[akira2501]

I don't find his methods particularly rigorous. He's just taking total generated kWh and multiplying it by current utility rates and then saying this represents savings.

Does it, though? We don't know how much of the generated power was actually used instead of sold back into the grid, or if this is even a grid tied installation, and what the return sales rate would be.

The only way to actually compare this is to look at the actual bills. What did you pay last year, what did you pay this year? That's _actual_ savings. This is calculated plausible savings. It's not at all clear they're the same thing in this scenario.

Finally.. if you're in a position to even say you're _saving_ $233/mo, then how inefficient is your home in the first place? How many people live there to generate this large of a bill? How much of a difference would it have made to make that house more thermally or electrically efficient instead?

[Kirby64]

If you live in a place that does net metering, it truly just is as simple as generated kWh * utility rate. That's what net metering means. Each kWh you provide via solar offsets the cost of a kWh from the grid.

Additionally, if you live in a place where power is $0.20-$0.30/kWh, then $233/mo is not a particularly large amount of electricity, especially for a single-family house. At $0.30/kWh, that's only ~775kWh of electricity.

[akira2501]

There are a few different forms and a few different rules surrounding it. I can probably assume what he means, but a more direct comparison would obviate any of these factors.

Right.. but that's not his total cost, that's his total savings. So, with those factors; which make sense for New England, he's got a 7kW system getting light for about 3 hours a day on average to net that 775kWh to earn the $233 savings in a month. Would that be right?

[Kirby64]

If the system was totally efficient, then yes, but the 7kW nameplate number is peak efficiency... so most likely it's some averaged number (say, 4-5kW?) that is across a longer period of time.