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re: solar question
19 jan 2000
duane c. johnson wrote:
>> (there is less energy in the north, right?).
>in general no. there are specifics of cloud cover and
>such. the north is colder mainly because the sun is
>low in the sky. this causes less solar intensity per
>unit area on the ground.
>for a concentrator that is tracking the sun the solar
>intensity is not much different than in the south.
but northern places get fewer hours of sun in the winter,
2/15cos^-1(-tan(lat)tan(delta)) daylight hours per day,
according to duffie and beckman, where the declination
delta changes from + to -23.5 degrees from summer to winter.
let's see. miami (lat 26) would have 10.4 daylight hours
on 12/21, and phila (lat 40) would have 9.1. nrel says miami
gets 1350 btu/ft^2 of sun on a horizontal surface on a clear
december day, and phila gets 780, and a 2-axis tracker can
collect up to 3.9 kwh/m^2 in miami vs 2.4 in phila, on an
average december day. and 5.2 and 3.3 on a clear day.
nick
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