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How to set up exhaust fan in greenhouse... on a budget

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Bellyman

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Mar 9, 2022
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I know what I want to accomplish but I think there are multiple ways to get there. I could use some advice in sorting it out.

Goal: Greenhouse exhaust ventilation. What I need to happen, I need to move air when it is hot. It is hot when the sun is shining. It is not hot when the sun is not shining. I have no need to run said fan(s) at night or when it's cloudy, rainy, or overcast. I do have some non-electric ventilation happening as well, it is just not quite enough when the sun is shining brightly.

I currently have a fan that I could install in a few minutes that would draw about 370 watts, a 1/2 hp 120 vac motor. It's a common item in greenhouses and I have one. But... I do not have ac power there.

I could easily come up with some 12 volt fans to move air as well, and they would likely add up to a similar power need, similar wattage, give or take a little. The panels would likely be about 25 feet away from the fan(s) so not a huge distance, but still notable. I do not have the panels yet.

I could use a battery to stabilize voltage for the load but I have no interest in actually running this thing on the battery. If the sun isn't shining sufficiently to power it, I don't need it.

So, it comes down to how to get the job done. I could use some advice on how to make it happen such that I don't have to babysit the system and yet not spend so much I'd just as well have run a new service from the grid. (I could, it's just expensive to make happen where it is located.) Dunno, it might be really simple but it kinda has me stumped.

Thoughts?


Thanks!
 
A few solar panels and a small inverter feeding a thermostatically controlled exhaust fan would do the job (similar concept as an attic fan) but it may not be cost & time effective, if you have access to grid power, unless you just like to experiment and learn.
 
z_zk_z said:
A few solar panels and a small inverter feeding a thermostatically controlled exhaust fan would do the job (similar concept as an attic fan) but it may not be cost & time effective, if you have access to grid power, unless you just like to experiment and learn.
Click to expand...

Grid power would be handy, no doubt. It would also be over $2k before I could get the little dancing power company electrons. Plus, I really would rather not have another electric bill.

It sounds like I might be able to go the AC route with panels, charge controller, and inverter but I'm guessing I'd have to keep the thing awake 24/7 so that it was there first thing in the morning, even if I couldn't be. Might not be a big deal as a small inverter might not draw too much off a battery to keep it going while the thermostat wasn't calling for anything, which it shouldn't be if the sun isn't shining.

What I didn't mention above is that I am already running an inflation fan, a small fan that blows air in between two layers of plastic that cover the high tunnel. It's 30' x 96' so substantial. I have one 60 watt panel, one deep cycle battery, and a small buck converter that keeps the tiny fan happy. (It's a 12 volt fan but when the solar panel is charging the battery, the voltage goes up to around 14.5 volts, and that does NOT make that little fan happy at all. Thus, the buck converter which was cheap, like $10 or $15. The whole setup works flawlessly and I love not having to worry about it during power outages. It'll go about 3 days in total darkness.) Maybe TMI, but just sharing.
 
"The most efficient way to use a solar pump is PV-direct, powering the pump directly off the solar panel, without using batteries. Rather than experiencing losses through storing power in batteries, the water itself is stored in a cistern or tank to be used when needed. It's much easier to store water than power."

Pump or fan what ever.


Many others came up in buying suggestions.
 
Interesting link at Amazon. Same fan as an electric automotive cooling fan and cheaper without the little "Solar" sticker slapped on it.

I've wondered about using something like those. They move a lot of air for not a whole lot of electricity.

Here's a question I have about a setup like this, though. How could you set it so that you wouldn't have it sitting humming for an hour or more a day because there is enough light to make some juice but not actually enough to run the fan? Would it require a timer to cut out the "just after sunrise but not really sunshine happening yet" and the "just before sunset when the sun isn't shining on the panel anymore" but it's still making something. (??) I'm sure there are 12 volt timers that could handle the current required that would take very, very little electricity, and easily piggybacked onto my inflation fan setup.

DC motors do tend to be fairly happy at lower than rated voltages. My inflation fan is happy as a clam running at a regulated 11 volts instead of the rated 12 volts. (I had mentioned above that it was VERY unhappy about 14.5 volts that the battery was seeing when charging. But that fan runs 24/7. Different setup.) I did wonder, though, how DC motors would react to voltages that are radically lower, like when they drop to 5 volts, then 4 volts, then 3 volts, than 2 volts, until it's finally dark and they're not receiving much of anything. (I'll assume moonlight isn't enough to matter.) Is that hard on the motor?

In order to run the fan directly off the panel, though, I would think the voltage of the panel would probably need to be close to what the motor needs. If the panel put out more like 24 volts, it would be entirely possible to put two of these motors in series (or three for 36 volts or four for 48 volts provide the panel wattage is there to run the load), though I don't know if I've heard anyone actually mention that.
 
I did a solar direct to 12 volt fan set up in my garage. It works great, moves a lot of air and , as you said works in conjunction with the sun's intensity. These 12 volt radiator fans are quite inexpensive. Hardwiring them two at a time in parallel to a 65 watt panel worked wonderfully.

 
littleharbor2 said:
Hardwiring them two at a time in parallel to a 65 watt panel worked wonderfully.
Click to expand...

Hmmm... each of them should be pulling about 120 watts so I'd guess they'd be running a good bit slower from just a 65 watt panel. (??) One thing about it, they'd run much quieter.

Interesting.
 
Bellyman said:
Hmmm... each of them should be pulling about 120 watts so I'd guess they'd be running a good bit slower from just a 65 watt panel. (??) One thing about it, they'd run much quieter.

Interesting.
Click to expand...
The motors on those fans are rated at 80 watts. When I connected a single fan to the 65 watt panel the fan was literally screaming, well not quite but spinning so freaking fast I was worried it would burn out in short order. When I paralleled two fans they run very fast in strong sun but will throttle down when clouds start rolling in. You hear a very noticeable speed change as clouds pass by
 
littleharbor2 said:
I did a solar direct to 12 volt fan set up in my garage. It works great, moves a lot of air and , as you said works in conjunction with the sun's intensity. These 12 volt radiator fans are quite inexpensive. Hardwiring them two at a time in parallel to a 65 watt panel worked wonderfully.
Click to expand...

I second this answer.

I know a guy who has done the same for years with a couple car cooling fans in series with a 250w panel. When the sun shines, they spin ... when the sun goes down, they stop. No speed controls, no timers, no nothing extra needed.

The same can apply to pumps as well ... I have a pool pump running off 6 x 250 watt panels in series, driving a 180v treadmill motor. Has been running two and a half years without any drama other than a couple belt replacements. Again, no controls of any type.
 
I'm thinking about retrofitting an old evaporative cooler to cool my inverter. It would involve replacing the 115V fan and water pump with equivalent DC parts, then powering it off my SCC load terminal, which is very programmable.
 
Thank you all for the input, and the actual experience doing what I'm contemplating. It is helpful! It also sounds like it need not be all that expensive, either, which is great!

Yeah, those motors / fans will make some noise. In their automotive applications, pretty much no one cares about that. Engine compartments tend to be rather noisy at highway speeds anyway and automotive cabins are insulated well enough that those noises don't usually become obnoxious. I don't think my plants will care, and I'm not inclined to be offended by noises like that, either.

I'm thinking I need to find the panel(s) first and then build the fan(s) to match since panels come in a rather large range of voltages. I can do this. :)

Thanks, guys! Much appreciated!
 
Bellyman said:
Thank you all for the input, and the actual experience doing what I'm contemplating. It is helpful! It also sounds like it need not be all that expensive, either, which is great!

Yeah, those motors / fans will make some noise. In their automotive applications, pretty much no one cares about that. Engine compartments tend to be rather noisy at highway speeds anyway and automotive cabins are insulated well enough that those noises don't usually become obnoxious. I don't think my plants will care, and I'm not inclined to be offended by noises like that, either.

I'm thinking I need to find the panel(s) first and then build the fan(s) to match since panels come in a rather large range of voltages. I can do this. :)

Thanks, guys! Much appreciated!
Click to expand...
The radiator fans really aren't that loud and IMO in any way offensive sounding I actually like the stereo type sound from the pair of fans. Kind of like a twin engine prop plane.

12 volt panel and 12 volt fans, KISS theory
 
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