Thermal heat reduction impact of solar panels on roof vs. shading optimization

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Great replies guys. That article and the reply by JPM were excellent. You guys are so good at this that I kind of wish someone like JPM could do my panels

[J.P.M.]

Since you ask, the short answer is do not worry too much about panel or array placement for the sake of the heat that it will keep from the interior - that's a minor advantage, and mostly a minor concern if adequate insulation is present - which is the no brainer solution if insulation is missing. So, the short answer to your first question is I wouldn't worry about it - add insulation.

The answer to your second question is a bit more complicated. Simply put, the panels should be placed in locations that result in the safest, most serviceable operation, and produce the most annual output. Aesthetics and other things are also considerations. Often, it's a bunch of tradeoffs.

FWIW, here's some numbers from my roof, winter,10/09/2014 - 02/09/2015 and summer, 06/14/2015 to 08/15/2015. The roof is med./dark brown lightweight concrete tile. All measurements taken at min. solar incidence angle for the days when measurements were taken. All reading taken and recorded with a hand held IR thermometer. All roof deck temps from under the array are the average of 32 readings for each day's readings - once under each of 16 panels on either side of min. incidence angle time. The exposed roof deck temps were only 4 - one on either side of the array at beginning/end of the 16 min. data gathering. All days when measurements were taken were "clear". All readings are instantaneous (well, not really, but sort of close), that is, they are a "snap shot" of conditions at the 16 min. - 8 min. on either side of the time of minimum incidence angle on the roof, and hence the array that's on it, for the days when measurements were taken. Results are applicable to my roof only, and only as examples of relative roof temps. Your conditions may be similar, or not. My guess is my #'s are somewhat representative of others in So. CA with similar roof materials, colors and conditions, bit no guarantees are expressed or implied.

Winter, 34 measurement days.

Average roof surface temp. under the solar array: 28.6 C.
Average temp. of the exposed roof: 60.3 C. (not under the array)
Average ambient air temp. on the roof: 23.9 C.

Summer, 26 measurement days.

Average roof surface temp. under the array: 38.6 C.
Average roof temp. on the exposed roof: 67.9 C.
Average ambient air temp. on roof: 33.1 C.

Ave. wind speed, winter & summer, ~ 1.9 m/sec., continuously recorded 1X/minute and averaged for the 16 min. period on event days.

A part of the array is over my living room and that ceiling has no crawl space over it - just wall board, rafters and insulation, then roof. During the summer, the ceiling where the array is runs about 2 or so deg.C. warmer than the rest of the ceiling in that room that is not under the array.

Take what you want of the above. Scrap the rest.

[DanKegel]

Just painting the roof white may be better at cooling the house, see http://link.springer.com/article/10....546-016-0160-y

So, no, don't spread them out, paint your tiles white

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This may be a question for the pros, but might help everyone to some extent with all the expert knowledge that is given in these forums.

My main goal is to save money and second is doing it with the least amount of time I have to waste in the future on these. I live in a part of southern California that gets very hot in the summer, over 100F for several weeks and over 90F for several months (total per year). My cement tiles get very hot and continue to heat the house well into the night and our somewhat inefficient AC has to run a long time, causing a lot of electricity use. I am hoping that getting some solar panels will make the roof cooler and decrease our energy needs for the summer

So question #1: how much do the panels help decrease the roof tempratures in the hot months? Is it enough to justify getting panels that are less efficient and spread them out, instead of just focusing on the South?

The second question has to do with the shading in this situation. I have a limited space in the South side. The East side has some minor shading issues (Direct sun starts after first 2-3 hours after sunrise then the shading hits again in the later parts of the afternoon. The west side has even more shading issues (partial then full shading starts 1-2 hours after mid day).

#2. Given these heat and shading issues, is it better to focus on putting panels on the least shaded areas for optimal efficiency (East and South), or spread them out for optimal heat control (East West, South)?

On a side note, the quotes I got have the Solaredge inverter with optimizers at $1000 more expensive than the old Sunny Boy inverter. I will probably go with the Sunny Boy if I have to have only 1 row on the South and 1 row on the east, but is it worth the extra $1000 if I have to spread them out to the West as well, given the shading issues?

Thanks a lot for any input