Right now, we can get a 3kW system installed for about $12K US (it's more expensive than that, but the installer gets a rebate that drops the cost for the consumer). Since my wife is working from home as a consultant, we may get to write off just under 9% of that from taxes (woo-hoo self-employment). By the time the state ($6000 across 4 years) and federal (30% on out-of-pocket costs) rebates are paid back, it will have cost us about $2100 (plus the lost opportunity for investing that money elsewhere). With our current energy use, we should have recovered that cost in (theoretically) 4 years. Potentially less, if electricity prices go up. Potentially longer if if stays cloudy more than usual in that time. Across the (warrantied) life-expectancy of the panels, we'll save about $35K -- not a lot, when spread across 30 years, but it's about 12% ROI, which is better than a lot of other returns that I can think of. Not to mention, it's a better way to use green energy than ticking the box on the utility bill saying "Charge me more for pretending to send me green energy."