Power in sunshine - winter vs summer

[gazrareth]

Hi all, newcomer here.

I've tried searching for the answer to my question but to no avail.

We have a recently installed 4.3kW solar system in Bristol in the UK. Faces South West (50 degrees past south) at a tilt of around 18 degrees).

I'm trying to understand if the system is getting the power output it should.

On a bright sunny day, the most power I've seen from the system is around 1.5kW. I'm obviously aware the sun's angle is lower at this time of year, but I would have expected more. Or am I being too optimistic?

On thick cloudy days, the power is often as low as 20W. Again I'd have expected more, even when under rainclouds.

Will the power really be significantly more in other months of the year, when the sun is higher? Can I expect the 1.5kW to jump up a lot as the seasons change?

I appreciate total energy output will be less in winter because of far fewer daylight hours, but when the sun is actually shining I'd have thought the power produced wouldn't be too different. Or does the angle of the sun really make that much difference?

Thanks in advance,
Gareth

 

[hwy17]

Or does the angle of the sun really make that much difference?

It does.

 

[Kenny_]

In playing around with my panels the last couple of months (they are really just temporarily in place on the ground) I've seen as much as a 30% difference depending on the angle of the panels to the sun.

 

[pollenface]

Optimal tilt for Bristol according to my app

 

[green mountain boys]

Try using the PVwatts calculator. you can input your variables and get very good answers. It is fun to play around with too.

 

[rpdom]

I'm lucky to hit 1.2kW from my 3kW system at this time of year. In summer I get 3kW or more. The peak I've ever seen (very briefly) with cold panels on a very sunny day was 4kW.

 

[profesor79]

Hi all, newcomer here.

I've tried searching for the answer to my question but to no avail.

We have a recently installed 4.3kW solar system in Bristol in the UK. Faces South West (50 degrees past south) at a tilt of around 18 degrees).

I'm trying to understand if the system is getting the power output it should.

On a bright sunny day, the most power I've seen from the system is around 1.5kW. I'm obviously aware the sun's angle is lower at this time of year, but I would have expected more. Or am I being too optimistic?

On thick cloudy days, the power is often as low as 20W. Again I'd have expected more, even when under rainclouds.

Will the power really be significantly more in other months of the year, when the sun is higher? Can I expect the 1.5kW to jump up a lot as the seasons change?

I appreciate total energy output will be less in winter because of far fewer daylight hours, but when the sun is actually shining I'd have thought the power produced wouldn't be too different. Or does the angle of the sun really make that much difference?

Thanks in advance,
Gareth

you could use this website to obtain all data including PV production and forecast.

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)

re.jrc.ec.europa.eu

 

[Balrog006]

Optimal tilt for Bristol according to my app

What everyone here is basically saying is that you’re fixed(?) tilt panels at 18degrees are poorly situated to collect the available energy from the sun for this time of year. According to the chart in the post I’ve quoted they should be more like 70degrees for December.

This is the major and primary reason you are not seeing your expected production from your system. On sunny days, correctly oriented, it should, at least momentarily, produce its rated 3kWh

 

[gazrareth]

Thanks everyone, that's helpful. So the optimal tilt angle would currently be about 76°, compared to my 18°, which makes sense.

So if I could hypothetically change the angle, we're saying that my power output would be significantly higher? Compared to my 1.4kW on a sunny December day, it would get up to the 4.3kW (even in December?).

The bits I've read suggest that although tilt angle is important, you wouldn't get that much difference in output just from angle, but I'm happy to be corrected!

Does anyone else have a real world example from their own system i.e. Max power in December vs June? I'm aware the answer will be different depending on how far North the location is.

Thanks again.

 

[pollenface]

The Android app i use is here

 

[rpdom]

Here are the actual logged figures for my 3kW system in December last year and June this year

June 2023: Total generated 493 kWh. Max level 3653 kW.
December 2022: Total generated 68 kWh. Max level 1662 kW.

I'm just a bit further North than you, I believe. 30° roof facing SSW ish

 

[shadowmaker]

Does anyone else have a real world example from their own system i.e. Max power in December vs June? I'm aware the answer will be different depending on how far North the location is.

Still under one year of experience/data, but maybe this may help you:
- spring best 340kWh (snow), worst 40kwh
- summer best 280kWh, worst 60kWh
- fall best 180kWh (rain and clouds, no snow), worst 20kWh
- winter (so far) best 85kWh (snow, but not a one single sunny day so far), worst 2kWh (and this was with snow, which usually doubles my yield)

These daily yields are from my 44kWp vertical/bifacial system with 135 azimuth. I'm also much norther from you and my panel angle is optimized for winter as we have enough sun in summer even with "wrong" tilt angle. My setup is totally different from yours, but you can see the effects of tilt and seasons. Even with optimized tilt winter sucks.

 

[SeaGal]

Welcome!

Thanks everyone, that's helpful. So the optimal tilt angle would currently be about 76°, compared to my 18°, which makes sense.
So if I could hypothetically change the angle, we're saying that my power output would be significantly higher? Compared to my 1.4kW on a sunny December day, it would get up to the 4.3kW (even in December?).
The bits I've read suggest that although tilt angle is important, you wouldn't get that much difference in output just from angle, but I'm happy to be corrected!

1.4kW is pretty good for December for 4.3kWp panels in the UK (as @rpdom's figures show too). I'm mostly getting around 1 to 1.2 from 6.6KWp panels, with the odd peak above that.

For sure, a higher tilt will get you a bit more instantaneous kW's _when_ it's sunny. But I'd not expect more than about 30% gain, IMHO. When it's cloudy a shallower tilt will be more advantageous anyway.

At the end of the day, for a month or so around the Winter Solstice, the sun is so low and weak from traversing more atmosphere, you won't get much in the UK.

Do you have battery storage? If so, it's probably yield in kWh/day that is more interesting than peak kW.

Does anyone else have a real world example from their own system i.e. Max power in December vs June? I'm aware the answer will be different depending on how far North the location is.

From 'sunny' East Anglia (not that it's felt very sunny for the last month and a half!), here are some actual figures from my E-W configuration 6.6kWp panels...

Dec 4th (awful weather).. Peak of 228W... total for day 0.6kWh
Best peak this Dec, 2.1kW;
Best total for a day this Dec: 4.3kWh.
Dec so far, total = 26.8kWh = average of about 2.3kWh / day.

Now for June/July 2023:
Best peak, approx 7kW (*)
Best day, 40.1kWh (*)
Best month, 1595kWh.
(*) these figures were clipped by about 15% due to the limits of my inverter, so raw output from the panels could have been a bit more.

So, basically you can make as much power in one day in peak summer than you will likely achieve for the whole of December.

Will the power really be significantly more in other months of the year, when the sun is higher? Can I expect the 1.5kW to jump up a lot as the seasons change?

So, the answer to that is absolutely Roll on May ?

 

[Steve_S]

For you the Optimal Year Round angle is 39 degrees.

 

[gazrareth]

Thanks everyone, that's been really helpful. Basically, I need to wait for Spring! ?

 

[millsan1]

I know I am late to the party, but these two arrays are identical. Same panels, same orientation, and about 14' apart (to account for shading), each goes into my 18 KPV. The difference is the angle, a difference of about 10-15 degrees. You can see the production difference.