Free · appliance-based calculator · private on this device
Off-Grid Solar System Builder: Size Panels, Batteries & Inverter
Start with the appliances you want to run, then explore what their energy use could mean for solar, battery storage and an inverter. Compare realistic alternatives, understand the uncertainty, and keep a versioned plan without creating an account.
Planning tool, not installation design. Example sun-hours and equipment factors are not local measurements or manufacturer approvals. Daily energy balance does not include recovery of an exhausted reserve unless you choose that extra calculation.
Start with your needs
Examples are illustrative. Adjust appliance specifications and site assumptions before relying on a planning estimate.
What will you power?
System assumptions
Planning examples, not site measurements or manufacturer ratings. Recovery is off unless enabled.
Appliance energy is counted at device input, converted to estimated battery-side daily Wh using only the stated AC/DC path losses plus one inverter idle allowance when AC loads exist. Usable no-PV storage equals modeled battery Wh/day × autonomy days. Divide by usable fraction for nominal battery Wh.
Daily-balance solar W equals battery Wh/day ÷ (equivalent peak-sun-hours × PV harvest fraction × battery charge-path efficiency). Optional reserve-recovery solar adds a separately identified stored-energy replenishment allowance. Both use raw, unrounded math before each independent 50 W planning step.
Inverter output W and estimated VA are not equipment ratings. Waveform, starting overlap/duration, ambient derating, charge limits and actual electrical compatibility must be verified.
Keep and share your project
Projects stay in this browser unless you download JSON or share a link. No accounts, network upload, or remote storage.
Two worked off-grid examples
These are calculated from the same versioned engine as the editor, using explicitly illustrative appliance data. They are not performance claims for an actual site or manufacturer model.
Cabin essentials — fridge available 24 hours
The illustrative refrigerator consumes 800 Wh/day at the device input, but it must remain available for the full 24 hours even when its compressor cycles intermittently. Other loads include lighting, internet networking, laptop charging and an intermittent water pump. The 12 W additional inverter idle draw is accounted for 24 hours, not just compressor run-time.
Remote internet and cameras — direct and regulated DC
One illustrative 55 W internet terminal and a 30 W camera/switch group are modeled through a regulated DC path, while an 8 W sensor is modeled as direct DC. All remain available 24 hours. Direct DC is energy accounting, not proof of compatible voltage or equipment.
How the calculation moves from loads to an energy plan
Device energy: per-unit W × available operating hours × duty fraction, measured Wh/day, or annual kWh/year ÷ 365. Multiply by quantity once.
Battery-side daily use: AC input Wh divided by incremental inverter efficiency, plus direct DC input Wh, plus regulated DC input Wh divided by converter efficiency, plus a single inverter idle allowance when AC loads exist.
Storage: modeled battery Wh/day × no-PV autonomy days = usable reserve; divide once by the specified usable nominal fraction for approximate minimum nominal battery energy.
Solar: model daily PV balance using user-selected equivalent peak-sun-hours, PV harvest fraction and charge-path efficiency. Round raw watts to a separate 50 W planning step; panel counts need the visitor's actual module wattage.
Conversion and idle losses are visible separately. Stored Ah uses a nominal 12/24/48 V class and is not a battery-product compatibility statement.
Why daily solar sizing and reserve recovery are different
Daily-balance solar replaces modeled daily use under a chosen equivalent-sun-hours assumption. It does not also refill an autonomy reserve depleted during no-PV days. If you enable recovery, a separate scenario adds usable reserve Wh × depleted fraction ÷ recovery equivalent-sun days to daily modeled demand before dividing by sun-hours and PV path factors. Recovery is an energy allowance, not a promise of calendar-day charging or a charger/BMS performance result.
How to estimate a refrigerator's electricity use
A refrigerator can draw running power in short compressor cycles while still requiring electrical service all day. Prefer a suitable measured daily Wh reading or documented kWh/year average when available, and provide actual running watts separately for the inverter screen. An annual label is an average, not a guaranteed hot-day or winter-day consumption. Do not reduce inverter-on time to compressor run-hours without proving the refrigerator can be unavailable the rest of the day.
What the inverter estimate cannot establish
The editor assumes enabled AC running loads may coincide and shows a fixed 1.25× running-W headroom screen only when every relevant running power is known. It cannot infer VA without load power factors, certify motor starting or simultaneous surges, assume a particular surge duration, model waveform/current crest factor, or prove derated output at elevated temperature. Battery/BMS instantaneous current, DC input ranges, wire protection, local electrical code and manufacturer selections all require separate review.
Continue with the technical guides
Quick solar and battery sizing starts from an aggregate known daily load rather than appliances and uses a different, explicitly conservative set of loss assumptions. The numerical results are not interchangeable.