1

I - V Characteristic of a solar cell The figure below shows the output characteristic of a solar cell. This I-V curve

illustrates the relationship between the current and the voltage under standard test

conditions (STD),i.e. 1000𝑊 per square meter of radiation and 25°𝑐 of temperature.

Where as in reality, the characteristics of the I - V curve depend on the solar cell

technology or on a number of environmental conditions like temperature, solar

radiations etc.

Figure 4: I-V Characteristic of a solar cell

The I-V curve consists of three important operating points,

𝑉𝑜𝑐 Open-circuit voltage.

𝐼𝑠𝑐 Short-circuit current.

𝑃𝑚𝑎𝑥 Maximum power point.

2

Open-circuit voltage (𝑽𝒐𝒄)

When there is no load connected to the output of the solar cell then the value of the voltage will

be at its maximum with no current being drown through it (i.e. Voc = V(at I = 0) ).That is

the point where open circuit voltage occurs.

Voc can be calculated from the equivalent solar cell circuit as,

Voc =nkT

q× (ln

Iph

Io+ 1)

Short-circuit current (𝑰𝒔𝒄)

Short circuit current occurs when the voltage at the output is zero and the value of the

current is at its maximum ((i. e Isc = I (at V = 0))

Isc can be calculated from the equivalent solar cell circuit as,

𝐼𝑠𝑐 = 𝐼𝑝ℎ − 𝐼𝑜(𝑒𝑞𝐼𝑅𝑠𝑛𝑘𝑇 − 1)

Maximum Power Point (𝑃𝑚𝑎𝑥)

As power is the product of current and voltage so therefore looking at the I-V curve the

power operating at the Iscand Voc is zero. As at Isc the output current is at max. value

but has zero voltage similarly at Voc the voltage is max. but has zero current, in both of

these cases the output power is zero, So therefor the point where the power will be at its

maximum will lie some ware between these two extreme point and that point is known

as maximum power point ( MPP ) or 𝑃𝑚𝑎𝑥 .This is the point which is desired for most of

the application which work on solar cell. Voltage and Current at this point are denoted

as 𝑉𝑚𝑝 and 𝐼𝑚𝑝 - [21].

Figure 5: Characteristic of a solar cell with

maximum power point

3

Types of solar cells

There are three main types of solar cells, listed as below.

Monocrystalline Silicon solar cell

Monocrystalline or also known as single crystalline silicon, are

made from a thin slice cut from a large crystal of silicon. They

appear black in colour and has the highest efficiency as they are

made from the best quality silicon. They have an efficiency of

about 15 – 20%. They are space efficient and require less space, as

the other types of solar cell with the same power output would

require more space. They are very long lasting and mostly come

with a warranty of about 25 years from the manufactures .At low

light conditions they performance is batten than polycrystalline

solar cell - [22].

Polycrystalline Silicon solar cell

Polycrystalline (or multi-crystalline) are made simply by melting

raw silicon and then pouring in a square shaped mold, Which later

is cooled down and cut into small square pieces. They are blue in

colour and have an efficiency of about 13- 16% .the process of

making this type of solar cell is simpler, has a less amount of

silicon wasted and costs less.

They have moderately less heat tolerance and therefor perform

slightly less than monocrystalline solar cell under extreme

temperature. Because of the square shape cut of the cells, thy pick

up the lights from many different angles and therefor work well

enough even if they are not properly angled towards the sun - [22].

Figure 7: Polycrystalline Silicon solar cell

Figure 6: Monocrystalline Silicon solar cell

4

Amorphous / Thin film solar cell

Amorphous / Thin film solar cell are made by depositing many thin

layers of amorphous silicon(a-Si) or other type of material like

Cadmium telluride ( CdTe ) or Copper indium gallium selenide (

CIS / CIGS ) directly into a substrate like glass or a steel sheet. This

technique has an efficiency of about 5 - 9 % only and requires a lot

of space but they are very cheep and easy to manufacture. They are

very flexible and have comparatively batter performance in shaded

or hot condition than other type of crystalline cells - [22]. Figure 8: Amorphous / Thin

film solar cell