Useful Installer Tools · Solar

Solar Load & System Sizing Calculator

Build a practical solar load schedule and estimate daily energy use, simultaneous peak load, inverter capacity, battery-bank size, solar-array size, panel quantity and charge-controller current. Adjustable assumptions include battery usable depth, autonomy, system voltage, peak-sun-hours, inverter reserve and solar-system efficiency.

1. Build the customer load

Add each appliance or circuit. Peak load assumes the entered appliances could be on together; daily energy uses quantity × watts × hours/day.

Appliance / LoadQtyWattsHours/dayPeak use %

2. Sizing assumptions

Battery type / usable depth

Backup / autonomy days

Battery system voltage

Peak sun hours/day

Solar system efficiency

Inverter reserve

Selected panel wattage

Controller safety factor

Planning guide: Motors, pumps, refrigerators, air conditioners and compressors can draw much more power at startup than their normal running watts. Always check surge/start current and the actual inverter, battery, BMS, MPPT and panel specifications before installation.

Estimated system

Results update from the load schedule and assumptions you enter.

Connected peak load0 WApproximate simultaneous running load.

Daily energy0 kWhTotal energy used by the entered schedule each day.

Suggested inverter0 kWPeak load plus selected reserve; surge requirements still need checking.

Battery usable energy needed0 kWhDaily load × autonomy days.

Nominal battery bank0 kWhAdjusted for selected usable battery depth.

Battery bank at system voltage0 AhApproximate nominal Ah at the selected DC system voltage.

Required solar array0 kWDaily energy ÷ sun hours ÷ selected system efficiency.

Selected panels required0 panelsRounded up using the entered panel wattage.

Approx. controller output current0 AArray watts ÷ battery voltage × safety factor; verify MPPT input limits separately.

Estimated array energy/day0 kWhApproximate daily output under the entered peak-sun-hours and efficiency.

Add loads and calculate to see the recommended planning range.

How to use it

Solar sizing workflow for an installer.

Use actual equipment labels/specifications whenever possible instead of guessing wattage.

01List every loadEnter appliances, CCTV equipment, lighting, fans, pumps and other loads the customer wants powered.

02Enter realistic daily hoursA 100 W TV used for 5 hours consumes about 500 Wh/day; runtime matters as much as wattage.

03Set peak useUse the peak-use percentage when not every unit is expected to run at the same time.

04Choose battery typeUsable depth changes the nominal battery bank. Lead-acid is normally sized with more reserve than lithium.

05Choose autonomyOne day means enough nominal battery capacity for roughly one day of the scheduled load before solar contribution.

06Enter local sun hoursUse a conservative peak-sun-hour value for the installation location and season.

07Check inverter surgeThe calculated inverter covers running load plus reserve, not motor/compressor startup surge.

08Check panel and MPPT limitsPanel count alone is not enough. Verify Voc, Vmp, Isc, string configuration and controller voltage/current limits.

09Confirm cable/protection designBattery cables, DC breakers/fuses, isolators, earthing and AC protection must be sized separately.