pay-back time

[Ampster]

The real question is what size system?. Go to PVWatts yo put in your location and system size to get another opinion about kWhr production. Maybe it assumes pretax numbers. Is that $0.41/kwhr the rate the power company will pay you all day and weekends?

[mckennatim]

I can't really make sense of the payback time. The calculator says I will generate 4,498 kWh/yr at an average cost(value) of $.41/kWh So that is $1844/yr that I save. The system cost after rebates is $8,624 So I calculate the payback time as $8624 / $1844 = 4.68 years. But the Calculator says 2yr 8 mo Why are my numbers off?