How many solar panels do I need for a greenhouse?

For fans and water pumps only: 2-4 x 400W panels (800-1,600W). Add supplemental grow lights: 4-6 panels (1,600-2,400W). Add electric heating: 8-15+ panels -- but electric heating from solar PV is usually impractical. Most greenhouse operators use solar for ventilation and pumps, then propane or solar thermal for heating.

Should I put solar panels on the greenhouse roof?

Generally no. Panels on the greenhouse roof block sunlight that your plants need, defeating the purpose of the greenhouse. Mount panels on a ground rack nearby, on the north wall (which receives little direct light anyway), or on an adjacent building. Some growers use semi-transparent solar panels that let partial light through, but these are expensive and reduce both plant light and electrical output.

Can solar panels heat a greenhouse in winter?

PV panels powering an electric heater are very inefficient for greenhouse heating. A 1,500W heater running 12 hours uses 18 kWh -- requiring 12+ panels in winter when sun hours are shortest. Solar thermal collectors (water or air) transfer heat directly with 60-80% efficiency vs PV's 20% electrical efficiency. For greenhouse heating, solar thermal wins over PV + electric heater.

What are the biggest energy loads in a greenhouse?

Heating is by far the largest (50-80% of total energy in cold climates). Next is ventilation fans (10-20%), then supplemental grow lights (10-30% if used), water circulation pumps (5-10%), and controls/sensors (under 5%). In warm climates where heating is minimal, ventilation fans become the dominant load.

Is off-grid or grid-tied solar better for a greenhouse?

Grid-tied is simpler and cheaper if the greenhouse is near a power connection. You avoid battery costs and can draw unlimited power for peak loads. Off-grid makes sense for remote greenhouses, hoop houses in fields, or small operations where running grid power costs more than the solar system. Many greenhouses use a hybrid approach: grid connection for heating and a small off-grid solar system for fans and pumps.

How do I size solar for greenhouse ventilation fans?

A typical greenhouse exhaust fan draws 200-500W. Most greenhouses need 2-4 fans for proper air exchange. At 3 fans running 8 hours/day (1,000W x 8h = 8,000 Wh), you need about 5 x 400W panels at 5 PSH. However, fans run mainly during sunny hours when solar production is highest, making this a good match for direct solar power without battery storage.

Can I run grow lights on solar?

Yes, but it requires significant solar capacity. Modern LED grow lights use 200-600W each. Running two 400W LED grow lights for 12 hours consumes 9.6 kWh/day -- requiring 6 x 400W panels at 5 PSH. The irony: grow lights are needed most in winter when solar production is lowest. For winter supplemental lighting, grid power is often more practical unless you have a large solar array.

How Many Solar Panels For A Greenhouse? (Heating, Fans, And Lighting)

A greenhouse's solar needs depend heavily on what systems you automate. Ventilation fans and water pumps alone need 2-4 x 400W panels. Add supplemental grow lights and you need 4-6 panels. Electric heating pushes the requirement to 8-15+ panels -- but heating a greenhouse with PV-generated electricity is rarely the right approach. Solar thermal collectors or propane heat are far more efficient for that job.

The biggest mistake in greenhouse solar is trying to do everything with PV panels. Solar panels convert sunlight to electricity at roughly 20% efficiency. Then an electric heater converts electricity back to heat at 100% efficiency. The combined path -- sun to electricity to heat -- is about 17% efficient after the PVWatts derate. A solar thermal collector converts sunlight directly to heat at 60-80% efficiency. For heating, solar thermal wins by a wide margin. Use PV for what it does best: running fans, pumps, lights, and controls.

Quick Answer: Panels By Greenhouse Load

Automation level	Daily energy use	400W panels needed	System size
Basic (fans + pump only)	2-4 kWh	2-3	800-1,200W
Moderate (+ sensors, timer, controls)	3-5 kWh	3-4	1,200-1,600W
Full (+ supplemental grow lights)	6-12 kWh	5-8	2,000-3,200W
Full + electric heating	15-30 kWh	Not practical -- use solar thermal or propane	---

These assume 5 peak sun hours and the PVWatts derate of 0.83.

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Solar panel wattage

Type any value 10–750 W. Common sizes: 100 W (portable), 400 W (residential 2026), 580 W (commercial).

Peak sun hours per day

hrs

Don't know your PSH? Find your exact value →
Benchmarks: U.S. avg 4.98 · Phoenix 6.54 (highest) · Seattle 3.95 · Anchorage 3.17 (lowest). Above ~5.5 = sunny · 4.5–5.5 = average · below 4.5 = cloudy.

Daily kWh production

0.00kWh

Based on a 400W panel and 5.32 peak sun hours per day

Daily

1.60kWh

average across the year

Monthly

48kWh

× 30 days

Yearly

583kWh

× 365 days

Monthly production for a 400W panel — US Average

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

kWh per month · Source: NREL PVWatts v8

216 kg

CO₂ avoided per year

0.05

equivalent US homes powered

trees planted equivalent

$93

estimated annual savings

Tap to see sensitivity analysisSensitivity analysis

Sensitivity range
Scenario	Value
Low (-20%)	1.3 kWh
Expected	1.6 kWh
High (+20%)	1.9 kWh

Your daily production scales linearly with both panel wattage and peak sun hours. A 10% change in either input changes your result by 10%.

See production for your state Try the system size calculator

Greenhouse Energy Loads Breakdown

Ventilation and Air Circulation

Proper airflow is critical for preventing disease, controlling humidity, and maintaining temperature. Most greenhouses need exhaust fans, circulation fans, and intake louvers.

Equipment	Watts	Hours/day (summer)	Daily Wh
Exhaust fan (24")	350	8	2,800
Exhaust fan (36")	500	6	3,000
HAF circulation fans (2-4)	200	10	2,000
Intake louver motor	50	4	200
Typical total			3,000-5,000 Wh

The good news: fans run mostly during sunny hours when panels are producing at peak capacity. A direct-drive setup (solar panels powering fans without battery storage) works surprisingly well. When the sun is strong and the greenhouse is hot, both the fans and the panels run at full capacity. When it is cloudy and cool, neither needs to.

Water Pumps and Irrigation

Equipment	Watts	Hours/day	Daily Wh
Drip irrigation pump	100	1	100
NFT/hydroponic circulation pump	50	16	800
Misting system pump	200	0.5	100
Sump/drainage pump	350	0.3	105
Typical total			300-1,000 Wh

Supplemental Grow Lights

Grow lights extend the growing season but consume significant power:

Light type	Watts per fixture	Coverage area	Hours/day (winter)	Daily Wh
LED grow bar (4 ft)	80	16 sq ft	12	960
LED grow panel (high output)	400	25 sq ft	12	4,800
LED grow panel (medium)	200	16 sq ft	12	2,400

A small greenhouse (10x12 ft, 120 sq ft) with full LED supplemental lighting needs roughly 600-800W of grow lights running 12-16 hours/day. That is 7,200-12,800 Wh/day from lights alone -- a significant load that requires 5-8 panels.

Heating (The Dominant Load)

Greenhouse heating dwarfs all other loads combined:

Heater type	Watts	Hours/day (winter)	Daily Wh
Electric space heater (small)	1,500	12	18,000
Electric radiant panel	750	8	6,000
Heat mat for seedlings	100	12	1,200
Heated water mat system	500	8	4,000

A single 1,500W electric heater running 12 hours uses 18 kWh -- which would require about 14 x 400W panels at 5 PSH. In winter, when heating is needed most, peak sun hours drop to 2-3 in northern climates, pushing the requirement to 25+ panels. This is why electric heating from PV is generally impractical for greenhouses.

The Seasonal Sizing Problem

Greenhouses face a fundamental mismatch between solar supply and heating demand:

Season	PSH (northern US)	Heating need	Grow light need	Solar production
Summer	5-7	None	None	High
Spring/Fall	3-5	Moderate	Low	Moderate
Winter	2-3	High	High	Low

In summer, you have abundant solar but minimal loads beyond fans. In winter, you have heavy loads (heating + lights) but minimal solar production. This mismatch means you either massively oversize for winter (expensive and wasteful in summer) or accept that solar covers only a portion of winter needs.

The practical solution: Size your PV system for fans, pumps, and controls (year-round loads). Use propane, natural gas, or solar thermal for heating. Use grid power for winter grow lights if available.

Panel Placement: The Shading Problem

Putting solar panels on a greenhouse roof creates an obvious conflict: panels block the sunlight your plants need. There are several alternatives:

Ground mount (recommended): Place a ground-mounted solar array south of the greenhouse, angled at your latitude. This provides optimal solar production without shading the greenhouse. Requires additional ground space but delivers the best performance.

North wall mounting: The north wall of a greenhouse receives minimal direct sunlight in the Northern Hemisphere. Mounting panels vertically on this wall avoids shading plants. Output is lower than optimal tilt (roughly 60-70% of south-facing ground mount) but requires no additional ground space.

Adjacent structure: Mount panels on a nearby shed, garage, or house roof. Run wiring from the panels to the greenhouse electrical system.

Semi-transparent panels: Specialized agrivoltaic panels let partial light through while generating electricity. These are expensive ($2-4/watt vs $0.80-$1.20 for standard panels) and produce less electricity, but they solve the shading problem for greenhouses where ground space is limited.

Solar Thermal vs PV For Greenhouse Heating

For greenhouse heating specifically, solar thermal collectors are worth serious consideration:

Factor	Solar PV + electric heater	Solar thermal collector
Efficiency (sun to heat)	17% (20% PV x 83% derate)	60-80%
Cost per BTU of heating	Higher	Lower
Complexity	Panels + inverter + heater	Collector + plumbing + tank
Maintenance	Low	Moderate (fluid, pump)
Summer use	Generate electricity	Excess heat (waste or pool heating)
Best for	Everything except heating	Heating specifically

A solar thermal system for greenhouse heating typically uses flat plate or evacuated tube collectors connected to a water storage tank inside the greenhouse. The hot water radiates heat at night, maintaining temperature. This approach heats 3-4x more greenhouse space per dollar compared to PV panels powering an electric heater.

Cost Estimates By System Size

System tier	Components	Cost
Basic fans + pump (off-grid)	2 x 400W panels, 30A MPPT, 100Ah LiFePO4	$1,200-$1,800
Full automation (off-grid)	4 x 400W panels, 40A MPPT, 200Ah LiFePO4, inverter	$2,500-$4,000
Automation + grow lights (grid-tied)	6-8 panels, grid-tie inverter	$4,000-$7,000
Solar thermal heating add-on	2-4 flat plate collectors, tank, pump	$2,000-$5,000

For most hobby greenhouses, the basic or full automation tier covers the essential loads. Let propane or grid power handle the heating, and your solar investment stays reasonable.