A solar powered greenhouse setup uses a small solar panel to run an exhaust fan, while automatic openers handle the vents with no power at all. For most backyard greenhouses, that means one solar exhaust fan sized to your greenhouse volume, an air intake, and wax-cylinder vent openers. You can see the kits we carry in our solar powered greenhouse ventilation collection.
✅ Quick answer
- Size your fan for about one full air change per minute in summer. Fan CFM = length × width × average height.
- A Riga 5 (165 sq ft) needs roughly 1,100 to 1,300 CFM. One Exaco solar fan, rated about 1,000 to 1,500 CFM in sun, is a good match.
- Give the fan an air intake at least 1.25 times the fan's size, low and on the opposite end.
- Automatic vent openers need no panel and no battery. They start opening around 72°F.
- A small fan panel and battery run a fan, not a heater. Plan heat separately.
We are a small, woman-owned greenhouse business in Georgia, and we answer every question personally. Solar fans are one of the add-ons our customers ask about most, usually right after a hot spring week. This guide is the practical setup: what to buy, how to size it and where to put it. If you are still deciding between storing the sun's heat and using solar power, start with our guide to active vs. passive solar greenhouse systems.
What do you need for a solar powered greenhouse?
A working solar powered greenhouse has four parts.
- A solar exhaust fan kit. The panel, fan and thermostat come together. The fan pushes hot, damp air out when the thermostat calls for it.
- An air intake. Air can only leave as fast as fresh air comes in. A louver, side window or open door does this job.
- Automatic vent openers. These open roof windows on warm days with no electricity. They are your first line of cooling.
- Optional backup batteries. They keep the fan running in weak light or after sunset.
💡 Tip: start with the free cooling. Automatic roof vents, an open door and shade on the hottest weeks do a lot. Then add a solar fan to finish the job on still, hot days.
Which solar exhaust fan kits do we carry?
We carry two complete solar exhaust fan kits and a solar-opener louver. Here is how the solar exhaust fan options compare with a standard plug-in fan, using the details on each product page.
| Product | Fan | Power | Included | Approx. price* |
|---|---|---|---|---|
| Exaco Solar Powered Exhaust Fan | 16" brushless, about 1,000-1,500 CFM in sun | ~50W panel, 20' cord | Thermostat, battery case (no batteries) | about $850 |
| MONT Solar Powered Ventilation System | 18" commercial fan | Solar panel with brackets | Louvered cover, thermostat, battery setup guide | about $1,600 |
| RSI 18" Louver with Solar Powered Opener | No fan (air intake) | Self-opening arm | 18" x 18" aluminum louver | about $300 |
| Exaco plug-in exhaust fan (16") | 16" (also 12" and 20") | 110V outlet, 9' cord | Thermostat optional | about $370 (about $470 with thermostat) |
*Prices checked in October 2026. Prices can change and sales may apply, so click the model name to see today's price.
Exaco Solar Powered Exhaust Fan
The Exaco solar exhaust fan is a 16" x 16" fan with a brushless 12-26V DC motor. Its panel is rated about 50 watts and measures 29.5" x 20". The fan's manual rates it at roughly 1,000 to 1,500 CFM, depending on how strong the sun is.
The thermostat can also reverse the airflow, so the fan can pull fresh air in.
MONT Solar Powered Ventilation System
The MONT system steps up to an 18" commercial fan with a five-louver aluminum cover. The fan, louvers and thermostat are made in the USA. Its maker says the panel produces more than twice the power the fan needs at full speed. It carries a 3-year limited warranty and can run from a deep-cycle marine battery when there is no sun.
What size solar greenhouse fan do I need?
Size the fan by the volume of air in your greenhouse. UMass Extension advises fans that give about one full air change per minute in summer. In winter, a quarter of that is enough, and the thermostat handles the difference.
📐 Greenhouse fan CFM formula
Fan CFM = Length × Width × Average height × Air changes per minute
Measure in feet · Average height = halfway between the wall height and the peak · Air changes = 1 for summer, about 0.25 for winter
🧮 Worked example: a Riga 5 in summer
- Floor space from the product page: 165 sq ft (9'8" x 17'6")
- Peak height 7'7". We estimate the arched roof gives an average height of about 6.5 ft
- 165 × 6.5 × 1 = about 1,070 CFM
Cross-check: Greenhouse Management magazine's rule of 7 to 10 CFM per sq ft of floor gives 1,155 to 1,650 CFM. So aim for roughly 1,100 to 1,300 CFM. One Exaco solar fan, rated about 1,000 to 1,500 CFM in sun, covers it. That matches our store's advice of a 16" fan for the Riga 5.
Fan size by greenhouse
Our product pages list these fan sizes for the greenhouses we sell:
- 12" fan: Riga 2, 3 and 4, and Junior Victorian (side panel only).
- 16" fan: Riga 5, Royal Victorian VI34, VI36 and VI46, and the EOS T-shaped 13x13.
- 20" fan: Riga XL 7, 8 and 9.
Larger houses, like a Riga XL, may need two solar fans. Call us and we will run the numbers with you.
How big should the air intake be?
A fan cannot push out more air than it can pull in. UMass Extension says the intake should be at least 1¼ times the fan area.
📐 Air intake formula
Intake area (sq ft) = Fan width × Fan height ÷ 144 × 1.25
Measure the fan in inches · 144 turns square inches into square feet
For a 16" fan: 16 × 16 ÷ 144 × 1.25 = about 2.2 sq ft of intake. The RSI 18" louver is 18" x 18", or 2.25 sq ft, so it just meets the target. Its slats overlap when closed to keep insects out.
An open door or side window also works. The Riga 5's 30" x 72" rear window gives about 15 sq ft.
For Royal and Junior Victorian greenhouses, the louvered window measures 40¼" x 28¾", about 8 sq ft. It costs about $525 when we wrote this (October 2026), or about $625 with its optional automatic opener.
Do automatic vent openers need solar power?
No. A standard automatic opener uses a cylinder filled with a special paraffin oil. When the air warms to about 72°F, the oil expands and the piston pushes the window open, up to about 14". When it cools, a spring pulls the window closed.
- Riga Automatic Window Opener: about $119 (October 2026). Its quick-release arm unhooks in a storm.
- Exaco Janssens Automatic Roof Window Opener: about $101 (October 2026), for Royal and Junior Victorian roof windows.
- MONT Automatic Roof Vent Kit: about $299 (October 2026). It adds a full 48" x 24" roof vent to any MONT greenhouse.
Do you have enough roof vent area?
UMass Extension suggests roof vents equal to about 15 to 20% of the floor area for natural ventilation. The Riga 5 has four 40" x 24" roof windows. That is about 26.7 sq ft, or 16% of its 165 sq ft floor. So it meets the target before you add a fan.
🌿 Our setup tip: let the openers work first. Set the fan's thermostat a few degrees above the point where the openers start, around 72°F. UMass notes that staged cooling like this saves energy.
For more on where vents and fans should go, see our guide to greenhouse vent positioning.
How many solar panels do I need for a greenhouse?
For ventilation, the panel comes with the fan kit, so you need no extra panels. Bigger loads are a different story. A panel makes about its rated watts for each "peak sun hour" it gets. Much of the US gets about 4 peak sun hours or less a day in December, according to NREL solar maps.
📐 Daily solar energy and usable battery
Daily watt-hours = Panel watts × Peak sun hours
Usable battery Wh = Volts × Amp-hours × Usable share
Real output is lower after wiring losses and dirt · Usable share is about 50% for lead-acid and 80% or more for lithium (LiFePO4)
🧮 Worked example: the Exaco solar fan kit in winter
- Panel: 50 W × 4 peak sun hours = at most about 200 Wh a day
- Backup: the fan manual calls for two 12V batteries rated about 7 to 10 amp-hours each
- 2 × 12V × 10 Ah = 240 Wh. At a 50% usable share, that is about 120 Wh you can draw
That is plenty to keep a fan going through cloudy spells. Now compare a 1,500-watt heater: it would drain those 120 Wh in under 5 minutes. This is why a fan kit can't run a heater.
What can an off-grid greenhouse run on solar?
- Good fit: exhaust and circulation fans, small sensors and thermometers, and small LED lights for short periods.
- Possible with a bigger system: pumps and grow lights. Multiply each label's watts by its daily hours, then size the panel and battery to match.
- Not practical: electric heaters. For heat, read our guide to the cost to heat a greenhouse and our tips on heating a greenhouse without electricity.
📌 About prices: manufacturers update their prices during the year, and we often run sales and promotions. The price on the product page is always the current one. Prices in this article are a guide from when we wrote it (October 2026), not a quote or guarantee. Found a lower price for the same model at an authorized retailer? We offer a Price Match Guarantee - please check the rules first. Call us and we will confirm today's price and any current deals.
How do I install a solar exhaust fan in my greenhouse?
These steps follow the Exaco fan manual and UMass Extension advice. Always read your kit's instructions first.
- Pick the fan spot. Put the fan high on the end wall opposite the door, since hot air collects up top. The manual says the mount must safely hold at least 35 lbs.
- Plan the intake. Place it low on the far end, so fresh air sweeps across the plants on its way to the fan.
- Mind the wind. UMass notes a fan blowing into the summer wind loses 10% or more of its output. Exhaust downwind if you can.
- Make the opening. In polycarbonate, cut the panel to fit the fan. Glass can't be cut, so swap one pane for a Lexan panel.
- Mount the solar panel. Use the roof or a pole in full sun, within reach of the 20' cord. Face it south and tilt it about the same angle as your latitude.
- Wire it last. The manual says not to connect the panel during assembly. Add batteries, then connect.
- Set the thermostat and airflow direction. Put a thermometer at plant height in the middle of the house to check it.
⚠️ Glass greenhouses: never try to cut a glass pane for a fan. It will shatter. For Exaco Victorian greenhouses, we can supply and cut a Lexan panel to fit the gable end. Just ask when you order.
How do I keep a solar greenhouse fan running well?
- Wipe dust, pollen and bird droppings off the panel each season.
- Check wiring and the battery case for damp or loose connections each spring.
Need cooling ideas for the hottest weeks too? See our four ways to cool a greenhouse without electricity.
Is solar or plug-in ventilation better for my greenhouse?
Choose a plug-in fan if you already have a safe, weatherproof outlet in the greenhouse. It costs less up front, and our 16" model runs at full speed whatever the weather.
Choose solar if the greenhouse is far from power. A solar fan works hardest on bright days, when a greenhouse overheats, keeps going in a power outage and adds nothing to your electric bill.
We offer free shipping to the continental US and optional assembly crews. Browse every option in our solar powered greenhouse fans and vent kits.
Frequently asked questions
Can you run a solar powered greenhouse completely off-grid?
Yes, for ventilation. A solar fan kit plus automatic vent openers keeps a greenhouse cool with no power line. Heating is the exception, since heaters need far more power than a small panel and battery can supply.
What size solar exhaust fan do I need for my greenhouse?
Multiply length × width × average height to get the CFM for one air change per minute. A Riga 5 needs about 1,100 to 1,300 CFM, which one Exaco solar fan covers in good sun. Larger houses may need two fans.
Does a solar greenhouse fan work on cloudy days or at night?
On its own, it slows down in weak light and stops after dark. Add the backup batteries, and the panel charges them so the fan keeps running. Both solar kits we carry can be set up with batteries.
Do automatic vent openers need batteries?
No. Standard openers use a paraffin-filled cylinder that expands as it warms, opening the window around 72°F. A spring closes it again as the air cools.
Planning a solar powered greenhouse?
Tell us your greenhouse model and your yard. We will help you size the fan, intake and vent openers, confirm today's prices and let you know about any current sale.
