A grow room is one of the most power-intensive loads you can put on a solar system. Lights alone can draw 1,500–5,000 watts for 12–18 hours per day, and that's before you add fans, dehumidifiers, AC units, and pumps. Solar can absolutely run a grow room — but only if the system is sized correctly from the start. An undersized system means midnight shutdowns and dead plants. An oversized system wastes thousands of dollars.
This guide walks through the math so you can spec your system with confidence.
Step 1: Calculate Your Total Daily Load
Start by listing every electrical device in your grow room and its wattage. Multiply each device's wattage by the hours it runs per day to get watt-hours (Wh). Sum everything for your total daily load.
Example for a vented 10×10 flower room:
4× LED grow lights at 600W each = 2,400W × 12 hrs = 28,800 Wh
1× inline fan at 150W = 150W × 24 hrs = 3,600 Wh
1× circulation fan at 60W = 60W × 24 hrs = 1,440 Wh
1× dehumidifier at 300W = 300W × 12 hrs = 3,600 Wh
1× water pump at 50W = 50W × 1 hr = 50 Wh
Miscellaneous (controllers, timers, sensors) = 50W × 24 hrs = 1,200 Wh
Total daily load: 38,690 Wh, or approximately 38.7 kWh per day.
That's a substantial load. For context, the average US home uses about 30 kWh per day total. A serious grow room can easily match or exceed your entire household draw.
Add a 20–25% efficiency buffer to account for inverter losses, wiring resistance, and battery charge/discharge inefficiency:
38.7 kWh × 1.25 = 48.4 kWh adjusted daily load.
Step 2: Determine Your Battery Bank Size
Your battery bank must store enough energy to power the grow room through the night and any low-sun periods. For grow rooms, size for at least 1–2 days of autonomy — meaning the system can run without any solar input for 1–2 full days.
Using our example with 1 day of autonomy:
38,690 Wh needed
LiFePO4 batteries (the correct chemistry for this application) can be safely discharged to 80–90% depth. Using 80% DoD (depth of discharge):
38,690 ÷ 0.80 = 48,363 Wh of battery capacity needed
In practical terms, that's approximately:
2× 24kWh LiFePO4 battery systems (e.g., EcoFlow DELTA Pro Ultra, BLUETTI EP900)
Or a custom 48V bank built from individual 100Ah or 200Ah LiFePO4 cells
Why LiFePO4? LiFePO4 (lithium iron phosphate) is the only battery chemistry worth using for a grow room application. It handles deep daily cycling without degradation, has a 10+ year lifespan, is thermally stable (no thermal runaway), and maintains voltage under heavy load. Lead-acid batteries degrade rapidly under daily deep cycling and are a false economy.
Step 3: Size Your Solar Array
Solar panel sizing depends on your location's peak sun hours — the average hours per day that solar irradiance reaches 1,000 W/m². This varies significantly by region and season.
Peak sun hours by location (annual average):
Philadelphia / Mid-Atlantic: 4.0–4.5 hours summer, 2.5–3.5 hours winter
Southwest US (Phoenix, Las Vegas): 6.0–7.0 hours year-round
Pacific Northwest (Seattle): 3.5–4.5 hours summer, 1.5–2.5 hours winter
Southeast (Atlanta, Miami): 4.5–5.5 hours year-round
Formula: Required panel capacity (W) = Adjusted daily load (Wh) ÷ peak sun hours
For our Philadelphia example in summer (4.5 peak sun hours):
48,400 Wh ÷ 4.5 hrs = 10,756W of panel capacity
For winter (3.0 peak sun hours):
48,400 Wh ÷ 3.0 hrs = 16,133W of panel capacity
This is why grow rooms are challenging for off-grid solar in northern climates: winter light reduction is severe, and the grow room load doesn't decrease with the seasons. A system sized for year-round operation in Philadelphia needs roughly 15–18 kW of panels to reliably charge the battery bank through winter.
In practical terms for our example:
Summer-only or southern US operation: 12–14 panels at 400W each (4.8–5.6 kW)
Year-round operation in Mid-Atlantic/Northeast: 35–45 panels at 400W each (14–18 kW)
Step 4: Inverter Sizing
Your inverter must handle both continuous load and surge load. Grow room equipment — especially fans, pumps, and dehumidifiers — draws 3–6× rated wattage for a brief period at startup.
Continuous rating: Must exceed your maximum simultaneous load. In our example, lights + fans + dehumidifier running simultaneously = ~3,000W. Size for at least 4,000–5,000W continuous.
Surge rating: Should be 2× the continuous rating minimum. A 5,000W continuous inverter with a 10,000W surge handles most startup conditions.
For large grow operations, a 48V system with a 6,000–10,000W inverter/charger (Victron Quattro, Schneider XW+, or Growatt SPF series) is the standard.
Step 5: Charge Controller
MPPT (Maximum Power Point Tracking) charge controllers are required for any serious solar installation. They extract 20–30% more energy from panels than PWM controllers under real-world conditions.
Size your MPPT controller for your panel array voltage and current. Most large systems use multiple controllers in parallel or a single high-amperage unit (Victron SmartSolar, EPEver Tracer, Renogy Rover series).
For our 15 kW array at 48V: 15,000W ÷ 48V = 312A of charge controller capacity needed. That typically means 3–4 controllers at 80–100A each, wired in parallel.
Practical Scenarios
Scenario 1: Off-grid small herb/lettuce room (400W LED, 18 hrs light)
Daily load: ~9 kWh
Battery: 15 kWh LiFePO4 (e.g., EcoFlow DELTA Pro + extra battery)
Panels: 3–4 × 400W panels
Inverter: 2,000W continuous
Feasibility: Very practical even in northern climates.
Scenario 2: Off-grid 4×8 vented flower room (1,200W LED, 12 hrs)
Daily load: ~18–22 kWh
Battery: 28–30 kWh LiFePO4
Panels: 8–12 × 400W panels (southern US) or 18–24 (northern US year-round)
Inverter: 3,000–4,000W continuous
Feasibility: Practical in southern US. Challenging but achievable in Northeast with proper winter sizing.
Scenario 3: Off-grid 10×10 serious flower room (2,400W LED)
Daily load: ~38–48 kWh
Battery: 50+ kWh LiFePO4
Panels: 15–20 kW of panels
Inverter: 6,000–10,000W continuous
Feasibility: Viable in southern US with significant investment ($30,000–$60,000+ installed). In northern climates, a grid-tied battery backup hybrid is more practical than true off-grid.
Grid-Tied vs. Off-Grid
For most growers, a grid-tied system with battery backup is more practical than true off-grid. Grid-tied systems:
Are significantly less expensive (no need to size for winter solar minimums)
Earn net metering credits when the grow room isn't running
Provide grid backup when solar production is insufficient
Can be sized much smaller because the grid fills the gaps
True off-grid makes sense for remote properties without grid access, or for growers who want complete energy independence. For urban and suburban growers, grid-tied with a battery bank for outage protection is usually the right call.
Use Our Solar Sizing Tool
The calculations above give you the framework, but every grow room is different. Use the Verdure Solar Sizing Tool to input your specific equipment list, location, and hours of operation and get a customized panel, battery, and inverter recommendation in seconds. It handles the peak sun hour lookup and efficiency calculations automatically.
The tool is free and doesn't require an account — just your wattage numbers and zip code.