Solar power for a shed: a practical sizing and wiring guide

A shed is the smallest realistic solar build, which is why it is also the best one to learn on. Loads are modest, permits are usually not required for a self-contained low-voltage DC system, and mistakes cost a Saturday morning instead of a renovation. This guide walks 3 realistic load tiers, a full bill of materials for each, a wiring schematic, and a plain-English safety section grounded in NEC Article 690. If you want the broader context, see our off-grid kit guide and how solar panels work. For step-up DIY beyond the shed, our DIY solar primer covers what is safe to do yourself.

Start with the load, not the panel

Every shed solar project starts the same way: list what you actually plug in, multiply by hours of use per day, and add a 20% safety margin for wire and inverter losses. That number, in watt-hours per day, sizes the panel and battery. Sourcing a 400 W kit because it was on sale and then discovering it cannot run your mini fridge through a 3-day cloud is the classic shed mistake.

The three realistic tiers

Those load lists sort almost every shed into 3 tiers. Below are the panel, battery, and inverter sizes for each, with the bill of materials.

Bill of materials, all three tiers

Those panel-and-battery numbers are the headline cost. The balance of system below — wire, fuses, mounts, conduit — is what most shed builders under-budget.

Wiring schematic and how it flows

That bill of materials wires up the same way regardless of tier: panel → charge controller → battery → loads (and/or inverter → AC loads). The fuse on the battery is the single most important component for fire safety; if you skip exactly one part of this list, do not let it be that.

Safety: NEC Article 690 in plain English

That schematic only works if the grounding does. NEC Article 690 governs all PV installations in the US. The headline rules below apply to any shed system with panels over a few amps; tiny single-panel lighting kits fall under accessory-use exceptions in many jurisdictions, but the safe defaults are the same.

Permits, codes, and when to call an electrician

That NEC language sounds heavier than the reality. Most US jurisdictions do not require a permit for a low-voltage, battery-only DC system that does not interconnect with the house or grid. The line gets crossed when you (a) run AC wiring from the inverter into fixed shed outlets, (b) tie the shed’s electrical back to the house, or (c) install over a certain DC voltage threshold. Below is the rough rule of thumb; check your local AHJ before you swipe the card.

Winter and the real-world derate

Once the wiring and permits are clean, the last variable is winter. A 200 W panel in Phoenix produces very differently from a 200 W panel in Maine in January. Use winter peak sun hours, not annual average, to size — 3.5 hours is a fair Mountain-West winter benchmark, 2 hours is realistic for the Pacific Northwest and northeast. Undersize for winter and you will be cold-cycling a lead-acid battery into an early grave.

The takeaway

That seasonality is the last design lever. A shed is the cheapest, lowest-risk place to learn solar: pick the load tier, source matched components, fuse the battery, ground to NEC, and check your winter peak sun hours. 3 tiers cover almost every real shed — LED-only on 30 W, lights and tools on 200 W, fridge included on 400 W — and the safety rules are the same at every size. Build it right and the same playbook scales to a cabin, a workshop, or an off-grid home.