Save your money! The solar fans usually don't move enough air to control temperature in even a small greenhouse. I have 750 watts, charge controller and inverter to run my swamp cooler here in the Phoenix area (110 summers) and barely break even in input vs. cooling. I can get the 10 by 12 to stay below 90 with lots of shade cloth and misters on at intervals. I have a 10by 12 HF and the solar was an experiment to see how much off grid I could make mine. I still have to heat with propane as I do house plants and tropical foliage that hates it below 55.

With just automatic vents (4) and an automatic misting system My Zone 4-5 10x16 GH seems to stay pretty stable temperature-wise so far. I've seen some high temps on the really hot/sunny days, but keep in mind this is with NO shade cloth and not a single fan of any sort. This is my first year and I am planning on adding fans to move some more air, so I thought I'd see how much supplemental solar I can do.

I've seen on ebay all sorts of small self-contained solar fans for everything from RV's, to attics. I'm curious if they're a total waste of time and money or not. They're all about $30 and pretty small so you'd need more than one.

I also looked at the HF $199 solar fan, but it looks a little complicated and I have not heard much good on here about it.

As far as heat...what if I added a 55-gal BLACK barrel filled w/water in the center of the GH. It heats up during the day and releases heat during the night. Anyone try something like that?

Keep in mind...supplemental is the word here. I know I can't completely heat or cool my GH with solar, but why not take advantage of whatever free BTU's you can get.

You could add a solar chimney to increase the passive ventilation performance,the height between inlet and outlets, vent area and temperature differential are the key things.

Barrels do heat up during the day but tend to dump the bulk of their heat as soon as the temperature drops leaving very little for the rest of the night.

Fuzzy, presuming you have a roof vent, you can affect far more effecient cooling and heating and at the same time, spend very little on electricity by installing an outdoor, wet location rated ceiling fan directly under the vent and benefit from it year round. Important, because heating any GH in winter is easy compared to cooling it in summer.

As the direction of ceiling fan blades can be changed with the flip of a switch, in summer, they can pull the cooler air up from the floor and turn the passive heat exhaust of the vent to active and in winter, with the vent closed and the blade direction reversed, force the warm air that rises up to the ceiling back down to where you and your plants need it.

In winter, when my GH is shut up tight, the 2, 52" 5 blade outdoor ceiling fans mounted at each end of the GH directly below the roof vents operate in opposite directions, creating a circular air flow otherwise difficult to achieve with a space heater. I admit to being a huge "fan" of ceiling fans, but once I discovered what a difference they could make in our home, the leap to the GH was an obvious, but pretty short step. Cheap to buy, cheap to operate and silent. Can't ask for much more.

Water as a heat source: The amount of water you would need to have heated during the day in order to radiate out enough warmth to have much of any impact on night time ambient air temps in your GH would leave you with litle space to use for growing plants.

The only place I can think of where stored water might effectively serve as a heat source would be in the desert, where it's blistering hot during the day, yet quite chilly at night, even in summer. I once met a lady who grew orchards in her Scottsdale AZ GH. She had a water wall in it and for the most part, it did give her just enough heat at night to avoid the need to turn on her supplimental baseboard heater, but the black plastic water bags took up better than half the space in her GH and in deepest winter, she still had to run the heater at night.

I have over 1,000 gallons of water in my GH, all of which is kept heated to an average of 76 - 78 degrees. I had though it might help warm my GH at night or when the outdoor temps drop below freezing, but can't say that it really makes much difference. If all that water wasn't in fact, to house my tropical fish, I wouldn't waste the space otherwise usable for growing plants on it.

So before you spend a cent on solar gadgets keep in mind that INSULATION is the real factor in GH operational heating or cooling costs, so virtually no amount spent on it is wasted, because the better the insulation, the easier and cheaper it is to regulate indoor temps, regardless of the weather.

Thanks..it sounds like the water barrel isn't worth the effort, at least not in a 55-gal size. I'll check out solar chimneys. I'm not too familiar with how that will work in a GH or if they can be purchased or have to be built.

I do plan to add fans, although so far I don't have the clearance, structure necessary below my roof vents or the electrical power necessary to be able to put traditional ceiling fans in the ceiling of my GH. I will put some sort of fans to move the heated and cooled air, but I don't think they'll be ceiling fans in my application. I DO think the idea of a reviersible fan located below the vents is a good idea...I'm just not sure how to do it in my GH yet.

As far as insulation I'm still figuring that out. The north side of my GH is my house, so that side is insulated. I haven't been thrilled about how bubble-wrap will look, perform, or how hard it will be to install and maintain. I'm also not sure how well a pool cover will perform or how awful it will look draped over the roof...or how you'd even do that (do you cover just the roof or the roof and all sides??). I'm really not sure how else I would even insulate...so for now I'm going to see how bad is bad as far as the expense to heat the GH with propane with no insulation. Again it's an experimental year.

At this point I'm just trying to supplement in any way I can, whether with insulation, or solar gadgets.

I'd love to see a solar chimney in use in a GH photo or some explanation of how to create or buy one and how much space it will take up.

Hi Fuzzy
This should give you some ideas
http://en.wikipedia.org/wiki/Solar_chimney

As your gh is on the side of the house, you may be able to ulilise the house wall to support the "chimney" a tall chimney will outperform a short one ;)

Birdwidow
Interesting observation about heated water. I had similar results in a much much milder climate lol.. I have almost 2000 gallons of heated water mainly for the fish and thought I could circulate it for the few hours that heat is necessary. At 45 degrees I could hold the water at 70 and the air at 55 but at 35 the heaters were unable to keep up.
Had to shut the whole system down ,cover the water with bubble wrap and resort back to air heating.
This coming winter I'm stepping up the wattage to 3200
watts from 2400. I suspect that it's not going to work completely but is cheap and easy addition. The warm water is not making near the impact I thought it would gary

Unless I'm missing a heating application, it seems in everything I read the solar chimney is used as a method to move or cool air. Again I'd have to see one in place in a GH to understand. Who sells such a system for a GH?? Is anyone using one??

I built a 650 gallon indoor "water garden" in my HFGH 10x12. Really it's a big tank with a couple of fish.

With the cooler nights (around 40), the greenhouse is staying about 12 degrees warmer than the outside air. I'm not going to heat it this winter, so I'm sure everything will freeze. I'm finding with the open tank, that basically rains in the greenhouse every night since the water is so warm......

Here is a link that might be useful: my greenhouse

Hi Fuzzy
If you consider the first picture in the link above,which uses an underground conduit/pipe in conjunction with the chimney.
In the summer it will help with passive ventilation and cooling which saves you running as many fans. The chimney inlet needs to be high up in the gh where the hottest air is, which also prevents the cool incoming air being drawn out..its near the floor ;)

Over the summer months the soil temperature will rise
and cause the soil cooling effect to diminish. The chimney will continue to passively ventilate though as its driven by the sun.

In the winter you seal the chimney inlet to prevent it drawing heat out of the gh and use the conduit/pipe to route fresh air in as required via a small fan.
The incoming air will be warmed by the soil and your propane heater then only has to raise the air temp by eg: 20F instead of 40F saving you around 50% on your heating cost.
Pipe is cheap and easy to find :)

hex2006 - I'd love to see a picture of a solar chimney in a GH. Can you send a photo of how yours is setup?

Is anyone actually using a solar chimney in their GH?

I'll take that as a no.

Fuzzy, it may be time for you to do a "desired lifestyle & available time to enjoy it" check.

You built a GH for pleasure. Please don't tell us it was to feed your family, because the simple truth is that building and operating a small home GH is far more expensive than simply buying fresh veggies and if you are into all natural, there are plenty of shops around these days to accomodate you. In fact, you could shop exclusively at Whole Foods and still not spend what it costs to build and operate a small home GH.

Ergo: you built it to ENJOY it and unless you are independently wealthy, the TIME available to you to ENJOY it is when you are NOT working to earn the $ it will cost to operate it.

So don't get so wrapped up in gadgets that you end up spending as much if not more TIME messing with the mechanicals than you do puttering with plants.

Perhaps it's my age, but the older one gets, the more one appreciates TIME- The Great Thief.

I thought I made it clear that I was looking for simple turn-key solutions with no mechanical engineering degree required. I also said I was looking for supplemental devices, not a primary source of heat or cooling. Unless I'm missing your point, I think you may have missed mine.

here's some products. I use one of the smart vents. It doesn't make a huge difference in my solar shed (south side and roof glazed), but the nice thing is I can turn it on or off, and with it on, it only works when the sun shines. I'm sure the greenhouse supply sites have more options to look at.
~tom

Here is a link that might be useful: northern tool

Excellent Tom...these are the sort of things I've been looking at. eBay has some cheaper versions but similar concepts.

Don't drink the Kool Aid about solar. If it was cheap and efficient every house would be equipped with it. We could be spending our tax dollars on finding cheap and efficient energy sources rather than going back to the moon or to Mars.

This looks like a very old thread, but I'd like to chime in on the subject. Since the last post, I know that solar panels have come way down on price.

This site has a good price comparison on solar attic fan manufacturers.

I guess the question is, if the payback was marginal at 3x the price, are solar attic fans a good deal today in 2012?

Here is a link that might be useful: Solar Breeze Fan Comparison