Surplus PC fans in greenhouse connected to solar panel

Free Greenhouse Ventilation Via Solar Panel

Greenhouse too hot in summer? Provide much-needed air movement by adding free greenhouse ventilation using computer power supply fans and a solar panel.

Surplus PC fans in greenhouse connected to solar panel

While automatic vent openers in your greenhouse roof can help, adding some kind of supplementary greenhouse ventilation will also help.

Running large fans can get very expensive, both in purchasing the equipment and then the electricity needed to power them.

You can however get free greenhouse ventilation by combining an inexpensive solar panel with surplus computer power supply fans.

And as a bonus you can also add a USB charging plug for your portable devices!

What you will need

The shopping list for this easy DIY greenhouse project is short. In fact other than the solar panel, most of the other supplies could be gotten for next to nothing, which makes this project especially appealing if you are trying to stay on a budget.

Here is the quick list of affiliate links from Amazon for easy shopping. More info after the list if you want to source your own parts locally.

Solar panel

This is the most important purchase. It is best to not cheap out too much on this, as cheap panels may not be that efficient or last a long time. doesn’t have the exact same panel that I have and I always have regretted not getting a slightly larger panel, so I’ve picked out a 100 watt panel with good ratings that comes with the charge controller (if you add batteries later), cabling and even mounting brackets. Here is the link: Renogy 100 Watts 12 Volts Polycrystalline Solar Starter Kit


These fans serve to exhaust hot air out of a computer case and are 12 volt which is what the panel is. They are built to work in a dusty environment.

These might actually be sourced for free from a computer repair shop if you ask nicely. I got mine from discarded PCs at work.

But if you can’t locate them easily for free, they are also available online in a convenient 4-pack: Rosewill 120mm Case Fan 4-Pack

Charging plug (optional)

If you want to also charge your portable devices such as smartphones, tablets and music players, you can add a USB charging adapter such as you will find that plugs into your car’s 12 volt accessory port. I got mine for free once at a technology conference but you can also find them online. Here is a reasonably priced one that also has a handy indicator light to let you know when your panel is producing power: USB Car Charger RAVPower 24W 4.8A Metal Dual Car Adapter

And to make it easy to power both the USB charging plug and greenhouse fans from the same solar panel, ideally you need a Y-adapter: TEZONG Y Splitter 1 to 2 SAE Power Automotive Extension Cable

WARNING: don’t try and charge your devices directly from the solar panel – USB is 5 volts whereas the panel is 12 volts. The adapter above converts 12 volts down to 5 volts safely to avoid frying your expensive electronic devices.


Finally you might need to obtain some wire to hook up the panel to your greenhouse, especially if the panel is far away. For this use standard house cable (Romex is one brand name) as you won’t lose power due to resistance. I happened to have a piece left over from another project and it was long enough. You just need two conductors (wires bundled up) so if your cable has more, just ignore the extra ones. Pick this up at your local hardware store or home centre. You may be able to simply buy it by the foot so you get the right length without too much excess.

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Your installation will likely be different from mine depending on what you are using and where you are installing it. So I’ll explain and show you what I did and then you can adjust to your specific situation.

Just 4 steps (or just 3 if you don’t install a USB charging plug)!

1. Solar Panel

First is to install the solar panel where you will get the maximum sun exposure. Usually this means on top of a roof. While mounting it to your greenhouse roof will keep your wiring short, it could also block much needed sun, especially in winter.

So I installed my panel on top of my deck’s pergola. This is located next to my greenhouse and as a bonus close to my kitchen for the optional USB charging plug.

As my panel had a kickstand, I simply placed the panel on top of the pergola and secured the bottom of the kickstand to the wood framing using some long zip ties.

Solar panel on top of pergola

The solar panel may not survive a hurricane but then we don’t get those here on the West Coast of Canada. If you have extreme weather then you may need to secure your panel better.

You definitely want the panel to face the sun, which means south. You might get away with west-facing, as afternoon is when you need the fans the most. Try it out but be prepared to move the panel if you don’t get enough power from it.

2. Fans

Next step is to install the fans.

You want the fans ideally to pull air from a cooler part of your greenhouse. In my case that was the overhang of my deck which serves as part of the ceiling on the north side of my lean-to greenhouse.

I screwed the fans using their mounting holes to a piece of wood and then that was screwed into place in the greenhouse. I found I had to isolate the fans from the deck framing as there was too much noise and vibration. I did that by adding a piece of foam between the wood the fans are mounted on and the deck framing.

Every installation location will be different so you may need to be creative!

Surplus PC fans in greenhouse connected to solar panel

Excuse the messy wiring – I will clean this up at some point, especially if I add batteries sometime down the road.

3. USB charging plug (optional)

If you are adding this, find a good location close to your panel that you can run a cable to. I picked our kitchen as it has an outside wall next to our patio door, is usually where we charge our devices and has a counter to place our devices on. There is also a regular electrical outlet close by where we can charge normally with a power brick and charging cable.

Drill a hole in your outside wall, thick enough to stick your cable through. Make sure before you drill that there are no electrical cables or water pipes in the wall!

Now drill a hole in your drywall or wall covering on the inside of the house. You will need to enlarge the hole so that it can accept the plug of the USB charging plug (the part that would plugin to the accessory port in your car).

Wire up the plug to a cable and make sure the connection is solid. You might have to use a soldering iron to do this properly, although I was able to attach the wire and tape it in place with electrical tape.

I used some white caulking to glue the plug into place on the inside wall and waiting until it was set. On the outside of the wall I sealed with more caulk to ensure no critters and cold wind could enter the house.

Charging plug in kitchen being fed from solar panel

4. Wiring up

The final step is to wire everything up. Here is a diagram showing all the connections. I haven’t included a connection to a battery as I have yet to add this to the system. And you might not need to as you really don’t need the fans running at nighttime or on very cloudy days. I plan to add another higher wattage solar system for heating and lighting to my greenhouse.

If you don’t have the USB charging plug, it literally is a one-wire connection from the panel to the fans – electrical wiring can’t get easier than this!

wiring diagram between solar panel, usb charging plug and greenhouse fans

I had to do a temporary wiring job where the solar panel connects to the USB charging plug in the kitchen and to the solar panel. I’ll pretty this up at some point with a proper y-adapter for the cable coming from the panel. Here’s one that would work well for this application: TEZONG Y Splitter 1 to 2 SAE Power Automotive Extension Cable

Wiring for solar panel to greenhouse and charging plug inside kitchen

Make sure you secure the wiring out of the way so no one trips over it and it doesn’t get snagged in any way. It is low voltage (12 volt) wiring so doesn’t need any special protection.

You may want to add an electric switch between the panel and the fans – that way you can switch off the fans in winter time when you don’t need them. In my case I just disconnected the one alligator clip that connects the panel to the fans.

Mind you in wintertime you may still want to have some air movement – if your greenhouse is damp inside, the air movement will help avoid mildew and other moisture-related diseases with your plants.

I am very happy with my setup. My greenhouse temperature in the afternoon when it is being blasted by full sunlight has been lower and the air inside seemed fresher and less stagnant. This is a very worthwhile upgrade if you have a greenhouse or sunroom.

If you have any questions about the setup feel free to leave a comment below or you can contact me.

Wishing you all the best with your greenhouse gardening efforts!

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