Off-Grid Tiny Home Power: The Complete Beginner's Guide
Power is the part of off-grid living that surprises people most. A tiny home uses a fraction of the electricity of a normal house, but every watt has to be generated, stored and delivered by equipment you choose and maintain yourself. This guide walks through the whole system in the order you should plan it, with a worked example so the numbers make sense.
Start with your loads, not your panels
The most common mistake is shopping for solar panels first. Panels, batteries and inverters are all sized from one number: how much energy you use in a day. So the first job is an energy audit, and it takes about an hour with a notepad.
List every electrical item you plan to run. Next to each, write its power in watts (look for the label or the manual) and how many hours a day it runs. Multiply watts by hours to get watt-hours per day, then add everything up. Items that cycle on and off, such as a refrigerator compressor, run only part of each hour, so use the manufacturer's daily energy figure if one is given.
Here is an illustration with made-up round numbers. Please replace them with your own: LED lighting at 30 W for 5 hours is 150 Wh. A laptop at 60 W for 5 hours is 300 Wh. A 12-volt refrigerator averaging 500 Wh a day is 500 Wh. A water pump, a fan and phone charging might add 300 Wh. That household totals about 1,250 Wh a day, or roughly 1.25 kWh. A modest, efficient tiny home can land in this neighborhood. Electric space heating, an electric water heater or air conditioning can multiply it several times over, which is why those loads deserve their own planning (see our guide to heating and cooling).
The four main parts of the system
Almost every off-grid electrical system has the same four building blocks, and understanding what each one does makes every product listing easier to read.
- Solar panels turn sunlight into direct-current electricity. See our solar guide.
- The charge controller sits between the panels and the batteries and manages how they charge, protecting the batteries from overcharging.
- The battery bank stores energy for nights and cloudy stretches. See batteries and inverters.
- The inverter converts battery power to the alternating current that ordinary household outlets and many appliances expect.
Between these parts you also need wiring of the right thickness, fuses or breakers, a disconnect switch, and good connections. Those unglamorous items are where safety lives, and we cover them below.
Choose a system voltage early
Small systems often run at 12 volts, which matches a lot of RV and marine gear. As your loads grow, 24 or 48 volts becomes attractive because the same power flows at lower current, which allows thinner, cheaper wire and reduces losses. If you expect to run an inverter for kitchen appliances or tools, plan for 24 or 48 volts from the start, because changing voltage later means replacing most of the system.
Work backward to size each part
With your daily watt-hours in hand, sizing becomes a short chain of steps.
- Panels: divide daily watt-hours by the peak sun hours for your location in the worst season you will live there, then divide again by about 0.7 to 0.8 to cover real-world losses. With 1,250 Wh and 3 peak sun hours in winter, that is 1,250 / 3 / 0.75, or about 555 watts of panels.
- Batteries: multiply daily watt-hours by the number of cloudy days you want to ride through, then divide by the fraction of the battery you can safely use. For 1,250 Wh and two days of backup with a lithium iron phosphate battery you can use about 80 to 90 percent of, you would want roughly 3,000 Wh of capacity. Lead-acid batteries should usually be used only about half, which roughly doubles the capacity you need.
- Inverter: add up the watts of everything that might run at the same moment, then add headroom for motors and compressors that draw extra at startup.
- Charge controller: match it to your panel array's voltage and current, with margin.
These are planning formulas, not engineering drawings. Peak sun hours vary a lot by region and season; the free PVWatts calculator from the U.S. National Renewable Energy Laboratory is a good way to look up your location.
Plan for the bad week
Solar output drops sharply on overcast days and in winter, and it is lowest exactly when heating and lighting needs are highest. People who run out of power are almost never short on summer sun. They are short in a stretch of December clouds.
There are three ways to handle it: oversize the panel array, add battery capacity, or add a backup source. A small inverter generator or a connection to shore power can top up the batteries in a pinch. If you use a generator, run it outside and well away from windows, doors and vents, and install a carbon monoxide alarm inside. Our guide to portable solar generators covers that middle path.
Safety and wiring basics that matter
Batteries can deliver enormous current, so a short circuit can start a fire or cause serious burns. A few habits prevent most problems.
- Put a correctly rated fuse or breaker close to the battery on every positive cable that leaves it.
- Use wire thick enough for the current it carries; undersized wire overheats. Wire charts are published by the wire and equipment makers.
- Keep connections tight and clean, and protect cables from chafing where they pass through walls or frames.
- Include a way to disconnect the battery and the solar array so you can work on the system safely.
- Mount batteries where they are secure, ventilated as their type requires, and protected from freezing and extreme heat.
Electrical codes and permit rules vary by location, and many places require inspection of permanent dwellings. If you are unsure about any part of the wiring, have a licensed electrician review it. This guide is general education, not engineering advice.
Common mistakes to avoid
- Skipping the energy audit and buying equipment first.
- Sizing for summer, then running short in winter.
- Buying a large inverter with a high idle draw that quietly drains the batteries all night.
- Mixing old and new batteries, or different battery types, in one bank.
- Ignoring shading: a single shaded panel can drag down a whole string.
- Leaving out fuses because the system is small.
Where to go next
Read the spokes in this order: solar systems, batteries and inverters, water systems, composting toilets and heating and cooling. For a broader overview of living off the grid, see off-grid tiny home living and the older off-grid power guide.
Key takeaways
- Everything is sized from your daily watt-hours, so do the energy audit first.
- Plan for the worst month, not the best one.
- Fuses, correct wire size and a battery disconnect are not optional.
- Electric heating and cooling are the loads that break small systems.