Solar panels in South of Spain

[vinceect]

Hi All
I live in the South of Spain so it seemed logical to take advantage of the sun here and we installed 3360 watts of solar panels a couple of years ago. Now they've changed the law here so we can now feed in to the grid and this means that for the inverter stats we now see exactly how much we are generating throughout the day and it's a bit surprising that the nearly 3.4kw is reaching a max of 2.5kw, even after a good scrubbing. The guy that installed them says heat is a factor, and it's hot here, but do you all think that is normal? Or should I be looking for faults in the system? The roofs here are flat so the panels are on a metal frame and get lots of ventilation. The inclination is 30 degrees due south.

Many thanks

Vince

[SunEagle]

Hello vinceect and welcome to Solar Panel Talk

While it is very common for a solar panel system to deliver about 80% - 85% of it's nameplate rating, there are multiple reasons it delivers less.
Sometimes the panels are not oriented to point at the correct angle to the sun.
In the Winter the sun is lower is the sky and the panels produce less.
The panels are dirty.
One or more panels is not producing for because they are bad or the wiring is not correct.
The inverter is limited to a specific output due to not being allowed to send back to the grid.
Heat reduces the % production
I can go on but it is a little hard to trouble shoot your system without having hands on it.

If you really think your system is under-producing due to product failure or poor installation the only suggestion would be to get your installer out there to check it. Of course unless you have a warranty stating a certain production amount the installer may push back and not help you in any way.

[J.P.M.]

As SunEagle writes, get the system checked out. Can't hurt.

At a 30 deg. tilt and equator facing, a nominally operating 3.4 kW system ought to be producing something like ~ 2.7 - 2.9 kW or so when new, clean and operating at near normal incidence angle to the sun (roughly around solar noon) this time of year.

2.5 kW might be a bit on the low side, but if the system is old(er) that 2.5 kW doesn't seem that far out of line for this time of year. Things don't work as well as they age.

Besides, Just like a vehicle's engine will never be called upon to produce its rated output, a PV cell/panel/array will rarely if ever produce full nameplate (or what's called STC) output.

Depending on system particulars such as how the array siting affects the cell temps. by sheltering an array from wind, surrounding terrain features/colors, etc., etc. array/cell temps. may be a more of a factor for your application than some others, but without being on site, it's hard to offer a valid opinion.

FWIW, a couple of rules of thumb: In general, panel efficiency, and so array output, decreases ~ 0.5 % or so for every 1 deg. C. increase in PANEL temp. > 25 C. Under bright sun/clear skies, at solar noon a panel temp. runs, very roughly, about 25 - 35 C. above the surrounding ambient air temp.

Being somewhat away from the mounting surface as it sounds like you're reporting it, I'd SWAG your array might be running on the lower side of that 10 deg. spread. So, on a hot, sunny, windless day with a, say, 40 C amb. air temp, which may get boosted to, say 45 C or so on a sheltered, dark colored roof (?), you might expect a panel temp of, say 45 C + 30 C = 75 C. That'll decrease panel output below STC efficiency by VERY approx. (75-25)*0.005 = 25 % before considering any losses for inverters/wiring, but assuming a clean array.

Given all that, a very hot sunny and windless day's instantaneous midday output at may well in the 3.4 * (1-.0.25) = ~ 2.5 kW range.

[bob-n]

SunEagle and JPM have given you a very good perspective and their calculations show that things are probably working correctly.

Please keep in mind that it isn't recommended to scrub solar panels with anything abrasive. If they collect a lot of dust, pollen or bird waste, you can rinse them clean but otherwise, it is best to leave them. The 30 degree angle should prevent them from accumulating waste and an occasional rainstorm will clean them sufficiently.

Some talk about risk from cleaning chemicals damaging the panel coating. These risks are not certain. Every panel is different and every cleaner is different. All we know for certain is that water is safe.

[Mike90250]

Water is safe when you do it early in the morning before the panels heat up. Cold water on hot glass will cause thermal shock and that can lead to cracked glass