# How is the efficiency of a solar cell measured? (Solar Energy Course 2020 Part 7 of 12) 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.