TRANSPARENCY
How we calculate
The planner gives you a system size, a self-sufficiency figure and an annual saving within two minutes. This page lists every number behind those results, where it comes from and when we last checked it.
They are an orientation based on public reference data and typical system behaviour. They are not a yield forecast and not a binding offer. A real project depends on your roof, shading, load profile, tariff and grid connection — which is why every result ends with a conversation, not a contract.
Solar yield
How much electricity a kilowatt-peak of solar produces per year at your location. This is where the difference between, say, Hamburg and Munich comes from.
Specific annual yield946–1097 kWh per kWp and year (DE) · 1132 (AT) · 1107 (CH)
PVGIS is the reference tool of the EU Joint Research Centre and the basis most European yield calculations start from. It uses satellite-measured irradiation averaged over nineteen years, so a single sunny or cloudy year does not distort the figure.
Assumptions behind the yield1 kWp · 35° pitch · facing south · 14 % system losses · crystalline silicon
We use a south-facing roof at 35 degrees, which is the common reference case for a German pitched roof, and the standard 14 per cent system loss for cabling, inverter and temperature. A roof facing east or west, or one that is shaded, will produce less.
European Commission, Joint Research Centre (JRC) — PVGIS API — PVcalc endpoint
Location from postcode0 Leipzig · 1 Berlin · 2 Hamburg · 3 Hanover · 4 Dortmund · 5 Cologne · 6 Frankfurt · 7 Stuttgart · 8 Munich · 9 Nuremberg
We resolve the first digit of a German postcode to its largest city and use that as the reference point. This is our own simplification: within a zone the real value varies by a few per cent, and we would rather show you the method than pretend to street-level accuracy.
EverVision Energy
Prices and emissions
What a saved kilowatt-hour is worth, and what it avoids in emissions.
Electricity price, Germany0.37 €/kWh incl. VAT, 3,500 kWh a year
This is the BDEW average for newly signed household tariffs. We use it deliberately rather than the higher figure for contracts already running, which the Federal Statistical Office puts at 40.55 cents for the second half of 2025. Taking the lower number means we understate rather than overstate what you save.
BDEW Bundesverband der Energie- und Wasserwirtschaft e.V. — BDEW-Strompreisanalyse August 2026
Electricity price, Austria0.327 €/kWh incl. all taxes
Austria's regulator E-Control publishes ranges rather than a single average, so we use the Eurostat series, which measures what households actually paid. Eurostat flags this particular value as an estimate.
Eurostat — nrg_pc_204 — Electricity prices for household consumers
Electricity price, Switzerland27.7 Rp./kWh ≈ 0.293 €/kWh
The median across roughly six hundred Swiss grid operators, converted at the European Central Bank reference rate of 16 September 2026. The spread between municipalities is wide, so your own tariff may differ noticeably. ElCom has already announced 26.5 Rappen for 2027.
ElCom — Eidgenössische Elektrizitätskommission — Medienmitteilung „Leicht sinkende Strompreise 2026“
Electricity price, commercial0.262 €/kWh, 20–500 MWh a year
Excludes VAT and other taxes a business can reclaim, so it reflects what a company actually bears. For Austria, Switzerland and the rest of the EU we derive the commercial price from the household price, which is our own assumption.
Eurostat — nrg_pc_205 — Electricity prices for non-household consumers, Band IB
Feed-in payment7.70 ct/kWh up to 10 kWp · 6.66 up to 40 · 5.44 up to 100
Surplus solar you cannot use yourself earns the statutory rate, which is fixed for twenty years from commissioning and falls by one per cent every six months for systems built later. The bands apply segment-wise, so a 15 kWp system earns the higher rate on its first 10 kWp. Austria and Switzerland have no comparable statutory rate, so we show no feed-in revenue there rather than invent one.
Bundesnetzagentur — EEG-Förderung und Fördersätze — anzulegende Werte für Solaranlagen
Emissions avoided352 g CO₂-equivalent per kWh
The German generation mix for 2025, counting carbon dioxide, methane and nitrous oxide but not the upstream supply chains. Including those raises the figure to 406 grams. The number falls every year as more renewables come online, so a system installed today avoids less over its life than this suggests.
Demand charge for peak shaving100 €/kW per year assumed
There is no national demand charge. We checked three large grid operators for 2026 and found 132, 99 and 67 euros per kilowatt and year, so we use a value in the middle. Two conditions matter: the charge only applies to metered commercial sites, and only in the tariff variant for at least 2,500 full-load hours a year. Below that threshold peak shaving saves very little. A further reduction under the rules for atypical grid use must be agreed with your operator and notified to the regulator.
Sizing rules
How we get from your consumption to a recommended battery size.
Default consumption4,000 kWh a year for a four-person house
The pre-filled consumption matches the upper end of the middle efficiency band for a four-person house without electric water heating. It is only a starting point — the slider is there because your own figure is the one that matters.
Battery size from consumption≈ 1 kWh usable per 1,000 kWh a year · +2.5 kWh car · +2 kWh heat pump · +1.5 kWh backup
HTW Berlin's storage study found that one kilowatt-peak of solar plus one kilowatt-hour of usable storage per thousand kilowatt-hours consumed lifts self-sufficiency from about 30 to about 55 per cent. The Verbraucherzentrale recommends up to 1.5 kilowatt-hours per thousand. We sit at the lower end, because beyond it each additional kilowatt-hour buys steadily less and ages the cells for nothing. The surcharges for a car, a heat pump and backup remain our own engineering allowance — no institution publishes a figure for those.
Electric car and heat pump+2,200 kWh a year for a car · +3,100 kWh for a heat pump
These consumption figures come from more than five thousand real solar households. Our storage surcharges are smaller than the consumption alone would suggest, in the heat pump's case deliberately: it draws most of its electricity in winter, when a larger battery has little solar to store.
Self-sufficiency estimatecapped at 80 %
We combine the solar you use directly with what the battery shifts into the evening. The ceiling comes from HTW Berlin, who find that self-sufficiency well above 80 per cent is reachable only in special cases. A calculator promising more is selling a number rather than a system. You can check our result against HTW's own independence calculator, linked here.
HTW Berlin — Dezentrale Solarstromspeicher für die Energiewende · Unabhängigkeitsrechner
Commercial system sizingcapacity from annual consumption and peak load · 120 kWh or 261 kWh cabinets
For a business we size on two drivers at once: the energy you could shift over a day, and the peak load you want to cut. The larger of the two decides the cabinet count. Peak-shaving savings depend on your grid operator's demand charge and on whether your site qualifies for reduced network fees, so we treat that figure as indicative until we see your load profile.
Bundesnetzagentur — § 19 Abs. 2 StromNEV — individuelle Netzentgelte bei atypischer Netznutzung
Grid-scale sizing5 MWh containers, 2.5 MW each · rounded up
Utility projects are sized in whole containers, so we round your target energy up to the next unit. Real projects are then shaped by the grid connection point, the intended market and local permitting rather than by energy alone.
EverVision Energy
The exact query
Yield values are not estimated by us. We query the European Commission's PVGIS service once per reference location and store the result. You can reproduce any figure with the call below.
https://re.jrc.ec.europa.eu/api/v5_3/PVcalc ?lat=<lat>&lon=<lon> &peakpower=1 &loss=14 &angle=35 &aspect=0 &mountingplace=building &outputformat=json
These figures are references, not your project. If something here looks wrong, or you want the assumptions checked against your own roof, load profile or tariff, tell us.
Prefer to talk it through? Contact us →