Off-Grid Solar Calculator
Size the panels, battery bank and inverter for a cabin or tiny home from the loads you run.
Solar array needed
526 watts
- Energy used per day
- 2,260 Wh
- Battery bank needed
- 837 Ah
- Battery bank energy
- 10,044 Wh
- Inverter size
- 838 W
Your loads use 2,260 Wh a day and need about 526 W of panels.
Calculation breakdown
| Step | Formula | Result |
|---|---|---|
| Energy per day | Sum of watts × hours for 4 loads | 2,260 Wh |
| Solar array | 2,260 Wh ÷ (5 h × (1 − 14%)) | 526 W |
| Battery bank | 2,260 Wh × 2 days ÷ (12 V × 50% × 90%) | 837 Ah |
How it works
List each load as name, watts, hours per day, then set your sunshine and battery choices.
Worked example
A fridge (150 W, 8 h), lights (60 W, 5 h), a laptop (60 W, 6 h) and a pump (400 W, 1 h), with 5 sun hours, 14% losses, a 12 V bank, 2 days of backup, 50% depth of discharge, 90% efficiency and 25% headroom:
- Daily energy: 1,200 + 300 + 360 + 400 = 2,260 Wh
- Array: 2,260 ÷ (5 × 0.86) = 526 W
- Bank: 2,260 × 2 ÷ (12 × 0.5 × 0.9) = 837 Ah
- Inverter: 670 × 1.25 = 838 W
Sources
Frequently asked questions
How do I size an off-grid solar system?
Add up the watt-hours your loads use in a day, then size the panels for that energy, the battery bank for your days of backup, and the inverter for the watts that run together.
How are daily watt-hours calculated?
Multiply each load's watts by the hours it runs in a day, then add them all. A 150 W fridge running 8 hours uses 1,200 Wh.
How many days of battery backup do I need?
That depends on how many cloudy days you want to ride through. The calculator uses 2 as an example, so change it to suit your site.
What peak sun hours should I enter?
Use an average for your location, and for an off-grid system use the lowest season you must still cover. Enter it yourself, because the national solar map data could not be opened to cite.
Why are depth of discharge and losses examples?
Battery University gives cycle life against depth of discharge but no single default, and the 14% panel loss figure is a common planning number. Replace them with your own data.
An estimate for information only. Have a qualified installer check an off-grid design, including wiring and a charge controller.