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Solar Panel Output Calculator

Estimates the energy produced by a photovoltaic array from the panel rating, number of panels, average peak sun hours per day and a performance ratio (default 0.75 for system losses), and optionally the electricity cost saved.

When to use

You want a first-order estimate of how many kWh a solar array will generate per day, month or year, or its yearly savings at a known tariff.

Do not use when: You need month-by-month production for a specific location, tilt and shading (use NREL PVWatts or a site survey), or battery sizing (use battery-runtime).

Formula

daily_kwh = panel_watts × panel_count / 1000 × peak_sun_hours_per_day × performance_ratio; yearly_kwh = daily_kwh × 365; monthly_kwh = yearly_kwh / 12; savings = kWh × price_per_kwh

Peak-sun-hour method. The performance ratio bundles all losses; NREL PVWatts defaults to 14 % system losses plus 96 % inverter efficiency and temperature derating, giving about 0.75–0.80 overall. Savings assume all energy offsets consumption at the given tariff (no export rate).

Inputs

ParameterTypeUnitRequiredDescription
panel_wattsnumberWyesNameplate STC power of one panel in watts (typical residential panels 350–450 W). Range: > 0, ≤ 5000
panel_countintegerdefault 1Panels in the array. Range: ≥ 1, ≤ 100000
peak_sun_hours_per_daynumberh/dayyesDaily solar irradiation in kWh/m² on the array plane, i.e. equivalent hours of 1000 W/m² sun. Typical annual averages: 3–4 northern Europe/Canada, 4–5 most of the USA, 5–6.5 desert southwest, Australia and southern Spain. Range: > 0, ≤ 12
performance_rationumberdefault 0.75Fraction of nameplate output actually delivered after inverter, wiring, soiling, temperature and mismatch losses; 0.75–0.80 is typical for grid-tied systems. Range: ≥ 0.4, ≤ 1
price_per_kwhnumberper kWhnoOptional tariff in your currency per kWh; enables the savings outputs. Range: ≥ 0

Outputs

OutputTypeUnitDescription
system_size_kwnumberkWppanel_watts × panel_count / 1000.
daily_kwhnumberkWh/daysystem_size_kw × peak_sun_hours_per_day × performance_ratio.
monthly_kwhnumberkWh/monthyearly_kwh / 12.
yearly_kwhnumberkWh/yeardaily_kwh × 365.
specific_yield_kwh_per_kwpnumberkWh/kWp/yearyearly_kwh / system_size_kw, a location-dependent figure of merit (≈ 800–1,800).
daily_savingsnumberdaily_kwh × price_per_kwh (only when price_per_kwh is given).
monthly_savingsnumbermonthly_kwh × price_per_kwh (only when price_per_kwh is given).
yearly_savingsnumberyearly_kwh × price_per_kwh (only when price_per_kwh is given).

Example

10 × 400 W, 4.5 sun hours, PR 0.75, 0.15/kWh: {"panel_watts":400,"panel_count":10,"peak_sun_hours_per_day":4.5,"performance_ratio":0.75,"price_per_kwh":0.15} → {"system_size_kw":4,"daily_kwh":13.5,"monthly_kwh":410.6,"yearly_kwh":4928,"specific_yield_kwh_per_kwp":1232,"daily_savings":2.03,"monthly_savings":61.59,"yearly_savings":739.13}

One 300 W panel, 5 sun hours, PR 0.8: {"panel_watts":300,"peak_sun_hours_per_day":5,"performance_ratio":0.8} → {"system_size_kw":0.3,"daily_kwh":1.2,"yearly_kwh":438}

GET https://tttkmbb.com/api/v1/calculate/solar-panel-output?panel_watts=400&panel_count=10&peak_sun_hours_per_day=4.5&performance_ratio=0.75&price_per_kwh=0.15

Machine access

Sources

FAQ

What are peak sun hours?

The daily irradiation in kWh/m² expressed as hours of full 1 kW/m² sun. A site with 5 kWh/m²/day has 5 peak sun hours even though the sun shines for 12; use annual-average values from NREL or PVGIS maps.

Why not use the nameplate wattage directly?

Panels rarely operate at the 25 °C, 1000 W/m² test conditions. Heat, dirt, wiring, inverter conversion and mismatch typically cut output by 20–25 %, which the performance ratio accounts for.

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