The national average for electricity from utilities (the grid) is $0.11 per kWh. A rough estimate for electricity from a permanent residential solar system installation today is four times that amount. Throw in federal and state incentives and you'll be lucky to pay $0.30 per kWh with installed solar. However, there is speculation of grid utility electricity tripling in cost very soon. (There is also speculation of major solar flares which could make the ROI priceless - comments welcome below.)
Alternative energy is not currently cheap or cost-effective, but as grid and gas prices rise, incentives increase, and renewable energy technology costs fall, it will get better.
It is also important to remember that SUNRNR is not trying to compete with the grid, so comparing our kWh cost to theirs is moot in a sense. (We certainly have the advantage if considering running hundreds of feet of power line.) And cost per kWh gets even fuzzier when you take into account a SUNRNR provides renewable energy.
Eventually SUNRNRs will become grid-tieable and with enough in a given area, they could have an impact on what would have been a utility peak. This concept of leveling peaks and recharging during low power consumption valleys could keep one more industrial power plant from being constructed.
In round numbers (and making assumptions slightly in our favor), let’s say a gas generator comparable in power output to a SUNRNR costs $1000, uses 0.4 gallon of gasoline daily at $3/gal to match a SUNRNR's sustainable rate. After six years and 900 gallons of gasoline, a SUNRNR would be paid for, fuel is free, and the next required maintenance would be over two years after that. Added bonuses: 2000 hours incessant putt-putt noise not heard and 900 gallons of gas not consumed.
So far, this discussion has been focused on personal and/or local use. It wouldn’t be complete without commenting in broader terms. Nationally and globally, the ROI could be dramatic, but difficult to define with a number. There would be numerous advantages for this country if FEMA would use solar generators instead of gas-powered at disaster sites like hurricanes or during the ice storm in the mid-West several years ago. (And remember, it is difficult to get the gas to run a gas generator for electricity when you need electricity to pump the gas.) As for globally, the US provides so much costly aid to other nations to help fight disease and improve quality of life. If we could get portable, renewable power to these people to allow for clean water, refrigerated medicine, and light at night, we would be teaching them to fish, not giving them one, and the investment could return many-fold.