Solar is genuinely useful in a greenhouse, just not for the job most people search for. It will open vents, run a fan and water your plants while you are away, all for less than £60 and with no cable from the house. What it will not do is heat a greenhouse through a British winter, and the "solar greenhouse heaters" on Amazon are the clearest example of a product that cannot do what its name suggests.
What solar does well in a greenhouse
The things worth doing share one feature - they are needed most when the sun is out. A greenhouse overheats on a bright day, plants dry out on a bright day, and a fan is most useful on a bright day. That neat overlap between supply and demand is why these products work.
| Job | Needs power when | Solar fit | Typical cost |
|---|---|---|---|
| Opening roof vents | Hot, sunny days | Excellent - no electricity at all | ~£20-£25 |
| Extractor fan | Hot, sunny days | Good | ~£24-£60 |
| Drip watering | Dry, sunny spells | Good | ~£22-£33 |
| Lighting | Winter evenings | Fine for short use | ~£17-£32 |
| Frost-protection heating | Cold, dark winter nights | Does not work | — |
Why solar greenhouse heaters do not work
Search Amazon for a solar greenhouse heater and you will find kits built around a panel of about 20 to 30 watts. At best - in full summer sun, pointed straight at it - a 30W panel produces 30 watts. A small electric fan heater for frost protection in a typical 6x8 greenhouse is usually rated at 1 to 2 kilowatts, so the panel is providing something like one-fiftieth of the heat, and it provides it at midday, when the greenhouse is already the warmest it will be all day.
At night, when frost actually happens, the panel produces nothing. Storing enough daytime energy in a battery to heat a greenhouse overnight would take a battery bank costing hundreds of pounds and a panel array bigger than the greenhouse roof. The listings we found for these heaters mostly carry low ratings from a handful of buyers, which is what you would expect. Our advice is not to buy one.
Ventilation - the best "solar" buy of all
Overheating kills more greenhouse plants in the UK than cold does, and the fix uses the sun directly with no electronics at all. An automatic vent opener has a cylinder filled with wax that expands as it warms, pushing the roof vent open from roughly 17C and closing it again as the greenhouse cools. They cost about £22, need no wiring or batteries, and fit most aluminium greenhouses.
A solar extractor fan is the next step for a greenhouse that still bakes, or one without enough roof vents. The simplest kits run the fan straight off a 12W panel, so the fan runs faster the brighter it gets - which is exactly when you want it. Versions with a battery and thermostat cost more and run into the evening, but are rated lower by buyers, so we would start with a direct-drive kit. Our solar extractor fan guide compares the types and explains how to fit one.
Automatic watering while you are away
A solar drip irrigation kit is a small pump powered by a panel, with a timer and a set of drippers you push into each pot. You drop the pump into a water butt or a bucket, set it to water once or twice a day, and it takes care of the holiday fortnight. Kits for 10 to 20 pots cost £22 to £33. Check the hose length against the distance from your water butt, and remember the pump needs to sit in the water, so the butt has to be kept topped up.
Keeping frost out, honestly
If you need frost protection, the options that actually work are, in order of cost:
- Bubble insulation fixed to the inside of the glass, which cuts heat loss through the glazing substantially and costs about £22 for a 10m roll
- A max/min thermometer, so you know how cold it actually gets rather than guessing - often it is warmer than you think
- Horticultural fleece over tender plants on the coldest nights
- A paraffin or mains electric heater for anything that needs a guaranteed minimum temperature
If you already have an off-grid battery system for a shed or garden office, it still will not run a heater overnight - see our garden office guide for why heating loads are the hardest thing to put on solar.
Recommended kit
Everything below was in stock on Amazon UK when this guide was written.
Bayliss XL Autovent automatic window opener
The most-reviewed greenhouse vent opener on Amazon UK, with over 4,000 ratings averaging 4.4 stars. It uses the sun directly, needs no panel or battery, and stops the midsummer cook-off that kills more seedlings than frost. If you buy one thing from this page, make it this.
amazon Check Price on Amazon →Automatic greenhouse window opener, 7kg lift
A strong alternative with a 7kg lifting force for heavier vents, rated 4.6 stars from around 1,700 reviews. Worth having one per roof vent - a greenhouse with two vents open stays far cooler than one with a single vent.
amazon Check Price on Amazon →12W solar panel fan kit
The simplest solar fan there is - the panel drives the fan directly, so it speeds up as the day gets hotter and stops at dusk. No battery to wear out. Rated 4.1 stars from about 600 reviews. The same kit suits a chicken coop or a shed.
amazon Check Price on Amazon →Mcbazel solar drip irrigation kit
A small solar pump with a timer and drippers for ten pots, rated 4.6 stars from 64 reviews. For bigger greenhouses, the Forever Speed kit (~£33) has a 15m hose and a digital display.
amazon Check Price on Amazon →Digital max/min greenhouse thermometer
Before spending anything on heating, find out how cold your greenhouse actually gets overnight. Rated 4.5 stars from over 3,600 reviews.
amazon Check Price on Amazon →Elixir Gardens greenhouse bubble insulation, 1.5m x 10m
Insulation does more for winter temperatures than any solar product can, and costs about the same as a solar heater that does nothing. Rated 4.3 stars from 166 reviews.
amazon Check Price on Amazon →Summary
- Solar suits greenhouse jobs that happen when the sun is out - venting, fans and watering
- An automatic vent opener (~£22) uses the sun directly and needs no electricity at all
- Solar heaters do not work. A 30W panel against a 1-2kW heating need, and nothing at night
- A direct-drive solar fan is simpler and more reliable than battery versions
- A solar drip kit from a water butt covers a fortnight away for about £22
- For frost, use insulation, fleece and a proper heater - and a thermometer to know when
If you are powering an allotment rather than a garden greenhouse, our allotment solar guide covers lighting, tool charging and what a plot-sized system can run. For lighting inside a greenhouse or shed, see our guide to solar shed lights.
Frequently Asked Questions
Can a solar panel heat a greenhouse in winter?
No. The solar heater kits on sale use panels of 20 to 30 watts, while frost protection for a small greenhouse typically needs a heater of 1 to 2 kilowatts. The panel also produces nothing at night, which is when frost happens. Insulation and a paraffin or mains heater are the realistic options.
Do automatic greenhouse vent openers need electricity?
No. They use a wax-filled cylinder that expands as it warms and pushes the vent open, then closes it as the greenhouse cools. They are solar powered in the most literal sense and have nothing to wire up or charge.
Is a solar greenhouse fan worth it?
Yes, if your greenhouse still overheats with the vents open. A direct-drive fan runs faster as the sun gets stronger, which matches when you need it. Versions with batteries and thermostats cost more and tend to be less reliable.
Will a solar drip irrigation kit work while I am on holiday?
For a week or two, yes, as long as the pump sits in a water butt or container large enough to last. Check the hose reaches, set the timer before you go, and test it for a few days first.
Can I light a greenhouse with solar?
For short use on winter evenings, yes. A solar shed light with a small panel gives enough light for half an hour of potting. For longer use you need a proper panel and battery kit.