Pouya Zohrabpour

Physics Case Study

Solar Battery / Photovoltaic cellsA solar battery is a battery that gets its energy from a source of light (e.g. the sun) by using photovoltaics. The first solar battery was first developed in 1833 by Charles Fritts. He deposited selenium (which was discovered to have photoconductive properties in 1873) on a thin layer of gold. That primitive solar cell had a conversion efficiency less than one percent. The solar cell timeline goes on from there [1]. The solar panels that we saw on rooftops today were invented by bell laboratories in 1954. These solar panels had a conversion efficiency of 6 percent. In 2013, we now have solar cells with up to 20 percent conversion energy. As time passes by, technology and science are constantly getting stronger and stronger. Who knows what kind of conversion percentages we will have in solar cells in 20 years. This is a huge benefit as in the years to come; we may be able to fully power a house by just using solar cells.

Solar cells are made using semiconductors such as silicon. When light strikes the photocell, energy is transferred to some of the free electrons in the semiconductor. An electric field within the cell provides a force on the electrons. The electron flow provides the current and the cell’s electric field cell’s electric field causes a voltage [2].

As stated before, solar cells can be seen on rooftops. These panels use the sun as a source of energy and thus provide the home with electricity. As of right now they are very expensive, costing thousands of pounds. You have probably also seen solar cells used in calculators. Solar calculators use a very power efficient display (liquid crystal) and operate at very low voltages. This means solar cells can provide enough electricity for them to fully function and thus not needing a replacement battery.

The efficiency of a solar cell is the most common property used to compare the performance of one solar cell to another. Efficiency is the amount of energy output from a solar cell compared to the input of energy it is receiving, whether it’s from a lamp or the sun. There are many complex formulas that can be used to work out the efficiency of a cell, but a simple one can be:

Solar cell efficiency = Totalenergy outputTotalenergy input

x100

Using this formula, a simple experiment can be conducted to work out the efficiency of a solar cell.

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A lamp with a constant energy output must be shone on to the solar cell. We should already know the energy input (from lamp) and the energy output can be read from the ammeter and put into the formula. We can use this to measure the efficiency of the solar cell.A

Pouya Zohrabpour

There are a few factors that can affect the efficiency of a solar cell. For example the temperature of the solar cell can change its efficiency. Changing the temperature can affect the semiconductor material and thus changing the resistivity of the solar cell. As temperature increases, the open-circuit voltage decreases, and thus efficiency decreases. This is demonstrated by the following graph:

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[4]

Pouya Zohrabpour

Reference1. “Who created the first solar panel?”, user: ra-tech-solar,

http://solar.calfinder.com/ask/who-created-the-2 , (visited 28/10/13)2. Mike Benn, Graham George, 2008, Edexcel Physics for AS (Advanced Physics for Edexcel

Series), published by Hodder Education in London 3. “What is a solar battery?”, http://www.wisegeek.com/what-is-a-solar-battery.htm , (visited

on 01/11/13)4. “solar cells”, http://www.pvresources.com/Introduction/SolarCells.aspx , (visited on

02/11/13)

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