.jpg){kind=link}
How an off-grid solar system works
- Solar panels turn sunlight into DC electricity.
- A charge controller (MPPT is the efficient kind) safely charges the batteries from the panels.
- The battery bank stores energy for night and cloudy days.
- An inverter turns battery DC into normal 120/240-volt AC power for your outlets.
- A backup generator (or a grid connection) charges the batteries during long cloudy spells.
A portable power station is the same system in one box — battery, charge controller and inverter — and you just plug in a folding solar panel.
Watts, watt-hours and amp-hours
- Watts (W) = how fast something uses power right now. A 60 W bulb.
- Watt-hours (Wh) = power over time. A 60 W bulb for 10 hours = 600 Wh. 1,000 Wh = 1 kWh, the unit on your electric bill.
- Battery capacity is often in amp-hours (Ah). Multiply by the voltage: a 12 V 100 Ah battery = 1,200 Wh.
Step 1: Add up your daily use
List what you want to run and for how long:
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Energy-efficient fridge | ~100–150 (cycling) | 24 | 800–1,500 |
| Chest freezer (efficient) | ~60–100 (cycling) | 24 | 500–1,000 |
| LED lights (5 bulbs) | 50 | 5 | 250 |
| Internet modem + router | 20 | 24 | 480 |
| Laptop | 50 | 4 | 200 |
| Phone charging (4 phones) | 10 | 3 | 30 |
| CPAP (no humidifier) | 40 | 8 | 320 |
| Well pump (½ hp) | ~1,000 | 0.5 | 500 |
| Furnace blower | ~500 | 6 | 3,000 |
Check labels or use a plug-in watt meter for real numbers. Heat, AC, electric water heaters, dryers and stoves use far too much for small systems — use wood, propane or gas for those.
Step 2: Size the battery
Battery Wh = daily Wh × days of backup ÷ usable fraction
- Lithium iron phosphate (LiFePO4) batteries can use about 80–100% of their capacity and last 3,000+ cycles. They're the standard now.
- Lead-acid batteries should only be drained to about 50%, are heavier, and wear out much sooner.
Example: 2,000 Wh/day × 2 days ÷ 0.9 = about 4,400 Wh of LiFePO4 (roughly four 12 V 100 Ah batteries, or one 48 V 100 Ah).
Step 3: Size the panels
Panel watts ≈ daily Wh ÷ peak sun hours ÷ 0.75 (the 0.75 covers real-world losses).
"Peak sun hours" is the equivalent number of hours of full, strong sun per day. It changes a lot with season and location.
Northwest winter sun
Around Spokane, summer days give about 6–7 peak sun hours, but December and January can drop to about 1–2 (the low end on flat or shaded panels), with long stretches of fog and cloud. A system that runs your house easily in July may barely charge in December. Plan on a generator for winter, more panels than summer needs, or panels tilted steeply (around 60°) to catch the low winter sun and shed snow.
Example: 2,000 Wh/day in summer (6 sun hours) needs about 450 W of panels. The same load in December (1.5 sun hours) needs about 1,800 W.
Loading calculator…
Batteries in the cold
- Don't charge LiFePO4 batteries below freezing (32°F) — it can permanently damage them. Use batteries with built-in heaters, or keep them inside the heated space.
- Lead-acid batteries lose capacity in the cold and can freeze if discharged.
- Keep any battery bank ventilated, away from living spaces if lead-acid, and protected by proper fuses and a disconnect.
Safety and permits
DIY solar is real electrical work
High-current DC can start fires and arc dangerously. Use correctly sized wire, fuses or breakers on every battery connection, and a proper disconnect. Grid-tied systems, and most permanently installed systems, need permits and inspection — and connecting to the grid requires utility approval. When in doubt, hire a licensed electrician or solar installer.
Getting started small
A great first step: a 1,000–2,000 Wh power station and a 200–400 W folding panel. That runs a fridge for part of the day, lights, phones, internet and a CPAP — and it teaches you how much power you actually use before you spend big.
Sources: Energy Saver (DOE) — Off-grid systems · NREL — PVWatts solar calculator