
dependant term of heat
loss coefficient)
[𝑊/𝐾2
]
𝑑𝑇 Temperature difference
between the collector
mean fluid temperature
and ambient air
temperature
[𝐾]

x
𝑛0 Optical efficiency
(combined efficiency of
the transparent cover
and the absorber
-
𝜂 Thermal efficiency of a
solar collector
[%]

Group Platinum 1 28/04/2014
Chapter 1: Introduction
There is a global need for efficient use of fossil fuels for the provision of energy
and also the use of renewable energy sources to reduce the dependence of the
country’s energy supply to reduce energy bills, reduce greenhouse gas
emissions, increase the number of jobs in the renewable energy industry, and
reduce the price of fossils fuel.
Figure 2 This is the total Primary Energy Requirement Ireland (Sustainable Energy Authority of
Ireland , 2013).
In developed countries most of the fuel consumption is used for heating,
cooling, ventilation and sanitary hot water. The potential of solar water heaters
is huge because all homes, commercial buildings and industrial facilities require
hot water. This type of technology is feasible and an economic attraction
compared with other kinds of solar energy utilization.
The Solar panels transform the solar radiation into hot water. It is stored in a hot
water cylinder during the day and it can be used when the heat is needed. They
are generally located on a south-facing roof. When the demand for hot water
rises it will be more beneficial to install a solar thermal collector since the
payback period will be short.
Almost all solar water heating systems used in temperate climates use flat plate
or evacuated tube collectors, which absorb both diffuse and direct solar
radiation and function even under clouded sky. In Northern Europe, solar
domestic water heating systems can meet up to 60-70% of the water heating

needs of a typical house and in southern Europe up to 90% so the evaluation of
solar thermal systems is very important (Elementary Energy Ireland, 2009).
1.1: European Solar Thermal Sector
The effects of the financial crisis in 2008-2009 are still being felt and it is
blocking the solar thermal sector from taking full advantage of the European
trend.
The promotion of the use of energy from Renewable Energy Sources was
adopted by the European Parliament and Council in 2009. Their treaty
incorporated an act which encouraged that all the state members incorporate a
share of renewable in their total energy mix and the EU is aiming for a 20% cut
in Europe's annual primary energy consumption by 2020. The Commission has
proposed several measures to increase efficiency at all stages of the energy
chain: generation, transformation, distribution and final consumption (European
Solar Thermal Industry Federation, 2012 ) .
Despite that, the National Renewable Energy Plan shows that there are a lot of
countries where the solar thermal market is very low or they do not have
markets like Estonia or Romania. The major markets would be Italy, Germany,
France, Spain and Poland.
1.2: Irish Solar Thermal Sector:
To develop the Irish market for solar thermal heating, it will be important for an
EU wide implementation of standards and a general promotion of this type of
technology.
The Irish Government has promised to guarantee a sustainable development.
They have also agreed to increase the contribution to the renewable energy
market and deliver a sustainable energy future central policy in Ireland. With
other EU Member States, Ireland has agreed a legally binding objective for 20%
of our total energy (heat, transport and electricity) to come from renewable
sources by 2020 (European Comission, 2009) .
The Government has set an objective for 12% of heat to come from renewable
sources by 2020. Moreover, the Government has made solar thermal more
attractive providing incentives which continue to increase the market (SEAI,
2014) .
The Solar thermal sector in Ireland is relatively undeveloped compared to other
European countries. The total number of installed solar thermal collectors in
2003 is around to 5000 [𝑚2
] producing more or less 2500 [𝑀𝑊/ℎ] of heat, and

saving more than 700 tons of [𝐶𝑂2] per year. The majority of the installations
are air-collectors followed by flat plate and evacuated collectors (European
Solar Thermal Industry Federation, 2012 ).
As it is not possible to depend on solar energy at all time in Ireland, a solar
water heater or a solar combo-system needs the support of a heating system
such as a boiler, a heat pump or an electric heater.
1.3: Project Aims
The aim of this project is the construction of one external circuit simulating one
real installation of a solar thermal panel and to evaluate the efficiency of the flat-
plate collector under laboratory conditions. Another important outcome is to find
out which type of solar collector is the best to install in Ireland. The last outcome
is to improve the group’s knowledge of the renewable energy sector in Ireland
and in Europe.
1.4: Project Objectives
 Perform a Literature review about the Renewable and sustainable forms of
energy production, especially into solar energy (the solar thermal panels).
 Evaluated the differences between evacuated tube collector and flat-plate
collector.
 Design and build one external circuit simulating a real system in a house to
obtain hot water with a solar thermal panel.
 Determine the efficiency under laboratory conditions of the flat-plate
collector and understand the relevant mathematics associated with it.
 Identify which collector will work better in Ireland´s climate.
 Work as a team during all the process.
1.5: Project scope
The project scope was to improve the system and to test the efficiency of solar
thermal panels. Time was a major constraint for this project since the external
circuit took longer than predicted to make. If there was more time more
experimental elements of the project could have been done like the comparison
between evacuated tube collector and flat-plate collector. Another such element
was to test the effect wind has on solar thermal collectors. All the laboratory
experiments were carried out inside the solar lab but a fan could have been
used to simulate wind just as the high intensity lamps were used to simulate the
sun.
The collector was not tested outside because of unstable conditions. The
ambient air temperature is one of the key factors in solar thermal collector
efficiency as was discussed in the literature review. The ambient air

temperature is one of three factors that govern the efficiency of the solar
thermal collector.
At the beginning of the project a risk assessment was done. This looked at any
possible risks that could occur during the course of the experiments. When the
project was being built all the work was carried out in workshop where again
there was a safety element involved. Within the circuit there was safety features
attached such as an expansion vessel for the primary circuit which was heated
by the solar thermal collector. There was also a safety valve put on that same
primary circuit which was a three bar expansion valve. The secondary circuit
was left open to the atmosphere so that a pressure would not build up in the
copper cylinder. The copper cylinder that was used was bigger than the one
originally planned but this meant that the water inside would take longer to heat
and thus the experiment would be finished as the max temperature of the panel
would be obtained before the tank would heat fully.
The safe operating temperature for the collector was researched as part of the
literature review. For the flat plate collector the maximum operating temperature
is 80 degrees Celsius. Once the operating temperature is reached the
experiments are were stopped for safety reasons.
1.6: Project budget
For each group doing the final year project there is a fund of €300 allocated to
each group. For the project there were a number of items purchased. The first
item was to buy a copper cylinder that cost €150. The next items that were
purchased were connections for the secondary circuit for the copper cylinder.
They cost €20. The last item that was bought was a lagging jacket for the
expansion cylinder and the pump. This was purchased and was used to insulate
the expansion cylinder and the pump. This small lagging jacket cost €9.99. After
all the items were bought there was €119 left from the budget.
1.7: Project methodology
The external circuit that was built for the project was built for a number of
reasons. The first reason was to improve the efficiency of the system that is
used to test the solar thermal collector because the original circuit that was
installed was inefficient.
On the original circuit, the pump was installed at the bottom of the collector.
This caused inefficiency within the system because it was adding heat while it
was running. Also, the bottom rows of the high intensity lights caused the
components to heat up.

As mentioned in the literature review, the incident radiation is one of three key
factors that govern solar thermal collector efficiency. Since only half of the panel
was used, the efficiency of the system was hampered.
To solve these problems the external circuit was built. The external circuit
consists of a pump, flow meter, expansion cylinder and the copper tank. This
was all connected using 22 [𝑚𝑚] copper pipe and 13 [𝑚𝑚] copper pipe. There
were also a number of valves that were attached at various different points to
control and regulate the flow of water.
The experimental procedures were to the standard that was mentioned in the
literature review. In the literature review previous solar thermal experiments
were looked at. The laboratory experiments that were researched included the
flat-plate and evacuated tube collectors in a controlled laboratory experiment as
well as in outside conditions.
The experiments in the laboratory were carried out exactly as the one that was
done in semester one for the module Solar Energy. In that class the group
learned how to run the solar collector experiment. There was slight variation in
the tests that included the external circuit, as the external circuit contained a
slightly different set up than that which was found in the original circuit.
During the building of the external circuit a number of plumbers were consulted.
They informed us on all the safety aspects of such as the expansion vessel and
the expansion valve and their suitable location.
Chapter 2: Literature Review
The literature review is a collection of research and findings that were found
from internet sources and books related to the solar thermal sector. Through
this section we will look at at solar sources and their data, the history of solar
technology and the various options on the market and their components that
make the system work.
2.1: Weather in Ireland
Ireland usually gets between 1100 and 1600 hours of sunshine per year,
provided by both types of sunlight: direct sunlight (40%) and indirect sunlight
(60%).
According to the geographical area the average hours of sunshine varies
slightly. For instance, on the south of the country, at Roche’s Point’s Weather
Station, an average of 3.9 hours of sunlight per day during the course of the

year (Met Eireann , 2014) while the north of the country at Belmullet Weather
Station receives an average of 3.5 hours of sunlight per day during the course
of the year (Walsh S, 2012).
Regarding the majority of areas in the country, they get an average of between
3.25 hours and 3.75 hours of sunshine per day. (Walsh S, 2012).
The sunniest part is the south-east coast, where Rosslare, County Wexford is
the sunniest area, receiving on average 4.38 hours of sunshine per day. On the
contrary, the dullest town is Birr, County Offaly, receiving an average 3.2 hours
of sunshine per day.
Logically, hours of sun varies depending on the season. In summer months,
May and June are the sunniest months receiving between 5 and 6.5 hours of
sun each day over most of Ireland.
On the contrary December is the worst month, with an average daily sunshine
of about 1 hour in the north and almost 2 hours in the south-east
Figure 3: Map of Ireland showing by the sunlight distribution
of the sun during the summer (Walsh S, 2012)
Figure 4: Mapof Ireland showing the sunlight distribution
of the sun during winter (Walsh S, 2012) .

In terms of sunshine hours during spring and Autumn periods, in spring the
country receives an average of 4.5 hours while in autumn the average of
sunshine hours is just around 3 hours.
Figure 7: Graph showing the overall sunshine hours in Ireland along the year (Weather and
Climate, 2013) .
Figure 5: Map of Ireland showing the sunlight distribution of the sun
during in spring (WalshS, 2012) .
Figure 6: Mapof Ireland showing the sunlight
distribution of the sun during autumn (Walsh S, 2012)
.

We can now conclude that the solar climate of Ireland varies greatly throughout
the year which makes us question the use of solar thermal panels in countries
such as our own. However, it can be seen in the next section that all is not lost
when analyzing the strengths and weaknesses involved.
2.2: Strengths and weaknesses of solar systems
2.2.1: Strengths
 Renewable energy solar energy is clean, inexhaustible and
environmentally friendly.
 Clean energy production this reduces the home´s carbon
footprint because It is carbon-free. However, there are some
emissions associated with the manufacturing, transport and
installation of solar power systems.
 Installation initiatives the government offer grants or discount
for the installation of renewable energy products. This means that
the real cost of solar panels is less than what they used to be.
 Abundant  The surface of the earth receives 20,000 times more
solar power than what the entire world need.
 Operating costs are low  Solar energy is free and the solar
water heaters require little maintenance. Therefore the operating
costs are lower compared to those of fossil fuels.
 Good availability solar energy is available all over the world.
 Reduced dependency you can generate your own heat and use
it when you need.
 High efficiency the technology in the solar power industry is
constantly improving.
 Silent  There are not moving parts involved, so there is no
noise associated.
2.2.2: Weaknesses
 Intermittent  Solar energy is an intermittent energy source
because the sun does not shine brightly 24 hours a day.
 Low energy density the mean of power density for solar
radiation is 170 W/m². This is a good value if we compare with
other renewable energy source, but not if we compare to oil, gas
and nuclear power.

 Expensive  Construction and installation costs can be relatively
high. Even with the installation initiatives, a solar system has a
high initial cost. Therefore, it is hard to compete against very
cheap natural gas.
 Relatively new technology involvedsometimes it requires
materials that are expensive and rare in nature.
 Site preparation they require a considerable amount of space
and to alter some of the home´s infrastructure systems.
 Some people find them unattractivethe solar panels are placed
on the roof of the property.
 Pollution  Some manufacturing processes often are associated
with greenhouse gas emissions.
 Efficiency is dependent on sunlight resourcesin cold climates
the efficiency is smaller and it cannot work if they are covered by
snow.
2.4: Feasibility of installing solar thermal panels in Ireland
. The feasibility of installing solar thermal panels is determined by the radiation
level that would be achieved.
The sun's radiation levels of Ireland would be able to heat as much hot water in
one year using only about 450 units of electricity. Even on cloudy days in winter
and summer the sun´s heat can still supply hot water providing on average up
to 70% of the annual hot water demand (Elementary Energy Ireland, 2009) .
Solar evacuated tubes have benefits over solar flat plates in Ireland, due to the
fact that they don’t have heat losses because they are vacuum insulated and on
an average day, the air temperature might be 10 º C so the panel at 70 ºC will
lose lots of heat to the outside air. (Elementary Energy Ireland, 2009)
In addition, solar flat plate collectors work properly when the sun is overhead
but they cannot take advantage of the energy at 4 p.m. in the afternoon when
the sun is facing the side of the flat surface, thus solar evacuated tubes work
better in Ireland conditions.
The cost of installation and supply of an entire solar water heating system in a
dwelling with a 3 m² solar collector tubes in Ireland start from 3900 € and there
is a SEAI grant of up 800€ (SEAI, 2014) .
Grants are available from the SEAI for some renewable energy projects which
will help decrease the capital cost involved.
Approximately it can be expected that the electricity usage for hot water will be
decreased by between 1200 and 1500 kWh per year with a 3 m² solar collector

tube installed. This is equivalent to between €192 and €240 every year
according to the Standard Tariff rate (Alternative energy ireland, 2014)
2.5: Natural circulation and forced circulation
There are two choices for circulation; natural circulation and forced circulation.
Natural circulation is called thermo siphon. This type of circulation uses the
thermodynamic properties and gravity to move the fluid in the solar panel.
Water rises when heated hence the name thermo siphon circulation. The water
rises, circulates and comes back down and the cycle begins again. These
systems are sometimes used on houses where the thermo siphon tank is
mounted above the solar collector.
At the start of the project this type of circulation was considered but after doing
the calculations it was found that there would not be enough gravity to push the
water up the proposed height difference. There was also a safety element within
this circulation, as the tank height was proposed to be over 2 meters tall and the
tank had the capacity of 18 litres. This was a hazard, especially since the tank
would collect the hot water from the solar thermal panel.
The other type of circulation is the forced circulation. This is where the pump is
used to circulate the water around the entire circuit. This method was used in
the project to run the solar collector.
The equation to determine solar collector efficiency takes into account the
electrical power supplied by the pump.
2.5: Selection of the Solar Collector Type
Each type of collector has its advantages and disadvantages, and in many
cases both can work for the same application and situation. It is very important
that your selection is the proper design, sizing, components and installation
otherwise the collector will not obtain the efficiency required.
In the market, there different types of solar thermal collectors but this report has
been focused on Flat-plate collectors.
2.5.1: Flat plate solar collectors
The main components of a flat-plate collector are: an insulated metal box with a
glass or plastic cover and a dark-colored absorber plate. Solar radiation is
absorbed by the absorber plate and transferred to a fluid that circulates through
the collector and into the copper pipes. The heat transfer fluid is pumped from
the hot water storage tank. If it is a direct system a heat exchanger is used. If it

is an indirect system, a copper storage vessel is used. (The Worlds of David
Darling, 2009) .
Figure 8: Flat-Plate Collector (The Worlds of David Darling, 2009).
2.5.2: Flat-plate collectors under laboratory conditions and solar collector
standards.
The picture below is from a report that was published by mechanical engineers
in Cyprus. In that report they mention the maximum temperature that FPC
should go to. This guideline was followed during the experiments that were
done for the project.
Solar energy collectors
Motion Collector type Absorber type Concentration ratio Indicative
temperature
range [ºC]
Stationary Flat plate collector
(FPC)
Flat 1 30-80
Evacuated tube
collector (ETC)
Flat 1 50-200
Table 1: Safe temperature ranges for solar thermal panels (Kalogirou, Soteris A., 2004).
The picture includes the temperature range for evacuated tubes but they were
not part of the experiments as only the flat-plate collector was used during the
experiments.
There are also standards that are used when caring out laboratory experiments

involving solar thermal collectors. The standard that is used more often is the
ASHRAE standard 93: 1986 (ASHRAE, 2003). In this standard there is three
elements that are analyzed. They are incident radiation, ambient temperature
and inlet fluid temperature. There is an also triple E eligibility criterion that is
used in Europe. For the solar collectors there are two standards the EN12975-1
(Part 1 General Requirements) and EN12975-2 (Part 2 Test Methods). The
other standard is for factory made systems and they are EN12976-1 (Part 1
General Requirements) and EN12975-2 (Part 2 Test Methods). They also
mention that the following standards should be used when comparing to other
products. 𝐺: 900 W/𝑚2
,𝑑𝑇 50𝐾 and A: 1𝑚2
(ASHRAE, 2003).
Equation 1 Triple E eligibility criterion
𝑞 = 𝐴(𝑛_0 𝐺 − 𝑎_2 𝑑𝑇 − 𝑎_2 𝑑𝑇^2 ) [𝑊] (SEAI, 2012)
The experiment that was carried out for the project was run to this standard.
The standard has the following criteria; rate of incident radiation falling on the
solar thermal collector was measured as well as the rate of heat transfer to the
fluid that is used during the experiment all of these were analyzed under steady
state or quasi-equilibrium conditions. Quasi-equilibrium can be defined as” A
quasi-equilibrium process can be viewed as a sufficiently slow process that
allows the system to adjust itself internally so that properties in one part of the
system do not change any faster than those at other parts” (Yunus A.C, John
M.C, Robert H.T , 2012).
In some of the laboratory reports that were published on this topic they look at
different types of absorber used when making flat plate solar thermal panels
and also look at the materials that the transparent cover is made of. There is a
number of absorber materials that where looked at as part of that report. That
report was written by mechanical engineers in India. They found that the
efficiency of the flat plate collector is increased with ambient temperature as the
heat loss was reduced (Vettrivel H.V, Dr. Mathiaragan, 2013) .
The other element of the experiment that was found was that the emissivity of
the plate had significant impacts on the system efficiency. The element that was
found during that particular experiment was that “It can be observed increase in
pε is to dissipate more heat to atmosphere and consequent reduction in
efficiency of the system”. So the transparent cover that the flat plate collector is
made of is a very important factor when determining efficiency of the system. In
a different report that was written by mechanical engineers in India from a
different technical institute they conducted their research into the different
coatings that are applied onto the transparent cover. The picture below shows
all the coatings that are applied on flat plate collector panels at present

(Sunil.K.Amrutkar, Satyshree Gholdke,Dr.K.N.Patil, 2012) .
Figure 9: selective coatings applied to transparent covers on flat plate collectors (Vettrivel H.V, Dr.
Mathiaragan, 2013) .
In this report there were a number of findings. These standards were the ones
used for solar thermal collectors when running experiments on them. Also, how
the emissivity of the coating applied to the transparent cover can affect the
efficiency of the solar collector.
2.5.2: Evacuated tube solar collectors:
Evacuated tubes consist into two concentric glass tubes fused together; the
inner absorbs the radiation while the outer is transparent and create the vacuum
between them. In this way it is possible to isolate the hot water from the outer
reducing heat dispersion outwards and therefore gets a much higher efficiency
than the solar flat panels. The copper pipe located in the center of the tube
connects with the collector and with the pump that circulates the water into the
storage tank (University of Strathclyde Glasgow, 2005).

Figure 10: Schematic for Evacuated-Tube Collector (The Worlds of David Darling, 2009).
2.5.3: Cost:
One of the primary considerations for the selection of the collector type is the
cost. Usually, evacuated tubes collectors may cost between 1.2 and 2 times
more but this can be interoperated in the different ways. However, in cold
climates the additional cost is easily recouped by increased performance.
For example, in the case of Dublin Institute of Technology to run an experiment
to compare the Flat Plate and Heat Pipe Evacuated Tube Collectors for
Domestic Water Heating Systems in a Temperate Climate and using one
evacuated tube collector of 3 m2 and one flat plate collector of 4m2 the price of
the first one was the double of the second one (L.M. Ayompe, A. Duffy, S.J.
McCormack, M. Conlon, M.Mc Keever, 2011) .
2.5.4: Size:
The typical domestic installations for families of 4-6 persons in temperate
climates consist of 4-6 m2 flat plate solar collectors or 3-4 m2 evacuated tubes
collectors connected to a 200-300 liters hot water tank (L.M. Ayompe, A. Duffy,
S.J. McCormack, M. Conlon, M.Mc Keever, 2011) .
2.5.5: Life Spam:
Generally both types of collectors are designed to last 20 years or more and
they are sold with 10 years limited warranty.
However, evacuated tubes need more maintenance and repair because:
 Flat plate collectors will use thick (usually 4 millimeters), the tempered glass
can support without breaking under harsh weather conditions such as hail
storms. On the other hand, evacuated tubes use thinner glass (usually 1.6

millimeters) which is more susceptible to breaking and needing to be
replaced. This is one of the reasons that flat-plate collectors are considered
the most durable collector type.
 Evacuated tubes rely on a vacuum seal to prevent heat loss. Over time this
seal can be lost and the tube will required to be replaced.
The main problem of flat plate is that if something does break (such as the
glass), the installer will usually need to replace the entire collector. Though
evacuated tube collectors, due to the modular design, if an individual tube is
damaged no fluid enters the tube anyway so the system does not need to be
drained and it can be easily replaced (Heliodyne, 2010) .
2.5.6: Payback Periods:
Payback periods vary, depending on a number of factors: the cost of the fuel
displaced the amount of hot water used and the initial cost of the solar thermal
system.
A typical payback time for a household of 5 people who normally use oil or gas
to heat their hot water would be about 6 to 8 years or 4 to 5 years if they use
electricity.
2.5.7: Installation:
Both collectors have their advantages and drawbacks in terms of installation.
Supporters of evacuated tube said that because they come unassembled, is
easy to easily carry the evacuated tube components onto the roof without
needing any special equipment.
Proponents of flat plate argue that because they are fully assembled, once
hoisted onto the roof, no assembly is required so the installation time is reduced
(Heliodyne, 2010) .
2.5.8: Useful Climates
Evacuated tubes collector, can be used in any climate, from extremely hot to
extremely cold.
Flat Plate collector, should only be used in warm climates where freezing
temperatures rarely occur (T. Christoph, W. Zörner, C. Alt, C. Stadler,, 2005) .
2.5.9: Orientation
Through their circular design evacuated tubes are less sensitive to sun angle
and orientation than flat-plate collectors. The total efficiency in all areas is
higher and there's better performance when the sun is not at an optimum angle
(when it’s early in the morning or in the late afternoon).

2.5.10: Efficiency:
Flat plate collectors aren’t as efficient as the evacuated tubes but as technology
is rapidly improving certain flat plate solar collectors have become just as
efficient as evacuated tubes.
The efficiencies of flat plate collectors make them very suitable for domestic
installations or for installations that don’t require very high temperatures.
Evacuated tubes collectors are generally less efficient than flat-plate collectors
in full sunshine conditions. However evacuated tubes collectors perform better
under cloudy windy conditions or extremely cold conditions. Due to the fact that
the heat loss to the environment has been reducing because the heat loss due
to convection cannot cross a vacuum of the evacuated tube collector but
sealing and maintaining a vacuum is difficult and an evacuated tube without a
vacuum performs very poorly (Kingspan Renewables Ltd, 2011) .
2.5.11: Conclusion:
Summarizing, after study all the information founded we can conclude that:
On one hand, evacuated tube collectors based systems, capture sunlight better
as they have a greater surface area exposed to the sun at any time so they
have a higher solar yield than flat plate with the same absorber area, are more
efficient in transferring heat (30%more) because they have a little thermal loss,
work in cold, windy and humid conditions , are durable and if a tube should be
broken, it can be easily and cheaply replaced, provide excellent performance in
overcast conditions, require a smaller roof area than comparable flat plate
collectors, do not have the same level of corrosion problems as flat plate.
On the other hand, flat plate collectors are cheaper, can be easy integrate into
the roof of the building but they need higher wind load.
2.6: Calibration for the project
In the project there are a lot of elements that require calibration. The various
measuring elements are the thermocouples, the flow meter, radiometer and the
pump is calibrated also. All these measuring instruments are calibrated in
different ways.
2.6.1: Thermocouple
Calibration insures that the measurements are in good working order and that
the result obtained using these instruments are very accurate. For
thermocouples there are a lot of methods for calibration. In a laboratory report
written by G.W Burns and M.G Scroger who work in the National Institute of

Standards and Technology that is part of U.S Department of Commerce, they
mention that during calibration thermocouples where put into ice baths as
reference points. The report also mentions that thermocouple must be
calibrated but how depends on the application the results of calibration should
be compared to other published figured that can be got from platinum
resistance thermometers (G.W Burns and M.G Scroger, 1989).
In the document for calibration they mention three methods for calibration of
one of which I mentioned up above. The first method is to compare the result to
the “calibrated reference thermocouple in an electric tube-type furnace”. The
second method is where a platinum resistance thermometer is put into cryostat
(which is a device that is used to keep low cryogenic temperatures of samples
or devices mounted within the cryostat itself) or into stirred liquid water and the
third method is “at certain thermometric fixed points of the IPTS-68 as realized
in metal freezing cells” (G.W Burns and M.G Scroger, 1989) .
In that document the calibration procedure is explained in detail, the SPRT
(Standard Platinum Resistance Thermometer) must be connected to a Rubicon
six dial potentiometer. The potentiometer is used to measure the emf produced
by thermocouple during calibration. Before the calibration the thermocouple
must be examined if the measuring junction is not made the must be silver
soldered together. If the thermocouple is bare wire and is not insulated then a
fiberglass sleeving can be used to insulate it. The test thermocouple is then
placed into a glass tube before being placed into the stirred liquid bath (G.W
Burns and M.G Scroger, 1989) .
The report suggests that the thermocouples depth of immersion should be 12
inches or 30.48cm in the bath that contains the stirred liquid. The 12 inches or
30.48cm should be below the surface of the stirred liquid. The actual
thermocouple is put into the sample that it’s measuring and a copper extension
wire is connected to the thermocouple and this copper extension wire
connection will go to the stirred liquid bath. The reason this is done is so when
the results of the calibration are done the thermocouple will have a reference
junction to compare against (G.W Burns and M.G Scroger, 1989) .
The results are recorded by the Rubicon six-dial potentiometer and an
automatic bridge. There is a sequence that the potentiometer follows is this
SPRT, TC, SPRT, TC and SPRT. The reason the SPRT reading is done three
times is that is the bath temperature can be determined from these results. The
thermocouple measurement is averaged between the two results. The
potentiometer applies correction and the data is normalized to desired
temperature. The bath temperature should be carefully monitored if it changes
by more than 0.05° C during the three readings then measurement at this
temperature is repeated (G.W Burns and M.G Scroger, 1989) .

The stirred liquid bath or calibration bath is a cell that contains the
thermocouple. The cell can be inserted into a Dewar flask that is full of liquid.
The actual liquid depends on the application itself. The cells are made of
highest purity material available and are insulated to minimize the result
derivation. The Dewar flask is used to maintain a temperature required for the
test. The liquid in the Dewar flask is usually 100 litres liquid nitrogen (LN2). But
for tests that require the temperature to remain constant for very long periods of
time 40 litres of ethanol is used. The system uses two-stage compression
system and temperatures up to -80 can be maintained (G.W Burns and M.G
Scroger, 1989) .
The main function of a thermocouple is to measure the temperature difference
between two metals to form an EMF. It is a pair of junctions, one at a reference
temperature (eg 00C) and the other junction at an unknown temperature. The
temperature difference will cause a voltage commonly known as the Seed beck
effect.
Figure 11: Schematic showing thermocouple calibration (Facstaff, 2014)
The thermocouples that are used in the project were k type thermocouples. The
accuracy of thermocouples is determined by the temperature that will operate
in. There are two tolerance classes for the k type thermocouple they are shown
on the table below. This class different to the other classes but operates on the
same principle as the other tolerance classes. The two classes are called
Standard Limits of Error and Special Limits of error.

Figure 12: Tolerance classes for k type thermocouples (Omega, 2014)
There is another chart that shows all the tolerance classes for the k type
thermocouple and is shown below. These classes are similar to the Standard
Limits of Error and Special Limits of error.
Figure 13: Tolerance classes for k type thermocouple (Uteco, 2014)
All the classes made choosing an accuracy tolerance very difficult so a way
around that was to find out if the thermocouple operated within the Standard
Limits of Error or within Special Limits of error. The thermocouple that was used
in the project was a nickel-chromium/nickel-aluminum. The tolerance class for
this particular thermocouple is class 2 or using the other tolerance classification
it’s Standard Limits of Error which is +/-2.5% or 0.0075×T. The first chart
mentioned Standard Limits of Error for k type thermocouples as +/-2.2% or
0.0075% but is dependent on the material composition of the wire so the figure
varies slightly. The thermocouples used in the project where calibrated as
mentioned in the report. The way the thermocouples were calibrated is shown
below in the illustration.
Figure 14: The above is thermocouple calibration (Marineinsight, 2014)

The thermocouple wires used had the two wires for plus and minus and an
additional wire for to create a reference junction in the report it was mentioned
that a copper wire was used for this extension into the ice bath. This calibration
was mentioned in the report. Another way to improve the thermocouple reading
is to place the thermocouple wire directly into the water flow. This can be done
two ways one is a thermo well or a binder point. Here is a simple diagram below
showing a thermo well.
Figure 15: Thermo well diagram (blogspot, 2014)
The problem with the thermo well is that the response time is very long as the
heat must travel through the thermo well wall in order to reach the thermocouple
inside. This can be prevented by reducing the amount space that the heat has
to travel to the thermocouple inside.
Binder points are similar to thermo wells but they have a smaller area for the
heat to travel. Here is a picture of the binder point below.
2.7.4: Flow meter
A flow meter is a device used for measuring the flow rate of a liquid in a pipe.
Using a flow meter allows for optimal balance across the system, ensuring peak
energy distribution which gives us more efficient operation as well as greater
performance.
An acrylic flow meter is sufficient for most solar thermal arrays, capable of
operating under temperatures of up to 650 C and maximum pressure of 6.9 bar
pressure.

Figure 16: Picture showing the acrylic flow meter (Inds, 2014)
The flow meter also requires calibration this can be done by the company that
manufactures the flow meter. When a variable area flow meter is calibrated
there is different number of ways it can be done. It also depends what type of
fluid is used during the calibration as results can vary. The ISA has
recommended practice when it comes to the calibration of variable area flow
meter both for gas and fluid. Also there are three basic methods when it comes
to variable area flow meter calibration, these are volumetric, gravimetric and
comparison (ISA 1961). In volumetric method “the volume of fluid flowing is
accurately measured and timed as it passes through the Rota meter into the
collecting chamber at a controlled rate” (ISA 1961). These are the variable area
flow meter used during the project contained water as the fluid. The equation
that is used for volumetric liquid calibration is this.
Equation 2: The equation used for liquid calibration volumetric method (ISA, 1961)
𝑄 𝑚 =
𝑉𝑐
𝑆𝑒𝑐
× 60 × √
(𝜌𝑓 − 𝜌 𝑚 )𝜌𝑜
(𝜌𝑓 − 𝜌𝑐)𝜌 𝑚
The gravimetric method involves using a very accurate scale to measure the
fluid that passes through the flow meter. The equation that is used in the
gravimetric method is this one below.

Equation 3: The equation used for liquid calibration gravimetric method (ISA, 1961)
𝑊𝑚 =
𝑊𝑐
𝑆𝑒𝑐
× 60 × √
(𝜌𝑓 − 𝜌 𝑚 )𝜌 𝑚
(𝜌𝑓 − 𝜌𝑐)𝜌𝑐
The comparison method involves using another accurately calibrated flow meter
to use as a comparison to the one being tested. The accuracy of this method
depends on the accuracy of the second flow meter. The next page shows the
schematic for all of the methods.
Figure 17: the volumetric calibration method for variable area flow meter (ISA, 1961)

Figure 18: the gravimetric calibration method (ISA, 1961)
Figure 19: the comparison calibration method (ISA, 1961)
2.7.1: Circulating pump
The nominal flow rate of a small solar heating system is 30 to 50 litres per
square metre of collector surface. This circulation pump has to be able to

guarantee this flow rate. Conventional pumps with an electric input between
40W and 80W are sufficient for most solar system arrays.
When a pump is calibrated the water flow is measured against back pressure.
This is done using a flow meter. There is also calibration devices that are used
one such device is below. This device is used to create a pressure so that it can
be measured. Some pumps can be calibrated digitally using various software
programs.
Figure 20: pressure calibration pump (Magnumpropumps, 2014)
There is also digital calibrator that can be linked into computers and can
analyze the pump and its performance.
. 
Figure 21 Pump Wilo-Star-RS 25/4 (Valgroup, 2014)

Table 2: Usefull pump information (Valgroup, 2014)
Material
Pump housing: Grey cast iron (EN-GJL-200)
Impeller: Plastic (PP - 40% GF)
Pump shaft: Stainless steel (X40Cr13)
Bearing: Carbon, metal impregnated
Approved fluids (other fluids on request)
Max. Volume flow: 4 𝑚3/ℎ
Max. delivery head: 4 𝑚
Pipe connections
Threaded pipe union: Rp 1
Overall length: 180 𝑚𝑚
Motor/electronics
Electromagnetic compatibility: EN 61800-3
Emitted interference: EN 61000-6-3
Interference resistance: EN 61000-6-2
Protection class: IP 44
Insulation class: F
Mains connection: 1~230 𝑉, 50 𝐻𝑧
Speed: 2350 / 2630 / 2720 𝑟𝑝𝑚
Nominal motor power:
15.5 / W9.5 / W5.5 W
Power consumption 1~230 𝑉: 28 / 38 / 48 𝑊
Current at 1~230 𝑉: 0.13 / 0.17 / 0.21 𝐴
Max. Current: 0.21 / 0.17 / 0.13 𝐴
Motor protection: Not required (blocking-
current proof)
Threaded cable connection: 1x11
Information for order placements
Art no.: 4032954
EAN number: 4016322364191
Weight approx.: 2 𝑘𝑔
Make: Wilo
Designation: Wilo-Star-RS 25/4

Figure 22: Pump Wilo-Star-RS 25/4 impulse and power absorbed (Valgroup, 2014)
2.7.6: Radiometer
The last element in the project that required calibration was the radiometer. The
radiometer that was used during the project was calibrated by a technician
when the project was started so it didn’t require calibration. When a radiometer
is calibrated the following factors are taken into account.
Direct normal ("beam") solar irradiance (Watts/square meter)
Diffuse horizontal ("sky") solar irradiance (Watts/square meter)
Radiometer body temperature (Degrees Celsius)
Pyrometer dome temperature (Degrees Celsius)
Air temperature near calibration tables (Degrees Celsius)
Relative Humidity near calibration tables (Percent)
The calibration standard for shortwave radiometer is governed by the World
Radiometric Reference. All their data is compiled from “seven self-calibrating
absolute cavity radiometers”. Every five years reference radiometers around the
world are brought to the World Radiation Centre in Switzerland and are
compared against the seven self-calibrating absolute cavity radiometers. These

radiometers are used in other laboratories and in industry to set a working
standard.
Chapter 3: Materials & Methods:
As we have seen, the aim of this project is to evaluate the efficiency of the flat-
plate collector under laboratory conditions.
To do that, had been decided the construction of one external circuit simulating
one real installation for a solar thermal panel because with the actual method
there are some problems and it is very far from the real system.
Figure 23: Original system to evaluate the efficiency of the solar thermal panel

Figure 24: New system to evaluate the efficiency of the solar thermal panel
The new system is more similar to the system of a typical house, it will be tested
and the results obtained will be commented.
3.1: Materials:
There was a number of Materials that were used during the course of the
Project
3.1.2: Circulating pump
A circulating pump works by pumping the liquid in a loop or closed circuit. In a
closed loop system, little energy is needed as the liquid travels around the loop
and returns to its original position. The pump only needs enough power to
counteract the drag or inertia in pipes to propel the water forward efficiently.
An electric motor powers an impeller, which sends the water forward or upward.
The motor is sealed in a waterproof casing and is connected to the impeller.
In the case of the Solar Thermal system in question, water is pumped to the
solar collector where it will be heated. That water then moves its way to the

water tank, where the heat is dissipated to the water. The pump then sends the
cooler water in the tank back to the collector and the process is repeated until
all water is heated and set at a cut of point.
Figure 25: Circulating Pump
3.1.3: Thermocouple
The main function of a thermocouple is to measure the temperature difference.

Figure 26: Thermocouple
3.1.4: Hot water tank
The hot water tank consist is a cylinder that contains a coil. This coil connected
to the solar thermal panel “primary circuit” transferred the heat into the water of
the tank it does not mix with the stored water in the cylinder. The “secondary”
circuit refers to the stored water in the hot water cylinder which is used for
domestic use. In the primary circuit the same water continuously circulates.
The characteristics of the tank are:
 Height  36𝑖𝑛 = 91.440𝑐𝑚
 Diameter  15𝑖𝑛 = 38.100𝑐𝑚
 Capacity  94 liters
 Date of Manufacture  13/12/13
 Type  Open Expansion Reservoir Supply
 Max Static Head  10metres
 Company  LB Cylinders

Figure 27: Copper cylinder used in the external circuit
3.1.5: Flow meter
A flow meter is a device used for measuring the flow rate of a liquid in a pipe.
One will be installed into the close circuit and the flow rate of the open circuit
will be measured filling one pipette and measuring the time.

Figure 28: Flow meter used in the external circuit
3.1.6: Copper and plastic pipes
Copper and plastic pipes are used for supply of hot and cold water systems.
Copper offers a high level of resistance to corrosion and the plastic is a good
insulation to avoid the losses of heat and with its flexibility facilitates the
connections of the circuit.
Figure 29: Copper and plastic pipes

3.1.7: Valves
Valves are used to regulate the flow rate for both circuits and to facilitate the
connection and disconnection of the system.
Figure 30: Valve on the hot return in the primary circuit
3.1.8: Pressure Valves
Using this type of valve, the security of the system is guaranteed because if in
some moment the pressure is too high the valves will be open before
discharging it.
Figure 31: Pressure valves on the copper cylinder

3.1.9: Insulation
The insulation is used to recoat as many parts of the circuit as is possible to
avoid the heat losses.
Figure 32: Insulation
3.1.10: Expansion tank vessel
The expansion tanks ensure that the system pressure does not exceed or drop
below the limits obtained in the design of the system. The design of the
expansion tank divides the air space inside the tank occupied by the pre-
charged gas and the solar liquid. As the liquid expands due to heat, the
diaphragm stretches into the gas chamber.
The idea of the expansion tank allows for your solar heating system to operate
at optimal pressures without activating the safety relief valve. The size of the
tank is chosen depending on the solar loop requirements
The expansion tanks are an essential component in the steam-back solar
design, allowing for high pressure performances, resulting in a long lasting and
high performing solar thermal system.

Figure 33: the expansion tank vessel
3.1.11: Panel with the lights
All the light will be turn on to simulate the light intensity of the sun.

Figure 34: the high intensity lamps used during the experiments.
3.1.12: Radiometer
This device was used for measure the incidence light radiation.
Figure 35: Radiometer

3.2: Methods
3.2.1: Procedure: for original system
1. Turn on the three rows up of lights (we do not turn on all the lights
because if we will do we would interfere in the measures of the sensors).
2. Measure the radiation flux that arrives at the solar thermal panel:
3. The solar thermal panel will be divided into two rows and five columns.
4. With the lux meter will be measured the W/m-2 that arrives to the panel
5. Make the average of the data and use it for make our calculations.
6. Obtain the mass flow of water that pass through the solar thermal panel.
To calculate it will be needed some test tube to measure the millilitres
per second and will be able to calculate to mass flow that go out from the
panel.
7. Collect the data of the temperature sensors (water from the tap (T1),
water to panel (T2), water out (T3), ambient air (T4)) approximately every
ten minutes to show the progression of the experiment until it arrives to
the steady state.
8. Finally, the efficiency of the solar thermal panel will be calculated.
3.2.2: Analysis For the original system
Analysing the circulation system of the solar vacuum tubes to know its
performance characteristics, the path the water takes would be:
 The water comes from the tap and enters the circuit.
 A pump drives water to fill the vacuum tubes.
 The water passes through the flow meter and you can then measure the
water flow.
 Vacuum tubes are filled with water and the water is heated.
 Finally the water exits the tube to finish the circuit in the sink, thus the
flow rate can be regulated by the valve.
First of all, the temperature sensor T1 give us the temperature of water from the
tap. Next, the water pass through the pump and the flow meter and with the
temperature sensor T2 we can obtain the temperature of water just before the
solar thermal panel.
After this, the sensor T3 show us the temperature of the flow out (hot water), we
will assume that the temperature of the water that go out from the system is T3
too.
Finally, in the temperature sensor T4 we will see the temperature of the ambient
air.

It is important to know that the inputs of the system are the Q̇ Radlight (from the
lights that heat the solar thermal panel) and the Ẇ elec (that need the pump for
work) and the output are the Q̇ water and Q̇ loss.
In the next picture, we can show a schematic diagram of the experiment.
Balance equation:
+𝑄̇ 𝑅𝑎𝑑𝑙𝑖𝑔ℎ𝑡 − 𝑄̇ 𝑤 − 𝑄̇ 𝐶𝑜𝑛𝑑 − 𝑄̇ 𝐶𝑜𝑛𝑣 − 𝑄̇ 𝑅𝑎𝑑𝑙𝑖𝑔ℎ𝑡 = 𝐸̇ 𝑆𝑇
Start = fixed – zero – zero – zero – zero = high
Later = fixed – increased – increased – up – up =
lower
End = fixed – high – high – high – high = very lower
Steady State = fixed – max – max – max – max =
zero
Analysing the balance equation we can see that when we start the experiment
all the components of the equations are negligible except Q̇ Radlight that it’s a fix
value, so the temperature will increase very fast at the beginning.
Next, the other components start to increase and the temperature raise up but
lower than at the beginning and finally these components get their maximum
Figure 36: Return reverse header design in
evacuated tube panel
Figure 37: steady state diagram

value and the temperature remain stable. The system is now in the steady
state.
3.2.3: Procedure: for the new system
With the new system the method of operation will be:
The system is divided into two circuits, the first one is a closed pressurized
circuit with a pump that must be capable of establishing a flow and overcome
the load losses of the circuit.
1. The direction followed by the water through the primary circuit elements
is described below:
2. The water pressurized to 2 bars, is boosted by the pump and goes to the
solar panel passing through the flow meter before.
3. On the solar panel, water is heated by the spot lights.
4. Then water comes from the solar panel and passes through the coil
inside the tank heating the water of the tank.
5. Finally water goes out of the coil and goes to the pump, starting the cycle
again.
The second one is an open circuit that run with the pressure obtained from the
tap. The direction followed by the water through elements is described below:
1. The cold water goes out from the tap with a pressure of 2 bars and
enters to the tank.
2. In the tank the water is heated by the coil inside it due to the temperature
of the water that pass through it is higher because the solar thermal
collector heated it.
3. After that, the hot water goes out from the top of the tank obtain the hot
water that can be used for the house demand. The flow rate is regulated
by the valves.

Chapter 4: Results
The behavior of a solar flat thermal panel is going to be analyzed making
several experiments in the lab, with the purpose of finding the thermal efficiency
for the original and new system through data collected.
The first experiment was to test the efficiency of the solar flat thermal panel with
the “original system” to know how it could be improved later. After that, the “new
system” was built and tested comparing both results obtained, and reaching a
conclusion.
Before starting the experiments, the solar radiation was measured as explained
below.
4.1 Radiation:
The high intensity lights were put as close to the panel as possible, to maximize
the radiation absorbed. The panel was inclined at 80º allowing the whole front
surface to absorb heat from the high intensity lights and therefore all the water
collector inside was heated.
The radiation that arrives to the solar thermal panel is shown on the tables
below.
Table 3: Radiation along the front of the collector during the experiment.
Solar flat plate (W/m2)
460 460 470
580 560 520
620 680 690
660 730 730
660 720 670
560 650 540
380 390 430
190 200 170
510 510 490
540 560 540
650 700 640
650 710 600
580 600 580
560 610 550
360 400 350
180 200 160

The values given by radiometer oscillated a lot and therefore writing down the
exact amount of radiation reached in each value so an average was taken, we
did an average of the tables above to make the calculations for the next
experiments.
485 485 480
560 560 530
635 690 665
655 720 665
620 660 625
560 630 545
370 395 390
185 200 165
Table 4: Average irradiance at each part of the solar flat panel.
The average irradiance along the surface knowing its dimensions can be
calculated as follows:
Height = 1.92m
Width = 0.98m
Area of the panel = 1.90 × 0.95 = 1.80m2
Average irradiance = 519.79 W/𝑚2
4.2: Original system
During this experiment, the flat plate solar thermal panel was tested with the
original system to calculate its efficiency.
The different components of the balance equation were studied until the system
reached steady state.
4.2.1 Results
As a result the flat-plate solar thermal collector received 519.79 W/m2, the
following data was obtained:

Time of sample in
[min]
0 1 2 3 4 5 6 7 8 9 10
Water from the tap T1
[ºc]
13.7 13.9 14.1 14.2 14.4 14.6 14.2 14.1 14.0 14.3 14.5
Water entering into
the panel T2 [ºc]
27.7 28.0 28.4 28.9 29.2 29.5 29.9 30.2 30.6 31.1 31.6
Water leaving the
panel (T3) [ºc]
28.0 29.5 34.3 37.4 40.9 43.5 45.4 47.1 49.2 53.0 55.5
Ambient air room
temperature (T4) [ºc]
17.0 16.8 16.7 16.9 16.5 16.6 16.7 16.8 17.0 16.9 17.0
Table 5: Temperatures measuredin the original system the first 10 minutes.
Time of sample in [min]
11 12 13 14 15 16 17 18 19 20
[ºc]
14.4 14.5 14.6 14.6 14.7 14.8 14.9 14.8 15.0 15.0
Water entering into the
panel T2 [ºc]
31.9 32.2 32.4 32.6 32.7 32.9 33.2 33.6 33.9 34.2
Water leaving the panel
(T3) [ºc]
56.9 58.2 59.4 60.5 61.4 62.3 63.7 65.0 67.0 68.5
Ambient air room
17.1 17.0 17.0 17.2 17.2 17.2 17.3 17.5 17.6 17.7
Table 6: Temperatures measuredin the original system between first 10 and 20 minutes.
Time of sample in
[min]
21 22 23 24 25 26 27 28 29 30
[ºc]
14.9 14.7 14.6 14.9 15.1 15.0 15.3 15.2 15.1 15.2
Water entering into
the panel T2 [ºc]
34.6 34.9 35.5 36.1 36.6 37.0 37.2 37.5 37.8 38.1
Water leaving the
panel (T3) [ºc]
70.0 71.4 72.6 74.0 75.5 76.5 77.4 78.4 79.2 80.0
Ambient air room
17.9 17.8 17.9 18.0 18.1 18.0 18.1 18.2 18.1 18.0
Table 7: Temperatures measuredin the original system between first 20 and 30 minutes.
It is observed that the results for the different temperatures from the tap T1 and
the temperature of the ambient air T4 remain stable. However, the temperature
of the water to panel T2 and the temperature of the water out T3 are increasing
along the time as is expected.
The next graph represents the variation of each temperature measured along
the time during the experiment.

Figure 38: Variation of temperature along time in the Original System.
As we can see on the graph above the water leaving the panel (T3) had not
arrived to a steady state yet. When the experiment was carried out the safe
operating temperature had to be observed and therefore once the panel
reached 80°C it was stopped in order to prevent damage to the equipment and
to the people doing the experiments.
4.2.2 Calculation of thermal efficiency for the original system.
The thermal efficiency of a solar panel varies along time depending on the
temperature difference between the system temperature and the room
temperature.
To make the calculations the following data was taken:
Pump [W] 87
Flow rate water out of the circuit [kg s-1
] 0.0038
Mass flow water out of the circuit [kg] 0.2280
Specific heat capacity of water [Jkg-1
K-1
] 4180
Area of the panel [m2] 1.80
Average Irradiance [W m-2
] 519.79
Flow rate into the panel [kg s-1
] 0.05
Mass flow into the panel [kg] 3.00
Table 8: Useful data for the original system.
The instantaneous efficiency represents the efficiency of the solar panel at one
precise moment of time during the experiment.
0
10
20
30
40
50
60
70
80
90
0 10 20 30
Temperature[ºC]
Time [min]
Original System
Water from the tap T1 [ºc]
Water entering into the
panel T2 [ºc]
Water leaving the panel (T3)
[ºc]
Ambient air room

Equation 4: Solar Thermal Efficiency
𝜂 =
𝑄̇ 𝑖𝑛
𝑄̇ 𝑅𝑎𝑑 + 𝑊̇ 𝑝𝑢𝑚𝑝 − 𝑄̇ 𝑜𝑢𝑡
As an example for knowing how to calculate this value, we have taken the
temperatures obtained with 4 minutes after starting the experiment shown
below in table 9.
As well as the temperature increases at different parts of the circuit.
The temperature inside the panel (T5) was taken making an average between
the water temperature entering into the panel (T2) and the water temperature
leaving the panel (T3). Thus the amount of heat produced by the panel can be
calculated as follows:
Equation 5: quantity of heat absorbed by the water
𝑄̇ 𝑖𝑛 = 𝑚̇ × 𝐶 𝑝 × ( 𝛥𝑇5
̅̅̅̅̅)
= 0.05[kg 𝑠−1] 𝑥 4180 [J𝑘𝑔−1
𝐾−1
] 𝑥(1.45[º𝐶])
= 303.05 [W]
Time of sample [min] 4
Water from the tap T1 [ºc] 14.4
Water entering into the panel T2 [ºc] 29.2
Water leaving the panel (T3) [ºc] 40.9
Ambient air room temperature (T4) [ºc] 16.5
Table 9: experimental data
Time of sample [min]
4
ΔT leaving the panel (ΔT3) [ºC]
2.60
ΔT leaving the panel, room (T4-T3)[ºC]
24.40
Average entering and leaving the panel (T5) [ºC]
35.05
ΔT entering and leaving the panel ( 𝛥𝑇5
̅̅̅̅̅) [ºC]
1.45
Table 10: experimental data

On the other hand, the amount of heat absorbed by the high intensity lights is
calculated taking into account the solar flat panel area, and its incident radiation
which is in m2 is measured in the equation below. Thus:
Equation 6: Incident light radiation
𝑄̇ 𝑅𝑎𝑑 = 𝐴 𝑥 𝐼
= 1.8 [ 𝑚2] 𝑥 519.79[W𝑚−2
]
= 935.62 [W]
The pump was running at its higher power, i.e.:
Equation 7: Pump power
𝑊̇ 𝑝𝑢𝑚𝑝 = 87 𝑊
The solar flat panel was transferring heat to the water in the tank. There was a
water flow rate from the tap connecting to the panel; this amount of heat can be
obtained in the following way:
Equation 8: quantity of heat output out of the system due to the water flow
𝑄̇ 𝑜𝑢𝑡 = 𝑚̇ × 𝐶 𝑝 × (𝛥𝑇3)
= 0.0038[ 𝑘𝑔 𝑠−1] 𝑥 4180[J𝑘𝑔−1
𝐾−1
] 𝑥 (2.6[º𝐶])
= 41.29 [W]
Once all different energies which enter and leave the panel are known the
instantaneous efficiency at that precise moment of time is:
Equation 9 Solar Thermal Efficiency final calculation
𝜂 =
𝑄̇ 𝑖𝑛
=
303.05
935.62 + 87− 41.29
= 0.3088 = 30.88%
Repeating the calculations above for each minute along the experiment, the
next graph was obtained:

Figure 39 System efficiency over the temperature difference in the Original System.
4.2.3: Conclusion for the Original System.
As we can see on the graph above, the instantaneous efficiency of the panel fell
down as the temperature difference between the panel and the ambient
temperature increase due to the higher heat losses. At the end of the
experiment the temperature of the system must be steady since the solar
thermal panel cannot get more energy due to all the energy input is lose with
the environment. This can be seen with the decreasing shape of the graph
showing an efficiency of 0% when the temperature difference is very high, in
other words when all the energy input is lost.
4.3 External System Built
During this experiment, the flat plate solar thermal panel was tested with the
External System Built to calculate its efficiency.
The different components of the balance equation were studied until the system
reached steady state.
In the experiment the tank was filled full of water and there was a low flow rate
in the open circuit.
4.3.1 Results
A pipette and a timer were used to measure the flow rate of the open circuit.
The amount of water came out from the tap during a controlled time of 1 minute
was 95 ml.
The flow rate was therefore:
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
10 20 30 40 50 60 70 80
Efficiency[%]
Temperature difference [ºC]
OriginalSystem

Equation 10: Mass flow rate
𝑚 𝑡𝑎𝑝̇ =
95 𝑚𝑙
60 𝑠
= 1.583
𝑚𝑙
𝑠
= 0.00158
𝑙
𝑠
The pressure inside the close circuit was measured by the manometer giving a
value of 2 bars.
As a result the flat-plate solar thermal collector received 519.79 W/m2, the
following data was obtained:
The results of this experiment are given below:
Time of sample
[min]
0 10 20 30 40 50 60 70 80 90
Closed circuit.
Water entering
into the panel T1
[ºC]
25.2 26.2 27.2 28 28.6 29.4 29.8 30.5 31.1 31.7
Closed circuit.
Water leaving the
panel T2 [ºC]
27.4 28.6 29.5 30.3 31 31.8 32.5 33.1 33.7 34.3
Open circuit.
Water entering
into the tank T3
[ºC]
15.9 17.5 18.3 18.7 18.3 18.3 18 18.2 18.4 18.5
Open circuit.
Water leaving the
tank T4 [ºC]
16.8 18.2 19 19.8 20.7 21.6 22.6 23.3 24 24.6
Ambient air room
temperature T5
[ºC]
16.8 16.9 17.2 17.9 18.3 18.4 18.9 18.9 19.3 19.7
Table 11: Temperatures measured in the first experiment along the first 90 min.
Time of sample
[min]
100 110 120 130 140 150 160 170 180
Closed circuit.
Water entering into
the panel T1 [ºC]
32.2 32.6 33.1 33.5 34 34.3 34.8 35.1 35.7
Closed circuit.
Water leaving the
panel T2 [ºC]
34.9 35.5 35.9 36.5 37 37.5 38 38.6 39
Open circuit. Water
entering into the
18.7 18.6 18.4 18.5 18 18 17.6 18.3 18.8

tank (T3) [ºC]
Open circuit. Water
leaving the tank T4
[ºC]
25.4 26.2 27 27.5 27.8 28.7 29.4 29.6 30.5
Ambient air room
temperature T5
[ºC]
18.9 19 18.6 18.7 18.4 18.5 18.9 18.6 19.6
Table 12: Temperatures measured in the first experiment between min 100 and 180.
Time of sample
[min]
190 200 210 220 230 240 250 260 270 280
Closed circuit.
Water entering
into the panel T1
[ºC]
36.2 36.7 36.9 37.2 37.5 38 38.3 38.8 38.9 39.2
Closed circuit.
Water leaving the
panel T2 [ºC]
39.4 39.9 40.2 40.7 41.2 41.4 41.9 42.3 42.5 42.8
Open circuit.
Water entering
into the tank T3
[ºC]
18 18.6 18 18.5 18 18.1 17.8 17.9 18.4 18.8
Open circuit.
Water leaving the
tank T4 [ºC]
30.9 31.3 31.7 32.3 32.8 33.1 33.4 33.8 34.2 34.7
Ambient air room
temperature T5
[ºC]
19.2 19.1 19.2 19 19.1 19.4 19.2 19.1 19.5 19.4
Table 13: Temperatures measured in the first experiment between min 190 and 280.
Time of sample
[min]
290 300 310 320 330 340
Closed circuit.
Water entering
into the panel T1
[ºC]
39.5 39.6 39.7 39.9 40 40
Closed circuit.
Water leaving the
panel T2 [ºC]
43 43.2 43.4 43.5 43.6 43.7
Open circuit.
Water entering
into the tank T3
18.8 19.2 19 19.1 19 18.8

[ºC]
Open circuit.
Water leaving the
tank T4 [ºC]
35.1 35.4 35.7 36 36.4 36.6
Ambient air room
temperature T5
[ºC]
19.4 18.8 19 19.5 19 19
Table 14: Temperatures measured in the first experiment between min 290 and 340s
Values obtained are represented on the following graph:
Figure 40: Temperatures measured at different parts of the circuit
As we can see at the end of the experiment the temperature of the close circuit
is stabilized in around 45ºC.
4.2.2 Calculation of thermal efficiency for the External System Built.
To make the calculations the following data was taken:
Pump [W] 48
V tank [l] 90
M tank [kg] 90
Specific heat capacity of water [Jkg-1K-1] 4180
Area of the panel [m2
] 1.80
Average Irradiance [W m-2
] 519.79
Flow rate out of the tank [kgs-1
] 0.00158
Table 15: Useful data for the External System Built.
The instantaneous efficiency represents the efficiency of the solar panel at one
precise moment of time during the experiment.
0
5
10
15
20
25
30
35
40
45
50
0 100 200 300 400
TemperaturesºC
Time (min)
Closed circuit. Water
entering into the
panel (T1)
Closed circuit. Water
leaving the panel
(T2)
Open circuit. Water
entering into the
tank (T3)
Open circuit. Water
leaving the tank (T4)
Ambient air room
temperature (T5)
Average
temperature of the
tank (T6)

Equation 11: Solar Thermal Efficiency
𝜂 =
𝑄̇ 𝑖𝑛
As an example for knowing how to calculate this value, we have taken the
temperatures obtained with 150 minutes after starting the experiment shown on
the table 1.
Time of sample [min] 150
Closed circuit. Water entering into the panel T1 [ºC] 34.3
Closed circuit. Water leaving the panel T2 [ºC] 37.5
Open circuit. Water entering into the tank T3 [ºC] 18.0
Open circuit. Water leaving the tank T4 [ºC] 28.7
Ambient air room temperature T5 [ºC] 18.5
As well as the temperature increases at different parts of the circuit.
The temperature inside the tank (T6) was taken and an average between the
water temperature of the close circuit entering into the tank (T1) and leaving the
tank (T2). Thus the amount of heat that arrives into to the tank can be calculated
as follows:
Equation 12: quantity of heat absorbed by the water in the tank
𝑄̇ 𝑡𝑎𝑛𝑘 = 𝑚̇ 𝑡𝑎𝑛𝑘 × 𝐶 𝑝 × ( 𝛥𝑇6
̅̅̅̅̅)
=
90
10 × 60
[kg 𝑠−1] × 4180 [J𝑘𝑔−1
𝐾−1
]× (0.5[º𝐶])
= 313.5[W]
Time of sample [min]
150
Average temperature of the tank T6 [ºC] 35.9
Temperature difference (T6 – T5) [ºC] 17.4

On the other hand, the amount of heat absorbed by the light sources is
calculated taking into account the solar flat panel area, and its incident radiation
by m2.Thus:
Equation 13: Incident light radiation
𝑄̇ 𝑅𝑎𝑑 = 𝐴 𝑥 𝐼
= 1.8 [ 𝑚2] 𝑥 519.79[W𝑚−2
]
= 935.62 [W]
The pump was running at its higher power, i.e.:
Equation 14: Pump power
𝑊̇ 𝑝𝑢𝑚𝑝 = 48 𝑊
The tank was exchanging heat due to there was a water flow from the tap
connecting to the tank, this amount of heat can be obtained in the following
way:
Equation 15: quantity of heat output out of the system due to the water flow
𝑄̇ 𝑜𝑢𝑡 = 𝑚̇ 𝑡𝑎𝑝 × 𝐶 𝑝 × (𝑇4 − 𝑇3)
= 0.00158 ∗ [ 𝑘𝑔 𝑠−1] 𝑥 4180[J𝑘𝑔−1
𝐾−1
] 𝑥 (28.7 − 18.0) [º𝐶]
= 70.66 [W]
Once all different energies which enter and leave the system are known the
instantaneous efficiency at that precise moment of time is:
𝜂
Equation 16: Solar Thermal Efficiency final calculation
=
𝑄̇ 𝑡𝑎𝑛𝑘
=
313.50
935.62 + 48 − 70.66
= 0.3434 = 34.34%
Repeating the calculations above for each minute along the experiment, the
next graph was obtained:

Figure 41: System efficiency over the temperature difference in the External System Built.
4.2.3: Conclusion for the External System Built.
As we can see on the graph above, the instantaneous efficiency of the system
fell down as the temperature difference between the system and the ambient
temperature increase due the higher heat losses. At the end of the experiment
the temperature of the system must be stable because all the energy input (high
intensity lights and pump) is equal to the energy output (heat loses and mass
flow going out from the system), that is all of the energy input is lost thus the
solar panel does not increase its temperature any more.
Chapter 5: Conclusion
In this last chapter of the project the literature review and results obtained were
analysed. Most of the project objectives were achieved.
First of all, a literature review about the solar thermal panels was done.
Secondly, an evaluation of the differences between evacuated tube collector
and flat-plate collector to know which panel works better in a climate like Ireland
was done. After that, the external circuit for the solar thermal panel to simulate a
real system in a house was built and tested.
5.1 Key findings:
Analysing the results of the experiments the following outcomes were found out.
34.34
0
10
20
30
40
50
60
70
80
10 12 14 16 18 20 22 24 26 28 30
Efficiency[%]
Temperature difference [ºC]
External System Built

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