Key takeaways
- Size in order: load → battery → array → controller → inverter.
- Everything flows from an honest daily watt-hour figure.
- Battery covers your autonomy; the array refills it each day.
- A 3,000 Wh/day cabin ≈ a 900 W array and a 12 kWh battery bank.
Step 1 — Total your daily load
An off-grid system is sized from energy, measured in watt-hours per day. List every appliance, multiply its watts by hours used per day, and add them up. The off-grid load calculator does this and also gives the peak load (everything on at once) you'll need for the inverter.
Step 2 — Size the battery bank
The battery stores enough to run your loads through the nights and cloudy days you want to cover (days of autonomy), without discharging past what the chemistry tolerates.
Run it in the battery bank sizing calculator. Use ~50% depth of discharge for lead-acid, 80–100% for LiFePO₄.
Step 3 — Size the solar array
The array has to put back what you took out, during your location's usable sunlight (peak sun hours), with losses.
The solar array sizing calculator turns that into a panel count.
Step 4 — Match the charge controller and inverter
The charge controller has to handle the array's current: MPPT amps ≈ array watts ÷ battery voltage × 1.25 (charge controller calculator). The inverter has to handle your loads: continuous watts ≈ running load × 1.25, with surge headroom for motors (inverter sizing calculator).
The five steps at a glance
| Step | Sizes | Key input |
|---|---|---|
| 1. Load audit | Daily Wh & peak W | Appliances × hours |
| 2. Battery bank | Ah / kWh | Autonomy & DoD |
| 3. Solar array | Panel watts | Peak sun hours |
| 4. Charge controller | MPPT amps | Array W ÷ bus V |
| 5. Inverter | Continuous & surge W | Running & starting load |
Worked example: a 3,000 Wh/day cabin
Load is 3,000 Wh/day. Battery: 3,000 × 2 days ÷ 0.5 DoD = 12,000 Wh ≈ 500 Ah at 24 V. Array: 3,000 ÷ 4.5 sun hours ÷ 0.75 ≈ 900 W of panel. Controller: 900 ÷ 24 × 1.25 ≈ 47 A → a 50 A MPPT. Inverter: sized to your peak running load plus motor surge. That's a complete, balanced system.
Frequently asked questions
What order do I size an off-grid system in?
Load → battery → array → charge controller → inverter. Everything flows from the daily watt-hour load.
How much solar and battery for 3,000 Wh/day?
≈900 W of panel and a 12 kWh (~500 Ah at 24 V) bank for 2 days autonomy at 50% DoD — less with LiFePO₄.
Why start with the load?
Battery, array, controller, and inverter are all derived from how much energy you use and how fast — so measure it first.