Sizing an off-grid solar system comes down to three numbers: how much energy you use per day, how big the biggest load you run at the same time is, and how many days you want to ride through without sun. Get those right and you can pick the inverter, battery and panels in about ten minutes. This guide walks through it for a typical US home or cabin.
Step 1: Work out your daily energy use (kWh per day)
List what you will run, its wattage, and how many hours a day it runs. Multiply watts by hours and add it up. Your utility bill also shows monthly kWh — divide by 30 for a daily figure, but expect to trim it once you go off-grid.
| Load | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Energy Star refrigerator | 150 (avg) | 24 | 1,200–1,500 |
| LED lighting | 100 | 5 | 500 |
| Well pump (1 HP) | 1,000 | 1 | 1,000 |
| Laptop, router, TV | 200 | 5 | 1,000 |
| Washer (per load) | 500 | 1 | 500 |
Typical results: a weekend cabin uses 2–5 kWh/day, a full-time small cabin 5–10 kWh/day, and a full-size home with efficient appliances 15–30 kWh/day. Electric heat, electric water heaters and central AC push it much higher — use propane or a heat pump for those if you can.
Step 2: Size the inverter for peak load
Add up everything that could run at the same time, then allow for motor start-up surge (well pumps and compressors can draw 2–3× their running watts for a second). Most homes need 120/240V split-phase output for a well pump, dryer or shop tools.
- Cabin with lights, fridge, small loads: 3–3.5 kW, 120V
- Home or cabin with a 240V well pump: 6 kW split-phase
- Full home with several big loads: 12 kW split-phase or more
Step 3: Size the battery for nights and cloudy days
Battery capacity = daily use × days of autonomy ÷ usable depth of discharge. LiFePO4 batteries can safely use 80–90% of their rated capacity, unlike lead-acid at 50%.
Example: 10 kWh/day × 1.5 days ÷ 0.9 ≈ 16.7 kWh. A 14.34kWh LiFePO4 battery covers most of that; two give you a full two days. If you have a backup generator, 1 day of storage is usually enough.
Step 4: Size the solar array for your worst month
Array size (kW) = daily use ÷ peak sun hours ÷ 0.8 (system losses). Use the sun hours for the month you need power most. Winter peak sun hours run about 2–3 in the northern states and 4–5 in the Southwest.
Example: 10 kWh/day ÷ 3 sun hours ÷ 0.8 ≈ 4.2 kW of panels. In Arizona the same home needs closer to 2.5–3 kW. Adding panels is the cheapest way to cut generator run time in winter.
Quick sizing chart
| Daily use | Inverter | Battery | Solar |
|---|---|---|---|
| 2–5 kWh (weekend cabin) | 3–3.5 kW | 5–10 kWh | 1–2 kW |
| 5–12 kWh (full-time cabin) | 6 kW split-phase | 14.34 kWh | 3–5 kW |
| 12–25 kWh (home) | 12 kW split-phase | 14.34–28.68 kWh | 6–10 kW |
| 25+ kWh (large home / farm) | 24 kW | 40–60 kWh | 12+ kW |
Matching systems
Each of our off-grid solar systems pairs the inverter, LiFePO4 battery and panels so the parts are already sized to each other (prices as of October 2026):
- 6kW split-phase off-grid system with 14.34kWh battery — $6,999.99. A good fit for a full-time cabin or small home with a well pump.
- 12kW split-phase system with 9kW of panels and 14.34kWh battery — $9,999.99. For a full home; add a second battery for more autonomy.
- 24kW off-grid home system with 57.36kWh of storage — $21,999.99. For large homes, farms and shops.
Smaller 2,000–3,500W systems and DIY kits without panels are also in the off-grid collection.
Common sizing mistakes
- Sizing for summer. Size panels for your worst month, or plan on a generator for it.
- Forgetting surge. A well pump that runs at 1,000W can need 3,000W to start.
- Undersizing the battery bank to save money. LiFePO4 lasts longest when it isn't cycled flat every night.
- Skipping room to grow. Pick an inverter and battery that let you add capacity later.
FAQ
How many solar panels do I need to go off-grid?
For 10 kWh/day in a northern state, about 4–5 kW of panels — ten to twelve 400–450W panels. Sunnier states need fewer.
How big a battery do I need for an off-grid cabin?
A weekend cabin can run on 5–10 kWh. A full-time cabin usually needs about 14 kWh, enough for a night plus a cloudy morning.
Can I run central air conditioning off-grid?
Yes, but it often doubles daily use. A high-efficiency mini-split heat pump is far easier to power.
Do I need a generator?
Not always, but most full-time off-grid homes in the northern US keep one for long winter cloudy stretches. It lets you size the battery and array smaller.
Not sure where you land? Send us your load list and we'll size a system for free.