Measuring Photovoltaic Cell Efficiency

[deleted-810040]

Hello,

For my science project, I need to determine the efficiency of a photovoltaic cell. I've researched how to do so online, but it seems that each source I visit has a different answer; additionally, the methods they use to find efficiency seem somewhat complicated/ above my grade level.

Although I am willing to learn how to find efficiency through the methods I've found on various online sources, I'm still curious if there is a less complicated way that is also somewhat easy to repeat.

[rmarz]

CVionis - What sounds like a simple project is full of many variables that will cause problems in your experiment. I think the definition of 'efficiency' would be the output energy produced by the solar cell as a % of the radiation energy it receives from the sun. Already several problems emerge. What is the input energy per unit of area? How do you measure it? Practically speaking, a rule of thumb about this figure is about 1,000 watts per square meter, in bright sun, with the target being perpendicular to the suns rays. Bright sun at 8 am at your latitude is different than at 'local noon' at the equator. What about atmospheric conditions? Clouds, smoke and haze.

I think you should limit your experiment and state you are using the estimate of 1,000 watts per square meter figure, do your experiment during a bright sunny day with the sun directly overhead, and your solar cell perpendicular to the sun. Make your power measurements at this point and calculate your cells power per square meter. We know solar cells operate somewhere between 10-20% efficiency, so if your results are anywhere in that range you are on target. I'd be interested in how you will make the output power measurements. Hope this helps, good luck.

Rick Marz

[deleted-810040]

I appreciate the response. To calculate the efficiency of a PV cell, would I divide 1,000 watts per square meter by the power per square meter of my PV cell? If so, how exactly would I determine the watts per square meter of an individual PV cell?

[rmarz]

CVionis - You are making relative measurements and begin by stating your assumptions. I mentioned a figure of about 1,000 watts per square meter of energy from the sun falling on the earth's surface. Calculate the area of your PV cell (in square meters) and divide that by our estimate of 1,000 watts/square meter. That should be the energy received by your cell at 100% efficiency. Now measure your power output in watts (voltage x current). That measurement will give you an approximation of your cell's efficiency. Measure the open circuit voltage, and short circuit current with a DC milliameter. Calculate that power. Then try to optimize the load impedence by using various 100 to 1000 ohm resistors to find a maximum power transfer. I think that would give you a well conceived and documented experiment.

Rick Marz