## Model

Powersim Sun uses Meteonorm to calculate irradiation and other relevant meteorological data for a given location. Meteonorm calculates interpolated, hourly values for an average year, and the data is interpolated for any location on the earth. The meteonorm database collects data from more than 8000 worldwide weather stations and from five satellites. This is the best starting point for Powersim Sun to calculate solar energy production.

### Batteries

If you choose to use batteries in your installation, the model will prioritize charging the batteries before selling to grid. When the batteries are fully charged, the remaining energy will be sold to grid if this is chosen in your settings.

If the solar production is less than the given consumption, the least value of what is available in the batteries and the max effect from the batteries will be used. The remaining consumption (not covered by batteries) will be bought from the grid.

### Return on investment

The return on investment functionality in the Powersim Sun model uses a standard net present value (NPV) calculation, where the result is shown for each year into the future. The cash flow is discounted for each year shown in the graph. If the time needed to return the investment is not reached within the timeframe of the graph, a linear calculation is made to extrapolate the NPV value in order to find the number of years and months before the investment has paid itself.

### Energy Production

Powersim Sun uses the irradiation and temperature data from Meteonorm together with the characteristics of the solar panel and inverter to calculate the solar energy production.

First the temperature of the solar panel module (Tm) is calculated using the following formula:

Tm=Tamb+kmt*G

Tamb is the ambient temperature (from Meteonorm), G is the irradiation (from Meteonorm) while kmt is the mounting type coefficient. The mounting type in this version is assumed to be building-integrated.

The module temperature is then used together with irradiation, maximum power of solar panel (Pmax), and temperature coefficient of Pmax to calculate the solar panel energy production (Pdc):

Pdc = G/1000 * Pmax(1 + kt(Tm − Tref))

Tref is the reference temperature according to STC (Standard Test Condition), 25°C, and kt is the solar panel's given temperature coefficient of Pmax in %.

A loss of 1% is assumed in the DC cables between the solar panels and the inverter. The expected efficiency and size of the inverter is then used to calculate the output power from the inverter. A loss of 2% is assumed in the AC cables from the inverter.