Researchers are continually striving to improve

the efficiency of solar cells. But what exactly does the term “efficiency” mean in the solar industry? How is it measured? Find out in this video. This video is part of iPolytek’s online course

on solar energy. iPolytek, Professional Development Courses for Engineers. The efficiency of a solar cell is equal to

the ratio between the electrical power it produces and the power it receives from the sun. To measure the efficiency of a solar cell

or solar module, the standard value of E=1000 W / m2 is used. According to this definition, the smaller

the area needed to produce Pmax, the higher the efficiency. So, how is Pmax measured? By constructing

the IV curve (or the current versus voltage curve) of the solar cell. The current that is measured when there is

no voltage is called the short-circuit current, Isc. At this point, power equals 0. The voltage that is observed when no current

is flowing is called the open-circuit voltage, Voc. At this point, power also equals 0. Since, Power=I x V : The P-V curve is obtained by multiplying,

point by point, all the voltages and currents between the short circuit and open circuit

conditions. Then we can simply read Pmax since it is the

peak of the P-V curve. Once we know Pmax, we can read Vmp (the voltage at maximum power)

from the P-V curve. Next, we use the I-V curve to determine Imp

(current at max power) from Vmp. In general, Pmax is found near the elbow of

the I-V curve. We see that Pmax decreases considerably as

the irradiance decreases (because of cloud cover for example). Temperature also has a strong influence on

Pmax. As the temperature of the solar cell increases

the voltage it generates decreases. At the same time, the current it produces

increases very slightly. Therefore, the net effect is an overall decrease

in the power produced by the solar cell. Standardized tests are used to determine Pmax.

They make it possible to compare devices that differ in technology and manufacturer. These

tests are carried out under the following standardized conditions:

– Incident radiation flux 1000 W/m2 – A solar cell temperature of 25 degrees Celsius

– 4 measuring points are used (2 for voltage and 2 for current)

– Spectral conditions Air Mass 1.5 This means that the composition of the spectrum

used is identical to the solar spectrum after it crosses an air thickness equal to 1.5 atmospheres.

This corresponds to an angle of incidence of 41.8 measured from the horizontal. Lamps meeting these specs are placed above

the solar cell. The solar cell is placed block allows the measurement its front and voltage

and current. Cooling water runs through block to maintain the cell temperature at 25 degrees

Celsius. Finally, a variable load is used to taking readings along I-V curve. In this video, we’ve seen how efficiency is

defined and measured. We’re ready to calculate the number of modules

we need for a given power output. What are the basic calculations involved in

sizing a PV system? Find out in our next video! Thanks for watching and see you soon.