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How to read IV charts for PV solar panels

Posted by Chris Rudge on 6 April 2010 at 10:14 am

Q: I'm being offered a Sharp 235w panel instead of Powerglaz 235w. The IV (current/voltage) charts look different. Can someone explain IV for me?

A: I've just had a look at the charts for the Powerglaz polycrystalline 660235 against the Sharp NU235 Monocrystalline, and see that they do have differing current/voltage (I/V) charts.
These charts allow us to see the point of maximum power output at different irradiations. Current in amps (I) is on the X axis of the graph and voltage (V) along the Y axis. Usually, these charts have curves for 500, 800 and 1000Wm2 irradiance at standard test condition (STC) temperature of 25 degrees C.

Temperature is very important for the PV module, the lower the better, so all manufacturers have to quote ratings at 25 degrees. If they used a lower temperature datum (ie 20 degrees), the module output efficiency will be falsely inflated. This is also why an 'in roof' system tends to provide less power per annum, as it has less airflow to keep the modules cool in hot weather.

Coming back to the point... Looking at the charts, there will be a difference in module characteristics simply because the cells are of different manufacture thus response, output, etc will differ. However, with both of them, at 1000Wm2 solar irradiation at 25 degrees C, the power rating will be 235W.
Photo by futureatlas

About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.

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