Enter how many modules you plan to wire and the coldest temperature the array will see. The calculator returns the array’s open-circuit voltage in the cold, the current to size the charge controller for, whether the hot-cell voltage still clears the battery’s charging voltage, and a rough battery size for your load. It uses the datasheet values and the Voc temperature coefficient of each module.
How it calculates
- Cold Voc = series count × (Voc + coefficient × (T − 25)). The coefficient is the datasheet’s Voc change in volts per °C, scaled for variants with a different Voc.
- Hot Vmp is a range: the datasheet gives no Vmp coefficient, so the calculator uses both the Voc coefficient scaled by Vmp/Voc (optimistic) and a typical crystalline −0.47 %/K (pessimistic), at 60 °C cell temperature.
- Controller current = 1.25 × array Isc, the usual allowance for irradiance above 1000 W/m².
- Daily energy = rated power × peak sun hours × 0.75 for losses. It is a planning figure.
- Battery = load × days ÷ (usable fraction × 0.85 round-trip efficiency), converted to amp-hours at the system voltage.
The module data come from the model pages, for example the SM55/SM50. For wiring rules read wiring Siemens modules, and for controller choice charge controllers.
This is a design aid, not a design. Check the controller manufacturer’s maximum input voltage and temperature rating, and have a qualified electrician review any installation connected to a building.