Solar Generation - Forecasting vs Actuals

cool_techie

Hi Forumites,
Apart from PVGIS, are there any other tools or online calculators for forecasting solar generation please?

I have a system, mounted on 4 roofs (so 4 strings, going into 2 inverters) - 33 x 385kW JAM60S20-385/MR panels. Have included a picture showing roof orientation and number of panels installed on each roof.

System was installed on 18th Dec 2020 and this morning's reading on the Generation meter is 141kWh. I understand the weather has not been the greatest, but to me, this seems more an impact of shading / incorrect set-up / panels going kaput!

I am taking this up with the installer, but wanted to check with you guys, about any additional tools to forecast solar generation and compare it with actual performance.

Thanks, CT

Exiled_Tyke

What does PVGIS reckon you should generate?  I presume you have done two separate calculations for the different orientations? 

For the record I always generate less than PVGIS forecasts in December and January.  This January was one of the gloomier ones and I produced less than half of the forecast.   You can pretty much write off this time of year as being pretty worthless. In a couple of months' time you will start to see some much more meaningful generation. 

cool_techie

Exiled_Tyke said:

What does PVGIS reckon you should generate?  I presume you have done two separate calculations for the different orientations? 

For the record I always generate less than PVGIS forecasts in December and January.  This January was one of the gloomier ones and I produced less than half of the forecast.   You can pretty much write off this time of year as being pretty worthless. In a couple of months' time you will start to see some much more meaningful generation. 

Hi,
PVGIS is showing 500 for January. Hence checking for other calculators.

I have spoken to the technical person at the installer, who reckons the low generation is due to shading and the impact of one shaded panel pulling down the whole string array.

He reckons this could be resolved by TIGO optimizers.

Thanks, CT

Exiled_Tyke

I'd see how it picks up in the coming months. Once the sun gets higher shading is far less of an issue.  Where I am,  on the 21st December the sun only gets to 13 degrees above the horizon so there's plenty to cause shading problems. And of course on an East & West system the panels won't see anything like the maximum angle of sun.  In contrast on the 21st June the sun reaches 59 degrees so there's a good many hours of the day where nothing can stand a chance of creating a shading issue.  Given this, I reckon there's a good chance that optimisers won't pay for themselves as the problem will be very much diminished from Spring to Autumn.    

mickyduck55

PVIS of 500 seems a lot for January.. I have almost 4 kW (a third the size of your system) and my PVIS is only 120?  This January was very poor with only 85kW... Im in the sunny south.

Annually since 2011 my system has been very near PVIS. Grey line is expected yield.

Please forgive me if my maths is wrong

cool_techie

mickyduck55 said:

PVIS of 500 seems a lot for January.. I have almost 4 kW (a third the size of your system) and my PVIS is only 120?  This January was very poor with only 85kW... Im in the sunny south.

Annually since 2011 my system has been very near PVIS. Grey line is expected yield.

Please forgive me if my maths is wrong

Hi mickyduck55,

Given the factor of 4 between our system sizes, isn’t the PVGIS estimate of 500 ~ 480 (120x4) correct? Or am I doing a mistake with my cells?

Thanks, CT

Martyn1981

I'm a tad confused as your post suggests 12.7kWp but your auto-sig says 3.84kWp.
If it helps, I see your system is E/W, and so is mine, so for not particularly sunny Cardiff I have a PVGIS target of 95kWh for Jan, which simply scaling up for size (ignoring any other factors for now) would be around 216kWh for you. [Note, my system is actually ESE/WNW and has a size bias towards the ESE, so E/W for me would probably be a tad lower.]

mickyduck55

cool_techie said:

mickyduck55 said:

PVIS of 500 seems a lot for January.. I have almost 4 kW (a third the size of your system) and my PVIS is only 120?  This January was very poor with only 85kW... Im in the sunny south.

Annually since 2011 my system has been very near PVIS. Grey line is expected yield.

Please forgive me if my maths is wrong

Hi mickyduck55,

Given the factor of 4 between our system sizes, isn’t the PVGIS estimate of 500 ~ 480 (120x4) correct? Or am I doing a mistake with my cells?

Thanks, CT

My maths says factor of 3?  Mine 4kW yours 12.7 kW? (385X33=12.7)

cool_techie

mickyduck55 said:

cool_techie said:

mickyduck55 said:

PVIS of 500 seems a lot for January.. I have almost 4 kW (a third the size of your system) and my PVIS is only 120?  This January was very poor with only 85kW... Im in the sunny south.

Annually since 2011 my system has been very near PVIS. Grey line is expected yield.

Please forgive me if my maths is wrong

Hi mickyduck55,

Given the factor of 4 between our system sizes, isn’t the PVGIS estimate of 500 ~ 480 (120x4) correct? Or am I doing a mistake with my cells?

Thanks, CT

My maths says factor of 3?  Mine 4kW yours 12.7 kW? (385X33=12.7)

Yes, you are right. A factor of 3. Thanks.

cool_techie

Martyn1981 said:

I'm a tad confused as your post suggests 12.7kWp but your auto-sig says 3.84kWp.
If it helps, I see your system is E/W, and so is mine, so for not particularly sunny Cardiff I have a PVGIS target of 95kWh for Jan, which simply scaling up for size (ignoring any other factors for now) would be around 216kWh for you. [Note, my system is actually ESE/WNW and has a size bias towards the ESE, so E/W for me would probably be a tad lower.]

Hi Martin,

Pls ignore the signature for now. That’s for the system at my old house.

Have had a system installed at my current house on 18th Dec and still in the fine-tuning/monitoring phase. 

Will update the signature shortly.

Thanks, CT

Solarchaser

In month of Jan my 6.6kw e/w system managed 70kwh.

I'm a fair bit further north, but essentially what I'm saying is Jan is a chappy month regardless.
Wait till you get to April...