How do I size an off-grid solar system?

Add the appliance wattage and daily usage hours, calculate daily Wh, divide by peak sun hours and system efficiency for panel wattage, then size the battery from backup hours, battery voltage, depth of discharge and inverter efficiency.

How much battery capacity do I need for off-grid solar?

Battery capacity in Wh is approximately load watts multiplied by backup hours, divided by inverter efficiency and usable depth of discharge. Convert Wh to Ah by dividing by battery voltage.

How do I choose charge controller size?

For a first estimate, charge controller current is solar array watts divided by battery voltage, multiplied by a safety factor such as 1.25. Always check controller voltage limits and PV string Voc.

Off-Grid Solar System Sizing Calculator | Panel Battery Inverter MPPT

Off-Grid Solar System Sizing Calculator

Calculate solar panel wattage, battery Ah/kWh, inverter size and charge controller current for off-grid solar systems from your appliance load and backup requirement.

☀️ Design Rule: Start from your real appliance load, then add margin for losses, weather and future expansion. Use this with the Solar Panel Output Calculator, Solar Battery Bank Calculator, MPPT Charge Controller Calculator and Solar Inverter Size Calculator.

🏠 Off-Grid Solar: Load → Battery → Inverter → Solar Array + Charge Controller

Appliance	Qty	Watts Each	Hours/Day	Surge ×	Backup?

Backup Hours

Peak Sun Hours

Battery Voltage

Battery DoD

Inverter Efficiency

Solar Loss Margin

Use this mode for real off-grid sizing. Tick “Backup?” for the appliances that must run during power outage/night backup time.

Presets:

Total Running Load

Backup Time

Daily Running Hours

h/day

Peak Sun Hours

Battery Voltage

Battery DoD

Inverter Efficiency

Battery Efficiency

Solar Loss Margin

Inverter Margin

Surge Factor

Quick mode is best when you already know the approximate total load. For appliances with motors, add surge margin or use the appliance schedule tab.

Presets:

Battery Voltage

Battery Capacity

Parallel Strings

sets

Usable DoD

Inverter Efficiency

AC Load

Runtime is only an estimate. Real runtime changes with battery age, discharge rate, temperature and inverter standby consumption.

Battery presets:

📐 Formula Reference

Daily Energy

Wh/day = Σ(W × qty × hours)

Solar Array

Panel W ≈ Wh/day ÷ (sun hours × system efficiency)

Battery Capacity

Battery Wh = load W × backup h ÷ (ηinv × DoD × ηbattery)

Charge Controller

Controller A ≈ Panel W ÷ Battery V × 1.25

📋 Quick Reference

Battery Voltage

Small system12 V

Medium system24 V

Large system48 V

Typical DoD

Lead-acid50%

AGM/Gel50–60%

LiFePO480–90%

Sizing Margin

Solar losses20–30%

Inverter margin20–30%

Controller safety125%

📚 Design Notes

Start with energy, not panel countOff-grid sizing should begin with Wh/day and backup hours. Panel wattage, battery size and controller current all depend on the load profile.

LiFePO4 can use more capacityLead-acid batteries are commonly sized around 50% usable DoD, while LiFePO4 systems often use 80–90% usable DoD depending on BMS and design target.

Motors need surge marginFridges, pumps, compressors and power tools may need inverter surge capacity several times higher than running watts.

Check PV voltage separatelyThis calculator estimates charge controller amps. Always check PV string Voc, MPPT voltage window and cold-weather Voc margin separately.

What is an Off-Grid Solar System Sizing Calculator?

An off-grid solar system sizing calculator estimates the major system parts needed to run loads without grid power. It converts appliance wattage, usage hours, backup time and sun hours into recommended solar panel watts, battery capacity, inverter size and charge controller current.

How to calculate solar panel size for off-grid system

Calculate daily energy in Wh/day, then divide by peak sun hours and practical system efficiency. A common first-pass estimate is Panel W = Wh/day / (sun hours × efficiency). Add margin for cloudy days, dirt, heat, wiring loss and battery charging loss.

How to calculate battery size for off-grid solar

Battery capacity depends on load watts, backup hours, inverter efficiency and usable depth of discharge. For example, a 500 W load for 6 hours needs more than 3000 Wh nominal battery capacity after efficiency and DoD are included.

❓ Frequently Asked Questions

List all appliances, watts and hours per day. Calculate Wh/day, size panels from sun hours, size batteries from backup hours and DoD, then choose inverter and charge controller with suitable safety margin.

Divide your required solar array wattage by the watt rating of one panel. Example: 2400 W array ÷ 400 W panel = 6 panels, before checking string voltage and controller limits.

Multiply the load watts by backup hours, then divide by inverter efficiency and usable DoD. For 1 day backup, use your critical load energy for the full required backup period.

Use 12V for small systems, 24V for medium systems, and 48V for higher power systems. Higher voltage reduces current, cable size and charge controller current.

A simple current estimate is solar array watts divided by battery voltage, multiplied by 1.25. Also check PV open-circuit voltage, MPPT input voltage range and controller power limits.

The inverter continuous rating should be above total running watts with margin. For motors, pumps, refrigerators and compressors, also check surge rating.

Peak sun hours represent the equivalent number of hours per day when solar irradiance is near 1000 W/m². It is not the same as daylight hours.

Heat, dust, shading, panel angle, wiring loss, MPPT loss, battery charging loss and inverter loss reduce practical output. That is why the calculator includes a solar loss margin.

Some MPPT controllers allow limited PV oversizing, but you must stay within maximum input voltage and controller current/power limits. Always follow the controller datasheet.

No. This is a practical first-pass calculator. Final design should check cable size, fuses, earthing, PV string Voc, battery BMS, local code and equipment datasheets.