About the Power Rating
Power rating selection for solar plant equipment determines the appropriate continuous and peak power ratings for inverters, transformers, PCS, and cable systems — ensuring no component is undersized for the plant's actual output under real operating conditions, including high irradiance and low temperature.
How to calculate it
- 1DC-to-AC ratio (ILR): solar array DC capacity ÷ inverter AC capacity. Typical ILR: 1.1–1.4 for fixed-tilt; 1.2–1.5 for single-axis trackers. This means the inverter is slightly undersized relative to the array — clipping occasional peak production.
- 2Clipping loss: at high irradiance, the array produces more than the inverter can handle — the excess is clipped. Acceptable clipping: 0.5–2% of annual yield.
- 3Inverter AC rating: must cover load at maximum inverter output. Transformer and cable rating: must handle maximum inverter AC output × 1.1.
- 4Temperature derating: at 45°C ambient, most inverters output 85–95% of rated power. Size for the hottest month's average to avoid clipping on hot days.
- 5For BESS: power rating of PCS = required charge/discharge rate (C-rate × capacity).
Worked example
A 1,000 kWp array with ILR 1.2: inverter rated at 833 kW (use 850 kW standard). Transformer rating: 850 ÷ 0.98 × 1.1 = 954 kVA → 1,000 kVA. AC cable: rated for 850 kW at 415 V, PF 0.98 → I = 850,000 ÷ (1.732 × 415 × 0.98) = 1,204 A → 2 × 240 mm² XLPE cables in parallel.
What you can calculate
- kW/MW rating
- C-rate
- Peak power
- Grid services
Frequently asked questions
What is clipping in a solar inverter and when is it acceptable?
Clipping occurs when the solar array's DC output exceeds the inverter's maximum AC power — the inverter limits its output and the excess DC power is wasted. A small amount of clipping (0.5–2% of annual yield) is economically optimal because the inverter cost saved by using an ILR > 1.0 outweighs the lost generation. Clipping > 3% of annual yield is generally uneconomical unless the array has very high bifacial gain or the site has a flat irradiance distribution.
Why do inverter ratings derate in hot weather?
Inverter power electronics (IGBTs, diodes) have a maximum junction temperature — typically 125–150°C. At high ambient temperatures, the inverter's heat sink is less effective at removing heat, so the maximum power must be reduced to prevent the junction temperature from being exceeded. Most inverters begin derating at 40–45°C ambient, reducing output by 1–3% per °C above the threshold. Proper ventilation, shading of the inverter, and HVAC in the inverter room prevent unnecessary derating.
Ready to build your solar project?
Get free quotes from verified EPCs and installers across India.
You might also need
Energy-to-Power Ratio
Determine optimal E/P ratio for use-case (1C backup, 0.25C arbitrage, 2C frequency regulation)
OpenAutonomy / Backup Time
Calculate backup duration from capacity, load, and DoD — validate against IS 16270 backup requirements
OpenRound-Trip Efficiency
Compute RTE from charge/discharge efficiency and auxiliary losses — benchmark vs IEC 62933 ≥85%
OpenDC/AC Architecture
Compare DC-coupled vs AC-coupled BESS architecture for efficiency, cost, and application suitability
OpenHybrid Solar + BESS
Size combined solar PV + BESS system for self-consumption, peak shaving, and grid export optimization
OpenUsable Capacity
Derive usable energy from nameplate capacity applying DoD, temperature, and aging derating factors
Open