Solar Inverter Output Calculator
Estimate AC output after temperature, irradiance, losses, inverter efficiency and clipping.
Step-by-step
- Enter valid values to begin.
Planning model: power scales linearly with irradiance and with 1 + γ(Tcell − 25), and the inverter efficiency is treated as one constant value (use a CEC or Euro weighted figure for annual estimates; peak efficiency overstates partial-load output). Clipping is a hard limit at the AC rating. Inverter temperature and altitude derating, MPPT voltage window effects, standby losses and low-light efficiency roll-off are not modelled. Coefficients and loss percentages are typical values; take real ones from datasheets. See the Grid-Tie Inverter Sizing page for string and DC/AC design. Verify against the inverter datasheet before relying on it.
Solar Inverter Output: From Nameplate kWp to Real AC kW
Core Engineering Principles
A panel’s kWp rating is earned at Standard Test Conditions: 1,000 W/m² and a 25 °C cell. A roof in July is nothing like that. Output scales almost linearly with irradiance, so at 800 W/m² we expect 80% of nameplate before anything else happens. Then temperature takes its cut. Crystalline silicon loses roughly 0.3–0.4% of power per degree above 25 °C, and a cell on a dark roof can sit 25–35 °C above ambient, so 55 °C cells give a factor near 0.895 with a −0.35 %/°C coefficient. Add 5% for soiling, wiring and mismatch and a 10 kWp array hands the inverter under 7 kW.
The inverter then converts that DC to AC at an efficiency of about 97–98% at its peak, and less at low load. Datasheets quote peak efficiency, but a plant spends most of its life at partial load, which is why Euro and CEC weighted efficiencies exist: they average several load points and come out one to two points lower. AC cable loss comes next. Finally comes clipping. The inverter cannot export more than its rating, so when the DC/AC ratio is above 1, the sunniest hours are flattened. Mild clipping is a deliberate economic choice, but we want to see the number.
PAC,raw = PDC × ηinv × (1 − LAC) • PAC = min(PAC,raw, Prated)
DC/AC = kWp / Prated
NEC & Standard References
IEC 61683 defines how to measure power conditioner efficiency, which is where datasheet figures come from. IEC 62109-1 and IEC 62109-2 cover the safety of PV inverters. In North America UL 1741 certifies inverters and IEEE 1547 sets grid interconnection requirements. NEC Article 690 covers PV systems and Article 705 covers interconnected power sources. Loss figures here are typical planning values; use datasheets. Verify the adopted code edition and your utility and AHJ requirements.1. Temperature factor = 1 + (−0.0035) × (55 − 25) = 0.895.
2. PDC = 10 × 0.800 × 0.895 × 0.95 = 6.80 kW.
3. After the inverter: 6.802 × 0.975 = 6.63 kW, then × 0.99 for cable loss gives 6.57 kW.
4. Clipping: 6.57 is below 8 kW, so the loss is 0 kW.
5. DC/AC = 10 / 8 = 1.25 and inverter load = 6.57 / 8 = 82.1%.
- STC is not field reality. Expect 75–85% of nameplate on a good summer day.
- Hot roofs cost real energy. Flush-mounted modules run hotter than rack-mounted ones, so use a realistic cell temperature, not ambient.
- Derating hides in the datasheet. Many inverters reduce output above a stated ambient temperature or altitude, which this simple model does not include.
- Over-paneling clips. A DC/AC ratio of 1.5 or more can waste a large share of midday energy, particularly on cold, clear days when output peaks.
- Standby and night losses are extra. Self-consumption is small but not zero.