Solar Power for a Shed or Workshop

A shed or workshop is the easiest off-grid system to get right, and a good first build. The loads are small, nothing is critical, and if it runs out you simply come back tomorrow. Nobody is left in the dark in February because you got the arithmetic wrong.

It is also the system where people most often buy the wrong inverter.

Why the inverter is the interesting part

Look at the load table above. The circular saw uses barely any energy, because you are cutting for minutes rather than hours. It contributes almost nothing to the daily watt-hour total, which is what sizes the panels and battery.

But it needs an inverter several times larger than everything else combined. A universal motor under load draws far more current starting than running, and an inverter that cannot supply that surge will simply shut down or fail to start the tool at all.

This is the general lesson for outbuildings: the daily energy figure sizes the array and the bank; the worst instantaneous load sizes the inverter. They are different questions with different answers, and a system sized only on the first will disappoint the first time you pick up a saw.

If your workshop will see a table saw, an air compressor, or a welder, price the inverter for those before anything else. It will likely be the largest single cost in the build.

Where the energy actually goes

Lighting dominates, which surprises people who assume the tools do. Four shop lights running three hours is more energy than a saw uses all week.

That makes lighting the first place to economize. Modern LED shop lights draw a fraction of what fluorescent tubes did, and in a workshop you rarely need every fixture on at once. Switching banks separately is a cheap way to cut the largest load on the system.

Three days of autonomy on purpose

The scenario above uses three days rather than the two a cabin would typically get. That is not because a shed matters more. It is because a shed gets used irregularly, often in bursts, and often in winter.

A workshop system that is dead when you walk in on a Saturday morning in January is useless in a way a cabin system that runs slightly short is not. Storage is cheap at this scale, so buying the extra day is easy.

Practical notes for an outbuilding

Mount the array where you can reach it. A shed roof is usually low enough to clear snow from the ground with a brush, which is a real advantage over a house roof.

Watch the cable run from the array. A ground mount twenty feet away at 12 V needs heavier cable than people expect. Run the numbers through the wire gauge calculator before buying wire, and remember it wants the one-way distance.

Keep the batteries inside the building, insulated. A shed is usually unheated, and a bank at freezing delivers meaningfully less than it does at room temperature. If you are using LiFePO4, confirm how it handles charging below freezing.

Fuse at the battery. A small system is not a safe system by default. The bank can still deliver hundreds of amps into a short. See battery safety.

If you want to change any of this

The specification above is computed from the load list, not written by hand. Your workshop will not have exactly these loads, so put your own into the appliance power budget, then feed the daily total into system sizing with the sun hours for your location.

Two inputs move the answer more than anything else: peak sun hours in your worst month, and whether you run a large motor.