Saturday, March 26, 2011

A Dollar a Watt?

One of my fantasies is to build a "green" RV. Not that I [am] a particularly big time green guy, I just like the idea. Hydrogen of course is a part of the fantasy and either wind and/or solar. My RV is 34 feet long and nearly 10 feet wide. allowing for basic access to junk on the roof I may have 300 square feet of space for solar cells. Let's round that off to 30 meters squared. Sun energy down here is about 1000 watts/meter^2. But solar cells are not that efficient so let's use the Nanosolar estimate of 15% efficiency. So I could get about 4.5 kilowatts hours while the sun is shining. The sun doesn't always shine all the time, so say 6 hours per day. That's 27 Kwh per day. More than enough for my RV. Less shipping and installation that solar array would cost me $4500. I would need to spend about $800 for a power inverter, some batteries plus some wiring and stuff, so let's say $6000 so nothing too unexpected comes up.

Assuming I did everything right and it all lasts 10 years, how neat would this system be? My average monthly electric bill is about $75. That is not much because I have gas heat, stove and hot water. If nothing broke I would save $3000 in ten years. Nothing is prefect, so stuff will break eating up that $3000, but the system should last longer, so everything is free after 10 years. A ten year pay pack is a lot sportier than I would have had with solar three years ago. So solar is making up some ground finally. Summer time is my maximum energy use time. The solar array provides enough power, but not when I need it, at night for the a/c. I only allowed for 5 deep cycle batteries which be pressed hard in the summer, but will make it. They would need to be swapped out every 18 months to 2 years, but they will do the job.

My ideal fantasy system would have a reverse cycle fuel cell and store about 60 kilograms of hydrogen. I will continue with those estimates later.

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