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Solar Garage & Workshop Calculator

Select your workshop tools, add EV charging if needed, and get solar panels, battery for surge loads, and payback period for your garage.

Workshop tools
Usage & setup
%
hrs/day
$/kWh
sq ft
Workshop solar sizing
4 × 400W panels — 1.3 kW system
Total installed tool watts4,800 W
Peak demand (simultaneous use)1.9 kW
Daily energy use5.8 kWh/day
Battery for surge loads2.7 kWh recommended
Est. system cost$8,110
Annual savings$273/yr
Payback period29.7 yrs
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How to Use This Calculator

Check the tools in your workshop

Select every power tool you have installed — not just what you use every day, but everything that could run during a typical session. The calculator uses each tool's actual running wattage (note: start-up surge for motors is 2-3x running watts, which affects inverter sizing separately). Don't forget shop lights — they're always on and add up.

Set simultaneous usage percentage

Rarely do all workshop tools run at the same time. A realistic percentage for a solo woodworker is 35-50%: table saw running while the dust collector is on, but the drill press sits idle. A welding shop might run at 60%+ with multiple stations active. This percentage determines your peak demand — the most critical number for inverter sizing.

Account for EV charging if applicable

If you charge an EV in the garage, this significantly increases solar system size. Level 2 (7.7kW) adds more daily kWh than most workshop tools combined. The calculator assumes 2 hours of Level 2 charging or 8 hours of Level 1 per day — adjust your daily hours input if your charging pattern differs significantly.

Note the detached garage flag

A detached garage typically requires a separate electrical sub-panel with its own wiring run from the main panel — typically $1,500-3,500 depending on distance and local labor rates. If you're building a new solar system for a detached garage, this cost should be included in your payback analysis.

The Formula

Total Tool Watts = Sum of all selected tool wattages Peak Demand (kW) = Total Tool Watts × Simultaneous % ÷ 1000 + EV Charger kW Tool Daily kWh = Peak Tool Watts × Daily Hours ÷ 1000 EV Daily kWh = EV Charger Watts × Charging Hours ÷ 1000 Total Daily kWh = Tool Daily kWh + EV Daily kWh System kW = Total Daily kWh ÷ Peak Sun Hours ÷ 0.80 Panels = System kW × 1000 ÷ 400W (round up) Roof Capacity = Roof Area ÷ 18 sq ft/panel Battery kWh = Highest Single Tool Watts × 3 (surge) × 0.5 hr ÷ 1000 System Cost = Panels × $1,120 + Battery kWh × $900 + $1,200 inverter + sub-panel if detached

The battery recommendation is based on surge current handling: induction motors (table saw, welder, air compressor) draw 3-5x their running watts at startup. A pure sine wave inverter handles this, but a battery buffer prevents voltage dip. The recommended battery is sized for one major tool startup cycle plus 30 minutes of buffer — you may want more if you run a welder for extended sessions.

Example

Dave's detached workshop in Denver

Dave has a detached 2-car garage converted into a woodworking shop with a table saw, bandsaw, drill press, dust collector, and shop lights. He works evenings for 3 hours daily and wants to go solar.

ToolsTable saw (1800W), bandsaw (1200W), drill press (750W), dust collector (750W), lights (300W)
Simultaneous use40%
Daily hours3 hrs
LocationDenver, CO (5.5 PSH)

Result

Total tool watts4,800 W
Peak demand (40%)1.9 kW
Daily kWh~5.8 kWh/day
System size4 × 400W panels (1.6 kW)
Battery for surge2.7 kWh recommended
Sub-panel (detached)$2,500
Est. system cost~$8,000
Annual savings~$275/yr
Payback~29 yrs

The honest truth: solar for a part-time hobby workshop has a long payback purely on tool energy. The economics improve dramatically if you add EV charging (10-20x the energy of shop tools), work longer hours, or have high electricity rates. The sub-panel, battery, and inverter for surge loads dominate the cost — consider if a grid-tied system without battery makes more sense for a connected garage.

FAQ

A MIG welder drawing 6kW running continuously is one of the hardest loads for a solar off-grid system to handle. For a 4-hour welding session, you'd need 24 kWh of energy — requiring a large battery bank plus 8-12 panels. The startup surge also requires a pure sine wave inverter rated at minimum 15kW surge capacity. Practically, most welders run a duty cycle of 20-60% (the welder runs, then cools), which cuts the actual energy requirement significantly. For a dedicated welding shop, a grid-tied solar system that reduces bills is far more practical than trying to go fully off-grid.
Size your inverter for peak surge demand, not running watts. Induction motors (table saw, air compressor, drill press) start at 2-3x running watts. For a workshop with a 1,800W table saw, size the inverter for at least 5,400W (1,800 × 3) surge capacity — meaning a 6,000W continuous / 12,000W surge inverter is appropriate for a general woodworking shop. For a welding shop, a 10,000W+ inverter is needed. Always buy more inverter capacity than you think you need — running an inverter near its limit reduces lifespan.
Not necessarily. You can run a sub-feeder from your main house panel to the garage (adding to your home's solar system), or install a separate solar system on the garage roof. The separate system approach has advantages: independent production monitoring, optimized panel angle for the garage roof, and no need to trench wiring to the house. The house-extension approach is cheaper if the trenching distance is short (<50 ft) and your home solar system has capacity to grow. For a detached garage 100+ feet from the house, a dedicated garage solar system often costs less than running a feeder cable.
For attached garages and most detached garages with access to utility power: grid-tied solar is almost always more cost-effective. No battery needed (or just a small backup battery), lower system cost, and net metering credits excess solar back to the grid. Off-grid makes sense only if: (1) utility connection would cost $10,000+ to run, (2) you're in a rural area far from the grid, or (3) you want complete energy independence. Off-grid with heavy loads (welder, air compressor) requires significant battery investment to handle surge and overnight backup.
It depends on your EV's battery size and daily driving. For an average EV driving 30 miles/day at 3.5 miles/kWh: you consume about 8.6 kWh/day. To offset this with solar at 5 PSH: 8.6 ÷ 5 ÷ 0.8 = 2.15 kW of solar — about 6 × 400W panels. If your EV is the main reason for adding garage solar, put all 6 panels on the garage roof before adding workshop tools. EV charging economics are excellent: at $0.15/kWh electricity, 30 miles/day costs ~$1.30/day vs ~$5/day in gas — solar turns that into near-zero fuel cost.

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Size your inverter for peak surge demand and continuous loads.
🚙 EV Solar Charging Calculator
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  title="Solar Garage & Workshop Calculator"></iframe>