shop-talk supported in part by Fat Chance Garage
http://fatchancegarage.com
> Keep in mind
> that the SA240 appears to be mounted vertically instead of at an angle so the
> available energy will be somewhat less.
Possibly quite a bit less. That map assumes a fixed angle from horizontal equal
to the latitude, which for Montana is 44 - 49 degrees. Assuming that's optimum,
mounting the collector vertically reduces available insolation by 30%.
> Let's assume you'll use this heater from October through March and
> over that time
> you're able to average 9-10KWh output per day (the collector is about
> 2.6 square meters).
Perhaps I missed it, but haven't you left out collector efficiency ?
> For gas, let's assume natural gas goes up to $1.40/therm (100k BTU) and stays
> there. Then you're looking at saving around $82/year. The solar
> heater would
> pay for itself after around 20 years.
Assuming of course that it costs nothing after being installed, no maintenance,
no repair, etc.
Lots of abandoned solar heaters around here, after people figured out what the
real payback is. And we get a lot more sunlight in winter than Montana does.
Randall
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