I agree with your math but disagree with your conclusion :)
this is why Google is funding it -- getting an 11% return is great if you have giant piles of cash sitting around doing nothing. Those margins become substantially thinner if your cost of capital is 7%, 8%, 12%, etc.
edit to add:
BTW, there's some great research that suggests when people "do the math" and figure out how much energy-efficiency/renewable energy technology will save, that they usually require ROI's of 50-100% -- i.e., "if your fluorescent bulbs/solar panels/low-flow shower head won't pay for itself within a year, i won't bother". It's sad, but it's a real obstacle.
"if your fluorescent bulbs/solar panels/low-flow shower head won't pay for itself within a year, i won't bother"
I'd guess this is largely caused by our psychological tendency to overly discount future gains combined with loss aversion (people are used to things failing after a year, so if it hasn't paid for itself by then, it never will (example: I just had a 4-year fluorescent bulb I installed one year ago fail, about a month after I threw away the packaging with the warranty info on it)).
My CFLs haven't lasted very long since production of most of them shifted to China. They last a year or two, which is a bit longer than the bulbs they replace, but not much. There's no place to dispose of them safely though so they are just stacking up in boxes for now. I found with the warranties that you have to ship the bulbs back at your own expense to an address, which because of the weight of the ceramic base costs more than the bulb did originally. This means in practice they don't really have a warranty, so you did the right thing throwing the warranty packaging out.
this is why Google is funding it -- getting an 11% return is great if you have giant piles of cash sitting around doing nothing. Those margins become substantially thinner if your cost of capital is 7%, 8%, 12%, etc.
edit to add: BTW, there's some great research that suggests when people "do the math" and figure out how much energy-efficiency/renewable energy technology will save, that they usually require ROI's of 50-100% -- i.e., "if your fluorescent bulbs/solar panels/low-flow shower head won't pay for itself within a year, i won't bother". It's sad, but it's a real obstacle.