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Balcony Solar Calculator: Is It Worth It?

How much does a balcony solar kit save in your home, and after how many years has it paid for itself? The yield comes from European Commission data (PVGIS) for 233 cities, the share you use yourself from the plug-in solar simulator of HTW Berlin – matched to your electricity use.

Total of the panels from the data sheet, e.g. 2 × 400 Wp.

German averages without hot water (source).

More accurate: the figure from your annual statement.

Leave empty for the typical value.

Ofgem, Oct–Dec 2026 (what this means)

Yield per year
Used yourself
Covers of your use
Saving per year
Worth it up to a price of
Payback
Balance after 15 years

      

    


    
An estimate, not a guarantee. Yield and self-consumption are averages: the
      yield over many years for the centre of the city, self-consumption over 41 measured households. Your home can
      be well above or below, and the calculation does not know about shade on your balcony.


    
What you need it for

    

    
Where the figures come from

    
The yield is the same as in the
      solar panel output calculator: PVGIS, the photovoltaic
      information system of the European Commission’s Joint Research Centre, for 233 cities, six tilts and eight
      directions, queried once in advance, with free-standing panels and 14 % system losses. The details are on
      the page of the solar panel output calculator.

    
Self-consumption is the hard figure. It depends on how much is running in your home while the
      sun shines – and that can only be worked out from measured load profiles. That is exactly what the solar
      storage research group of HTW Berlin (University of Applied Sciences) did for its
      plug-in solar simulator
      (German): 41 measured yearly load profiles of flats and detached houses, weather data from the German
      Meteorological Service in Lindenberg (Brandenburg), simulated in one-minute steps over a year.

    
HTW Berlin does not publish a table. So on 12 November 2026 I queried the simulator for
      400 combinations – five directions from east to west, 90° and 30° tilt, systems from 400 to
      2,000 Wp, yearly use from 500 to 5,500 kWh, no battery and no shade – and read off how much power
      the system produces and how much of it the household uses. It turns out that the share depends almost only on
      two figures: yearly use and yearly yield. Whether the same amount of power
      comes from an east-facing balcony or a south-facing frame shifts it by only a few percentage points. The
      calculator therefore uses a smoothed table over use and yield; it differs from the 400 values read off by at
      most 4.3 percentage points.


    
How the tool calculates

    
    
      
  1. Yield per year = specific yield from PVGIS × panel power in kWp
    2. 
      
  2. Share = HTW typical value for your yearly use and this yield (linear between the table values) – or your
        own figure
    3. 
      
  3. Used yourself = yield × share; the rest goes to the grid
    4. 
      
  4. Saving = kWh used yourself × electricity price in pence ÷ 100
    5. 
      
  5. Worth it up to = saving × 15 years, payback = purchase price ÷ saving
    6. 
    

    
15 years is the period that HTW Berlin’s simulator also uses in its default settings. According to the HTW
      documentation nothing speaks against running a plug-in solar device for longer; it does assume, however, that
      the inverter has to be replaced after about 15 years.


    
Worked example: two people in London

    
A couple in a flat uses 2,100 kWh a year according to the German averages of HTW Berlin. Two panels with
      800 Wp in total hang upright on a south-facing balcony railing in London. These values are already in
      the calculator when you open it, with the Ofgem price cap unit rate of 26.32 p/kWh as the price.

    
    
      
  1. Yield: 743 kWh/kWp × 0.8 kWp = 594.4 kWh per year
    2. 
      
  2. Share: the table for 2,100 kWh of use gives 67.5 % at 400 kWh of yield and 54.3 % at
        600 kWh; for 594.4 kWh that makes 54.7 %
    3. 
      
  3. Used yourself: 594.4 kWh × 54.7 % ≈ 325.0 kWh, 269.4 kWh go to the grid. That covers
        15.5 % of the yearly use.
    4. 
      
  4. Saving: 325.0 kWh × 26.32 p ÷ 100 ≈ £85.53 per year
    5. 
      
  5. Worth it up to: £85.53 × 15 ≈ £1,282.93 – any kit that costs less has paid for itself
        within 15 years. The exact point the calculator works out as soon as you enter the purchase price:
        purchase price ÷ £85.53.
    6. 
    

    
The same kit brings a single person noticeably less and a family noticeably more, because more appliances run
      during the day and take up the solar power:

    

      
        
        used yourself
        
        to the grid
        1 person
        
        
        1,500 kWh · 44.7 %
        2 people
        
        
        2,100 kWh · 54.7 %
        3 people
        
        
        2,600 kWh · 61.8 %
        4 people
        
        
        3,000 kWh · 66.9 %
        5 people
        
        
        3,500 kWh · 72.6 %
        594.4 kWh yield per year, 800 Wp, London, south, 90°
      
      
How much of 594.4 kWh of solar power a year a flat uses itself: 44.7 %
        for one person, 72.6 % for five. Own illustration from the typical values of this calculator (PVGIS,
        HTW Berlin).

    


    
All household sizes in the example

    
The usage per household is the set of average values that HTW Berlin’s simulator works with. They come from
      the German “Stromspiegel” (electricity benchmark) and do not include electricity for hot water. A household in
      the UK may use more or less. Same kit, same place, 26.32 p/kWh:

    

      

        Balcony solar 800 Wp, London, south, 90°: 594.4 kWh per year
        
          
HouseholdUseUsed yourselfShareSaving per year

        
        
          
Flat, 1 person1,500 kWh266.0 kWh44.7 %£70.01

          
Flat, 2 people2,100 kWh325.0 kWh54.7 %£85.53

          
House, 1 person2,500 kWh358.8 kWh60.4 %£94.43

          
Flat, 3 people2,600 kWh367.2 kWh61.8 %£96.65

          
Flat, 4 people; house, 2 people3,000 kWh397.5 kWh66.9 %£104.63

          
Flat, 5 or more3,500 kWh431.3 kWh72.6 %£113.51

          
House, 3 people3,700 kWh442.9 kWh74.5 %£116.57

          
House, 4 people4,000 kWh460.3 kWh77.4 %£121.15

          
House, 5 or more5,000 kWh506.3 kWh85.2 %£133.26

        
      

    

    
The calculator is tested against this example and the table.


    
Why you do not use all the solar power yourself

    
A balcony solar kit feeds into a circuit in your home. Whatever is running at that moment – the fridge, the
      router, devices on standby, perhaps the washing machine at midday – takes up the solar power, and your meter
      draws that much less from the grid. If the kit produces more than is needed right then, the rest goes to the
      grid. That is why the share falls the bigger the kit is compared with your use: on a sunny midday,
      800 Wp quickly deliver more than a small household needs.

    
The typical values are averages over many households. If you are at home during the day or run the washing
      machine and dishwasher at midday, your share is higher; if the home is empty all day, lower. If you know your
      share, for example from your meter after the first year or from a plug-in energy meter, enter it yourself. A
      battery raises it; this tool does not model one, HTW Berlin’s simulator does.

    
The solar panel output calculator assumes a flat 30 %
      in its example. With the typical value for two people, the saving here is noticeably higher – the assumption
      about self-consumption matters more than any other input.


    
Rules for plug-in solar

    
In Germany the Renewable Energy Sources Act (EEG) defines plug-in solar devices (section 3
      no. 43 EEG). Devices with up to 2,000 W 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 exported power – which is why the calculator does not ask for one. Other countries have their own rules
      for plug-in solar, and some only allow it installed by an electrician; the calculator does not know them.
      Check what applies where you live before you buy.

    
More than 800 Wp of panels on an 800-VA inverter bring more in the morning, the evening and in winter, but
      on sunny middays the inverter limits the output, and the PVGIS values do not include this limit. For a German
      city with more than 800 Wp the calculator points this out. HTW Berlin’s values show how much it matters:
      1,000 Wp on 800 W facing south at 30° produce 983 kWh, hardly less than 1.25 times
      800 Wp (989 kWh). 2,000 Wp produce 1,556 kWh instead of 1,978 kWh, about 21 %
      less; upright on a railing it is 1,219 instead of 1,380 kWh, about 12 % less.


    
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 kit produces.

    
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 tables are part of the page. Your
      inputs are not sent to xmoo.app, PVGIS, HTW Berlin or anyone else.


    
Sources

    
    
Page last updated: 12 November 2026