Home/Off-grid power/Off-Grid Solar Power for a Cabin: A Beginner's Guide
Off-Grid Solar Power for a Cabin: A Beginner's Guide
Off-grid solar is four parts and one honest number: how many watt-hours you actually use per day.
Direct answer: An off-grid solar system has four parts: panels that make DC power, a charge controller that regulates it, a battery bank that stores it, and an inverter that turns it into household AC. Size the battery from your daily watt-hours and days of autonomy, then size the panels to refill it. Start with loads, not equipment.
Parts of the system
| Part | Job | Typical spec for a small cabin | Cost (approx.) |
|---|---|---|---|
| Solar panels | Generate DC | 800–1,600 W total | $400–$1,200 |
| Charge controller | Regulate charging | MPPT, 40–60 A | $150–$500 |
| Battery bank | Store energy | 5–15 kWh LiFePO4 | $1,500–$6,000 |
| Inverter | DC to AC | 1,500–3,000 W pure sine | $300–$1,200 |
| Balance of system | Wiring, fuses, breakers, mounts | — | $300–$900 |
How the parts connect
Panels → combiner box → charge controller → battery → inverter → AC loads. Every DC circuit needs a fuse or breaker rated for the wire, and the inverter needs a disconnect. If this sentence sounds like a wiring diagram you cannot draw, stop and use a licensed electrician for the DC side — mistakes here start fires.
Sizing in plain language
- List loads. Lights (10 W × 5 h = 50 Wh), fridge (1,000 Wh/day), laptop (60 Wh), phone charging (10 Wh), pump (300 Wh).
- Add them up. A modest cabin runs 2–4 kWh/day. A cabin with a fridge and a pump is closer to 5–7 kWh/day.
- Add losses. Multiply by 1.3 for inverter, wiring, and battery round-trip losses.
- Size the battery. Daily kWh × days of autonomy ÷ depth of discharge.
- Size the panels. Daily kWh ÷ peak sun hours × 1.3.
Example: 3 kWh/day, 2 days autonomy, 80% usable depth on LiFePO4 → 3 × 2 ÷ 0.8 = 7.5 kWh of battery. Panels: 3 ÷ 4 peak sun hours × 1.3 = about 1 kW.
A realistic starter system
| Load | Daily Wh | Notes |
|---|---|---|
| LED lights (5 × 8 W, 4 h) | 160 | Use DC bulbs to skip the inverter |
| 12 V fridge (efficient) | 600–1,000 | The largest single load in most cabins |
| Laptop and phone charging | 100 | — |
| Water pump (intermittent) | 200–400 | Depends on head and tank size |
| Fan or small tools | 150 | — |
| Total | 1,200–1,800 | Before losses |
That load profile suits a 600–800 W array, a 3–5 kWh lithium bank, and a 1,500 W inverter. Anything involving heating — a kettle, a hot plate, a space heater — moves the system into a different budget entirely. Heat with propane or wood, and keep electricity for lights, electronics, and motors.
Mounting and shading
Panels produce most when they face true south (not magnetic south) at an angle roughly equal to your latitude, minus 10–15° if you want better summer output, plus 10–15° for winter. A fixed mount at latitude angle is the usual compromise.
Shading is the silent killer. A single bare branch across a panel in December can cut a string's output to near zero, and partial shade on a series string drags the whole string down. Walk the array site at 9am, noon, and 3pm in December before committing to a position. Ground mounts need clearance for snow and mowing; roof mounts need a structure rated for the load and a plan for cleaning.
Costs and realistic expectations
A small, honest cabin system — 1 kW of panels, 7–10 kWh of lithium battery, 2 kW inverter — costs roughly $3,000–$7,000 in components if you install it yourself, more with an electrician and mounting. It will run lights, electronics, a small fridge, and a pump. It will not run an electric stove, a hot water tank, or air conditioning without a much larger budget.
Winter is the reality check: production can drop 50–70% in northern latitudes, and snow on panels produces nothing. Plan for a generator or a seasonal load reduction.
Frequently asked questions
Can I start small and expand?
Yes, if you plan the voltage and controller capacity for expansion. Buying a 12 V system and later wanting 48 V means replacing the inverter and controller.
Do I need a generator?
Most off-grid cabins have one for cloudy stretches and heavy loads. A small inverter generator is cheaper than oversizing the battery.
How long do solar panels last?
25–30 years with slowly declining output. Batteries are the shorter-lived component: lithium 8–15 years, lead-acid 4–7 years.
Can I run a fridge off solar?
Yes, a modern efficient fridge uses 0.8–1.5 kWh/day. That is a significant share of a small system and should be in the load calculation from the start.
Next: size the battery bank with a worked example, then compare solar and generators. The power chapter in The Self-Sufficient Backyard covers this at a planning level.
Frequently asked questions
Can I start small and expand?
Yes, if you plan the voltage and controller capacity for expansion. Moving from 12 V to 48 V later means replacing the inverter and controller.
Do I need a generator?
Most off-grid cabins have one for cloudy stretches and heavy loads. A small inverter generator is cheaper than oversizing the battery.
How long do solar panels last?
25–30 years with slowly declining output. Batteries are shorter-lived: lithium 8–15 years, lead-acid 4–7 years.
Can I run a fridge off solar?
Yes, a modern efficient fridge uses 0.8–1.5 kWh/day, which is a significant share of a small system.