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re: home aux pwr motor/gen
13 dec 2000
wrote:
>ray munro wrote:
>>given the quantity of heat that can totally be generated from, say
>>a 80 hp. 1.5 litre ic auto engine, plus the ability to drive a large
>>size electric generator; would the cost of fuel be excessive to use
>>the device to power an off-the-grid, well insulated home ?
probably not. gasoline is now cheaper than heating oil where i live.
lifetime is an issue with a small engine, vs a big one with hot water
storage and an electric meter that runs backwards to allow it to make
more power over fewer running hours. say your engine wears out after
150k miles at 60 mph, ie 2,500 hours...
>>has anyone played with capturing the heat from the exhaust pipes as well
>>as the cooling system heat, with such a device ? i realize that a
>>safe heat exchanger would be a high priority.
sure. intelligen's home system used an 11 hp lister-petter diesel and
a 5 kw induction motor/generator. the cogen efficiency was 93%, with
a small exhaust gas heat exchanger (a 4" cube) and a 150 f chimney temp.
>...if you can get 60 miles/gallon (canadian) with a honda civic at
>60mph, you are burning a gallon an hour. at $3 per gallon that is $72
>per day if it runs day and night.
but most houses don't need that much power. ray said "a well-insulated
home." suppose the engine delivers 20% of the fuel's heating value as
electricity and 60% as hot water, and 20% goes up the chimney, and the
house needs 600 gallons of oil over a 200 day heating season, burned
in a 100% efficient furnace...
so the engine burns 600/200/0.6 = 5 gallons per day, about 5x130k = 650k
btu/day. if it makes 80 hp (59.7 kw) at 30% efficiency, it burns 59.7/0.3
= 200 kw or 688k btu/h of fuel, so it only runs 650k/688k = 0.94 h/day (or
maybe 3 hours every 3 days) while making 0.2x0.94x688k/3412 = 38 kwh/day
or 1140 kwh/month of electricity, right?
ray also said "off-the-grid," which sounds harder to do, with lots of
batteries and a huge charger. it would be helpful if the utility allowed
"seasonal load-banking," ie generating more electricity than is used in
wintertime and using more than is generated in the summer.
>...just buy an old rabbit diesel and run it on furnace oil.
sounds good to me, with a 20 hp induction motor bolted on top, eg
grainger's $1109 (new) 5n819 360 pound 93% efficient 230v 1770 rpm
motor. (the largest single phase 230v motor i saw in the catalog.)
nick
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