Off-Grid Power Calculator

Size your off-grid solar power system. Calculate panels, battery bank, and system cost based on daily energy usage and sun hours.

Inputs

Daily Energy Usage

kWh

Peak Sun Hours

hrs

Panel Wattage

Current Battery Capacity

kWh

Backup Generator

Tab to move between fields

Results

Panels Needed

Recommended Battery Bank

28.1 kWh

≈ 28 loads of laundry

Estimated System Cost

$19,159.00

≈ 10 gaming PCs

Total Solar Capacity4 kW

Current Autonomy1.6 days

Generator Cost$3,250.00

Annual Fuel Cost$1,000.00

How to Use This Calculator

Enter Daily kWh Usage from your current electricity bills or a load audit of planned appliances.
Input Peak Sun Hours (4–6 for most US locations) and Panel Wattage for the solar panels you are considering.
Enter Battery Capacity kWh and Backup Generator kW to size the storage and backup portions of the system.
Review Panels Needed and Total Solar Capacity (kW) to request quotes from solar installers.
Check Recommended Battery Bank (kWh) for 2 days of autonomy and Current Autonomy (days) with your current batteries.
Use Estimated System Cost and Days of Autonomy to decide on the right balance of solar, battery, and generator backup.

How the result changes with Daily Energy Usage

Daily Energy Usage	Panels Needed	Recommended Battery Bank	Estimated System Cost
11	8	20.6 kWh	$15,246.00
36	24	67.5 kWh	$41,431.00
65	44	121.9 kWh	$72,517.00
90	60	168.8 kWh	$98,703.00

What each input means

Daily Energy Usage: Average daily electricity consumption (US average: 30 kWh; off-grid efficient: 10-20 kWh).
Peak Sun Hours: Average daily peak sun hours for your location (check NREL maps).
Panel Wattage: Wattage rating of each solar panel.
Current Battery Capacity: Total battery bank capacity you have or plan to install.
Backup Generator: Backup generator capacity for cloudy periods.

What each result means

Panels Needed: Number of solar panels required.
Total Solar Capacity: Total solar array size in kilowatts.
Recommended Battery Bank: Battery capacity needed (reduced with backup generator).
Current Autonomy: Days your current batteries can power without sun.
Generator Cost: Estimated cost for backup diesel generator (~$650/kW).
Annual Fuel Cost: Estimated annual generator fuel cost (~500 run hours/year).
Estimated System Cost: Total cost: panels, batteries, inverter, installation, and generator.

How this is calculated

Worked example, using the default values

Identify Input Parameters
5 parameters
Daily Energy Usage = 15 kWh, Peak Sun Hours = 5 hrs, Panel Wattage = 400 W, Current Battery Capacity = 30 kWh, Backup Generator = 5 kW = 5 input(s) provided
Calculate Daily Production Needed
Daily Usage / System Efficiency
15 / 0.75 = 20 kWh/day
Calculate Panels Needed
⌈Production Needed / (Panel W / 1000 × Sun Hours)⌉
⌈20 / (400 / 1000 × 5)⌉ = 10 panels (4 kW)
Calculate Recommended Battery Bank
Daily Usage × Autonomy Days / DOD
15 × 1.5 / 0.8 = 28.1 kWh
Calculate Current Autonomy
Battery Capacity × DOD / Daily Usage
30 × 0.8 / 15 = 1.6 days
Calculate System Cost
(Solar + Battery + Inverter) × (1 + Install Factor) + Generator
($2800 + $8438 + $1000) × 1.3 + $3250 = $19,159

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