Yield and sizing
Array size from panel count
- where
- array peak power (kWp)
- number of modules
- module STC rating (W)
Explain this equation
Works out the peak power of an array from the number of panels and their rating.
Each module is rated in watts at Standard Test Conditions (1000 W/m² of sunlight at 25 °C cell temperature). Adding them, N × W_p, gives watts peak; dividing by 1000 gives kWp, the unit used for yield estimates and DNO forms.
Simple multiplication of number by rating.
Sense check: ten 430 W panels is 4.3 kWp.
Watch out: kWp is a rating, not what the array delivers on a typical day. Inverter output is usually lower than the array peak.
Total DC peak power of an array, the kWp figure used in the MCS yield estimate, the DNO notification and the inverter ratio.
Enter your values to see the result.
Good to know
Use the nameplate Pmax at STC (1000 W/m², 25 °C cell, AM1.5) from the module datasheet. Mixed module types: add each group separately.
Common mistake
Using the inverter AC rating or a rounded marketing figure instead of the exact datasheet Pmax of the modules fitted.
Limits
STC rating only. Real output is lower most of the time because of temperature, irradiance and losses.
Sources
- Module manufacturer datasheet: STC values (Voc, Vmp, Isc, Imp, Pmax), temperature coefficients of Voc, Pmax and Isc, NOCT/NMOT and dimensions
- MCS solar PV performance estimate as submitted with a planning application (Camden): estimated annual output = kWp × Kk × SF; Kk from the MCS table; SF = 1 − 0.01 × shaded segments; shade circles for objects within 10 m
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow MCS standards, manufacturer data, BS 7671, the ENA connection rules and Building Regulations. System design and DNO applications need a competent, certified installer.