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And, FWIW, some data:
Between 06/14/15 and 08/1515 on 26 sets (days) of measurements under clear skies, among lots of other data, I measured the following average data based on N=26:
GHI irradiance: 942 W/m^2, std. dev. 24.6 W/m^2
POA irradiance: 965 W/m^2, std. dev. 16.2 W/m^2
Ambient temp: 33.0 C. , std. dev. 3.4 C.
Wind speed: 1.8 m/sec. std. dev. 0.38 m/sec.
Cell temp.: 59.6 C. , std. dev. 3.6 C.
Exposed (to irradiance) roof deck temp.: 68.4 C., std. dev., 3.8 C.
Under panel roof deck temp.: 39.0 C., std. dev. 4.2 C.
All temp. data for each of the 26 dates is the average of 32 separate temps., each of which are themselves averages of 4 random location temp. readings across each of 16 panels, taken immediately before and after the time of minimum incidence angle of direct beam irradiance on the array. Or, in the case of the under array roof temps., the same sampling method done at the same time. All temps. taken with IR thermometer I calibrated using an ice, bath, boiling water and my body temp.
Thus the roof deck under the panels was, on average, ~ 29 C. lower than the same roof material exposed to direct sunlight,.
The roof deck under the array was above the ambient temp. due to thermal radiation from the array heating that portion of e roof deck. That cell temp. to roof deck is also some information to corroborate approx. cell temp. with measurements of cell temp., although there are too many variables involved to get very quantitative about it, it can still serve as another quasi independent equation to help cover all the unknowns in getting an energy balance on the array which is the overall goal, as can the roof deck to cell temp. itself.
About half of the array is over a cathedral ceiling in the living room. The other half is over a crawl space. The insulated ceiling temp. over the array (the south portion of the ceiling) in the living room was ~ 1.5 - 2 C. higher than the north portion, but a lot of that can probably be attributed to orientation. I don't have data on the crawl space underoof temp. diff. between those parts under the array and those parts not under the array.
I believe array shading can help lower the temp. of an attic of a crawl space when there is no insulation directly under the roof. How that may influence the temps. in the rest of the dwelling is largely dependent of the level of insulation between an attic or crawlspace and the rest of the building space.
Between 06/14/15 and 08/1515 on 26 sets (days) of measurements under clear skies, among lots of other data, I measured the following average data based on N=26:
GHI irradiance: 942 W/m^2, std. dev. 24.6 W/m^2
POA irradiance: 965 W/m^2, std. dev. 16.2 W/m^2
Ambient temp: 33.0 C. , std. dev. 3.4 C.
Wind speed: 1.8 m/sec. std. dev. 0.38 m/sec.
Cell temp.: 59.6 C. , std. dev. 3.6 C.
Exposed (to irradiance) roof deck temp.: 68.4 C., std. dev., 3.8 C.
Under panel roof deck temp.: 39.0 C., std. dev. 4.2 C.
All temp. data for each of the 26 dates is the average of 32 separate temps., each of which are themselves averages of 4 random location temp. readings across each of 16 panels, taken immediately before and after the time of minimum incidence angle of direct beam irradiance on the array. Or, in the case of the under array roof temps., the same sampling method done at the same time. All temps. taken with IR thermometer I calibrated using an ice, bath, boiling water and my body temp.
Thus the roof deck under the panels was, on average, ~ 29 C. lower than the same roof material exposed to direct sunlight,.
The roof deck under the array was above the ambient temp. due to thermal radiation from the array heating that portion of e roof deck. That cell temp. to roof deck is also some information to corroborate approx. cell temp. with measurements of cell temp., although there are too many variables involved to get very quantitative about it, it can still serve as another quasi independent equation to help cover all the unknowns in getting an energy balance on the array which is the overall goal, as can the roof deck to cell temp. itself.
About half of the array is over a cathedral ceiling in the living room. The other half is over a crawl space. The insulated ceiling temp. over the array (the south portion of the ceiling) in the living room was ~ 1.5 - 2 C. higher than the north portion, but a lot of that can probably be attributed to orientation. I don't have data on the crawl space underoof temp. diff. between those parts under the array and those parts not under the array.
I believe array shading can help lower the temp. of an attic of a crawl space when there is no insulation directly under the roof. How that may influence the temps. in the rest of the dwelling is largely dependent of the level of insulation between an attic or crawlspace and the rest of the building space.
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