Try using a 12v system in your greenhouse and buying a couple of marine batteries..

(deep cycle)

You get power in there on cloudy days and you also get fit carrying them!

My experience with solar fans has been dissapointing . The fan sold under the "fantastic fan" name used for RV vents has the most air movement for the money but they aren't cheap. The other fans that run on a solar panel of 5-8 watts barely move much air in my 10 by 12 with barely any movement of the free swinging vents. If you do try, put inlet vents as close to the floor as possible and outlets up high.

You will need 50-100 watts to do any meaningful air movement.
If I have that much solar panel wattage, I would much rather store it and use it to power Fl. lights for the house at night.

Just MHO.

dcarch

I like Chris's idea but you'd need a DC fan or exhaust to get the best efficiency out of the power source. Problem is, I haven't seen any except expensive ones.
~tom

"I like Chris's idea but you'd need a DC fan or exhaust to get the best efficiency out of the power source. Problem is, I haven't seen any except expensive ones.
~tom"

You can get very good DC fans cheap. The best is computer type brushless DC fans. Very quiet, long lasting, extremely effficient. 6 volts to 48 Volts.

eBay "cooling fan".

dcarch

great idea dcarch. I was looking for bigger, more cfm ones, but you are right. very efficient little blowers. they would fit nicely in some duct work with a little imagination also.
~tom

Just bought three. You will need to come up with 48VDC power.

dcarch

http://www.allelectronics.com/cgi-bin/item/CF-320/search/48VDC_120MM_COOLING_FAN_.html
48VDC 120MM COOLING FAN
Minebea Electric, NMB Model 4710NL-07W-B69. 48 Vdc, 0.20A DC brushless cooling fan. 120mm x 120mm x 26mm (4.7" x 4.7" x 1").
Your Price: $1.75 each

how may of these fans will it take to move 1500 cubic feet of air a minute? Is cooling a need or just circulation to keep mold from forming?

According to some posts related to these fans, each produces 102.7 cfm. For 1500 cfm you would need 14.6. You may need both air circulation fans and exhaust fans, depending on the max. temps your plants (and you) can tolerate. With one complete air exchange per minute, the GH will be at least 8 degrees warmer than outside without other measures- i.e. shade, mist, etc. At 0.5 air exchanges, the expected temp. rise is 15 deg. At 0.25 air exchanges, +25 deg.

These fans are not big air movers.
I am suggesting them only for those of you who really want to use solar power.

dcarch

dcarch,
I have two similar fans, and a solar panel just big enough to power them. They produce enough air movement to improve the microclimate around my six gh tomato plants, with no fungal problems after several years.

FB- A quick check of solar attic fans, 1275 cfm, about $500 complete. With a little imagination and duct work, it should be possible to fit one of these to your vertical requirements. Comparing this to all the needed parts and supplies for a home-made system of equal output would be interesting. Let us know. CR

For the same size, you get the most powerful blowing action using car radiator 12v fans. from 3,000 to 5,000 cfm.

some of them are reversible.

dcarch

dcarch,
3-5000 cfm should be enough for most of us hobby sized growers. Approximately how much would it cost for the solar panels, converters, etc to power a car radiator fan for greenhouse use? My little 350 cfm 120 v. fan cost $90, plus of course the electricity to run it, and the wiring costs, and ... But, I work in places with no electricity possible and would really like to know what you think the complete solar cost would be for the car radiator fan. CR

Roughly:

Fan - $80
solar panel - $1,500
regulator/charger - $150
Batteries - $400

dcarch

*smiling*

""solar panel - $1,500 ""

Hence my idea of trucking out a fresh charged battery every morning!

I was doing that for my inflation blower before a shingle pierced the outer covering.

One 17Ah battery lasted 3 days....

dcarch,
Thanks very much. About $2000 for a solar ventilation system that would work for a 700 sq. ft. greenhouse, at one air exchange per minute, sounds like a good option if electricity is not available. That should be about 12 ft x 60 ft, if I figured it correctly. (does "dcarch" have anything to do with DC power??)
I would like to discuss this with you further if you have time. Please email me, my address is connected with my cuestaroble link here on gardenweb. CR

"I would like to discuss this with you further if you have time."
No problem discussing the topic in this forum to get different views.
Batteries:
Ideally you need deep cycle type batteries.
Cheap way; All old car batteries have still planty of cranking power left to drive fans. get them in you local garages for free.

dcarch

Let me preface the following by saying I am an amateur at solar and I am a mechanical engineer that thinks that if you hold a wire down all the volts run out!

I am in the process of converting my HFGH (10 by12) to mostly solar and have done some research. The controllers don't like batteries of different capacities as they look at the resistance and older batteries and batteries of lesser amp hours have different capacities and resistance.
12 volt systems are less complicated but need much larger diameter wire to have less resistance so the voltage /amps are used efficiently, the reason DC power was dropped in favor of higher volts and AC current. Voltage inverters are only about 90% effesient an that means losing 10% of your capacity off the top if you convert to AC. If possible use AGM batteries as there is way better life and very low loss of power during storage times but they are expensive. Added benefit is you don't need to constantly check water levels. Cooling a small house is doable but heating with solar electricity isn't paractcal due to the immense wattage required. Now if the sun shines everywhere else like it does here in sunny AZ and money grew on trees we all could use solar.

If one were considering the use of solar panels and fans just for ventilation on sunny days, would batteries still be necessary? For cloudy days and night time, there would be less need for the fans anyway. Do the panels have enough "instantaneous" output or do they need to charge batteries to get enough stored energy for the fans?

Without a battery the fan speed will be controlled by the wattage of the solar panel and the amount of usable sunlight. I have 2 fans for ventilation that operate on a t-stat and a battery so energy can be stored between "on" times. Don't believe the CFM ratings of the solar fans as others have measured them and the rating is usually double of reality

great question cuestaroble, fans can run just when the sun shines! I'll await that answer along with you. my question though is to dcarch, why 1500 for a solar panel? you can add 7 15 watt $100.00 panels connected for 1/2 that. Of course, I don't know what wattage you were calculating for, since I don't know what it takes to run a car radiator fan.
~tom

In checking prices for some of the ideas presented here, I found several new 3000 cfm electric radiator fans for $100. They draw 7.5 to 12 amps depending on brand, so I guess that would be 90-144 watts. There is a Sharp 165 watt solar panel for $775, which sounds similar to the idea for 7x15w connected, $700. Maybe we can get the price down for this set up yet.

I have found that panels over 130 watts usually are a higher voltage used in multiples for home or commercial use. It is easy to buy a 24 volt controller but then comes the issue of 24 volt motors. Also look into the type of amorphous or crystal material the panel is made of as each has pros and cons. If the panel doesn't have a blocking diode built in, the energy will be returned to the panel draining the battery after power stops flowing from the panel. Most controllers have blocking diodes built into them. Until the industry invents a better sunlight conversion method, the cost of solar won't get much cheaper than right now. The electronics industry pays top dollar for silicon for their transistors etc and that is the component of solar cells too.

dang DC thermostats are expensive too.
~tom

I use direct contact t-stats that are cheaper and will handle both DC or AC They are called line t-stats and found mine on e-bay. They come in both heat/cool or just heat or just cool. As long as there is a gov't rebate, both federal and state, the solar cost will remain high since the seller/ installer knows you will get money back from sam. When the rebates stop then prices may be a little more realistic except for copper, silicon, labor and on and on.

Random replies, thoughts:

1. Blocking diode is the same as regular diode. You can wire one if the solar cells do not have one.
2. Some times you can get broken solar cells cheap. They work just the same.
3. Budget about $5 to $6 per watt.
4. You can get 12V dc CF lights with regular sockets.
5. Get more watts than your fan rating so that extra current can be stored in the batteries.
6. If you can handle a soldering iron, some 24v panels can be rewired to 12 V.

dcarch

line t-stats. can't find a source. but here's a pretty good price for 15 watt panels with blocking diode. It's 79.00
~tom

Here is a link that might be useful: Northern Tool Solar Panel

Since I am a plant guy, please bear with me as I try to understand this stuff. What would be the advantage of 7 Northern Tool 15 watt panels ($560,105 watts,total area 3457 sq.in.), to One Kyocera,($600,130 watts,1456 sq. in.) other than the obvious $40 lower price(and lower wattage, and much larger size)? The voltages seem to be similar.
For my purposes, I am trying to solar power the largest CFM car electric cooling fan possible for the lowest cost.
Any help will be appreciated.

The "K" brand is intended for solar power applications like you want and will take a lot less construction of a holder than multiple panels. I have both , not by choice but by a bad e-bay seller, and the 15 watters are intended as portable auto battery chargers with a plastic frame that I think will deteriorate too quickly and a small pre-wired connection not intended for permanent installation. The "K" bransd is likely a mono crystalline with at least a 20 year, probably longer life, and the other is amorphous, more cheaply made.

Hello Everyone,

FYI. Here are some of the solar fans I have been looking into...

This one is $314.95, has thermostatic control, and a 24V storage battery (not included). CFM not specified.

Here is a link that might be useful: AZM SOLAR POWERED GREENHOUSE EXHAUST FAN

"This one is $314.95, has thermostatic control, and a 24V storage battery (not included). CFM not specified."

That's total robbery!!
That's the same kind of brushless DC Fan That I bought for less than $2.00! Look above this thread my other post. So it has a thermostat. Look into ebay. You can find the same thing with thermostat.

dcarch

dcarch

In checking many other links to the AZM fan, none give the CFM. Without that important figure, it is not possible to determine if it is worthwhile or not. There are "solar attic fans", that do give the cfm ratings, and they are about $500 for 1400 cfm, enough air movement for a 10 ft x 18 ft greenhouse.

Hey, Have any of you guys thought about WIND? Cause all of you are BLOWING HARD. :Milk you say? = goats, as goats can and will eat seaweed. Of course if you are on a low salt diet their milk might not make your Doctor happy.

1eyedJack and the Dawg

The same system that is here is also the one that Harbor Freight has for $199. Just for your onfo. Have not heard very good things about it.

for low wattage solar fans, you can get a house heating/cooling thermostat to operate it (mostly 24V)

I got mine for $7.00 on ebay.

dcarch

dcarch, if you have a 24v heat/cool thermostat and use it on a 12v system, how do you convert it?
~tom

Actually, the thermostat is mechanical bi-metal with the contacts rated for 24v typical heating system voltage.

So the power you need will be for the fan only.
Fan - $2.00
Theomstat $7.00
24vDC power supply I have. ($10 to $20 if you ahve to buy)
Done, operating with accurate temperature control.

dcarch

{{gwi:294794}}

The standard heat/cool t-stat (24 volt) is only designed to handle millivolts and won't last long if you are running any more than a muffin fan meant for computer use. If you are using a fan that draws amps use a line t-stat as they will handle several amps.

You can use a 12v automobile relay (30Amp) with a mechanical stat. The coil won`t pull much current and they are dirt cheap.

There are two kinds of contacts of the thermostat I shown.
One is metal-to-metal, the other is mercury tilt switch.
The mercury kind can take a lot of watts.

dcarch

here's a retail site that says the fans run just when the sun shines. you can see there hookup. pretty simple. no battery storage.
~tom

Here is a link that might be useful: solar fan kits

Preface: I have been using PV panels for 10+ years and currently have 5 KC-120 panels with Outback Inverter running part of my house.

First, when looking at where to purchase PV (photovoltaic/solar electric) panels do not purchase from some retailer who sells them on the side like Northern Tools. You will generally get the best prices from retailers who are selling to the renewable energy crowd/installers and have been around for 5+ years.

As far as DC fans see the link below which is to Schaefer Ventilation Equipment. I have both their 8' 466 ccfm and 12' 1649ccfm 12 volt DC fans. For smaller areas I use the 8' fan with two 5 watt PV panels connected to it. Feels like a desk fan on medium when in full sun. With the 12' fan I have a 75 watt PV panel connected to it and it blows a substantial amount of air (its uncomfortable putting your face in front of it).

I believe when I bought the 12' fan several years ago it was in the $120 range and is VERY high quality as you can see in the picture. They have full protection all around to prevent anything from hitting the blades which are high-quality aluminum blades. I have these fans connected directly to the PV panel ( you should add a fuse inline for protection). Whenever the sun light hits the panels the fan is blowing, even with some clouds it does move some air. A BP Solar 80 watt 12V solar panel is around $440. So with fan and panel you are looking at around $600. That panel is slightly more powerful then the one I have so you want to verify it is still ok to use with that fan (verify max amperage panel outputs with what fan can safely handle).

I have used that combination for several years during the summer months for cooling and have not had any problems. I also do not use any temp controller, I just flip the panel over to expose it to the sun when I know it will be needed.

Here is a link that might be useful: Schaefer Ventilation Equipment

Thanks everybody! following this thead has been very educational. Lots of good info.

1eyedJack and the Dawg

Anyone think of roman air conditioning?

It's solar, but not electric and works on air currents (or some more complicated arrangements with water vapour).

Basicly, you have a 'convection chimney' that is like a greenhouse in itself with it's back walls painted black. The air rising in the chimney draws air in below.. depending on where you get this air from, it can cool quite well.

Roman Air conditioning

Worth checking into if your short on $$$.