How do I power an off-grid shed or cabin?
Scenarios Updated 2026-08-01
Three separate sizing questions, in this order. Add up the watt-hours you use in a day; that sets the array. Decide how many cloudy days you must survive without sun; that sets the battery. Find the largest single thing you will switch on and its start-up demand; that sets the inverter.
Getting them in the wrong order is the classic mistake: people buy an inverter big enough for a well pump and a battery sized for a laptop, or an array that covers the annual average and never the December week that actually matters.
Step one: the daily watt-hour total
What a small off-grid building actually consumes
Published figures for the loads a shed or cabin usually has. Lighting and communications are almost free; refrigeration is the first real cost; anything that heats or pumps is in another class again.
Multiply by the hours you use it. A whole cabin of these is a rounding error against a fridge.
See the record →Continuous, so it is one of the larger daily totals despite the small wattage.
See the record →Usually the largest steady load in a small off-grid building, and the one that sets the battery.
The 410 kWh a year on this model’s energy label, divided by 365 days. The annual number is the maker’s; the division is ours.
See the record →Brief, but it is the load that decides the inverter rather than the battery.
See the record →A submersible motor’s locked-rotor demand, and the number that decides the inverter. Eleven of the twelve published US machines in this library are refused on it. The twelfth is not, and what separates it is a published surge rating rather than a larger battery.
Official spec + Derived by WattPairverified 2026-08-01appliance records
Step two: days of autonomy, not hours
A cabin battery is sized by how long you can go without generation, not by peak power. Multiply your daily watt-hour total by the number of consecutive poor-sun days you are willing to lose, then divide by the usable fraction of the battery — not by its nameplate. On the record we use as the worked example throughout this site, BLUETTI publishes both coefficients, so the usable figure is derivable; for most builds we have found neither, and their pages here print no runtimes at all for that reason.
Step three: the biggest thing you switch on
The load that decides the inverter
A live run of a well pump against two of the largest portable machines in this library — one that is refused and one that is not. What separates them is the specification a shed system with a pump has to shop on.
Refused on the start, not the run: the running draw is about a quarter of continuous output. This record carries no published surge figure, so the engine holds the locked-rotor demand against the continuous rating instead — and the demand is more than twice it.
Show the working →The one machine here that clears the start, and it does so on a published surge ceiling rather than on capacity. It still prints no runtime: this record carries no usable-capacity figure to divide.
Show the working →The exception is more useful than the rule here. The machine that clears the start does it on a published surge rating, not on a bigger battery — so if your building has a submersible pump, surge is the specification to shop on, and for eleven of the twelve the sizing conversation is about an installed system with a motor-rated inverter, a soft starter or a pressure tank arrangement that lets the pump run less often. Lights, communications, refrigeration and tools are a different matter and sit comfortably in the portable class.
A shed is not a balcony
The two most common small-solar questions look similar and are almost opposites. A balcony system is grid-tied, small, and constrained by law and by mounting; a shed system is off-grid, constrained by the worst month of sun and by whatever motor you own, and answers to nobody but the code official. The shed gets to choose its array angle, which is the single largest advantage it has. If your building is grid-connected, most of this page still applies to sizing but the legal chapter of the balcony article applies to you instead.