Battery runtime
In the battery runtime calculator, nominal energy is voltage × amp-hours. Planned usable energy applies state of charge, allowed depth of discharge and a separately labeled planning reserve. For a load stated at the appliance, battery-side watts equal appliance watts divided by system or inverter efficiency. Runtime is usable Wh divided by battery-side watts.
Temperature, age, BMS cutoffs, wiring loss, inverter idle draw, surges and variable loads can change actual runtime. Lead-acid capacity may also fall at high discharge rates because of the Peukert effect.
Wh and Ah conversions
Wh = W × h
Wh = V × Ah
Ah = Wh ÷ V
Wh = (mAh ÷ 1,000) × V
These conversions describe nominal quantities and do not automatically include usable capacity or losses. The watt-hour calculator and amp-hour calculator implement these relationships directly.
Solar array and battery sizing
The solar and battery calculator defines required delivered energy as daily Wh × autonomy days. Planning headroom is an extra sizing margin: required with headroom = delivered energy ÷ (1 − headroom). Nominal battery Wh then equals that result ÷ maximum usable fraction, and nominal Ah equals nominal Wh ÷ battery nominal voltage.
Minimum solar watts equal daily Wh ÷ (peak sun hours × system efficiency). When a recharge target is entered, solar daily energy needed equals ongoing daily load + battery deficit ÷ recharge days. The deficit is added once.
Peak sun hours and system efficiency are planning inputs. Weather, seasonal irradiation, shading, temperature and hardware design must be considered for a final system.
Solar panel tilt
The solar panel angle calculator uses absolute latitude as a practical annual starting tilt. Monthly and seasonal modes use solar declination δ = 23.45° × sin[(360° ÷ 365) × (284 + n)] and approximate solar-noon zenith as |φ − δ|. Results are constrained to 0–90° and the displayed facing direction is toward the equator.
This is a geometry-based solar-noon reference, not a monthly energy optimum or full irradiance optimization. It does not integrate direct and diffuse irradiance over a day or month and does not model weather, shading, horizon, ground reflection, roof geometry, trackers, east/west layouts or local rules.
Rounding and validation
Calculators retain full precision internally and round displayed values for readability. Invalid, zero or out-of-range divisors produce a clear validation message rather than Infinity or NaN.