BalkonWatt: Balcony Solar

BalkonWatt is not a government app and does not represent any government or public authority. All official information in the app comes exclusively from the five sources listed with links below under SOURCES.

Does a balcony solar kit pay off for you? Not somewhere in general — right on YOUR balcony? BalkonWatt answers that before you spend €400 or more.

MEASURE INSTEAD OF GUESSING
Hold your phone against the railing: BalkonWatt measures the orientation with its compass rose and corrects interference from metal railings with a sun calibration — just aim at the sun, the app does the rest. Then lay the phone on the panel for the tilt, done. And with the camera you sight buildings and trees that cast shadows: BalkonWatt overlays the sun's summer and winter path live on the camera image.

SOLAR DATA FOR YOUR LOCATION
The calculation uses the long-term irradiation data of PVGIS (sources 1 and 2) for your location. It covers Germany, Austria and Switzerland.

A CLEAR ANSWER — FREE
• Traffic light: clearly worth it / partly / rather not
• Annual yield in kWh for your chosen kit
• Rough savings per year
• Shading loss in percent

EVERYTHING FOR YOUR PURCHASE DECISION — BALKONWATT PRO (one-time, no subscription)
• Payback calculator: set price and electricity tariff yourself and see instantly when the system pays for itself
• Battery calculator: try any battery size — the curve shows when a bigger battery stops paying off
• 20-year balance (including inverter and battery replacement)
• Monthly curves: generation vs. consumption
• Tilt optimizer: find the best mounting angle
• Self-consumption, self-sufficiency, clipping losses
• Letter template to your landlord or owners' association as PDF (drafting aid for German § 554 BGB and § 20 WEG, sources 3 and 4 — not legal advice)
• Pointer to registration in the German market master data register (source 5)
• Complete measurement report as PDF
• Yield widget for your home screen

WHO IS IT FOR?
For tenants and owners who want to know before buying what their balcony can really do — vertical, tilted or on a flat roof, south as well as east/west. All values are forecasts; real yields vary with the weather year.

SOURCES
BalkonWatt uses no other sources.
1. PVGIS – Photovoltaic Geographical Information System of the Joint Research Centre (JRC) of the European Commission, © European Union: https://re.jrc.ec.europa.eu/pvg_tools/en/
2. SARAH-3 irradiation dataset by CM SAF, included in PVGIS: https://www.cmsaf.eu/
3. German Civil Code § 554 BGB (plug-in solar devices in rented flats): https://www.gesetze-im-internet.de/bgb/__554.html
4. German Condominium Act § 20 WEG (plug-in solar devices in condominiums): https://www.gesetze-im-internet.de/woeigg/__20.html
5. Market master data register of the Federal Network Agency: https://www.marktstammdatenregister.de/MaStR

Recent changes:
First version for Android: measure your balcony, calculate annual yield and savings, payback and battery calculators, letter to your landlord or owners' association as PDF and a yield widget.