Yield against consumption, hour by hour.

In step 2 you enter the annual consumption and choose the customer type. A house has morning and evening peaks and slightly higher consumption in winter. A housing association has building electricity around the clock with an evening peak, and a business uses most on weekdays from 07:00 to 17:00.

For a house there are two options. Heat pump makes winter roughly 2.5 times as heavy as summer, and EV adds charging from 22:00 to 06:00 every night – the charging is included in the annual consumption. If the customer has hourly readings from their grid operator, you upload the file, and it then drives the whole profile.

Once the panels are on the roof, the designer fetches a typical meteorological year (TMY) for the site from PVGIS 5.3, the European Commission’s solar service, and the horizon from the PVGIS terrain model. Yield is then simulated hour by hour for each panel orientation.

The simulation follows a loss chain. Irradiance is transposed to the plane of the panel with the Perez model. Horizon, shading, reflection in the glass, soiling and snow are included, as are module temperature from air temperature and wind using the Faiman model, mismatch per string, cables, the inverter’s efficiency curve with clipping at rated power, and degradation. Each step becomes a line in the loss waterfall in step 8, in kWh and per cent.

Alongside it is what PVGIS’s own annual calculation gives for the same panels, and the difference in per cent. If the weather year cannot be fetched, the designer uses PVGIS monthly values per orientation, and without PVGIS a rule-of-thumb value of 950 kWh per kWp, adjusted for orientation and tilt. The source is shown next to the figures.

Yield is set against consumption hour by hour. Self-consumption is the share of the solar energy used in the building, directly or via the battery. Self-sufficiency is the share of consumption covered by solar. The rest is exported and imported electricity respectively.

Step 8 shows the result per year, month by month and as a typical day in July and in January. Imported electricity is valued with the energy price, grid fee, energy tax and VAT, exported electricity with the spot price and the grid benefit payment – using the prices you enter in step 2.

The battery can be controlled in two ways. Solar only charges the battery with surplus solar energy and discharges it when the building needs power. By hourly price, the default, plans each day with a 48-hour horizon: the battery saves solar energy for expensive hours and can charge from the grid when electricity is cheap. Surplus solar energy that the plan does not use is charged anyway.

The hourly prices are the 2025 spot prices for Sweden’s four bidding zones SE1–SE4 (Nord Pool day-ahead), built into the designer; prices for other markets are not included. The bidding zone follows the address and can be changed. The purchase price follows the spot price around the average price you have entered, so that the annual average stays the same – the value of the control comes only from the differences between hours.

The value of the panels without a battery is calculated on the average prices, so that designs with and without a battery can be compared.