I'm trying to make some rough calculations about the cost of putting in a solar power system at work, and am hoping someone can tell me if I am doing this wrong, because the cost seems prohibitively expensive the way that I am calculating it.

I'm assuming two things (taken from a MN government publication on solar power) - that the cost is about $10/w ($10,000 per kW), and that 1kW system provides 1,000 kWh each year.

Our department currently uses 80,000 kWh a year (9,950 w running 365 days a year), so we would need an 80 kW system. At $1,000 kW installed, even with the Federal and State tax incentives that is still $550,000... spread that over 15 years, and it's $35,000/year. Grid electricity is only $7,900 a year. :(

Am I doing something wrong in my calculations?