re: solar energy
27 mar 1996
brain :-) hendricks wrote:
>does anyone know how to calculate the solar intensity on a flat surface as
>a function of frequency, date, solar time, environmental conditions?
i don't think so, but you might try looking in the second (wiley, 1991)
edition of duffie and beckman's _solar engineering of thermal processes_.
they have some statistical clues.
>by environmental conditions i mean cloud cover, atmospheric density, and
>anything els i have forgotten.
cloud cover is hard to predict, but easy to measure. you may have forgotten
fog, rain and snow. snow on the ground can make vertical collectors work a lot
better. fog is less helpful. you can find averages based on 30 years of
historical data for 239 us cities in nrel's _solar radiation data manual for
flat-plate and concentrating collectors_, which may still be available free
on paper or floppy disks from steve rubin at email@example.com (303)
275-4099 this info is also on their web page, i think, as well as "typical
meteorological years," for those cities, ie hourly weather data for a typical
year in each city. the raw data itself, or a good simulation thereof, is
available on 3 $130 cd-roms (east, midwest, and west) in hourly form for the
last 30 years, from firstname.lastname@example.org.
>i am trying to write a program to evaluate different panel designs.
"solar panels" seem economically useless these days, especially if they are
mounted on roofs in cold air and they use pumps and electrical energy to run
the pumps and piping and antifreeze and tanks and heat exchangers, and cost
$30/ft^2 for the panels alone, and only collect $1/ft^2/year of solar heat.
pv economics is far worse, today, and likely to remain so, with oil companies
making pvs and electrical utilities getting interested in pvs. altho they can
make microeconomic sense if you live far from the power lines or get a
government subsidy, ie take money out of everyone elses' pockets to make
your system "economical." on the other hand, the right kind of passive solar
house heating makes good economic sense to me, at a cost of <$0.01/peak watt,
today, with a lower first cost than conventional house construction, eg with
some south "solar siding" or a steep south polycarbonate plastic roof, over
rafters on 4' centers, with no shingles or sheathing, and a lot less labor...
(i guess you could put some amorphous pvs under the rafters with a long
galvanized water tank tucked up under the insulated peak of the roof, if
you were wealthy, and so inclined to spend money.)
>i have looked at the ashrae handbook of fundamentals and it doesn't make
>sense to me.
that's a fine book, but it's hard to predict the weather...
the fourteenth-century byzantine saint sabas pretended to be deaf,
dumb and mad--a pretense that he kept up with great skill for 20 years.
yet he could not escape the danger of fame. on visiting cyprus, he reacted
to the attention given to him by large crowds by suddenly sitting down
on a dung heap, where he spent the remainder of the day. the emperor of
constantinople sought to persuade him to accept the office of patriarch,
but sabas refused. he refused even to be ordained as a priest. when the
emperor attempted to have him ordained by stealth, sabas fled; keen to
have the saint remain, the emperor had to chase after him, beg his
forgiveness, and solemnly promise to make no further attempts to
interfere with sabas's saintly ways.
from _holy madness_, by georg feuerstein