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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have the Sunny Boy 3300u inverters for a solar system. They are convection cooled. If I have a fan blow cool air around them will I increase the maximum power they can produce before they derate or am I waisting my time? They are capable of delivering 3300W before the heating of the IGBTs increases beyond their safety margin and they derate.
They are listed as 95% efficient. I have a 4kw array so the maximum AC power I should be able to produce is 3800W; yet, the specifications say they should have a 4000-4200W DC array supply power to them. I would think I should have a 3800W unit but it requires a 4800W array. Why would this be if the 3300U is listed as only being able to deliver 3300W? Does this have to do with minimum turn-on voltages or my lattitude?
EDIT: As I have read further, I can see why a 3300U inverter was chosen for a 4000W (STC) array. See link
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
First of all, congratulations on your new solar system! You're doing your bit to reduce global warming and earn major geek points
Now, as you figured out, the wattage rating of a solar panel is for 1kW per square meter of incident solar radiation (which corresponds to full sunshine at sea level and midday) with the panel at 25'C. Now, the efficiency of a PV drops with increasing temperature, and a dark coloured object like a PV panel sitting in full sunshine will not stay at 25'C for long!
So in practice, you only see the full rated output of your array if the sun suddenly bursts out of the clouds near noon on a cold day, and then only for a short time. Your contractor will have taken this into account when sizing your inverters for you.
If you are curious to learn more about how your PV system is doing, you might want to consider installing a data logging system on it. Then you can draw nice graphs in Excel and get energy statistics, or even publish live data to the Web so we can see what your PVs are doing too. A data logging system would also tell you whether your inverters were getting too hot and derating. If you want one, it's probably best to ask your contractor first.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have 12kw on my roof and on a cloudy day I was watching my meter flying backwards. Early in the morning when the sky was clear and the air was cold (about 10-12 deg C) I saw my inverts hit around 3320W each. Over the next few hours as the skies got cloudy they settled at about 2800W. I need to see what they do on a totally clear day. Nonetheless, on this cloudy day I made about 25kwhours of electricity that was fed back to the grid.
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Inverters for a solar system
