U.S. Department of Energy Energy Efficiency and Renewable Energy

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July 30, 2012
Q.

Our community just added a dozen 240 watt panels to our courthouse annex.  I was planning on 240 watt max from the panels, but the inverters are of a lower wattage, 200.  Is this common across all applications?  

A.

First, we recommend using a professional PV system designer and installer. If I understand the question correctly, the answer is yes, inverters are typically sized at 10-20% below the maximum capacity of the PV panel array. This is because a PV system rarely, if ever, operates at its maximum capacity because of clouds, temperature, dust, inverter efficiency losses, etc. Real-world performance should be taken into account when designing a PV system and so a smaller inverter capacity is usually used to match actual PV system output and because larger inverters are more expensive. In some climates, however, it might make sense to spend the extra money on a larger capacity inverter. A larger capacity inverter will run cooler and last longer and leaves the PV system owner the potential opportunity to expand the size of the PV array without having to replace the inverter with one of a larger capacity. I have also read about sizing inverters larger in order to be able to take advantage of "edge of cloud" effects—which is really cool and really geeky. See this from Bill Brooks.

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