How much would a solar panel generate on your balcony, roof or campervan?

Roughly 800 to 1,000 kWh a year for every kilowatt of panels, if they face south and tilt at about 35 degrees. Southern England is at the top of that range and Scotland below it. Mount the same panel flat against a balcony railing and it loses about a quarter; face it east or west and it loses another third; face it north and most of the output is gone. WattSnap uses the same EU PVGIS solar data that installers use, but for the exact spot you point at.

Yes, since 27 August 2026 in Great Britain. A kit can plug into an ordinary socket if its inverter is limited to 800 watts, the panels total no more than 2,000 watts, it is certified to the IPS v2 plug-in solar standard, and it contains no battery. You must tell your electricity network operator within 28 days (a G98 notification), but you don't need an electrician for a standard kit. Renters can use freestanding or clip-on kits without asking the landlord; anything fixed to the building needs written consent.

South, tilted at about 35 degrees, gives the most in the UK. South-east or south-west costs you about 4%. East or west costs 25 to 30%. North-facing gets less than a third of south. Tilt matters as much as direction: a panel standing upright on a railing makes about 27% less than the same panel tilted. WattSnap reads direction and tilt from your phone's compass and sensors, so you don't have to guess.

Only the electricity you use yourself counts, at your unit rate (around 26 to 28p per kWh in 2026). With a full installed system and an export tariff most of the output earns something. A UK plug-in kit gets no export payment and can't have a battery, so a typical home uses only 25 to 40% of what it makes. An 800 W kit on a south-facing London railing makes about 594 kWh a year: worth about £165 if you used all of it, nearer £50 to £65 in practice. On a £500 kit that is an eight to ten year payback, not three.

A postcode calculator gives one regional average for an ideal roof. WattSnap uses your phone's compass and tilt sensor to read the direction and angle you aim it at. You can also trace the skyline around you, and the heights you trace are passed to PVGIS so the estimate includes shade from nearby buildings and trees. Then it asks the PVGIS solar database for that position. Same data as the professionals, real inputs instead of assumptions. It runs free in the browser with nothing to download.