Question

In: Physics

1. Why don’t the short circuit and open circuit voltage produce power in a p-n cell?...

1. Why don’t the short circuit and open circuit voltage produce power in a p-n cell?

2. The power supplied by a solar cell is proportional to its surface area. Using the flux of solar energy under AM1 conditions, estimate the power a 1-cm2 solar cell will yield. State explicitly any assumption you make.

Solutions

Expert Solution

(1)

Remember that the power efficiency of the solar cell is the output power (Pmax) over the input power (Psolar). It can also be expressed in terms of the fill factor: the power efficiency of the solar cell is equal to the product of the fill factor times the short circuit current Jsctimes the open circuit voltage Voc over the input power Psolar. This is an expression that will often come up literature when people discuss solar cells. The goal is to maximize the fill factor, the open circuit voltage, and the short circuit current. You would want the photocurrent as large as possible. The open circuit voltage is actually a measure of the work that can be done by the generated electrical current. The more work done by the current, the more power that was generated.

(2)

in order to rate solar panels for comparison, manufacturers assume an average available solar energy of 1,000 watts per square meter. The percentage of that energy that is converted into electrical energy is the panel's efficiency. For example, a 1-square-meter panel might have a power output rating of 150 watts. Assuming 1,000 available watts, this panel converts 15 percent of that solar energy into electrical energy. Therefore, this panel has an efficiency of 15 percent. The average silicon solar panel produces power at roughly 15 to 18 percent efficiency, depending on silicon crystal type.

A typical silicon solar cell generates between 0.5 and 0.6 volts. The output current varies depending on the size of the cell. In general, a typical commercially-available silicon cell produces a current between 28 and 35 milliamps per square centimeter.

So power P= V*I

P= 0.5* 28*10^-3

P= 0.014 W (power produced by a typical cell of area 1 cm^2)

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