Photovoltaic Training - Session 6 - Off-grid installations

Photovoltaic Systems Training

Session 6 – Off‐grid installations

Javier Relancio & Luis Recuero
Generalia Group

October 6th 2010

http://www.leonardo-energy.org/training-pv-systems-design-
construction-operation-and-maintenance

PHOTOVOLTAIC SYSTEM
Design, Execution, Operation & Maintenance

STAND ALONE FACILITIES

Javier Relancio. Generalia Group. 06/10/2010
www.generalia.es
2
http://www.leonardo-energy.org/training-pv-systems-design-construction-operation-and-maintenance

INDEX

Introduction

Elements. Storage System & Backup System

Trends: Hybrid Systems. Efficiency. Smart Grids

Applications. Examples

Design

Maintenance

3

INDEX

Introduction




Design

Maintenance

4

Basic topology

PV modules

PV regulator

DC Consumption

Inverter AC Consumption

5

Introduction

Differences with a grid connected system

Designed for self-consumption

An electricity storage is required

Regulator / charger

Batteries

Inverters with capacity " to create a grid"

For facilities with consumptions in DC and output power below 2 kW, we may require modules
with particular characteristics:

If the consumptions are in DC 12 V, modules of 18 V

If they are in DC 24 V, modules of 30-32 V

NOTE: The modules of 12 V are more expensive, but it is possible to avoid their use by using
regulators with power maximizers. Only for powers over 2 kW

6

Introduction

Criterion of “winter production maximization” VS “annual production maximization”

In the grid connected facilities, the objective is to obtain the maximum annual profitability of
the installation

In stand-alone facilities, the objective is to feed the demand for any day of the year. For it:

We have to design the installation for the " worse day of the year "

We will choose the modules tilt that maximizes the production in the above mentioned
month
Sofia, Bulgaria Madrid, Spain 6
Ed (32º) Ed (61º) Ed (34º) Ed (60º)
Jan 1,65 1,79 2,66 2,96 5
Feb 2,25 2,34 3,05 3,19
Mar 2,75 2,63 4,32 4,23 4
Apr 3,42 3,01 4,1 3,63
3
May 3,61 2,95 4,63 3,75
Jun 3,79 2,97 4,78 3,69 2
Jul 4,06 3,23 4,91 3,85
Aug 3,95 3,37 4,79 4,08 1
Sep 3,48 3,28 4,38 4,14
Oct 2,68 2,74 3,54 3,63 0
Nov 1,71 1,84 2,66 2,9 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Dec 1,3 1,41 2,15 2,39
Sofia, Bulgaria (32º) Sofia, Bulgaria (61º)
Total year 1050 960 1400 1290 Madrid, España (34º) Madrid, España (60º)

7
Note: we can use backup system for the worst production months

INDEX

Introduction




Design

Maintenance

8

Elements

Inverter

Lower range of powers than for grid connected facilities

Possibility of connection in parallel or series

Prepared for auxiliary inputs in parallel, in case of hybrid systems:
diesel, grid, modules …

Manufacturers:

Manufacturer Power (per unit) System Power Observations

• It integrates a battery charger
• It allows to inject surplus to the grid
Xantrex 6 kW 36 kW
• It allows different configuration modes for the
management of the generation and the consumption

100 kVA
Victron 10 kVA • It allows different configuration modes for the
(90 kW)
Ingeteam 15 kVA 120 kVA • It allows different configuration modes for the

9

Elements

Regulator / Charger

It is used to:

... protect the batteries against overcharging

To avoid excessive discharges within a cycle

It is recommended to work with a oversizing of 125 %

Differences between regulator and charger

Charger: it is only used to charge the batteries

Regulator: it is used both for charging the batteries and
managing the loads in DC

NOTE: The chargers are not simple devices:

The battery charge stage depends on many factors and is difficult to determine

Multiple algorithms exist to optimize the battery charging and to increase its
lifetime

10

Batteries

Introduction

Batteries are used for storing the energy that is produced by the
modules during the day, for being consumed in the periods that
there is no solar irradiation

This storage takes place due to chemical reversible reactions

A battery is composed by the connection of several "cells” in series

Between the electrodes there is a certain potential difference (Generally: 2V)

In photovoltaic applications we can generally find batteries of 12, 24 or 48 volts

Normally, the system is designed to store energy for several days of consumption

In case of several days of low irradiation: clouds, rain, etc

Three days can be a good recommendation, depending on each case

11

Batteries

Capacity
Electricity that can be obtained during a full discharge of a completely charged battery
The capacity, in Amperes - hours (A - h), is the current that the battery can supply,
multiplied by the number of hours in which the above mentioned current is delivered

Real capacity

Theoretically, a battery of 200 A - h might supply: 200A during an hour, 100A for two hours,
1A for 200 hours and so on.
However, in the reality, the capacity of the battery will change according to the regime of
charge and discharge. (Generally, lower speed of discharge implies a bigger capacity)
For example: a battery which specifies a capacity of 100 A - h during 8 hours (C-8):
It might supply 12,5 A during 8 hours. C = 12.5 x 8 = 100 A - h
But it might provide 5.8 A during 20 hours. C ' = 5.8 x 20 = 116 A - h

12

Batteries

Depth of discharge

Percentage of the total capacity of the battery that can be used without need of recharge
and without damaging the battery.

As a general rule, the less depth of discharge is reached in every cycle, the longer
the battery lifetime will be

Classification:

Light cycle Deep cycle

‐ Designed for high current in the initial ‐ Designed for long periods of utilization without
discharges being recharged
‐ Constant charges and discharges ‐ They are more robust and have higher energetic
‐ Depths of discharge lower than 20 % density
‐ Depth of discharge around of 80 %'

Note: This classification is generally used for Lead-Acid batteries

Several manufacturers

Isofoton, Hoppecke, BAE, TABB, Tudor, etc

Batteries

Type of batteries
For photovoltaic applications the most suitable batteries are the stationary ones, designed to
have a fixed emplacement and for the cases in which the consumption is more or less
irregular. The stationary batteries do not need to supply high currents during brief periods of
time, but they need to reach deep discharges

Lead – Acid Lead – Acid Gel-Cell NiCad
(deep cycle) (light cycle)
Observations • High commercial • High commercial • The acid is in gel • Better performance
availability availability state with high temperature
• Sudden death could • Sudden death could • They need less • They cost the double
happen happen maintenance than Lead – Acid
• They are • They are manufactured • They can operate in batteries
manufactured with with lead - calcium any position
lead – antimony • They are more
expensive than lead
batteries
Discharge depth 40-80% 15-25% 15-25% 100%
Self – discharge per month 5% 1-4% 2-3% 3-6%
Typical capacity (Ah/m3) 35,314 24,720 8,828 17,660
Capacity range (Ah/m3) 7,062 to 50,323 5,791 to 49,000 3,672 to 16,400 3,630 to 34,961
Typical capacity (Ah/Kg) 12.11 10.13 4.85 11.10
Capacity range (Ah/Kg) 4.18 to 26.65 2.42 to 20.26 2.20 to 13.87 2.64 to 20.90
Minimal temperature (oC) -6.6 -6.6 -18 -45

Diesel generator

The diesel generator as a backup (I)

The use of a diesel generator can allow us to avoid the oversizing of solar modules
and batteries.

The diesel generator would cover the periods of low irradiation or the situations of
extraordinary consumption

Nowadays, the energy generated by a diesel group can be more expensive than
the energy obtained from a photovoltaic solar system

It will depend on the price of the fuel in each country

NOTE: In the following slide we can find an example

15

Diesel generator

Price per kWh: Diesel generator VS Solar Facility

1,40

1,20

1,00

0,80

0,60

0,40

0,20

‐
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Precio kWh hibrido Precio kWh G Diesel Precio kWh G Diesel CO2

Notes:
1. For this study we have considered that the price of the electricity from a Diesel Generator is, today, 0.35 € per
kWh (Including the costs that the logistics of the fuel supposes).
2. The study has considered a radiation of 1500 HSP
3. In the graph we can find, in green, an estimation of the repercussion that would suppose the extra charges for
the emission of pollutant gases (Price of ton of CO2).
4. The prices are in Euros
5. The word "hybrid" refers to a photovoltaic installation with a diesel generator as a backup.
16

INDEX

Introduction




Design

Maintenance

17

Hybrid System: Diesel - Solar

Inverter

PV regulator DC
Consumption

AC
PV modules Consumption

The generator is connected to the AC BUS The chosen diesel generator must have
The diesel generator is automatically switched on if automatic starter:
the batteries are under a certain level Using its own electronic starter to
The generator can produce energy exclusively to automatically switch on when an auxiliary
supply the consumption or, also, to charge the batteries signal is received

The inverter has to be specially designed with Using an external electronic starter
this function (AC/DC Converter) specially designed for this function

18

Hybrid System: Wind - Solar

Description

This type of system is currently being studied on the R&D departments of many
institutions and companies.

Good correlation between the wind and the solar resource

Generally, the wind & solar systems are connected to the DC BUS (of the batteries)

There is not too much information about the wind resource

The guarantees for the wind system are lower than for the PV system

Average, three years

The wind potential is determined by:
Speed of the wind: the kinetic energy of the wind
increases according to the cube of its speed
Wind resources become exploitable where
average annual wind speeds exceed 4‐5 m/s
Also it is influenced, to a lesser extent, by the
characteristics and density of the wind

19

Hybrid System: Wind - Solar

Topology
PV
modules

PV
DC Consumption
regulator

DC BUS

Wind
regulator

Inverter

AC Consumption
Wind
generator

20

Efficiency in the consumption (I)

The importance of reducing the consumption …

Nowadays, we can find great evolutions in the consumption reduction of many
massive devices: electrical appliances, lighting, air conditioning, PCs, etc
Considering the high initial investment per kWp for an isolated solar system…
and considering the dependency between this peak power and the consumption…

…every stand alone solar facility should begin by the
optimization of its consumption efficiency

Example:

Electricity price: 0,40 € per kWh

Fridge consumption “A+ Class”: 150 kWh/year Saving: 260 € per year
Source: IDAE
Fridge consumption “G Class”: 800 kWh/year

* If we reduce our energy consumption, installing a more efficient
21 device, we will be able to reduce the price of our solar PV Facility

Consumption efficiency (II)

Examples

Low Ordinary
Element Energy Energy
consumption consumption More efficient class consumption Evaluation

Class A Class G
Fridge
150 kWh/year 800 kWh/year LOW

Washing Class A Class G
Machine 1.42 kWh 6.9 kWh MED
Incandescent LED
Lighting 1
100 W 10 W HIGH

Incandescent Low Consumption
Lighting 2 Less efficient
100 W 18 W
PC
250 W 70 W
(Desktop)

22

Smart Grids (I)

Global objective

International governments commitment (such as the EU)
Minimize the environmental impact.
Reduce the CO2 emissions
Reduce the dependency from fossil fuels
Increase the use of Renewable Energies
Reduce costs & Increase the energy efficiency

To success:
Increase the integration of renewable
energies in the Global electric grid
The need of dealing with an
intermittent & distributed generation

23

Smart Grids (II)

Mechanisms towards the smart grids

Improve the control & supervision of the generation Demand profile for an
average day in Spain
Intermittent generation profile of the Renewable Energies
Low forecast on the production
Improve the demand management
High peak–valley ratio
Low correlation with renewable production

Improve the international grid connection
Source: REE

Improve the electricity storage
New facilities to pump water and then produce energy
R&D for new in situ storage systems: hydrogen/ batteries
The electrical vehicle


INDEX

Introduction




Design

Maintenance

25

Application Areas

Zones distant from the grid

Zones currently supplied by diesel generators

Exceptionally, areas with instabilities from the grid

Great potential in
African countries

Especially, areas with
high fuel prices

Source: World energy outlook 2009

26

Application examples

Single family houses

Public buildings: hospitals, schools, etc

Public lighting and traffic lights

Communication Stations

Water pumping

For human consumption

For agriculture

Desalination & Water sewerage

Industrial uses

27

Particular case:
Water pumping facilities

Great advantages to be fed with solar
energy:

There is no need for batteries

The construction of a high water tank
can be used as a energy storage

Therefore we do not need regulator
either

Neither inverters

Nowadays, we can find great quality
DC bombs

Installation with few elements:

We reduce the price of the installation

We reduce the possibilities of
breakdown

28

Other considerations

Limits on the system Lead-Acid batteries, each cell
allows a maximum of
Maximum power output 3.000Ah en C-10(2V).
If we are using 48 V rows,
It is limited by the inverters: nowadays <120 kWp which is generally the
maximum voltage that we can
use, each row would store
Maximum capacity of storage up to:
3.000 Ah x 48 V = 144 kWh
It is limited by the batteries

Lead - acid: it is recommended not to install more than three or four blocks of
batteries in parallel

If we use Ni-Cad this quantity can be higher (according to the manufacturers) *

* It is recommended to verify this information with the manufacturer

Towards the system scalability

With the goal to supply energy to growing populations

By the mix of different technologies

29

INDEX

Introduction




Design

Maintenance

30

System design (I)

Study of consumptions
We begin by creating a table with all the consumptions we will find in the system

Device Number of Peak Average Hours of usage Consumed energy
Units Power (W) Power (W) (h per day) (Wh per day)
Lamp 10 11 88* 8 880
PC 1 300 150 6 900
Fridge 1 1000 400 24 9600
TV 1 90 90 8 720
TOTAL 1500 W 728 W 12.100 Wh per day
* Simultaneity ratio 80%

The peak power will affect the inverter calculation

The daily energy consumption will affect:

The storage system

The solar modules
31

System design (II)

Solar generator calculation
According to the consumption study, we have to produce 12.100 Wh per day (average)

As we have explained previously, this production must be guaranteed even the worst
day of the year, in this case, in December

Madrid, España We have to consider the losses in all the elements of the system:
Ed* (34º) Ed* (60º)
Jan 2,66 2,96 modules, inverters, chargers, batteries and cables.
Feb 3,05 3,19
Mar 4,32 4,23
Apr 4,1 3,63 The battery losses can be estimated around 15 %
May 4,63 3,75
Jun 4,78 3,69 The whole system losses, can be estimated around 34 %
Jul 4,91 3,85
Aug 4,79 4,08
Sep 4,38 4,14 Energydemanded 12100
Oct 3,54 3,63 Psolar = = =7.670,85W
Nov
Dec
2,66
2,15
2,9
2,39
HSP× Losses 2,39 × 0,66
Total year 1400 1290
*Ed: Average daily electricity
production for 1kWp We could install, for example:

34 modules of 230 W = 7.820 Wp

32

System design (III)

Battery calculation
According to the consumption study, the batteries should supply 12.100 Wh/day (average)

In this example, the system will consider that the batteries have to be able to store energy
for two days without solar radiation

The batteries, then, should be able to store 24.200 Wh

For this example, we will choose Lead-Acid batteries, with a Cycle-Depth of 80%

In order to increase the battery life-time, we will consider a maximum discharge
depth around 60 %

We will consider the battery losses around 15%.

Energy demand × nº days 12100 × 2
Capacity A−h = = = 1977.12 A − h
Discharge depth× Losses × Voltage 0,6 × 0,85 × 24

Conclusion: 12 batteries of 2000 A-h (C-20)

33

System design(IV)

Inverter calculation (I)

Now, we have to consider the peak power of the system

In this case, the maximum power would be 1500 Wp

However, usually we use a “Simultaneity Ratio”, because normally all the devices will
not be connected at the same time

Furthermore, the inverters are prepared to supply the double of their nominal output
power, during a certain period of time

In this case, we will consider that the
peaks from the washing machine and
the fridge will not be longer than these
periods

34

System design (V)

Inverter calculation (II)

We will reach a maximum output power of 1500 Wp, so the Nominal Output
Power should be higher than 750 Wp

Considering the average consumptions, and applying a “Simultaneity Ratio” of
80% for the lights, the nominal Output Power of the inverter should be higher
than 728 Wp

So, we will choose any inverter with a Nominal Output
Power higher than 750 Wp

35

System design (VI)

Conclusions
Demanded energy: 12.100 Wh

Solar modules peak power: 7.820 Wp

Batteries capacity: 2.000 A-h (C-20) x 24 V = 48.000 W-h

Inverter nominal output power: 750 – 1000 Wp

Observations
We have considered that the consumption is homogeneous during the year

If this was not the case (For example, if we had an air conditioning system) we
would have studied also the maximum demanding day

We could reduce the amount of batteries, by reducing their autonomy or increasing
their discharge depth and introducing a diesel generator as a backup for the periods
that the batteries cannot assume

36

INDEX

Introduction




Design

Maintenance

37

Solar modules maintenance

Periodical cleaning of the modules

Depending on the pollution of each area

Generally, once per year

Checking the cables and connections

Retightening the screws

Checking the structure

If it is not protected against open air (aluminum, galvanized steel, etc) it will
require a periodical antioxidant paint

Checking any shadowing effect

38

Batteries maintenance (I)

The battery is a dangerous element, due to its chemical and electrical properties

Main risks

The electrolyte is, generally, dilute acid: it may
produce burns if contacting the skin or the eyes

Electrocution risk Recommendations:

From 24 V, in wet environments Use appropriate gloves and shoes
Use plastic handle tools
From 48 V, in dry environments
Avoid wearing any metallic object
Risk of fire or explosion Avoid sparks and flames close to the
batteries
The batteries produce hydrogen gas

An appropriate ventilation system is needed

39

Batteries maintenance (II)

Main tasks

Checking that the room is well ventilated and protected against the sun light

Checking that the electrolyte level is between the manufacturer limits

Add only distilled water

Except for Gel type batteries

Protecting the connection terminals with antioxidant grease to avoid sulfurizing

Checking the tightness of the battery connections

Cleaning the battery covers and terminals

40

End of Session 6

Thank you for attending

http://www.leonardo-energy.org/training-pv-systems-design-
construction-operation-and-maintenance

41

Photovoltaic Training - Session 6 - Off-grid installations

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to Photovoltaic Training - Session 6 - Off-grid installations

Similar to Photovoltaic Training - Session 6 - Off-grid installations (20)

More from Leonardo ENERGY

More from Leonardo ENERGY (20)

Photovoltaic Training - Session 6 - Off-grid installations