Off-grid by project · Workshops
Off-grid workshop solar: sizing for power tools, surge and batteries
A workshop uses less energy than you'd think. What it needs is an inverter strong enough to start a table saw or compressor without tripping.
At a glance
Tools are an inverter problem, not a battery problem
A table saw might run for 15 minutes in a day, so it barely touches the battery. But when its motor starts, it can briefly draw two to three times its running watts. If the inverter can't deliver that surge, it shuts off or the tool bogs down. That's why workshop systems often have a small battery and a large inverter.
Typical values from the appliance wattage chart. Startup varies by model; check the nameplate amps or the manual.
Two example workshops
These use 400 W panels and the same sizing math as the off-grid planner. Battery sizes are shown for one and two days, since most shops can skip a cloudy day.
Hobby workshop: 2.05 kWh a day
Lights, a fan, a cordless tool charger, a corded drill, a circular saw and a shop vacuum.
| Season | 400 W panels | Battery (1 day) | Battery (2 days) |
|---|---|---|---|
| 5 sun hours (summer) | 2 (0.8 kW) | 3.08 kWh | 6.15 kWh |
| 2.5 sun hours (winter) | 4 (1.6 kW) | 3.08 kWh | 6.15 kWh |
Inverter: the worst realistic moment is the circular saw with the shop vacuum collecting dust, plus lights and a fan. That's 2,560 W running, so plan about 3,200 W continuous and 3,560 W surge.
Woodworking shop: 3.1 kWh a day
Adds a 15 A table saw and a portable air compressor.
| Season | 400 W panels | Battery (1 day) | Battery (2 days) |
|---|---|---|---|
| 5 sun hours (summer) | 3 (1.2 kW) | 4.65 kWh | 9.3 kWh |
| 2.5 sun hours (winter) | 5 (2.0 kW) | 4.65 kWh | 9.3 kWh |
Inverter: the worst realistic moment is the table saw and shop vacuum running while the compressor kicks on, plus lights and a fan. That's 4,160 W running, so plan about 5,200 W continuous and 6,860 W surge.
Run one big tool at a time and the woodworking shop's inverter shrinks. Fill the compressor tank before you start sawing, and the table saw, shop vacuum, lights and fan need about 3,700 W continuous and 5,660 W surge instead of 6,860 W.
Size your own workshop system
- Daily use
- 2.05 kWh
- Battery (1 day)
- 3.08 kWh
- Inverter
- 4,075 W
- Startup surge
- 4,260 W
Uses the same math as the off-grid planner at 4 peak sun hours. A planning estimate, not a design.
The calculator's inverter figure assumes every selected tool runs at once. If you run one big tool at a time, size the real inverter from that, as in the examples above.
How a workshop system fits together
- Roof or ground arrayShop roofs are often unshaded
- Charge controllerOften built into the inverter
- 24V or 48V batteryAway from dust and fumes
- Inverter/chargerSized for motor surge
- Shop panel and outletsWired by an electrician
A generator can plug into the inverter/charger as a backup input. Fuses or breakers sit between the array and controller and between the battery and inverter.
Ways to cut the surge
- Buy tools with soft start. Many newer table saws, routers and miter saws ramp up gently and draw far less at startup.
- Choose an inverter that handles motors. Low-frequency inverters with a heavy transformer usually deliver more surge, for longer, than high-frequency models with the same rating. Check the surge spec and how many seconds it lasts. See inverter sizing.
- Stagger the big loads. Let the compressor fill its tank before you start the saw, and don't start two motors at the same moment.
- Go cordless where you can. Battery tools move the load to a charger that draws about 100 W and can run while the sun is out.
- Use 24V or 48V. A 4,000 W surge pulls over 300 amps from a 12V battery. Higher voltage keeps current and cable size down.
Work with the sun
- Use the big tools at midday. When the panels are producing, they power the tools directly and the battery only covers the gaps.
- Charge tool batteries in the afternoon rather than overnight.
- Watch the always-on loads. A dehumidifier or space heater uses far more energy in a day than every tool combined. Try them in the calculator. Use wood or propane for shop heat.
- Plan for winter if you work year-round. Shorter days can double the panels you need. See off-grid solar in winter.
Dust, fumes and 240V tools
- Keep electronics away from sawdust. Fine dust clogs inverter and charger cooling fans and can cause overheating. Put the equipment in a separate closet or enclosure with filtered air.
- Keep batteries away from heat and fumes. Don't install them near welding, grinding sparks or solvent storage, and keep lithium batteries above about 32°F (0°C) for charging.
- 240V tools need split-phase output. Larger table saws, dust collectors, welders and compressors often run on 240V. You need a 120/240V split-phase inverter or a stacked pair, and the wiring is a job for an electrician.
Permits and professional help
A power station or plug-in kit for a few tools rarely needs a permit. A detached shop wired with its own panel needs proper grounding and overcurrent protection, and most counties require a permit and inspection. Running power from the house to the shop means trenching and service work for a licensed electrician. Plan the system yourself, then have a professional review it before you buy. The DIY vs. professional guide breaks down who does what.
FAQ
Can you run a workshop on solar?
Yes. Power tools use little energy because they run in short bursts: a hobby shop uses about 2.05 kWh a day and a woodworking shop about 3.1 kWh. The hard part is the inverter, which has to start motors like a table saw that surge to 4,500 W or more.
What size inverter do I need for a table saw?
A 15 A table saw runs at about 1,800 W but can surge to 4,500 W. With lights, a fan and a shop vacuum running too, plan about 3,700 W continuous and 5,660 W surge. A low-frequency inverter handles motor starts better than most high-frequency models of the same rating.
How much battery does a workshop need?
Less than a home. Most shops are used in the daytime, when the panels can power tools directly, and you can skip work on a cloudy day. One day of storage is often enough; add a second if you rely on the shop.
Can I run 240V tools off-grid?
Yes, with a split-phase (120/240V) inverter or two stacked inverters. Many 120V-only inverters can't run a 240V table saw, dust collector or welder at all, so check this before you buy.
Do I need a permit for solar on a detached shop?
Usually, if the system is wired into the building. A detached shop with its own system still needs proper grounding, overcurrent protection, and in most counties a permit and inspection. Trenching power from the house is a job for a licensed electrician.