From 15-minute sun to 8 760 hours
The panels' production comes from the sun model: 12 typical days, one per month, in 15-minute steps, with the shade of trees, roof objects and the house. The production, your household's use, the car and the battery are then run hour by hour over all 8 760 hours of the year. Each hour the model decides where each kWh goes: from the roof to the house, to the battery or to the grid; from the grid to the house, the car or the battery; from the battery to the house. A run takes tens of milliseconds, so it repeats on every change you make.
Every kWh at its hour's price
Each imported kWh is billed at that hour's price: the month × hour spot average for your price area, plus markup, grid fee, energy tax and VAT. Each exported kWh earns that hour's spot price. The bill without a system is your household and car at those prices; the bill with it is what remains after the roof and the battery. The saving per year is the difference.
A battery's saving is one more difference: the same year with and without the battery, in the strategy that saves most. Every battery size and strategy is simulated, so the comparison table is 4 sizes × 4 strategies of real runs, not a rule of thumb.
Payback, self-use and self-sufficiency
Payback is the installed price divided by the first year's saving: a simple payback with no interest, no price escalation and no panel ageing in it, so you can redo it in your head. On an installer's card the price is that installer's total after grön teknik, and the saving is re-simulated with its equipment. A battery is recommended only when its payback is strictly shorter than without one.
Self-use is the share of your solar you do not sell. Self-sufficiency is the share of your use that comes from the roof, directly or through the battery; energy the battery took from the grid is not counted, so the figure errs low, never high.
What you see on the result
The result card shows production in kWh per year, the saving in kr per year, the cost and payback when a price exists, and the battery comparison per size and strategy. The energy flow chart shows the year's kWh per flow and a typical day per month, hour by hour; the money view shows the saving per month. The running list names the sources used: measured solar data for your area (PVGIS) and real spot prices for your price area over the last 12 months.
An estimate, not a meter reading
One typical day stands in for each month's weather, so a cloudy fortnight averages out and a record summer is not in the number. Prices are the last 12 months, not next year's. Shade comes from what is in your 3D model: the house, its roof objects and the trees the AI found or you added; a missed tree lowers the real yield, and a tall building next door that the model does not hold casts no shade in the estimate. The installer confirms the roof on site, and the card's price is indicative until the installer's own quote.
