How to calculate the generation in kWh of the PV Panels

[Bob Smith]

Hello everyone

I have this website I would like to share it seems it has not been shared here (at least I could not find it)

https://www.pvfitcalculator.energysavingtrust.org.uk/
I only use it to estimate the kWh generated all the savings etc.... I am not interested it is missing information to be correct.
The estimated kWh is based on the rate of sunlight in your area and some characteristics of the installation

For information, I already have PV since 2016. As an average, they generate 3850kWh per year. The installer at that time has given me 3200-3400kWh.
The website finds 3360kWh.

I have done this check to see if I could rely on it or not to see how much additional panels could generate.

Does anyone know any other websites?

Thanks

 

[binky]

find your roof pitch and orientation to south in the document below, and multiply by the size of your array. Unfortuanetly this site wont allow me to attach the full excel file as outputs will vary by region, but you can search this online.

 

[binky]

shade evaluation tool, this really needs to be printed onto acetate and placed in a little viewing holder, but if you curl it in your hand and squint a bit it should give you some idea, for every square that shading affects, you knock off 1%, so if shade affecs 10 squares, you knock off 10% from the annual figures.

 

[Bob Smith]

Thanks Binky, I have seen this diagram before. I did not realised you need it to print it out. I'll try

The website I provided the link has a parameter for the shade, It ranges from
<20%
20-60%
60-80%
>80%

It might not be as accurate as your diagram though.

 

[Bob Smith]

find your roof pitch and orientation to south in the document below, and multiply by the size of your array. Unfortuanetly this site wont allow me to attach the full excel file as outputs will vary by region, but you can search this online.

OK thanks

 

[binky]

Thanks Binky, I have seen this diagram before. I did not realised you need it to print it out. I'll try

The website I provided the link has a parameter for the shade, It ranges from
<20%
20-60%
60-80%
>80%

It might not be as accurate as your diagram though.

it's a rough guide, shading is also dependent on distance from the array, the further away it is, the more indirect / ambient irradiance you get so the less performance drop.

Also forgot tp say the official average outputs are also out of date, panel efficiency has improved since that was constructed, so you can expext to do better than those figures.

 

[Bob Smith]

find your roof pitch and orientation to south in the document below, and multiply by the size of your array. Unfortuanetly this site wont allow me to attach the full excel file as outputs will vary by region, but you can search this online.

Did you try the website I have found?

 

[Bob Smith]

it's a rough guide, shading is also dependent on distance from the array, the further away it is, the more indirect / ambient irradiance you get so the less performance drop.

Also forgot tp say the official average outputs are also out of date, panel efficiency has improved since that was constructed, so you can expext to do better than those figures.

I agree on both points
and it will depend if the shading is cause to a tree 20m or 100m away or a building.

For your second point, I have considered that point because I am lucky enough to be able to check the calculation with real figures based on 6 full years.
If I am happy with the minimum or worst case scenario then I'll be over the moon with the real data

 

[Bob Smith]

I have found another website but this one is very primitive

https://www.expertsure.com/uk/home/tools/solar-panel-calculator/
very little number of options and choices and it does not give the results in kWh

 

[Bob Smith]

Another useful reference

https://www.inbalance-energy.co.uk/solar_pv_information_calculators.html.

This site contains a list of many websites that will help size up a new system, calculate the generation in kWh and much more. It is a lot more technical. It should provide references for most, if not all, what is needed to size a new PV system.

One website listed is this one

https://joint-research-centre.ec.europa.eu/pvgis-photovoltaic-geographical-information-system_en
It looks like this

 

[binky]

PVGIS was linked to professional solar design software I used to use.

 

[Bob Smith]

I hope this thread will help people to design the size of their PV System.

 

[+Sid]

Bob,
Have you checked the PVGIS system against your actual figures to see how they compare?

I've just used it to calculate the annual output for a 4.8kW array that I was planning for my roof and it gives 2738 kWh pa. A national company has told me to expect 4000 kWh per annum and that this estimate is on the conservative side. They also said that their figures would be independently validated by the EVPS (Energy Performance Validation Scheme).

Am I doing something wrong?

12 x 400W panels, 35 degree pitch, 130 degrees azimuth (just South of East) next to no shading, 14% system loss. Stockport area

 

[binky]

for that pitch and orientation in Manchester (near enough) you can expect 884 kWh per kw of panels installed per annum according to official irradiance charts, approx 4243kWh .

 

[+Sid]

Thanks for that binky!

 

[bladerunnerpv]

Note that for PVGIS the user note says

"The azimuth, or orientation, is the angle of the PV modules relative to the direction due South. -90° is East, 0° is South and 90° is West."

So "130 degrees azimuth (just South of East) ", if entered in PVGIS as an azimuth of 130, would be 40 deg N of West, so almost NW facing

[Edit] 130 deg compass, would be -50 azimuth in PVGIS [End edit]

[Edit] and select 'roof added' ! [end edit]

hope this helps

 

[KeithC]

I have had 3.68Ksystem 19 degrees west of South and @ 45 degree pitch. My average yield over the 10 years I have had the system for is 3190kwHrs/year.
There are a number of free PV sol like calculators on the net which should confirm that the national company is probably exaggerating the expected yield.

 

[+Sid]

Yes, using -50° instead of 130° gives c.4000kWh/yr which sounds impressive until you look at what is being generated over winter which is when we need it. Summer time it's there in spades when we don't need it. I'm afraid solar is a non-starter for me, but thanks for all your help.

 

[Bob Smith]

Bob,
Have you checked the PVGIS system against your actual figures to see how they compare?

I've just used it to calculate the annual output for a 4.8kW array that I was planning for my roof and it gives 2738 kWh pa. A national company has told me to expect 4000 kWh per annum and that this estimate is on the conservative side. They also said that their figures would be independently validated by the EVPS (Energy Performance Validation Scheme).

Am I doing something wrong?

12 x 400W panels, 35 degree pitch, 130 degrees azimuth (just South of East) next to no shading, 14% system loss. Stockport area

Hi,

I posted this for information as I could not find any other posts about this topic.
I used the website around the time I created that post to check its results vs my actual generation.

I have a 4kWp (16 panels @ 250W, 0.15% efficiency) facing South East in Cheshire. They were installed in Jan 2016.
At that time I was told they would generate ~3300kWh/y.
The website above gives me 3350kWh/y

In 6 years and 10 months. I generated a total of 26300kWh. so that is roughly 3850kWh/y

I have also learned that those websites are usually based on old equipment specs. For instance PV panels these days are minimum 20% efficient. that is 33% more than mine.
Hope this helps.

 

[binky]

I have also learned that those websites are usually based on old equipment specs. For instance PV panels these days are minimum 20% efficient. that is 33% more than mine.
Hope this helps.

The official figures are very much out of date, and not hard to beat, which is part of the reason why I don't like undesizing inverters. But, last few years have been rather cloudy for long periods of time, part of climate change, so it's harder to predict outputs than ever before.