— Show your work
Every number Solune returns is traceable. Here are the formulas we use and the sources they rest on — so you can check them, argue with them, or rebuild them yourself.
S = daily kWh ÷ (peak sun hours × 0.78)We divide your daily consumption by the product of your local peak sun hours and a 78% derating factor. The 78% accounts for inverter losses, wiring, soiling, and temperature — the gap between a panel's nameplate rating and what actually reaches your wall.
N = ⌈(S × 1000) ÷ panel watts⌉The number of panels is the system size in watts, rounded up over the wattage of a single panel. We always round up so the array can meet demand even at its weakest.
A = N × 2.0 m²Each panel occupies roughly 2 m² including spacing and mounting clearance. Multiply by the count to know how much roof or ground you'll give to the sun.
P = S × sun hours × 365 × 0.78The same derating factor applied across a full year. This is the energy you'd expect to produce, not the energy the panels are rated for.
C = P × 0.4 kgEach kilowatt-hour of solar displaces roughly 0.4 kg of CO₂ that a fossil plant would have emitted — the 2023 world average for grid electricity.
B = cost ÷ (P × 0.15)Years to recover the investment, assuming each solar kilowatt-hour offsets about 15¢ of grid electricity — a blended retail-rate estimate.
The 30-year annual average of all-sky surface shortwave downward irradiance (ALLSKY_SFC_SW_DWN) — the value we use as your peak sun hours when you pick a location on the map.
power.larc.nasa.govThe 78% performance ratio we apply is a simplified relative-loss multiplier consistent with NREL's PVWatts model, covering inverter efficiency, soiling, mismatch, and availability.
pvwatts.nrel.govReference method for sizing a photovoltaic array from daily load and solar resource, the basis of our system-size formula.
nrel.govThe ~0.4 kg CO₂/kWh emission factor reflects the 2023 global grid average published by the International Energy Agency.
iea.orgThe 15¢/kWh figure used in the payback estimate is a blended U.S. retail electricity rate drawn from the U.S. Energy Information Administration.
eia.govCost-per-kW values for monocrystalline, polycrystalline, and thin-film systems are rounded from NREL's annual solar cost benchmarks for residential PV.
nrel.govReverse geocoding of your clicked coordinates into a human-readable place name.
nominatim.openstreetmap.orgThe panel-type efficiencies we cite are drawn from datasheets of modules qualified under the IEC 61215 design-qualification standard.
webstore.iec.chThese figures are educational estimates, not an engineering stamp. Real systems need a site survey, local permitting, and a licensed installer. Use Solune to frame the conversation — then bring the numbers to a professional.
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