Most effective angle for PV panels

[sunspot]

The PV panels on our roof are angled towards the south by around 15%. The original angle was greater but our architect said we had to reduce it to get planning approval after construction.

Our daily harvesting has declined by half from its peak in the summer. Is this normal? To what extent does the angle matter? Thank you.

[Dominic]

How are you measuring your daily harvesting? If you are taking monthly figures and dividing then you have to bear in mind the amount of clouds we've had recently.

[cyprusmax47]

One of my many studies about PV one can see at my post last year, here concerning tilt for photovoltaic.

viewtopic.php?f=3&t=15816&p=144729&hili ... pv#p144729

Even Devil had a positive note about it

Max

[trevnhil]

I assume that when people are talking about what tilt to have the panels at this is on a flat roof.
Ours are on a sloping tiled roof and are at the same angle as the roof tiles. Again we really had no choice as to which direction they are facing, but it is South East. We have 12 panels and yesterday they made 14.8 kw

[cyprusmax47]

The PV panels on our roof are angled towards the south by around 15%. The original angle was greater but our architect said we had to reduce it to get planning approval after construction.

My personal opinion is that a tilt lower than the "experts" tell us (the tilt is recommended to equal the latitude multiplied by 0.85 = ca 29% in CY).
You will produce much more in the month of the year when the daytime is much longer and the sun stands higher with a low tilt like yours (15%) and no clouds are effecting the system. So in winter much more clouds, less sunshine hours and long shades are more important than the lower tilt....
The only bad side effect are high temperatures in mid summer, however when modules are not fixed directly on the roof tiles and the air can circulate around the modules like on flat roofs, good quality modules will cope with that situation.

There are modules on the market with water cooling, the idea is good, but not for our Cyprus climate (what to do with all that hot water?)

Max

[Devil]

I live and learn! For many years, our hot water heaters were fixed at an angle of about 50° on the notion that there was an excess of solar radiation in summer and more or less anything would go but that, in winter, one would get better water heating if the panels faced directly towards the sun. This worked fine and we were getting hot water when our neighbours were complaining about having to switch on the immersion heater.

I thought it would be similar with solar panels. How WRONG I was! https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6611928/ is a technical paper, probably beyond the scope of the readers of this forum, myself included, but it explains to me that the angle of the panels, within reason, has very little effect on their efficiency. Notwithstanding, I suggest that a vertical slope of about 10° to 60°, facing due south, would not unduly change the kilowatt-hours generated.

The reason for the difference between water heating and solar panels lies in the construction of the latter in several internal reflective layers.

[cyprusmax47]

I assume that when people are talking about what tilt to have the panels at this is on a flat roof.
Ours are on a sloping tiled roof and are at the same angle as the roof tiles. Again we really had no choice as to which direction they are facing, but it is South East. We have 12 panels and yesterday they made 14.8 kw

I would be interested how much your system produced today, after the eclipse this afternoon Trev.

Max

[Dominic]

I took a picture of the sun through an ND filter at 2PM this afternoon and it looked round.

[trevnhil]

I assume that when people are talking about what tilt to have the panels at this is on a flat roof.
Ours are on a sloping tiled roof and are at the same angle as the roof tiles. Again we really had no choice as to which direction they are facing, but it is South East. We have 12 panels and yesterday they made 14.8 kw

I would be interested how much your system produced today, after the eclipse this afternoon Trev.

Max

I have just had a look Max and they only made 12.6 kw today. And of course there is just a little less sunlight every day

[cyprusmax47]

Thank you Trev for the information. I expected lower reading, but not so much. 2,2 kW/h less in this 2 hours eclipse time is amazing.

Max

[sunspot]

Thanks to all for your comments and the links. The paper cited by Devil is particularly relevant.

[WHL]

Being a bit thick here, but surely the experts who are installing the panels
should know the correct angle for installation ?

[trevnhil]

You would think so WHL. Ours is on a sloping roof so the panels are at the same angle as the roof, with a small gap underneath them

[cyprusmax47]

I live and learn! Notwithstanding, I suggest that a vertical slope of about 10° to 60°, facing due south, would not unduly change the kilowatt-hours generated.

You are completely wrong Devil.

Why do you think many commercial PV installations worldwide using Sun Tracker, with billions invested in their technology, in order to produce more electricity than without. Have a little look at the Wikipedia link and find out yourself.
https://en.wikipedia.org/wiki/Solar_tracker

I had myself sun tracker 25 years ago, when prices for solar modules were so expensive and it was more economic to produce electricity with sun tracker and less amount of solar modules. Since the prices for solar modules came down so much it is less interesting in my opinion.
So I had plenty experience with tilts already so many years ago. I prefer practice more than theory as you already should know...

Max

[Devil]

Being a bit thick here, but surely the experts who are installing the panels
should know the correct angle for installation ?

The whole point of my previous post is that there is no correct angle within limits; the design of the panels takes care of the angle by combining reflection and refraction with the thickness of the construction under an ad hoc type of glass.

[Devil]

Yesterday, we got maximum radiation of 735 W/m2 between 12:40 and 12:45. It dropped to 411 W/m2 to a minimum at 14:11 and then rose again to about 600 with a new maximum of 450 W/m2 at 15:00. Simultaneously, the temperature maxed at 13:06 at 26.8° C, dipped to 26.3° C at 14:10 then rose again to 26.6° C at 15:11, before dropping normally at the evening. It could be said that the eclipse had very little effect on the temperature.

[PolemIan]

I assume that when people are talking about what tilt to have the panels at this is on a flat roof.
Ours are on a sloping tiled roof and are at the same angle as the roof tiles. Again we really had no choice as to which direction they are facing, but it is South East. We have 12 panels and yesterday they made 14.8 kw

I would be interested how much your system produced today, after the eclipse this afternoon Trev.

Max

FYI. We are in the same village is Trev, we have 12 x 260w panels installed in 2017, also installed on our roof at whatever pitch that is - quite shallow I think, only cleaned by rain for the last 2 or 3 years and facing 140 degrees on the compass so so just SSE

Monday 24/10 = 15kw
Tuesday 25/10 = 13.3kw

Ian