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(I know this seems
to be getting off the list-topic, but I think it is somewhat interesting,
especially since Judith will soon be posting a related Rosen message on solar
and sustainable energy.)
Regarding using a
photovoltaic system as a real-time off-the-grid system, I found this link to a
company in Minnesota which sells such systems:
The cost of a
standalone (no-grid) system which supplies 3000W and produces 2400kWh/yr is
approximately $45,000-$48,000US.
How much of a
"typical" house 2400kWh/yr will power is unclear to me. Recall that Pete
mentioned that his annual usage was on the order of 28,000 kWh/yr. That
usage requires over 10 times the output of the system mentioned above. At
various websites, I have found "average" annual home usage numbers varying
widely from 6,500-14,000 kWh. Even at the low end, that is still nearly three
times the size of the system above.
The battery units
for an off-grid home using 10,000kWh/yr would have to hold ~82kWh if it was to
power the home for 3 days and nights of snow. If we assume that we will be
careful and intentionally cut our usage in half during that time (because we saw
the storm coming), then it will only have to hold ~41kWh. A single 62lb
T-105 Trojan battery will supply 225Ah*6V=1.35kWh. (http://www.trojanbattery.com/TrojanPartNumber_2.asp)
This means that approximately 31 of these batteries would be needed. However, it
is bad to fully discharge those batteries, so we really would
need something more like 40 batteries. (Also, these kinds of batteries
can stand only a limited number of deep-discharges, less than a 1000, so it
is harmful to their lifespan to use less batteries.)
Regards,
Tim
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