Frequently Asked Questions about Solar Panels
Guides
- Determining roof orientation and tilt angle – South, south-west or east-west? How to find your roof orientation and tilt angle with your phone, and what every deviation from south really costs in yield.
- From kWp to kWh: calculating your solar yield – How many panels for 4,000 kWh? The complete calculation chain from module rating to annual yield, with location values for Central Europe and the 60 percent feed-in rule.
- Sizing battery storage and self-sufficiency – How big does the battery need to be and what self-sufficiency rate is realistic? Rules of thumb, a worked example and when storage really pays off.
- Balcony solar: calculating the yield and orienting it correctly – What an 800 W balcony solar kit on the railing delivers, per direction, calculated with PVGIS – plus the German rules for 2026, shading and registration.
FAQ
What roof orientation is best for solar panels?
The optimal direction for solar panels is due south (180° azimuth). Deviations of up to 45° east or west reduce yield by only about 5–10%. Even pure east- or west-facing roofs still achieve around 80% of the maximum possible output.
What tilt angle produces the highest solar yield?
In Central Europe, the optimal tilt angle is 30–35°. Shallower angles (15–20°) generate more in summer, steeper ones (40–50°) more in winter. The annual difference between 20° and 40° is usually less than 5%.
How much electricity does a solar system produce per kWp per year?
In Germany, an optimally oriented solar system generates about 900–1,100 kWh per kWp per year. In southern Germany and Austria up to 1,200 kWh/kWp is possible, in Northern Europe rather 800–950 kWh/kWp. The exact value depends on location, roof orientation, tilt angle, and shading.
What does self-sufficiency (autarky) mean for a PV system?
The self-sufficiency rate indicates what percentage of your own electricity consumption is covered directly by the solar system. With a system of about 1 kWp per 1,000 kWh of annual consumption it is 30–40% without storage and 55–65% with a battery of about 1 kWh per 1,000 kWh; larger systems and batteries reach 70–80%. The calculator shows the value for your inputs. The higher the self-consumption share, the more economical the system operates.
Is a battery storage system worth it for my solar installation?
A battery storage system significantly increases self-consumption and self-sufficiency. At 3,500 kWh annual consumption and 4 kWp on a south-facing roof, the calculator shows self-sufficiency rising from about 35% without storage to 56–59% with 2.7 kWh and 68–74% with 5 kWh (Hamburg to Munich). Whether storage pays off financially depends on electricity prices, storage costs, and the feed-in tariff.
What data does SolarFinder calculate with?
Immediately with an estimate based on the latitude of the location. One or two seconds later the calculator loads hourly irradiation data from PVGIS (the European Commission's Joint Research Centre) for the location and orientation and simulates the whole year hour by hour, including battery and inverter – weather year 2019, 18% system losses. Only without a connection to PVGIS does the estimate remain; the printout states which data basis was used. The payback divides the total cost by the annual saving. The total cost is preset to the shop price of a kit matching the system and battery size, or to a preset marked as an estimate if there is no matching price – or you enter your own value.