Alternative Energy

Great article and links. If I were a bit more confident on cutting holes into the home for the vents this setup would pay for itself in 3 winter months.

Was the majority of the $350 cost due to the solar panel to power the fan? I would think that the total cost of the fan, the wood, and the duct would be about $100. Perhaps powering the fan electrically on a timer during peak sun hours would cost even less to build, and save even more money during the first year of running it?

As the best solar panels in the world only take in around 25% of the energy and make use of it, this is a long winded way. Maybe wait until the technology gets better.

If you wait, it may be too late! NOW is the time to move into using renewable energy, with the best tax incentives available & affordable oil in the shadow of us all! The cost of panels is down now & when the oil price gets higher, so will the cost of the solar panels, if they can even manufacture them!

Wouldn’t it make more sense to connect the intake hole to an opening inside of the trailer? By doing this, the cold air inside the trailer gets recycled through solar panel and back inside. It just might raise the inside temperature much more quicker.

Hi,
Just to address some of issues in comments above.

- The collector has no fan, no controller. Its a thermosyphon collector — the lower density of the heated air makes it rise up out of the exit vent, which pulls cool air into the inlet vent. The $350 was all for the materials to build it — this is a large collector — about 160 sq ft, so this is just a bit over $2 per sq ft of collector — almost free compared to $30 a sq ft commercial panels.

- Solar thermal collectors are much more efficient that solar electric panels. Efficiency depends on the sun and out side temperature, but 60% efficiency might be a good average. Payback is very short for this kind of collector.

Gary

Cheesiest most hillbilly looking design I ever saw. No reputable engineer would make a platform that silly, let alone spend $350 to do it.

Interesting, I happened to build something like this as an experiment.

I took a 4′x4′ piece of scrap plywood, spray painted it black. I screwed scrap 2×4’s around the perimeter to make a box about 3″ thick. I bought a $2.99 pack of window film and stapled it on the box. I put a 3 inch hole at the bottom and the top.

I laid the box up against a stone wall angling it towards the sun. Then I went to go get a thermometer (I had a digital one). So not to get direct sunlight on the thermometer probe, I put a piece of insulation over the probe. This was I was sure to read the true temperature of the air coming out of the top vent hole.

Well within a minute, the temperature of the air coming out had pegged the thermometer at it’s max of 130 degrees. So then I got my meat thermometer that I use for grilling, and the temperature read 160 degrees. There was a bit of an air flow coming out of the hole, so I know I was getting the hot air to rise, being replaced by cool air at the bottom.

So, the concept works. I haven’t done anything with it though.

About six months ago I purchased a 24 foot enclosed trailer that is pulled by a big Ford F-350. I live here in South Dakota where the winters are pretty brutal. At night I normally plug in a space heater to keep my trailer mounted carpet cleaning equipment from freezing. Is there anyway that I can mount solar panels on the top of the flat roofed trailer and have it store the collected energy at night for use in a space heater that runs at night and as I drive down the highway early in the morning? Thanks everyone and have a great day!!

Hi Anthony,

You could put solar electric panels on the roof and use them to charge batteries during the day, then run the space heater via an inverter at night. This is inefficient, expensive and heavy (batteries).

A better way might be to put a water heating collector on the roof (maybe better on the south side). Use it to heat a water tank in the trailer, and let the water tank radiate heat during the night to keep it above freezing. Solar heating collectors are about 4 times more efficient than solar electric panels, and (therefore) you only need 1/4 the area for the same amount of heat.

The best thing you could do would be to insulate the trailer, or at least the part you want to say above freezing) as well as you possibly can. This would allow a smaller solar collector or small space heater.

I think if it were me, I would try for the best insulation possible, add some thermal mass in the trailer, and use a simple solar air heating collector to heat the mass up during the day, and store enough heat to avoid freezing at night. A small space heater set to come on at (say) 35F could be the backup for cloudy days.

You can email me if you want to discuss some actual collector and tank sizes that would make sense.
gary AT BuildItSolar DOT com

Gary

This looks like it would be a great thing to do. Has anyone who isn’t necessarily very tech savvy tried this?

Hi Christina,
I’ve received emails from a lot of people who have built this collector — not all of them ‘dyed in the wool’ do-it-yourselfers.

Some of them took the time to send in pictures and descriptions — have a look here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

I’m happy to answer email questions if you run into a problem.

If you are looking for a warm up project that is a bit smaller, there are several listed at the link above — they are all fun and will get you hooked on solar

Gary

I think I’d mount it on the trailer and feed it with an intake from the trailer floor. Also, I wouldn’t use styrofoam. I’d be worried about outgassing. Maybe use some foil lined celotex.

I think the solar heaters would be a perfect combination with “geo-air” technology.

http://www.citrusinthesnow.com

After reading the geo-air report by Russ Finch I see how a solar heater will be a perfect partner.

And this is nice design. Recirculating air from the trailer to some degree would make sense. perhaps an adjustment for a fresh air/recirc air mix would be nice.

The fundamental flaw in the concept is that cold air from outside is being heated before being introduced into the building. Would it not make more sense to pump air from inside the building into the solar heat collector then circulating it back into the building? If you continuously circulated the air from inside the building through the solar collector would this not lead to the possibility that the solar collector would act as a radiator because of the difference in temperature of the heat inside and outside of it? Perhaps high U value glass in the solar heat collector would prevent heat escaping from it.

Whatever the theoretical issues of this solar heating John Spencer’s experiment shows that it has great potential.

Hi Motorcycleboy,
The collector does circulate air from inside the building, through the collector and back into the building.

The inlet vents are down near the floor and typically take in air about 65F. The outlet vents are about a foot below the ceiling and typically deliver air to the room about about 110F.

http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

Gary

what kind of a fan did you use? size, name, etc.

Hi Dan,
There is no fan — its a thermosyphon collector.

The flow is driven only by the density change of the air as its heated in the collector. The lighter heated air rises out of the collector, which pulls in new cool air from the room.

Gary