NASA POWER supplies gridded monthly climate averages of global horizontal and diffuse solar radiation. The returned reference period is shown with each result. These are long-term averages, not a weather forecast or measurements at your exact site. You can also enter your own monthly data.

We use an isotropic sky approximation: panel irradiation = direct horizontal irradiation × beam geometry ratio + diffuse irradiation × (1 + cos β)/2 + horizontal irradiation × albedo × (1 − cos β)/2. The beam ratio integrates sun geometry in 30-minute solar-time steps over a 365-day year, assuming uniform daytime direct-normal irradiance within each month. Monthly daily averages are multiplied by days per month. The recommended tilt searches 0–90° in 1° steps at your chosen azimuth.

Estimated energy (kWh) = panel irradiation (kWh/m²) ÷ reference irradiance (1 kW/m²) × installed capacity (kWp) × performance ratio. See the isotropic diffuse model.

Self-consumed energy = estimated generation × your self-consumption share. Exported energy = generation − self-consumed energy. Annual bill savings = self-consumed energy × your electricity purchase price. Annual export income = exported energy × your surplus export price. Total electricity value is their sum, before costs and taxes.

Prices are entered by you and stay in your selected currency. No supplier tariff or exchange rate is retrieved. The same assumed self-consumption share and flat rates are applied to each month in CSV exports. Hourly matching, time-of-use tariffs, tiered rates and financial payback are outside this estimate.

This simplified, monofacial fixed-tilt model does not simulate hourly weather, shading, terrain horizons, row spacing, bifacial gain, tracking, clipping, temperature, snow, or degradation individually. The performance ratio is a user-set combined loss assumption. Results are not a production guarantee, structural calculation, or bankable yield study.