Solar powered attic fan

[turbo6bar]

I have been thinking about one or more of these fans for an attic gable. The prices, however, are outrageous. An AC powered fan is less than $100. The solar powered units are $400-600 for similar output. Even with a Federal tax credit, that's still a huge premium. It would take decades to recoup the extra expense. The only way I can see making it work is a DIY solution.

I've noticed fan outputs vary wildly. The sellers of solar fans claim 800-1000 CFM output with only 25 watts. On the other hand, if I bought a set of SPAL electric radiator fans, the electrical need is 12 amps for 1200-1400 CFM. I know fan output is dependent on pressure head, so how do I choose the right match? Naturally, I want the highest output per watt, so the solar panels do not have to be huge and expensive. jurgen

[Joe Ricard]

Interesting look outside of the box. I bet it would work.

Don't understand the CFM requirement. I only have ridge vent and sofit vents. and a gable vent. Attic is under 140 during mid day. South Mississippi is Freaking hot.

[gt350mike]

I have no idea how much a solar panel cost so after a quick search, I found this link:
http://www.solarhome.org/21-30wattsolarpanels.aspx

They're listing a 21-30 watt SP for over $200 so that might explain why the solar powered attic fan is so expensive. I'm wonder if a panel can be bought cheaper........there isn't much ROI if you have to pay $200+ for a 20w to 30w panel.

[daepp]

Government got into solar, and the price went up. Go figure...

[Danimal16]

Solar IS NOT cost effective without government rebates. It is very simple, if it were cost effective we would all be doing it. Just like wind. Why was nuclear so popular in its day, because it penciled out in a big way.

[RWebb]

I'd put in a an Ac powered fan; run it and wait 3-5 years. Then I'd check on the conversion cost to a solar run motor...

I'd also plant some deciduous trees on the S. side of the house...

[porsche4life]

Needing to cultivate something in the attic?

[slodave]

I built a solar powered fan system for my parents garage. Keeps the garage about 15-20 degrees cooler in the summer. Total cost was about $150.- and the CFM's are about 1200.

[idontknow]

Originally Posted by slodave

I built a solar powered fan system for my parents garage. Keeps the garage about 15-20 degrees cooler in the summer. Total cost was about $150.- and the CFM's are about 1200.

And he did it all with the solar cells from landscape lighting.

Well maybe not but what was the itemized price list on that?

[HardDrive]

Maybe you should not be so focused on the cost, and think a bit beyond saving a few bucks.

[Evans, Marv]

Costco has one for $350 plus rebates. I didn't look at the specs though. You might check it out.

[slodave]

Originally Posted by idontknow

And he did it all with the solar cells from landscape lighting.

Well maybe not but what was the itemized price list on that?

I installed the fan about 5 years ago. I had a smallish panel that I had bought a few years before that, but could never use. So....

If memory serves me correctly, the panel was about $75-100 and the fan, a 12" circular, was about $75-100 as well. OK I'll revise what I said earlier... Total cost was not more than $200.-

EDIT: I think the main panel is 25 watts.

It was originally installed with an included thermostat (triggered at 90d), but it was not kicking on at the right time, so it was removed and the fan starts spinning when enough power is generated and spins down at about sun down. About once a year, I will get on a ladder and spry some lithium grease around the bearings. I will also adjust and clean off the panels. The panels (I added a small 12v panel I was using for R/C hobby) are about 100' away from the fan. I tried to keep the lengths to a minimum, in order to keep the line resistance to a minimum.

We talked about adding a battery to extend the fan run time into the evening, but it really wasn't needed. I think the fan will pump out around 2000 CFM's if I convert to a 24V system - which is probably what I will do, when the existing panels become inefficient.

The trick to keeping the garage cool, is to have the fan spinning before the heat builds up.

I wish I could provide a more accurate price breakdown. Done right today and an attic fan or garage fan can really help with some electricity costs, but it really is nice, as there is no pollution produced to power the fan (OK, very little. The fan/motor/panel still have to be produced.)

[Heel n Toe]

Dave, is the roof of their garage a hip or gable end design, and does it have soffit and ridge vents also?

[slodave]

Originally Posted by Heel n Toe

Dave, is the roof of their garage a hip or gable end design, and does it have soffit and ridge vents also?

It's a flat roof, no insulation inside. There are two show box sized vents at the bottom of one wall and about a 1/2 gap under the side door.

They do have an attic fan, but it is not solar. That roof is a gable, with ridge vents on either end. I don't know how hot it gets up there in the middle of summer, but that fan is on a thermostat.

[Heel n Toe]

Originally Posted by slodave

It's a flat roof, no insulation inside. There are two show box sized vents at the bottom of one wall and about a 1/2 gap under the side door.

Okay, I think I know what you mean. So when you're in the garage and look up, you see the joists and the plywood or OSB sheathing, right? No ceiling and your vent is installed up high on one of the walls?

Is the roof perfectly flat, or is it sloped slightly... aka a shed roof?

I've seen those low box vents like that in a garage that did have a ceiling with an uninsulated attic space above it, and the owner didn't have any way to get the hot air up and out of there... it was VERY HOT in there during summer.

[slodave]

It was a completely flat roof until a few years ago, when they did away with the roof rock and went the route of shingles. The roofers added a very slight angle, enough to keep water from collecting, but it is still very flat. On the inside, there are only rafters and plywood. We cut a hole in one corner of the roof. They have two water heaters, one gas(garage corner), one solar (outside). We cut a hole in the roof between two rafters, basically above the heater and the fan exhausts straight up into a galvanized t-top roof vent.

Similar to this one:


The fan runs for about 10 hours a day, 365 days a year. I have yet to replace the brushes in the motor.

[slodave]

Looks like I could build a 24V system with a 12" fan, putting out about 1800 CFM's for about $430.- today.

Prices have gone up .

With some shopping around and buying solar cells and making your own panels, the cost would go down.

[turbo6bar]

Originally Posted by HardDrive

Maybe you should not be so focused on the cost, and think a bit beyond saving a few bucks.

Way to think with your emotions instead of your brain.

I worked the numbers for a 25 watt system "ready to go," and the time to break-even was 35 years. There are other means to save energy with far lower payback times: solar water heater, radiant barrier in attic, extra insulation, and numerous others. The energy savings on a 25 watt panel: 25 watts * 12 hours * 180 days/yr * $0.13/kwh = $7.02/yr. This is a very simplistic check that does not account for the cost of an AC-powered unit, but I did use a low price for the solar powered fan. $300. Many larger solar fans were well over $500.

IF I can get the cost down to under $300, it begins to look more attractive, particularly with a rebate from the government. Personally, I think the solar companies jacked up the prices to match the 30% tax credit. Screw that. I'll DIY if I must.

slodave, any info on the DC motor? I also think it would be a great benefit to run the fan after sunset to remove heat soaked into the attic, but that's not possible without a charge controller and battery($$$). Yeah...I AM focused on cost, but that's the reason for doing this: remove heat from attic to reduce A/C expenses.

Joe Ricard, I am up the road in TN, so my attic isn't much better than yours. I sprayed Sherwin-Williams E-Barrier (radiant barrier paint) and I am not impressed. It is not a true radiant barrier. The next house I build will have radiant barrier in the roof sheathing. THAT is a great investment.

Evans, going to check out the Costco fan. I admit to being pessimistic at this point. Seems like the best way to save/make money is to start manufacturing solar fans and reap the large profits.

Will report in when I have more info.
jurgen

[jyl]

Anyone paint their roof white?

[RWebb]

My neighbor did - there is also a roll roofing product made for low angle roofs.

Look! I have data: