«-- Odds 'n Sods: | Main | Letter Re: Spot Shortages at a COSTCO Store a Portent of Things to Come? --»
Letter Re: Sizing a Retreat AC Power Generator
Jim -
Great blog! I wanted to point out an important calculation everyone missed
- internal combustion engines produce less power at higher elevation. Generators
are (of course) rated at sea level. It's important to de-rate generator capacity
by 3.5% per 1,000 feet of elevation or your generator will be undersized.
(A 5,000 "label watt" generator is [effectively] only a 4,000 watt
generator where I live at 6,000 feet.) Density altitude on a warm summer
day can
easily be
2,000 feet higher than that. My rule of thumb: after sizing for load, size
generously for elevation or you'll be buying twice. Hope this helps everyone...
Other food for thought: You don't need to run all your big loads simultaneously.
If the grid stays down, it'll be a blessing just to have refrigeration - it
doesn't need to be like today where we run everything at once while blow-drying
the dog! There's no reason you can't shut off the freezer if you need the well
pump. The simplest transfer switch allows you to control power to various loads,
and this allows you to use a smaller generator to accomplish everything. My
genset is home built using a Listeroid (Lister clone) diesel engine and generator
head purchased separately. This generator (significantly oversized to run a
MIG welder,
lathe, mill or compressor/plasma cutter combo) cost me less than $3,000 including
truck freight and welding up a stout steel frame (probably
$4,500 now, given the weak dollar, steel prices and current shipping rates).
Based on decades of British Empire experience with these beasts in third world
countries, I expect it will give 30,000-to-50,000 hours of service with minimal
maintenance. It gingerly sips fuel and is easily operated on biodiesel or waste
vegetable
oil without modification.
Regards, - Fred H.
