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Tool · Energy & electrics

Solar Panel Output Calculator

How much electricity will panels on a balcony railing or a roof produce? Choose a city, orientation, tilt and panel power – the yield comes from European Commission data (PVGIS) for 233 cities across Europe, and with your electricity price you get the saving.

Total of all panels from the datasheet.

Share you use yourself – how to estimate

Ofgem, Oct–Dec 2026 (what this means)

specific yield
yield per year
of which
saving per year
payback
best combination

        

          

            
          

        

      

    


    
A forecast, not a yield survey. The figures are long-term
      averages for the centre of the chosen city. A single year can be higher or lower, and the
      calculation knows nothing about shade from neighbouring buildings, trees or your own roof. For an
      investment decision on a large roof system, get a quote with a yield forecast for your roof.


    
What it is for

    

    
Where the figures come from

    
The yield comes from PVGIS, the Photovoltaic Geographical Information System
      of the European Commission’s Joint Research Centre (JRC). From satellite data on solar radiation
      and weather data, PVGIS calculates what one kilowatt of panel power produces at a place in a year.
      The data may be used freely with attribution.

    
PVGIS cannot be queried directly from your browser – its interface does not allow such calls. So
      I asked PVGIS once in advance for 233 cities in 47 countries, six tilts
      and eight compass directions, each for 1 kWp. The rounded results are built into the calculator
      as a table. The cities are every capital and the cities with at least 300,000 inhabitants according
      to Wikidata, plus a denser set for Germany. The settings were:

    

    
The terms

    

    
How the tool calculates

    
    
      
  1. Yield per year = specific yield from the table × panel power in kWp
    2. 
      
  2. Self-consumption = yield × self-consumption share, export = yield − self-consumption
    3. 
      
  3. Saving = self-consumption × electricity price, plus export × export payment (prices in pence,
        cents or rappen are divided by 100)
    4. 
      
  4. Payback = purchase cost ÷ saving per year
    5. 
    

    
The tool also looks for the combination of orientation and tilt with the highest yield in your
      city’s table and shows what percentage of it your choice reaches.


    
Worked example: balcony solar in London

    
Two panels totalling 800 Wp hang on a south-facing balcony railing, so upright (90°). These
      values are already in the calculator when you open it; the button inserts the Ofgem price cap
      unit rate of 26.32 p/kWh, and 30 % self-consumption is an assumption for the example.

    
    
      
  1. Yield: 743 kWh/kWp × 0.8 kWp ≈ 594 kWh per year
    2. 
      
  2. Self-consumption: 594.4 kWh × 30 % ≈ 178.3 kWh, 416.1 kWh are exported
    3. 
      
  3. Saving: 178.3 kWh × 26.32 p ÷ 100 ≈ £46.93 per year
    4. 
    

    
The same panels on a south-facing frame at 30° would produce 1,010 kWh/kWp, so around
      808 kWh per year – 36 % more. Upright, the railing loses out in summer when
      the sun is high. From November to February, with the sun low, it even produces a little more than the frame:

    

      
        
        90° upright: 743 kWh per kWp per year
        
        30° on a frame: 1,010 kWh per kWp per year
        
        0
        
        
        J
        
        
        F
        
        
        M
        
        
        A
        
        
        M
        
        
        J
        
        
        J
        
        
        A
        
        
        S
        
        
        O
        
        
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        D
        125
        43 | 34
        kWh per kWp and month, London, south – PVGIS 5.3
      
      
Monthly yield per kWp in London facing south: upright (orange) and tilted at 30° (grey). In June the frame produces 125 instead of 63 kWh, in December 34 instead of 43 kWh. Own illustration from the PVGIS values in this calculator.

    

    
The calculator is tested against this example.


    
Plug-in solar: rules differ by country

    
Small solar kits that plug into a socket (“balcony solar”, “plug-in solar”) are allowed under
      different rules in each country, and some countries do not allow them at all without an
      electrician. Before connecting one, check the rules of your country and your network operator.
      The calculator does not know these rules; it only calculates the energy.

    
In Germany the Renewable Energy Sources Act (EEG) defines plug-in solar
      devices: panels, inverter and a plug for connecting to a circuit in the home (section 3
      no. 43 EEG). Devices with up to 2 kW of installed power and up to
      800 VA of inverter power behind a household’s meter fall under simplified
      rules; what they feed into the grid is assigned to acceptance free of charge
      (section 8 (5a) EEG). There is no payment for it – so for a balcony kit in Germany leave
      “export payment” empty. For a German city with more than 800 Wp of panels, the calculator
      points out that the inverter will limit the output.


    
How much you use yourself

    
Self-consumption decides the saving more than any other input – and it is the most uncertain.
      It depends on how much runs in your home at the same time as the sun shines: the
      fridge, the router and devices on standby always run, the washing machine only if you start it
      during the day. If you are at home during the day, you use more yourself than someone who only
      gets home in the evening. A large roof produces far more at midday than a household needs at that
      moment; there the share is smaller than with balcony solar.

    
The 30 % in the example is therefore only an assumption. The
      plug-in solar simulator of HTW Berlin
      (German) estimates for your consumption how much of the solar power you use yourself – or look at
      your meter after the first year. What individual devices use, the
      electricity cost calculator works out.


    
Which electricity price to enter

    
Most accurate is your own unit rate per kilowatt-hour from your contract or
      bill. You keep paying the standing charge however much the system produces – it does not belong
      in the calculation.

    
If you do not have the price to hand, the button next to the field inserts the national average
      for the country of the chosen city, the same values as in the
      electricity cost calculator: for the United
      Kingdom the Ofgem price cap unit rate (26.32 p/kWh for October to December 2026, Direct Debit,
      without the standing charge), for Germany the BDEW average (37.0 c/kWh, data as of August 2026),
      for Switzerland the ElCom median and for the other European countries Eurostat household prices
      for the first half of 2026. The Eurostat and BDEW figures include a share of the standing charge,
      so the real saving per kilowatt-hour is a little lower. For a few countries there is no official
      average here; enter your own price there.


    
Limits of this tool

    

    
Privacy: the calculator runs entirely in your browser, the table is part of the
      page. Your entries are not sent to xmoo.app, PVGIS or anyone else.


    
Sources

    
    
Page last updated: 11 November 2026