Photovoltaic Training - Session 6 - Off-grid installations

Photovoltaic Systems Training

Session 6 – Off‐grid installations

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

Javier Relancio & Luis RecueroGeneralia Group

October 6th 2010

PHOTOVOLTAIC SYSTEM

Design, Execution, Operation & Maintenance

STAND ALONE FACILITIES

Javier Relancio. Generalia Group. 06/10/2010www.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


INDEX

Introduction




Design

Maintenance


5

Basic topology

PV modules

PV regulator

Inverter

DC Consumption

AC Consumption


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

7

Introduction

Sofia, Bulgaria Madrid, SpainEd (32º) Ed (61º) Ed (34º) Ed (60º)

Jan 1,65 1,79 2,66 2,96Feb 2,25 2,34 3,05 3,19Mar 2,75 2,63 4,32 4,23Apr 3,42 3,01 4,1 3,63May 3,61 2,95 4,63 3,75Jun 3,79 2,97 4,78 3,69Jul 4,06 3,23 4,91 3,85Aug 3,95 3,37 4,79 4,08Sep 3,48 3,28 4,38 4,14Oct 2,68 2,74 3,54 3,63Nov 1,71 1,84 2,66 2,9Dec 1,3 1,41 2,15 2,39

Total year 1050 960 1400 1290

0

1

2

3

4

5

6

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Sofia, Bulgaria (32º) Sofia, Bulgaria (61º)Madrid, España (34º) Madrid, España (60º)

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

INDEX

Introduction




Design

Maintenance


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:

9

Elements

Manufacturer Power (per unit) System Power Observations

Xantrex 6 kW 36 kW

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

Victron 10 kVA 100 kVA(90 kW)

• It integrates a battery charger• It allows different configuration modes for the management of the generation and the consumption

Ingeteam 15 kVA 120 kVA• It integrates a battery charger• It allows different configuration modes for the management of the generation and the consumption


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

10

Elements

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


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

11

Batteries

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


Real capacity

12

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

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


Depth of discharge

Batteries

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:

Several manufacturers

Isofoton, Hoppecke, BAE, TABB, Tudor, etc

Light cycle Deep cycle

‐Designed for high current in the initial discharges‐ Constant charges and discharges‐Depths of discharge lower than 20 %

‐Designed for long periods of utilization without being recharged‐ They are more robust and have higher energetic density‐ Depth of discharge around of 80 %'

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

Type of batteries

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(deep cycle)

Lead – Acid(light cycle)

Gel-Cell NiCad

Observations • High commercial availability

• Sudden death could happen

• They are manufactured with lead – antimony

• High commercial availability

• Sudden death could happen

• They are manufactured with lead - calcium

• The acid is in gel state

• They need less maintenance

• They can operate in any position

• They are more expensive than lead batteries

• Better performancewith high temperature

• They cost the double than Lead – Acid 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

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


16

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 HSP3. 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 Euros5. The word "hybrid" refers to a photovoltaic installation with a diesel generator as a backup.

‐

0,20

0,40

0,60

0,80

1,00

1,20

1,40

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

Price per kWh: Diesel generator VS Solar Facility

Diesel generator


INDEX

Introduction




Design

Maintenance


18

Hybrid System: Diesel - Solar

PV modules

PV regulator

Inverter

DC Consumption

AC Consumption

The chosen diesel generator must have

automatic starter:

Using its own electronic starter to

automatically switch on when an auxiliary

signal is received

Using an external electronic starter

specially designed for this function

The generator is connected to the AC BUS

The diesel generator is automatically switched on if

the batteries are under a certain level

The generator can produce energy exclusively to

supply the consumption or, also, to charge the batteries

The inverter has to be specially designed with

this function (AC/DC Converter)


19

Hybrid System: Wind - Solar

The wind potential is determined by:Speed of the wind: the kinetic energy of the wind increases according to the cube of its speedWind 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

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

Description

Wind generator

20

Hybrid System: Wind - Solar

PV modules

PV regulator

Inverter

DC Consumption

AC Consumption

Wind regulator

Topology

DC BUS


21

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

Fridge consumption “G Class”: 800 kWh/year

Saving: 260 € per year

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

Source: IDAE

22

Consumption efficiency (II)

Examples

Element Low consumption

Ordinary consumption

Fridge Class A150 kWh/year

Class G800 kWh/year

Washing Machine

Class A1.42 kWh

Class G6.9 kWh

Lighting 1 Incandescent100 W

LED10 W

Lighting 2 Incandescent100 W

Low Consumption18 W

PC (Desktop) 250 W 70 W

Energy class

Energy consumption Evaluation

LOW

MED

HIGH

Less efficient

More efficient

23

Smart Grids (I)

Global objective

To success:

Increase the integration of renewable energies in the Global electric grid

The need of dealing with an intermittent & distributed generation

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

Smart Grids (II)

Improve the control & supervision of the generation

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

Mechanisms towards the smart grids

Improve the international grid connection

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

Source: REE

Demand profile for an average day in Spain


INDEX

Introduction




Design

Maintenance


Zones distant from the grid

Zones currently supplied by diesel generators

Exceptionally, areas with instabilities from the grid

26

Application Areas

Great potential in

African countries

Especially, areas with high fuel prices

Source: World energy outlook 2009


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

Application examples


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

Particular case: Water pumping facilities


Limits on the system

Maximum power output

It is limited by the inverters: nowadays <120 kWp

Maximum capacity of storage

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) *

29

Other considerations

Towards the system scalability

With the goal to supply energy to growing populations

By the mix of different technologies

* It is recommended to verify this information with the manufacturer

Lead-Acid batteries, each cell allows a maximum of 3.000Ah en C-10(2V).

If we are using 48 V rows, which is generally the maximum voltage that we can use, each row would store up to:

3.000 Ah x 48 V = 144 kWh


INDEX

Introduction




Design

Maintenance


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

31

System design (I)

Device Number of Units

Peak Power (W)

Average Power (W)

Hours of usage (h per day)

Consumed energy(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

The peak power will affect the inverter calculation

The daily energy consumption will affect:

The storage system

The solar modules

Study of consumptions

* Simultaneity ratio 80%


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

32

System design (II)

Solar generator calculation

Madrid, EspañaEd* (34º) Ed* (60º)

Jan 2,66 2,96Feb 3,05 3,19Mar 4,32 4,23Apr 4,1 3,63May 4,63 3,75Jun 4,78 3,69Jul 4,91 3,85Aug 4,79 4,08Sep 4,38 4,14Oct 3,54 3,63Nov 2,66 2,9Dec 2,15 2,39

Total year 1400 1290

We have to consider the losses in all the elements of the system:

modules, inverters, chargers, batteries and cables.

The battery losses can be estimated around 15 %

The whole system losses, can be estimated around 34 %

WLossesHSP

EnergyP demandedsolar 85,670.7

66,039,212100

=×

=×

=

We could install, for example:

34 modules of 230 W = 7.820 Wp

*Ed: Average daily electricity production for 1kWp


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%.

33

System design (III)

Battery calculation

hACapacity hA −=×××

=××

×=− 12.1977

2485,06,0212100

VoltageLossesdepth DischargedaysnºEnergydemand

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


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

34

System design(IV)

Inverter calculation (I)

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


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

35

System design (V)

Inverter calculation (II)

So, we will choose any inverter with a Nominal Output

Power higher than 750 Wp


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

36

System design (VI)

Conclusions

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

Observations


INDEX

Introduction




Design

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

Solar modules maintenance


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

39

Batteries maintenance (I)

Main risks

The electrolyte is, generally, dilute acid: it may

produce burns if contacting the skin or the eyes

Electrocution risk

From 24 V, in wet environments

From 48 V, in dry environments

Risk of fire or explosion

The batteries produce hydrogen gas

An appropriate ventilation system is needed

Recommendations:

Use appropriate gloves and shoes

Use plastic handle tools

Avoid wearing any metallic object

Avoid sparks and flames close to the batteries


40

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


41

End of Session 6


Thank you for attending

Documents

Photovoltaic Training - Session 6 - Off-grid installations