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Solar Photovoltaic (PV)
Last Post by MichelleC 1 week ago
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 MichelleC
(@michellec)
Active Member Member
70 kWhs
Joined: 1 month ago
Posts: 5
Topic starter 10/03/2025 1:25 am  

Is there some table or an online calculator that I can look up expected solarPV kWh generated by month, for my latitude/longitude & azimuth & tilt? Need the figures by the month. Thanks, Michelle


   
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solarPV online calculator
 Gary
(@gary)
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2728 kWhs
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Posts: 318
10/03/2025 7:44 am  

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#api_5.1


   
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Majordennisbloodnok
 Majordennisbloodnok
(@majordennisbloodnok)
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7310 kWhs
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10/03/2025 9:18 am  

I'd be interested what others find whilst using that web app, @gary. It's a great resource but it does also highlight how local variations in conditions can affect the theoretical output.

For me, it overestimates by about a quarter which on the face of it is quite a significant margin. However, in practice there are some extras to factor in:

  • Shading isn't a big issue but we're not completely immune.
  • Although our kWp is calculated on the number and capacity of all the panels, there are four which are not on the main South-facing elevation. This is really important in capturing the early sun and therefore extending the period when we don't have to draw from the battery but it is at the expense of absolute amount of electricity generated.
  • Our panels are now four years old so there will be some degradation in their generating capabilities now.

 

All that is entirely reasonable and if I factor those points in then the web app is doing a pretty reasonable predictive job. However, it's worth remembering these points since if I was making a buying decision based on expecting to generate 6MW/year and ended up getting 4.5-5 then I'd be a bit miffed.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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 Old_Scientist
(@old_scientist)
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10/03/2025 7:24 pm  

Posted by: @majordennisbloodnok
↑

I'd be interested what others find whilst using that web app, @gary. It's a great resource but it does also highlight how local variations in conditions can affect the theoretical output.

We've only had our solar since last June, but so far for me it's been very accurate and within the published standard deviation each month.

Posted by: @majordennisbloodnok
↑

For me, it overestimates by about a quarter which on the face of it is quite a significant margin. However, in practice there are some extras to factor in:

  • Shading isn't a big issue but we're not completely immune.
  • Although our kWp is calculated on the number and capacity of all the panels, there are four which are not on the main South-facing elevation. This is really important in capturing the early sun and therefore extending the period when we don't have to draw from the battery but it is at the expense of absolute amount of electricity generated.
  • Our panels are now four years old so there will be some degradation in their generating capabilities now.

 

All that is entirely reasonable and if I factor those points in then the web app is doing a pretty reasonable predictive job. However, it's worth remembering these points since if I was making a buying decision based on expecting to generate 6MW/year and ended up getting 4.5-5 then I'd be a bit miffed.

Yes, I think you'd need to create separate arrays for each roof aspect, and then combine them to get a representative total. Mine is straight forward as it's a single aspect that is unshaded, hence the results seem remarkably accurate.

 

 


   
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 MichelleC
(@michellec)
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70 kWhs
Joined: 1 month ago
Posts: 5
Topic starter 12/03/2025 10:14 am  

@majordennisbloodnok what degradation per year is typical with aging?


   
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