PV Online Brochure en Final 3

8/12/2019 PV Online Brochure en Final 3

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ReGrid: Photovoltaics

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Table of Content

1 LEARNING TARGETS ................................................................................................................. 3

2 THE SUN AS A RESOURCE FOR PHOTOVOLTAIC USE .................................................................................... 3

2.1 APPLICATIONS ......................................................... .............................................................. .......... 4

2.2 POTENTIALS AND POSSIBLE OUTPUT ................................................................ ................................................... 4

2.3 DEVELOPMENT OF ITS USE ......................................................... .............................................................. .......... 5

3 PHYSICAL ASPECTS ................................................................................................................. 6

3.1 SOLAR RADIATION (DIRECT/DIFFUSE/GLOBAL/ALBEDO/AIR MASS - AM) ............................................................ ....... 6

3.2 SOLAR RADIATION DURING A DAY/MONTH/YEAR ........................................................... ........................................ 8

3.3 ORIENTATION OF MODULES AND ITS INFLUENCE ON THE OUTPUT ........................................................... .................. 9

3.4 SOURCES TO RESEARCH FOR SOLAR RADIATION DATA ................................................................ ............................ 10

4 SYSTEM CONFIGURATION: HOW DOES A PV PLANT WORK? ..................................................................... 11

4.1 GRID-CONNECTED PV PLANT ............................................................................................................................. 11

4.2 OFF-GRID PV PLANT ......................................................... .............................................................. ........ 12

5 COMPONENTS OF A PV PLANT ............................................................................................................... 14

5.1 SOLAR CELL (CONFIGURATION, FUNCTION – PHOTOVOLTAIC EFFECT -, TYPES (MONO, POLY, THIN-FILM)) ........................ 14

5.2 SOLAR MODULE (CONFIGURATION, CURRENT-VOLTAGE CURVE, SPECIFICATION DATA, COMPARISON OF EFFICIENCY) .......... 16

5.3 INVERTER (FUNCTION, TYPES, EFFICIENCY, GRID-CONTROLLED VS. SELF-CONTROLLED, SPECIFICATION DATA) .................... 205.4 OTHERS: CHARGE CONTROLLER, ACCUMULATORS, FEED-IN METER, CONNECTION TECHNOLOGY ................................... 22

6 PLANT DESIGN: THE MOST IMPORTANT POINTS TO CONSIDER ................................................................ 23

6.1 LOCATION ......................................................... .............................................................. ........ 23

6.2 DEFINING TYPE OF PLANT AND PLANT SIZE ........................................................ ................................................. 23

6.3 MODULES: SELECTING THE RIGHT MODULES AND MODULE WIRING ........................................................ ................ 24

6.4 EMBEDDING THE INVERTER (MODULE INVERTER, CENTRAL INVERTER, STRING INVERTER, DESIGN …) .............................. 25

6.5 SHADOWING ......................................................... .............................................................. ........ 26

7 ENERGY YIELD ............................................................................................................... 29

7.1 METEOROLOGICAL DATA ......................................................... .............................................................. ........ 29

7.2 PERFORMANCE RATIO OF A SOLAR PV PLANT ............................................................... ...................................... 30

8 CONCLUSIONS ............................................................................................................... 36

FURTHER READING ............................................................................................................... 37

KEYWORD INDEX ............................................................................................................... 37



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1 Learning TargetsIn this chapter, the reader will be acquainted with the basics of photovoltaic solar energy. This

technology, which has shown an enormous development in the last years, will represent an im-

portant part of our future energy mix. Therefore, it is important to know its potential and ener-

gy conversion mechanism.

First of all, the chapter introduces the solar energy radiation and its different components. Lat-

er, the different photovoltaic technologies commercially available are briefly introduced. The

chapter continues with the differences arising between grid-connected and off-grid systems as

well as the wide range of applications of photovoltaic solar energy. Finally, the most important

parameters for photovoltaic plant design are presented to the reader.

2 The sun as a resource for photovoltaic use

Approximately 80% of our energy we get from non-renewable energy sources, e.g. fossil fuels.

They have been produced by biomass stored beneath the Earth’s surface for more than 200

million years. Pollutants and greenhouse gases develop when fossil fuels are converted into

electricity or heat. Thus the atmosphere is damaged and global warming increases. Fortunately,

as the resources are limited, our dependence on fossil fuels is close to its end.

The sun provides the earth with a tremendous amount of energy which triggers many differenteffects affecting our lives. Incoming solar radiation causes winds, oceanic currents, evaporation,

condensation (rains), and regulates the temperature of the earth. The remaining energy is dissi-

pated and therefore lost. The huge amount of energy supplied by the sun is illustrated by the

following example: the amount of energy humans consume annually exceeds 4.6 x 1020

joules,

which is equal to the amount of solar energy that the earth receives in one hour.

With the help of photovoltaics it is possible to convert solar energy into electricity. This is a ze-

ro-emission conversion as no sub-products are emitted during energy production.



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2.1Applications

There are two main different types of application for PV: Grid-connected and off-grid systems.

Grid-connected PV systems feed their energy production into the grid. Off-grid PV systems refer

to those separated from the grid. In this case, the produced energy is consumed locally.

Off-grid PV systems could be applied in the following areas:

Water pumping for irrigation or human consumption.

Solar home systems: Households in rural areas or developing countries.

Communication antennas and telephone stations.

Clinics and hospitals. Rural business.

Tourism: Small solar boats, cars.

Grid-connected systems could be applied in the following areas:

Large scale energy production with PV power plants.

Household or industry energy supply.

2.2 Potentials and possible output

But, how much energy can be produced by a PV power plant? The output yield of a PV plant iscommonly measured in kWh/kWp*yr. The unit kilo watt peak (kWp) is the amount of power a

photovoltaic module will produce at standard test conditions. PV plants are rated according to

their size in kWp and this unit gives the amount of energy (measured in kWh) that an installed

kWp produces per year. Depending on the selected technology, a kWp represents an area cov-

ered with PV modules ranging from 6-20 m2.

This value strongly depends on the way how the system is installed and irradiation level. PV

plants in northern countries like Germany do not have a high irradiation level and consequently

the output yield ranges between 700-1100 kWh/kWp*yr. By contrast, PV installations in sunnier

countries like Spain show output yields between 1400-1800 kWh/kWp*yr. Nowadays, the coun-

tries with the highest output are India, South Africa, and some regions in the Middle East withmeasured output yields exceeding 2000 kWh/kWp*yr.



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2.3Development of its use

In the last decade, PV solar energy has shown its huge potential. The amount of installed PV

power has rapidly increased. Nowadays, nearly 100 GW of PV power are installed worldwide.

Figure 1 below shows the cumulative installed PV power.

Figure 1: Cumulative installed PV power 2000 to 2012. Source: EPIA (2013)

Due to high subsidies in Germany, Spain, and Italy the market has shown an exponential in-

crease in the capacity. Thus aprox. 22 GW have been installed within the EU in 2011 alone,

hence being by far the largest market in the world. The tendency of the market is to move to

new large markets like USA, India, and China. These countries will play a very important role in

the near future of PV.

Figure 2 shows the new PV installed capacity. The increase in the capacity installed yearly has

been coupled with a strong decrease in the components price. Since 2006, the PV system price

has shown a reduction of more than 50%, e.g. the standard final price in 2006 was around 5500-

6000 €/kWp for a residential system, whereas in 2011 the standard final price was 2400-2700

€/kWp. The industry still has capacity to reduce the margins and further PV system price reduc-

tions are expected. The grid parity, i.e. the price at which conventional energy sources will be as

expensive as PV, will be reached in the following years.

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Cumulative installed PV power 2012 in MWTotal 1425 1753 2220 2798 3911 5341 6915 9443 15773 23210 40020 69684 100000

Europe 154 248 389 590 1297 2299 3285 5257 10554 16357 29777 51716 68716

America 146 177 222 287 379 496 645 856 1205 1744 2820 5053 8253

China 19 30 45 55 64 68 80 100 145 373 893 3093 7093

ROW 1106 1298 1564 1866 2171 2478 2905 3230 3869 4736 6530 9822 15938

1425 1753 2220 2798 3911 5341 6915 9443

1577323210

40020

69684

100000

0

20000

40000

60000

80000

100000

MWp



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Figure 2: New PV installed capacity 2000 to 2012, ROW: Rest of World. Source: EPIA (2013)

3 Physical aspects

In this section, the basics of solar radiation and its main parameters will be presented. The

power output of the solar array is proportional to the solar radiation. It is therefore important

to understand some parameters in order to foresee the yield of the array.

3.1 Solar radiation (direct/diffuse/global/albedo/air mass - AM)

The sun radiates in all regions of the spectrum, ranging from radio waves to gamma rays. Our

eyes are sensitive to wavelengths ranging from 400-750 nm approximately. In this narrow range,

called visible range, the sun emits about 45 % of the total radiated energy.

The solar constant is defined as the power density of the solar radiation in the outer space and

it is equal to 1360 W m-2

. The surface solar constant is defined as the power density of the solar

278 328 469 578 1114 1539 15752529

63307437

16817

29665 30000

0

5000

10000

15000

20000

25000

30000

35000

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Total 278 328 469 578 1114 1539 1575 2529 6330 7437 16817 29665 30000

Europe 53 94 142 201 708 1002 987 1972 5297 5803 13367 21939 17000

America 23 31 46 65 92 227 149 212 349 539 983 2234 3200

China 0 11 15 10 9 4 12 20 45 228 520 2200 4000

ROW 202 192 266 302 305 306 427 325 639 867 1947 3292 5800

MWp



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radiation a surface receives at sea level facing the vertical sun on a clear day. This surface solar

constant is equal to 1000 W m-2

.

The Air Mass (AM) defines how many times a ray of sunlight passes the perpendicular thickness

of the atmosphere. When the sun is located at a height of 90º, i.e. at noon of the spring or au-

tumn equinox, the AM is equal to 1. Otherwise, the AM increases with the decreasing of the

sun’s height.

Figure 3 shows the different radiation components that are available on the earth ’s surface.

Direct radiation is available on clear sunny days. However, cloudy days usually present diffuse

radiation and low direct radiation. The intensity of the radiation varies from a few hundred W

m-2

for cloudy days up to 1000 W m-2

for days with clear sky. PV solar modules are able to ab-

sorb both direct and diffuse radiation. However, crystalline-based technologies are more sensi-

tive to direct radiation than to diffuse radiation. Thin-film based technologies show a better

performance than crystalline technologies with diffuse radiation but still have a lower overall

efficiency.

Figure 3: Schematic view of the different radiation types. Source: RENAC



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The albedo represents the amount of light that is reflected in the surroundings of the PV sys-

tem. High albedo values imply higher reflection and high diffuse radiation. Albedo varies from 0

(no reflection) for black bodies up to 0.8-0.9 for fresh snow.

3.2 Solar radiation during a day/month/year

The position of the sun in relation to one’s position is given by the zenith angle (γs) and the azi-

muth (αs). The zenith angle is the angle between the local vertical and the line that connects the

observer with the sun. The sun´s azimuth is the deviation of the sun´s position with respect to

the south. The azimuth of the PV module with respect to the south is noted as (α) and the incli-

nation is defined as (β).

Figure 4: Angle explanation. Source: RENAC

The zenith and the azimuth depend on the local time of the day (t), the day of the year (d), and

the latitude of the observer (λ). The hour angle (h) is given in degrees and defined as follows:

)12(24

360 t h (2.1)



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Each day is defined by the declination angle (δ), which represents the latitude of the sun. The

declination angle is given in degrees and defined as follows:

25.365

80360sin44.23 d

(2.2)

The zenith and the azimuth angles are given by the following equations:

)cos(coscossinsincos hS

(2.3)

tancos)cos(sin

)sin(tan

h

hS

(2.4)

3.3 Orientation of modules and its influence on the output

The orientation and inclination of the PV modules determine the amount of irradiation that the

surface receives to a very great extent. They influence the amount of energy finally produced

and it is obviously very important to take them into account. If the modules are not mounted on

a tracking system that follows the position of the sun in order to get a high radiation income,

the modules must be oriented facing south in the northern hemisphere and facing north in the

southern hemisphere. This guarantees the maximum irradiation level for an array throughout

the year. In regions close to the equator, the orientation is not important but a minimum of 10º

inclination is necessary in order to evacuate water in case of rain.

The optimum tilt angle of the modules depends strongly on the location. As a rule of thumb, the

angles shall be tilted to an angle equal to the latitude minus 10º. However, roof mounted sys-

tems usually incorporate modules that are placed parallel to the roof and use the roof pitch as

their tilt angle. Correcting the tilt angle would not be beneficial, as the added costs will certainly

do not compensate the amount of energy that will be incremented.



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Figure 5: Different orientations and inclinations and the amount of solar radiation received on each surface in com-

parison to an optimum of 30° and facing south. Source: RENAC

Figure 5 shows different orientations and tilt angles and the proportional amount of irradiation

that is lost in comparison to an array that has been placed with an optimum orientation and tilt

angle. Nowadays, some installations are even facing north (!) in the northern hemisphere, as

the price for modules is decreasing rapidly and sometimes only the north face is available.

3.4 Sources to research for solar radiation data

Data from many countries and cities around the world are usually incorporated into the weath-

er data bases of PV design and simulation tools like PVSyst or PV*SOL . However, there are sev-eral freely accessible solar radiation data:

PVGIS (http://re.jrc.ec.europa.eu/pvgis/index.htm)

NASA (http://eosweb.larc.nasa.gov/sse/)

Furthermore, commercially available radiation data programs like Meteonorm permit the calcu-

lation and weather data in any point of the world. This software permits to export the weather

data to standard PV simulation tools in order to perform yield simulations on a desired exactlocation.



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4 System configuration: How does a PV plant work?In this chapter the working principle of grid-connected and off-grid PV power plants is described

and thus the process of energy conversion from sun radiation to energy fed into the grid illus-

trated.

4.1 Grid-connected PV plant

The working principle of a PV plant is simple: Photovoltaic cells are connected in series or paral-

lel in order to obtain the desired current and voltage value for the PV module. Modules are also

connected in series or parallel in order to increase the output voltage or current respectively.The PV array has some electrical protections for short circuits, maintenance works, or for the

(improbable) case of a lightning strike.

Modules are mounted on structures (typically aluminum anodized) that fix the modules either

to the roof or to the ground. Ground mounted systems usually tilt the inclination angle of the

modules in order to optimize the radiation input during the year. Some ground mounted sys-

tems use trackers (one or two-axes) in order to follow the sun path and increase the amount of

solar radiation received at the surface of the modules. Roof mounted systems usually fix the

modules parallel to the roof if the slope is sufficient for good radiation levels. On the other

hand, tilted systems are also available for flat roofs.

The modules are interconnected using standard electric copper cables. The cross section of the

cables depends on the power of the PV array. Overvoltage and lightning protections have to be

installed at the latest by this time. The PV array is then connected to the inverter, which con-

verts direct current (DC) into alternating current (AC). The inverter incorporates Maximum Pow-

er Point Trackers (MPPT) in order to follow the constantly changing current-voltage output of

the array. The current-voltage output is changing mainly because of changing conditions like

irradiance and temperature. The inverter output is then connected to a meter which registers

the amount of energy that has been fed into the grid.

There are two connection methods to the grid: Full feed-in or net metering. The first method is

commonly used in Germany and the second method is mainly used in the US, although it is nowalso permitted in Germany. Full feed-in means that the total production of the PV array is fed

into the grid and there is no possibility of own consumption. There is one meter in order to

measure the sold energy and one meter for energy consumption. On the other hand, net me-

tering uses a single consumption and production meter. The produced energy is first consumed

on-site. In case of exceeding energy, it is fed into the grid; in case of the amount of locally re-

quired energy exceeding the production of the PV array, the additional energy is supplied by the

grid. Figure 6 shows schematically the differences between these two methods.



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Figure 6: Overview. Source: RENAC

4.2 Off-grid PV plant

The working principle of an off-grid PV plant, also called stand-alone system, strongly differs

from grid connected PV systems. In this case, the energy is not fed into a grid, but is either

stored in batteries or it is locally consumed immediately. The PV array slightly differs from the

grid-connected systems and its size is typically much smaller, especially for small stand-alone

applications like solar home systems.

PV modules are interconnected using copper cables and are mounted on stain steel structures

as in grid-connected systems. Overvoltage protections, fuses, and eventually lightning protec-

tions have to be installed as well in both DC and AC side if available. The output of the PV array

is then connected to a controller that controls the charging and discharging of the batteries, thetemperature, the state of charge, and the discharge velocity. The batteries are thus connected



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to an inverter that converts the incoming DC into AC. The inverter is only necessary if AC loads

are used. Figure 7 shows schematically a stand-alone system.

Figure 7: Schematic view of a stand-alone system. The solar modules are connected to a charge controller regulat-ing the charging and discharging of the batteries. The inverter converts DC to AC, which is supplied to the AC loads.

Source: RENAC

There are lots of different stand-alone systems which might incorporate only some of the com-

ponents previously mentioned. For example, water pumps powered by PV usually do not in-

clude batteries and inverters, but only a controller and a DC water pump. On the other hand, PV

stand-alone systems can become extremely complicated and serve, for example, as back-up

systems for mini-grids. The automatic control of such mini-grids, which usually include diesel

generators and other renewable energy sources like small wind generators, is generally compli-

cated but there are good technical solutions available on the market.



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5 Components of a PV plantSunlight can be converted into electricity in a photovoltaic (PV) solar cell, thanks to the photoe-

lectric effect. The solar cells are connected in series and form modules, which are then either

connected to a DC load or connected to inverters in order to convert the DC into alternating

current (AC). The output from the inverters is thus fed into the grid for consumption. This sec-

tion presents the main components of a PV system in detail.

5.1 Solar cell (configuration, function – photovoltaic effect -, types (mono, poly,

thin-film))When semiconductor materials

are exposed to sunlight, elec-

trons excite from the valence

band to the conduction band

creating charged particles

called holes. By doping the sili-

con, i.e. adding tiny amounts of

other materials like boron or

phosphor to the crystalline

structure, p- or n- type semi-conductors are formed respec-

tively. By bringing them togeth-

er, a p-n junction serves for

creating an electric field within

the semiconductor, which is

able to separate electrons and

holes and which creates a di-

rect current (DC) coming out

from the solar cells through the

contacts. Figure 8 illustratesthis process.

Figure 8: Crystalline solar cell working principle. Sunlight impinges the solar

cells. Some light is reflected at the surface and some light passes the solar

cell unaffected. The rest is absorbed creating electron-hole pairs, which are

separated by an electric field and brought to the contacts. Some electron-

hole pairs recombine before arriving at the contacts and heat the solar cell.

Source: RENAC



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The PV market is clearly dominated by crystalline Si (cSi) based solar cells. Nearly 80% of the

cells on the market are cSi based cells, either monocrystalline or multicrystalline. However,

there are many other technologies available or being investigated. The share of thin-film solar

cells in the PV market is growing as manufacturing costs have been significantly reduced and

their production is easy. Figure 9 shows a schematic view of the different cell technologies avail-

able.

Figure 9: Schematic view of the different solar cell types. Source: RENAC

Monocrystalline and polycrystalline cSi cells are wafer-based with thicknesses varying in the

150-250 μm range and sizes from 4 to 6”. The wafers are gained from a silicon melt by different

methods, condensed into blocks and then cut with a wire saw. Due to their high purity, a lot of

energy is consumed during the manufacturing process and high temperature processes are

necessary in order to remove defects. Monocrystalline solar cells are more efficient than poly-

crystalline cells. However, the manufacturing costs of polycrystalline cells are lower and thus

their lower efficiency is compensated. The electrical contacts on both front and back-sides aredeposited by screen printing. Then metal strips connect the front side of a cell with the back



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side of the next cell in order to form a string of cells in series. Hence, a module consists of sev-

eral strings of cells interconnected in series or parallel in order to obtain the desired current and

voltage. Crystalline Si solar cells have a silicon nitride antireflection layer which gives them their

characteristic blue color. Figure 10 shows some photographs of cSi solar cells.

Thin-film solar cells (amorphous Si, cadmium telluride, CIGS) are commonly deposited on a

piece of glass. The surface is then prepared with a laser and the electrical contacts are deposit-

ed. The energy consumed for thin-film fabrication is much lower than for cSi solar cells because

the deposition is a low temperature process. Furthermore, the fabrication process is much

quicker than for cSi.

5.2 Solar module (configuration, current-voltage curve, specification data,comparison of efficiency)

Solar modules are composed of solar cells in series and parallel in order to obtain a desired final

power, which is determined by a module’s current and voltage. The amount of solar cells in

crystalline modules varies typically between 36 and 72 cells. The solar cells are embedded in a

glass-EVA-solar cell-Tedlar sheet-Aluminum frame in order to protect them from weather condi-

tions. Bypass diodes are placed on the back side of the module in order to avoid high power

output losses due to shadowing.

The solar cells (and modules) are characterized by their electric characteristics. Solar cells be-

have similarly to diodes and therefore the electrical characteristics of a solar cell and a module

are represented by using current-voltage curves (I-V curve). Figure 11 shows the I-V curve of a

Figure 10: On the left hand side, a monocrystalline solar cell is presented. On the right hand side, a polycrystal-

line solar cell is shown. Note the tonality differences between both cells. The monocrystalline structure produc-

es a homogeneous color whereas the polycrystalline solar cell shows different colors for each crystalline orien-

tation. Source: RENAC



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solar cell and gives the electrical behavior of different current-voltage ranges. Isc

represents the

short circuit current, i.e. the value at which the current is at maximum and where the voltage is

equal to zero. Voc represents the open circuit voltage, i.e. the value at which voltage is at its

maximum and where the current is equal to zero. The green line represents the resulting power

curve (power = current x voltage).The maximum power point (MPP) is the current and voltage

value at which the power output of the solar cell is at its maximum. The maximum of the green

line will give the current value of the MPP (Impp) and from here the voltage value of the MPP

(Vmpp) can be found by using the I-V curve.

Figure 11: I-V and power curve of a solar cell. The blue line represents the I-V curve of the solar cell (MPP = maxi-

mum power point). Source: RENAC

The I-V curve of a module strongly depends on the incoming irradiation. The output current of a

solar cell directly relates to the incoming irradiation: The higher the irradiation, the more elec-

tron-hole pairs are produced and therefore the current increases. On the other hand, the volt-

age slightly varies with varying radiation. Figure 12 shows I-V curves of a solar module for dif-

ferent irradiation levels.



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Figure 12: Dependence of the I-V curve on the irradiation level. Source: RENAC

Module data sheets typically incorporate a similar I-V curve for the total module as well as the

most important parameters of a module that are necessary for system sizing. Figure 13 shows a

data sheet of a module. The electrical parameters (VOC, VMPP, ISC, IMPP, maximum system voltage,

and temperature coefficients) are included. The peak power, measured in watt-peaks (Wp), de-

fines the power at which the module is rated. Additionally, the sizes and weight of the modules

as well as mechanical properties are included. Data sheets also include the corresponding com-

pliant certifications.



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Figure 13: Module data sheet with module data parameters and specifications. Source: Q-Cells

The performance of the solar cells varies with the temperature. As the cells get hot, current andvoltage vary, hence diminishing the power output of the cell. For this reason, temperature coef-



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ficients of current, voltage, and output are given. With these parameters it is possible to simu-

late the real behavior of the module on the field. PV magazines for experts like Photon or Pho-

tovoltaic prepare an extensive yearly report with all modules available on the market. Nowa-

days, more than 2,000 different modules with different technologies are available. Table 1 pre-

sents a comparison of the main PV technologies, their efficiencies, and the surface needed for

an installation of 1 kWp.

Material Module efficiency Surface needed for 1 kWp

Monocrystalline Si 14-20 % 7.5-5.5 m2

Polycrystalline Si 11-16 % 6-9 m2

Cadmium Telluride 9-12 % 10-11 m2

Copper-Indium-

Gallium-Selenide

(CIGS)

10-13 % 8-10 m2

Amorphous Si (aSi,

aSi/μcSi)

5-9 % 11-20 m2

Table 1: Comparison of different technologies, their standard module efficiency, and the surface needed for 1 kWp.

5.3 Inverter (function, types, efficiency, grid-controlled vs. self-controlled, spec-

ification data)

The inverter is responsible for the conversion of

DC into AC and for the regulation of voltage and

frequency. There are mainly two types of invert-

ers: Single- and three-phase inverters. Single-

phase inverters deliver AC to one phase of a pow-

er transmission line, whereas three-phase invert-ers deliver AC to all three phases of a power

transmission line. Small systems, typically below 5

kWp, commonly use single phase inverters be-

cause one line is enough to absorb the power de-

livered by a PV system. Larger systems commonly

use three-phase inverters (the electricity delivered

by the PV system is split into three parts, each be-

ing delivered to one of the three phases), which

give more freedom with regard to system sizing.

Figure 14: Principle scheme of single- and three-phase

inverters. Source: RENAC



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It is also possible to connect multiple single phase inverters to

form a three-phase system. In this case, the power difference

between phases shall not exceed 5 kW as defined by the grid

utility. Because the maximum output power is wanted, the Maxi-

mum Power Point has to be known. However the MPP of the

PV array is continuously changing due to changes in the irra-

diation, which is why inverters do need electronic power de-

vices that are able to follow the changes in current and volt-

age. Inverters therefore commonly incorporate Maximum

Power Point Trackers (MPPT) in order to guarantee that theinverter adjusts to the MPP. The response velocity to changes

in the irradiation, accuracy, and efficiency of the MPPTs de-

termines the efficiency of the inverter.

Some inverters additionally incorporate transformers. They serve for matching the voltage of

the grid and the galvanic separation in case of thin-film based systems. Transformers typically

have an efficiency of 90-95 % and furthermore they cause additional costs. Therefore, inverters

without transformers are being intensively studied and some companies do offer already

transformerless inverters with the same features as inverters which incorporate transformers.

However, grid utilities in some countries still do not accept transformerless inverters.

The efficiency of an inverter is defined as follows:

DC IN

AC OUT

P

P

,

, (2.5)

Equation 2.5 comprises the losses caused by the transformer (if available), MPPT, and all other

losses caused by current conversion.

Inverters can also be categorized depending on their working principle. The grid-controlled in-

verters use the grid voltage for determining the switch-on and -off pulses for the internal elec-

tronic devices. As a consequence of this technique, the quality of the outcoming frequency sig-

nal is low and does not present a complete sinusoidal shape. By incorporating power electron-

ics, the quality of the signal can be improved. Self-commutated inverters do have a more com-

plex internal structure that allows for a better sinusoidal signal formation. They are commonly

used for stand-alone systems, but also for grid-connected systems.

Regarding system sizing, there are many parameters that have to be taken into account. The

nominal power, the MPPT range, the maximum input voltage, the maximum DC current are pa-

rameters that are commonly used for system design. Furthermore, one has to bear in mind that

the thin-film based modules require transformers in order to separate the modules from the

grid galvanically.

Figure 15: Principle of single- and three-

phase inverters each feeding into one

phase. Source: RENAC



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5.4Others: Charge controller, accumulators, feed-in meter, connection tech-nology

Charge controllers are used in stand-alone systems for controlling the system. The output volt-

age of the PV array has to be matched with the voltage of the battery, which is typically rated to

12 V, 24 V, or 48 V. Since the voltage of the PV array continuously changes with the weather

conditions, the charge controller plays an important role as it matches both voltages. It com-

monly includes a MPPT in order to optimize the output of the array. Controllers also protect the

batteries from overcharging or deep discharges, which might damage the battery irreversibly.

The batteries play a very important role in stand-alone systems, as storage is required in most

applications. Rechargeable lead-acid batteries are commonly used, as their price is moderate in

comparison to other technologies. Furthermore, lead-acid batteries work appropriately with

low currents, which is common for PV systems. However, there are many other rechargeable

batteries available such as Li-Ion batteries or Ni-Cd.

The feed-in meter in a grid-connected installation is necessary in order to determine the energy

that has been fed into the grid. They are commonly installed close to the consumption meter (if

available). Otherwise, a meter at the feed-in point has to be installed first by the utility. In case

of net-metering, smart meters are necessary. These meters are able to measure simultaneously

the energy consumed and the energy supplied by the grid.



23


6 Plant design: The most important points to considerThe design of a PV plant is a complicated process where optimization plays an important role.

The location of the array and shadowing strongly determine the power output. It is therefore

important to be aware of their influence and select appropriate components for each location.

This section presents the parameters that have to be taken into consideration while designing a

PV array: Location, shadowing, and components.

6.1 Location

The location of a solar plant must be carefully investigated during sizing and prior to installation.A badly selected location can have a strong impact on the output and performance of the sys-

tem. An on-site visit to a potential location is therefore strongly recommended.

First, it is important to determine whether the building or the field is suitable for a PV installa-

tion. For this reasons as much information as possible regarding the following parameters has to

be obtained:

Location description and site plan.

Take photographs for clear understanding and shadowing analysis.

Planned system size, technology and installation. Orientation by compass and inclination.

Future access and roof openings.

Soil quality and type. Type of roofing. Structure mounting possibilities.

Usable space, roof, or façade.

Shadowing objects like houses nearby, trees and growing vegetation, chimneys, win-

dows, overhead cables (telephone and electricity), …

Cable lengths, wiring routes and method.

Lightning and earthing protection available?

Investigate the future position of the feed-in point and whether there is enough place

for inverters, junction boxes, meters, … Special subsidies related to the location (cropland, former military land).

Draw a plan with measures and distances.

Shade analysis with special equipment.

6.2 Defining type of plant and plant size

The type and size of a PV system depends on many factors: Customer, economic situation, tech-

nical and material viability, situation, radiation characteristics, and many other characteristics.

Typically, these parameters are intensively studied and several configurations are prepared.Subsequent to a simulation and commercial feasibility studies the best configuration is selected.



24


It is recommended to consider different technologies when sizing a system. Some technologies

perform well under determined weather conditions. For example, thin-film modules perform

better than cSi modules under diffuse light or high temperatures. By contrast, cSi modules per-

form better under high radiation levels. Similarly to the weather conditions, the negative influ-

ence of shadows is lower for certain module technologies. For example, shadowing is critical in

case of cSi but thin-films do not decrease their output as much as cSi does.

Regarding ground mounted systems, there has to be a minimum distance of two meters to any

road or something similar in order to avoid dust formation. If economically viable, use protect-

ing fences that avoid burglary and leave enough distance in order to avoid shadowing.

Enough distance (> 10 cm) to any roof edge has to be left in roof mounted systems in order to

avoid excessive wind loads on the PV array. One has to bear in mind during system sizing thatmounted modules have an additional interstitial space of at least 1-2 cm caused by module

clamps which serve for fixation to the mounting system.

6.3 Modules: selecting the right modules and module wiring

The selection of appropriate modules for an installation is a difficult process. Usually, a company

has supply contracts with manufacturers so that the selection is already limited. The customer

probably has a limited budget and/or a limited area to install. Therefore, the amount and type

of modules is limited. For example, roof mounted systems usually have cSi modules rather thanthin-film modules because the area is limited and the customer wants to install as much power

as possible. The use of thin-film modules for ground mounted systems is growing, as the mod-

ule price, which is the most expensive part of an installation, is getting lower. The use of semi-

transparent PV modules is interesting for building integrated PV systems as an architectural

component.

In case of two modules being connected in series, the module wattages and voltages are added

together whereas the current remains the same. But in case of two modules being connected in

parallel, the module wattages and the current are also added together but here the voltage re-

mains the same. The interconnection of several modules in series, also called string, and in par-

allel gives the final PV array. By increasing the voltage in a string, the wiring losses diminish.However, the system voltage is commonly limited to 1000 V due to the physical limitations of

the inverters and modules. Thin-film modules have much higher voltages than cSi modules due

to their composition. Therefore, the amount of modules in a string is limited.

Weather conditions have to be considered prior to installation. In case of less direct radiation,

thin-film modules are recommended due to their better performance under diffuse radiation,

but cSi modules are recommended in case of high direct radiation.

Module wiring is mainly divided in two parts: DC and AC side. There are some rules of thumb in

order to size the wiring. Typically, the power losses caused by the DC cables shall not exceed 1

%. On the AC side (after inverter), the power losses must not exceed 3 %.



25


6.4Embedding the inverter (module inverter, central inverter, string inverter,design …)

The inverters can be classified according to their connection to the modules. There are mainly

three different types of inverters: Module inverters, string inverters, and central inverters. Each

connection concept presents advantages and disadvantages. The selection of one of these con-

cepts depends on many parameters and it has to be optimized during sizing. Figure 16 introduc-

es schematically the different inverter configurations.

Figure 16: Different inverter configurations: Central, string, and module inverters. Source: RENAC

Module inverters are small inverters located at the back side of the modules. The advantage of

module inverters consists in quickly transforming the current from DC to AC, hence avoiding DC

cables and losses. Since there is only one PV module per inverter, the MPPT works very accu-rately. However, nowadays the installation costs are much higher than for external inverters.

Their use is marginal nowadays and only a few companies offer this possibility.

String inverters are commonly used in small and medium sized installations, like household or

small ground mounted installations. Since they are easy to install, many installers prefer to in-

stall them also for large field installations. Central inverters manage a few module strings and

typically have one MPPT. String inverters are prepared for both indoor and outdoor installation.

Their size varies depending on the rated power but they are usually smaller than 50 x 50 x 30

cm. Generally, string inverters are rated from less than 1 kWp up to 12-20 kWp. The advantage

of this concept consists in their close location to the PV array so that the DC wiring is reduced,

hence reducing losses and wiring costs. Additionally, in case of failure, the system continues



26


working and only a small part of the system does not work. This effect does not happen with

central inverters, where the entire system is stopped if an inverter failure occurs.

Central inverters connect many module strings. They usually have more than one MPPT in order

to optimize the power output of each string and always convert directly into a three-phase sys-

tem. The rated power of a central inverter varies from 25-50 kWp up to 2.5-5 MWp. Their size

varies from 0.5-1 m3 up to container-sized inverters that are placed with cranes. Central invert-

ers commonly incorporate transformers. Their use is recommended in very large installations as

the inverter price-per-watt ratio diminishes with increasing size. However, wiring costs increase

as the strings are located far away from the inverter. Central inverters are commonly placed in

the middle of a ground mounted PV installation in order to diminish wiring costs. They are

mostly located outdoors and are prepared for bad weather conditions with a rated protectionlevel of IP 65.

Inverter sizing is a difficult task. The voltage and current values of each string coming out from

the PV array have to match the limits of the inverter. Large inverters, i.e. central and some string

inverters, are able to interconnect more than one string and therefore it becomes complicated.

The sizing procedure starts selecting an inverter and a module type and a desired peak power.

Then, bearing in mind the different voltage and current limit values of the inverter, different

string combinations which match the inverter requirements have to be considered. Voltage and

current values must be corrected with the temperature coefficients at the maximum and mini-

mum ambient temperatures as the temperature strongly influences PV sizing. The final configu-

ration, i.e. the amount of modules and inverters, is selected depending on the size and budgetof the project.

6.5 Shadowing

Shadowing of PV modules must be avoided if possible. It is often underestimated and leads to

strong decrease in the output yield of the PV array. If a solar cell within a module is shaded, it

will generate less current than neighboring solar cells. The solar cell becomes reverse biased,

receives current from other solar cells, and dissipates power in form of heat. If the module does

not have bypass diodes mounted, this effect might lead to irreversible damages of the solar cell

and module.

Shadowing is sometimes unavoidable. Correct shadow analysis is thus necessary in order to

avoid large power output reduction. The use of a professional camera-based shade analyzer like

HORI catcher or Solar Pathfinder is strongly recommended. Such systems are based on photo-

graphs that serve for shadow investigation. Professional shade analyzers incorporate special

software that allows for shadow recognition and loss estimation for each daytime and date.

The influence of shadowing on the output and performance of the solar array must always be

investigated with PV system simulation software like PV*Sol or PVSyst. These programs incorpo-

rate AutoCAD-based 3D shadowing simulation tools that permit the evaluation of losses caused

by shadowing.



27


There are several types of shading. They are listed here:

1. Direct shadowing: This particular case of shadowing causes strong losses in the output

yield of the PV system. In this case, a shadowing object is placed close to modules and

shades the PV array constantly. The closer the shadowing object is to the array, the

darker the shadow is and the less diffuse light reaches the module surface, the more

problematic the situation gets. .

2. Temporary shadowing: This is caused by natural conditions, like snow, leaves, soiling, etc.

This effect is especially important in ground mounted systems in rural areas, where the

PV arrays come much easier in contact with dust. The tilt angle of the array shall exceed

10° in order to allow self-cleaning and water evacuation after raining. In snowy regions,

the lower part of the module is commonly covered a long period of time. Therefore, a

horizontal arrangement of the modules is recommendable in order to minimize losses.

In this case, the snow will cover only one string of the modules and the bypass diodes

will avoid high shadowing losses.

3. Self-shading: A bad system design might cause shading on modules caused by other

modules that have been placed ahead. As a rule of thumb, the modules located in a row

must be separated from each other approximately 4-6 times the height of the tilted

module. Generally that depends strongly on the latitude where the system is installed. It

has to be calculated for each project separately.Under these conditions, mutual shading

is avoided. Figure 17 shows schematically the minimum separation between module

rows.



28


Figure 17: Separation between module rows in order to avoid mutual shading. Source: RENAC

Last but not least, shadowing of other components like inverters and cables is desired. Shadow-

ing leads to lower working temperatures, hence allowing for longer lifetimes and better perfor-

mance of the components.



29


7 Energy yieldThe economic feasibility of solar photovoltaic plants critically depends on the electricity yield,

which is a function of both the meteorological conditions and the performance of the solar pho-

tovoltaic plant itself. Firstly, as the energy production of solar PV systems is strongly dependent

on the irradiance reaching the PV modules, a profound knowledge of the climate conditions at

the given location is of capital importance. Secondly the quality of the components used in the

plant, the layout of the plant itself and a professional engineering will affect the performance of

the plant and consequently the energy yield of the plant. In this section, both climate data and

plant performance and their impact in the energy yield of the plant will be analyzed in detail.

7.1 Meteorological dataRelevant meteorological data for the yield of a solar PV plant are mainly solar radiation, tem-

perature and wind speed. We will focus in this section in the most important factor, namely so-

lar radiation.

Solar radiation is not constant during different years and therefore measurements must be con-

ducted over long periods. Climate data supplied by third-party service providers has usually

been recorded with an instrument mounted horizontally, so that it sees the whole sky. Referring

to Figure 3, this means that the type of radiation recorded is global radiation, with the compo-

nents direct and diffuse radiation. The total irradiance on a horizontal surface on Earth (also

called global irradiance) Eglobal,hor is therefore the sum of the direct irradiance Edir,hor and the dif-fuse irradiance Ediff,hor on the horizontal surface:

Instruments mounted horizontally do not record reflected radiation (albedo). Climate data is

provided in the form of a typical meteorological year (TMY). A TMY of a climatological parame-

ter dataset (e.g. global radiation) is a year which should be representative of the dataset, in or-

der to give the most likely scenario for this parameter or group of parameters. The time step is

usually hourly and the plane orientation horizontal. It is recommended to use longtime averag-

es (10 to 20 years) to build typical meteorological years as basis for yield estimations.

As mentioned in previous sections the energy yield of a PV plant is optimized by adjusting arrayorientation and tilt. The optimal orientation is heading to the equator (so for example in the

Northern Hemisphere the optimal orientation is south. Regarding tilt a rule of thumb to maxim-

ize annual energy production is to choose a tilt angle close to latitude. Slight variations depend

on local weather conditions. Consequently the relevant radiation to estimate the energy yield

will not be the radiation on a horizontal but on a tilted plane.

The global irradiance on a tilted surface is composed of the, the diffuse sky irradiance and the

ground reflection (a component that does not exist for horizontal surfaces):

being Eglobal,tilt the global irradiance on a tilted surface, Edir,tilt direct irradiance on a tilted surface,Ediff,tilt diffuse sky irradiance on a tilted surface and Erefl,tilt the ground reflection on a tilted sur-

tilt refl tilt diff tilt dir tilt global E E E E ,,,,

hor diff hor dir hor global E E E ,,,



30


face. The different components of global radiation on a tilted surface must be now inferred

from the components of global radiation on the horizontal plane, Edir,hor and Ediff,hor, which are

the components provided by third-party weather data providers. Calculations for the direct ra-

diation are straightforward and based on trigonometric relations. For the calculation of the dif-

fuse and reflection components in the plane of the PV array a model will be necessary. An iso-

tropic model assumes that the intensity of diffuse sky radiation is uniform over the sky dome.

Hence, the diffuse radiation incident on a tilted surface depends on the fraction of the sky

dome seen by it. Furthermore the reflected radiation incident on a tilted surface also depends

on the fraction of the ground seen by it. An isotropic model is not the most accurate model

available; however it is amply sufficient to get enough accuracy. Using this model the global

radiation on a tilted plane will be given by the expression:

being θ the incidence angle of direct irradiance on the array, γs is the elevation angle of the sun,

β the PV array tilt angle and ρ represents the ground albedo (reflectance).

7.2 Performance ratio of a solar PV plant

The performance ratio (PR) is a parameter that describes the performance and the quality of PV

systems. It is independent of system size and irradiance and time period chosen. Low values ofPR indicate high overall losses due to high module temperature, incomplete use of irradiance by

reflection from the module front surface, soiling, component failures, etc.

The performance ratio is calculated as the ratio of energy delivered to the load per day and kWp

(Final Yield Yf) and the theoretically available energy (reference yield Yr).

PR = Yf / Yr

With Yf being the energy delivered to the grid per year and kWp (e.g.: Yf = 1200 kWh /

year*kWp [h/year]) and Yr being the theoretically available energy, which is the global irradi-

ance on tilted plane divided by the reference irradiance G (1 kW/m2) (e.g.: Yr = 2,100 kWh

/m2*year/1 kW/m2 = 2,100 [h/year]). Yr defines the solar radiation resource for the PV sys-tem. It is a function of the location, orientation of the PV array, and weather variability and pro-

vides the Peak Sun Hours1 (PSH) during the year.

The closer the PR value determined for a PV plant approaches 100 %, the more efficiently the

respective PV plant is operating. Summarizing the performance ratio represents proportion of

the energy that is actually available for export to the grid after deduction of energy losses. The

following figure represents a schematic representation of a solar PV plant and the sources of

energy losses which consequently will have an influence on the PR value.

1 PSH refers to the solar insulation at a particular location if the sun were shining at its maximum value of 1kW/m2

for a certain number of hours.

2

1

2

1

coscos

sin

cos,,

,, hor global hor diff

s

hor dir tilt glob al E E E E



31


Figure 18: Losses affecting PR and yield on solar PV systems. Source: RENAC

Following we will briefly elaborate on the different influencing factors, that is to say, sources of

energy losses.

Shading losses

As explained in section 6.5, shading can cause high losses of performance for solar energy sys-

tems, in particular for photovoltaic systems. Derate factors for shading must be taken into ac-

count for situations when PV modules are shaded by nearby buildings, objects, or other PV

modules and array structure.

Very simple instruments can be used to estimate obstacles height and azimuth angles easily. A

solar position diagram with a trigonometrically subdivided height axis and a regular 180° azi-

muth axis is the basis for such an instrument.

This diagram must be copied onto a transparen-

cy, which is then bent in a semicircle. The ob-

server looks through this diagram to the objects

and can directly read height and azimuth angles.

The result is a polygonal approximation of the

surrounding’s silhouette drawn into the solar

position diagram. More sophisticated instru-

ments, with higher associated costs, like the

ones introduced in section 6.5 can also be used.

For PV arrays consisting of multiple rows of PV modules and array structure, the shading derate

factor should be changed to account for losses occurring when one row shades an adjacent row.

Spacing between rows is a compromise between optimizing the use of space and self-shading

losses. The plant designer decides what will be the separation between module rows. An ex-pression that can be used is the following:

Figure 19: Shadow analysis using sunpath indicator.

Source: RENAC



32


being d the separation between module rows (in m), L the height of the PV-array (in m), β the

module inclination (in º), the ground inclination (º) and α the solar elevation (º) at the worst

irradiation day. The obtained separation d between module rows guarantees that at noon on

the worst irradiation day, that is to say, the day where the sun at noon has the lowest elevation,

there will not be any self-shading between rows.

Furthermore the quotient L/D is equivalent to the Ground Cover Ratio (GCR), defined as the

ratio of the PV array area to the total ground area. This metric can be used to predict yields perland-area. Ground coverage ratio values depend on the geographical location, type of system

(fixed, 1-axis or 2-axis tracking) and the shading derate factor. They vary typically between 60%

and 20% percent (for solar plants with 2-axis tracking systems).

Temperature losses

Temperature affects negatively the performance of PV modules. To determine the variation of

Pmpp at different temperatures the following expression issued

Pmpp (T) = Pmpp (STC)* (1+ΔT x Tk )

being Pmpp (STC) the rated power of the module at Standard Test Conditions (STC, 25°C ambienttemperature and radiation on the module 1000W/m2), Pmpp (T) the module power at another

conditions and Tk the corresponding temperature coefficient. The temperature T which must be

plugged into the expression is not the ambient temperature, but the module temperature. The

temperature of the module cells can be estimated by using the expression:

Tcell = Tamb+ (NOCT-20)*G/800

where NOCT is the Nominal Operating Cell Temperature expressed in °C (usually given by the

module manufacturer in the module data sheets and G the irradiance in W/m2. If NOCT is not

given, 48°C is recommended as a reasonable value which describes well most of the commonly

used PV modules.

Inverter losses

During the conversion of direct current (DC) produced by PV generators to alternating current

(AC) that is the one fed into the grid carried out by inverters losses occurs. Therefore the effi-

ciency of the inverter needs to be taken into account, but not only at rated power. Photovoltaic

inverters operate at the rated power for only very few hours in any year. Due to the changing

solar irradiance, the inverters predominantly operate under part load. Therefore, it is very im-

portant that photovoltaic inverters have high efficiencies even when operating under part load

conditions.

)cos(

)tan(

)sin(

Ld



33


Figure 20: Inverter efficiencies at different load conditions. Source: RENAC

Here the maximum inverter efficiency is 95,5% at the half of inverters nominal rating. In Euro-

pean Efficiency definition inverter spends 48% of it´s working time at that level.

Therefore weighted inverter efficiencies have been defined for different geographical regions,

which take into account the inverter efficiency at different load conditions. The best know ones

are the euro efficiency and the Californian Energy Comission (CEC) efficiencies:

Since the radiation in Arab countries corresponds more to California values, the method accord-

ing to CEC has to be prefered to determine the weighted inverter efficiency for MENA re-

gions.Another factor contributing to DC/AC conversion losses is the sizing ratio between invert-

er and solar PV array. A too under dimensioned inverter cannot process all the power delivered

by the generator under peak load conditions and overheating can occurs. Temperature derating

occurs, which means the inverter reduces its power to protect components from overheating.

On the other side, it is not recommended to oversize inverters, since losses due to permanent

part-load operation may be high. Figure 21 shows an example of relative energy yield compared

to maximum available depending in the inverter to PV array sizing ratio which is valid for conti-

nental European conditions. The invterter design ratio in Arab regions may differ, therefore, the



34


inverter size should be adjusted to the regional radiation conditions. Appropriated inverter to

PV array sizing ratio depend on the local weather conditions.

Figure 21: Impact of inverter size on system yield. Source: RENAC

Other sources of losses are wiring losses, soiling, etc. The following figure shows two represen-

tations, a list and graphic representation obtained from the software PVSYST, of the factors in-

fluencing the performance ratio of a solar PV plant and its impact given by the derating factor.



35


Figure 22: Representations of factors influencing the performance ratio. Source: PVSYST

Typical values for the performance ratio of a solar PV system range between 60% and 80% de-

pending upon the size and performance of the plant. Taking into account that Y f in the following

expression is the energy delivered to the grid per year and kWp

PR = Yf / Yr

good estimations of the energy yield of the plant can be obtained. Let’s carry out a small exam-

ple. Assuming a PV system of 4 kWp rated power with a performance ratio of 0.75 on a location

with 2100 peak sun hours of solar radiation per year the expected energy yield of a will be:

Yield = 0.75 * 2,100 * 4.0 = 6,300 kWh per year

A more detailed calculation of the expected yield of a solar PV plant can be obtained using

simulation software. The input is usually in the form of hourly climate data (radiation, tempera-

ture, etc). The yield is then calculated for all the hours of a typical year using the given climate

data and software algorithm and then summed up to provide a specific energy yield per year.



36


8 ConclusionsTo sum up, PV is a zero-emission energy source that will play an important role in the short-

term future of the energy mix. In a couple of years, increasing electricity prices of conventional

energy sources and strongly decreasing prices of PV components will lead to producing energy

with PV, which will be more cost-efficient than purchasing energy from the grid operator.

This chapter has presented the basics of solar radiation and photovoltaic energy conversion.

Furthermore, the main commercially available PV technologies and components have been de-

scribed, including their advantages and disadvantages. The chapter has additionally shown the

differences in the working principles of grid-connected and off-grid PV plants. Finally, the main

parameters, that has to be taken into consideration when designing a PV plant, has been intro-

duced and it was shown how to deal with them.



37


Further readingWeblinks

http://pvcdrom.pveducation.org/index.html

www.solarbuzz.com

http://www.solarexpert.com/GlossaryPV.html

http://www.pvresources.com/en/glossary.php

http://www.windsun.com/Solar_Panels/pv_glos.htm

Grid connected PV

Solar Energy International; Photovoltaics: Design & Installation Manual; ISBN-10: 0865715203;

2004

DGS/earthscan; Planning and Installing Photovoltaic Systems; ISBN: 978-1-84407442-6; 2008

Off-grid PV

Hankins, Marc; Solar Electric Systems for Africa; ISBN-10: 0850924537; 1995

Ecofys; Stand-Alone Photovoltaic Applications; ISBN: 9781873936917; 1999

Keyword index

Accumulator An apparatus by means of which energy can be stored.

Alternating Current (AC) An electric current that reverses direction periodically

AM – Airmass defines how many times a ray of sunlight passes the perpendicular thickness of

the atmosphere. When the sun is located at a height of 90º, i.e. at noon of the spring or autumn

equinox, the AM is equal to 1. Otherwise, the AM increases with the decreasing of the sun’s

height.

Albedo or reflection coefficient The diffuse reflectivity or reflecting power of a surface. It is de-

fined as the ratio of reflected radiation from the surface to incident radiation upon it.

Array A collection of electrically connected photovoltaic (PV) modules.

Battery A device that converts the chemical energy contained in its active materials directly into

electrical energy by means of an electrochemical oxidation-reduction (redox) reaction.

Bypass Diode A diode connected in parallel with a PV module to provide an alternate currentpath in case of module shading or failure.



38


Charge controller An electronic device which regulates the voltage applied to the battery sys-

tem from the PV array. Essential for ensuring that batteries obtain maximum state of charge and

longest life.

Crystalline Silicon A type of PV cell made from a single crystal or polycrystalline slice of silicon.

Current (Amperes, A) The flow of electric charge in a conductor between two points having a

difference in potential (voltage).

Diffuse Radiation Radiation received from the sun after reflection and scattering by the atmos-

phere and ground.

Diode Electronic component that allows current flow in one direction only. See Blocking Diode

& Bypass Diode

Direct Current (DC) Electric current flowing in only one direction.

Efficiency The ratio of output power (or energy) to input power (or energy). Expressed in per-

cent.

EVA (ETHYLENE VINYL ACETATE) An encapsulant used between the glass cover and the solar

cells in PV modules. It is durable, transparent, resistant to corrosion, and flame retardant.

Feed-in meter A grid-connected installation necessary in order to determine the energy that

has been fed into the grid.

Frequency The number of repetitions per unit time of a complete waveform, expressed in Hertz(Hz).

Grid Term used to describe an electrical utility distribution network.

Grid Connected PV System A PV system in which the PV array acts like a central generating

plant, supplying power to the grid.

Inverter In a PV system, an inverter converts dc power from the PV array/battery to ac power

compatible with the utility and ac loads.

Irradiance The solar power incident on a surface. Usually expressed in kilowatts per square me-

ter. Irradiance multiplied by time equals Insolation.

Irradiation - The solar radiation incident on an area over time. Equivalent to energy and usually

expressed in kilowatt-hours per square meter.

I-V Curve The plot of the current versus voltage characteristics of a photovoltaic cell, module, or

array. Three important points on the I-V curve are the open-circuit voltage, short-circuit current,

and peak power operating point.

Joule (J) Unit of energy equal to 1/3600 kilowatt-hours.

Kilowatt (kW) One thousand watts. A unit of power.

Kilowatt Hour (kWh) One thousand watt-hours. A unit of energy. Power multiplied by time

equals energy.



39


Load The amount of electric power used by any electrical unit or appliance at any given time.

Load Current (A) The current required by the electrical device.

Maximum Power Point That point on an I-V curve that represents the largest area rectangle

that can be drawn under the curve. Operating a PV array at that voltage will produce maximum

power.

Maximum Power Tracking Operating the array at the peak power point of the array's I-V curve

where maximum power is obtained.

Multicrystalline Material that is solidified at such as rate that many small crystals (crystallites)

form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are

jumbled together. These numerous grain boundaries reduce the device efficiency. A materialcomposed of variously oriented, small individual crystals. (Sometimes referred to as polycrystal-

line or semicrystalline).

Off-grid system System living in a self-sufficient manner without reliance on one or more public

utilities.

Open Circuit Voltage The maximum voltage produced by an illuminated photovoltaic cell, mod-

ule, or array with no load connected. This value will increase as the temperature of the PV ma-

terial decreases.

Peak Watt The amount of power a photovoltaic module will produce at standard test conditions

(normally 1,000 w/m2 and 25° cell temperature).

Photovoltaic System An installation of PV modules and other components designed to produce

power from sunlight and meet the power demand for a designated load.

Semiconductor A material that has a limited capacity for conducting electricity. The silicon used

to make PV cells is a semiconductor.

Short Circuit Current (Isc) The current produced by an illuminated PV cell, module, or array

when its output terminals are shorted.

Stand-Alone PV System A photovoltaic system that operates independent of the utility grid.

Thin Film PV Module A PV module constructed with sequential layers of thin film semiconduc-tor materials.

Tilt Angle The angle of inclination of a solar collector measured from the horizontal.

Transformer A device that transfers electrical energy from one circuit to another through induc-

tively coupled conductors.

Volt (V) The unit of electromotive force that will force a current of one ampere through a resis-

tance of one ohm.

Zenith Angle The angle between directly overhead and the line intersecting the sun. (90°- ze-

nith) is the elevation angle of the sun above the horizon.

http://en.wikipedia.org/wiki/Electrical_energy

http://en.wikipedia.org/wiki/Electrical_network

http://en.wikipedia.org/wiki/Inductive_coupling




http://en.wikipedia.org/wiki/Electrical_network

http://en.wikipedia.org/wiki/Electrical_energy




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PV Online Brochure en Final 3

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