Re: ENERGY: State of the Art in Photovoltaics?

From: Michael S. Lorrey (
Date: Tue Oct 10 2000 - 11:54:32 MDT

"Robert J. Bradbury" wrote:
> Mike wrote:
> > Which is much as I said in my post. However, the average American roof
> > (only half of which is useful as a collector, the other half facing away
> > from the sun (and only if the home is lucky enough to have one side facing
> > south. Facing east and west is useless)) is around 12 x 5 meters, or 60
> > square meters. A 10% efficient system that covers the entire roof, with
> > no skylights, will generate 6 kilowatts ONLY at the peak period at noon.
> > Power generation will begin at a very low level around 7 am and end at
> > about 7 pm, and increase along a bell curve up and down through the day.
> > Such a system will generate around 20-24 kilowatt hours per day,
> > assuming no cloudy weather. This is less than 10% of the power needs
> > of the average home.
> I think your roof size may be too low (depends a lot on how many stories
> the home is) and your energy peak may be too high (Robert Freitas keeps
> beating me up anytime I use a number over 400 W/m^2). But I don't see
> why you say 10% since my electric bill says I'm averaging 40 kWh/day
> (and thats with a lot of computers on all the time).

Where are you located? Do you use any gas/oil heating/cooking appliances? How
many kids do you support and in what age groups? Kids are very wasteful of
energy, my parents use less than 1/4 of the electricity they used when all four
kids lived in the house, also, you will see some losses from converting energy
to battery storage and back. I based the peak on optimistic sunny climate low
latitudes. The average would obviously be lower due to weather, seasons, etc.

The roof size I based on a two story raised ranch of 12 x 8 meters, roof slope
of about 30 degrees, with an internal square footage of around 2200 square feet.
This is actually on the large size for my community, with four bedrooms, two
baths, living room, family room, dining room, kitchen, roofed balcony along one
side of the house and two car garage.

> Your point is taken though. The efficiency needs to go up. You can
> always double the roof area by doing a little reconstruction. And
> if the material is really cheap (like tar paper), you would put
> it on the exterior wall surfaces as well. You probably couldn't
> disconnect yourself from the grid, but you could make a good dent
> in your electric bill. The real trick will be lowering the electrical
> requirements of the refridgerator, since that is generally the biggest
> draw in the house. We need some more progress with magnetic cooling
> using gandolinium or acoustic cooling.

Actually, I think constructing the home to take better advantage of passive
solar thermal, as well as providing cooling from ground sink, needs to be
emphasized in home construction much more.

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