Question

Standard test conditions (STC) for panels are 1000 W/m²incoming radiation, panel oriented normal to the sun, and 25 °C.  If all other conditions are the same but we decrease the temperature, how will this affect power output of the panel, relative to its STC rating?  Why?

How is solar energy wasted when the frequency of incoming solar radiation is too low? When the frequency is too high?

How does a multi-junction solar cell improve efficiency compared to a single-junction cell?

Answer 1

(b) How is solar energy wasted when the frequency of incoming solar radiation is too low? When the frequency is too high?

Solar energy is created by nuclear fusion that takes place in the sun. The energy, heat and light from the sun which flow away in a form of electromagnetic radiation (EMR).

Low frequency waves are low energy waves with a long wavelength. The length of a wave itself is very long for a given period of time. E.g ; radar, TV and radio waves

High frequency waves are high energy waves with a short wavelength. The length of a wave itself is very short for a given period of time. E.g ; gamma rays, X-rays and ultraviolet rays

The frequency of an electromagnetic wave which determines how much energy it carries. Electromagnetic waves that have longer wavelengths and lower frequencies which carry much less energy than those with shorter wavelengths and higher frequencies.

(c) How does a multi-junction solar cell improve efficiency compared to a single-junction cell?

"Multi-junction solar cell" are solar cells with more than one p-n junction. Each of these junctions is made up of different semiconductor materials. They have higher efficiencies than conventional solar cells.

A single junction solar cells have a theoretical maximum efficiency of about 35% and a multi-junction solar cells have a theoretical maximum efficiency of about 80%.

We know that, a multi-junction solar cell improve efficiency as compared to a single-junction cell.

Such a high efficiency will be achieved under a very large number of junctions. In an experimental labs, with a reasonable number of junctions, a multi-junction cells have demonstrated efficiencies of about 43%. As Compare it with the best efficiencies achieved for a single-junction in labs, around 25%.

Basically, a multi-junction solar cells which require high concentration of sunlight at any point in time. They will need a tracking devices in order to provide satisfactory output.