this house has a 2 yr old Sunny Boy 2100u system installed. 4BR, 2.5 Bath House.
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{ 3 comments… read them below or add one }
If you have 8 hours of sun a day, that is 2100*8 = 16800 watt hours of energy, or 17 kW-hrs.
17 kW-hrs purchased from the power company is about $ 1.70, so you will save about $ 50 per month.
This assumes power costs 10¢ per kW-hr
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The Sunny Boy 2100 watt rating is the rating of the inverter. The number of solar panels and their ratings will determine the output. If the panel ratings add up to 2100 watts, you can expect a maximum effective output of about 1600 to 1700 watts. If the system has batteries, the output will be less.
Look on the Internet for “insolation tables”, to see your average effective hours per day. Where I live, the insolation value is 5. Multiply the effective output by the insolation value to get the number of kilowatt hours per day. And multiply that number by the cost per kilowatt hour from your power company.
When someone has a 2100-watt inverter installed, that usually means they’re running 1800 watts or so through it, in real life. We can project power generation based on all kinds of assumptions about the panels and your location, but that’s unnecessary. The Sunny Boy should have a log on its display of the total power produced. You can just look at that, and see the total number of kWh’s produced over the last 2 years, or however long it was actually installed. Then, you can multiply that my the cost of electricity in your area.
Also, ask the homeowner (seller?) how much they think they save per year. It will be nuanced by how much power they use, and whether their electric rates are tiered or not. For example, if they use a lot of electricity, they might be paying a lot, maybe 30 or 50 cents a kWh, for those last few kWh’s. If the Sunny Boy is displacing those, then it’s saving an awful lot of money.