Water heating: parabolic trough solar collector

TnAndy

Found some used trough type collectors for sale....pretty cheap, 40 bucks...( like just about scrap metal price ), guy has 8 of them.



Says they are 8' long and have 1.5" copper pipe for the water.
I haven't seen them in person yet, but they don't appear to be homemade items....


Anybody have any experience on what kind of water temps they will turn out at what flow rate ?

Or am I just gonna have to experiment here....


Thanks....

Solar Guppy

Re: Water heating: parabolic trough solar collector

These type of collects only work well with a active tracking system, other wise the copper area is much to small and they are not insulated, so beyond scrap metal prices they have little value

niel

Re: Water heating: parabolic trough solar collector

sg is right for they have parabolic concentrators behind the tubes and without high accuracy tracking they really won't heat up.

FL SUN

Re: Water heating: parabolic trough solar collector

Any type of concentrated solar power (CSP) requires tracking to maintain focal on the collector tube like sg and niel said.

Also CSP works only in full sun. Days with hazy or cloudy conditions will not give any solar results unlike flat plate type thermal collectors.

They are fun to mess around with and chock up to solar experience, but for real results, they are not practical for the homeowner.

cow_rancher

Re: Water heating: parabolic trough solar collector

The used parabolics that I have collected for scrap had trackers, but you can get some usefull heat out of them if you orient them east and west and manually adjust the north south angle thru out the year. Tracking solar collectors will put out some heat (steam) in full sunlight, but the problem is with anything that moves, needs maintenance, most people didn't bother to grease the drive screw or anything else. There was a company named Sunpower out of phoenix that was marketing the ones in AZ in the early 80's when we had the last re-bates.

Rancher

TnAndy

Re: Water heating: parabolic trough solar collector

I went ahead and got 4 of these. My use for them is to heat water for a small greenhouse I have, so the only time I really need them is Nov-March, and even then, not a whole lot of water.

They look like something that was made up in a sheet metal shop......the inside is a polished aluminum, near mirror finish, with a plexiglass top on them. The copper pipe in the center is 1 1/4", and it runs thru a hole in a couple of 2x4 blocks in the ends, which allows the sheet metal parabola to rotate on the pipe, but really isn't a bearing as such. I think in their former install, they were probably oriented E-W and simply tipped toward south manually...there is an arm riveted to one end of each collector that sticks up about 6" ( you can see one in the photo..top, far left ) so it looks like they are all connected via that arm, so you moved all at once.

My intent right now to so experiment a little with them, using one with a small circulator pump I already have to see what kind of temperature rise I can get with it in a fixed position.....assuming it will crank out enough for my needs, I'll hook 2- 4 in series, and mount them behind the greenhouse, then use a differential thermostat and a "Maid O Mist" air vent ( already have both ) and come up with some kind of storage system in the greenhouse for heated water that will radiate it back at night.

I'll let ya'll know how it works out.

FL SUN

Re: Water heating: parabolic trough solar collector

Not a bad idea to experiment with parabolics to learn more about how energy can be harnessed from the sun. It is intriguing to see how focused solar energy is so hot.

I made a parabolic trough one time, recirculated oil through the collector, and burned up several pumps due to the heat of the fluid. I was seeing fluid temps of 600 - 700 deg F easy.

Keep in mind the magic of CSP is that it concentrates the energy to a focal. The energy collected from the sun is only the area of the aperture. There is a loss in the reflection / refraction of sunlight to the focal and is still not as efficient as flat plate collection believe it or not.

It takes a lot of aperture area to really do any amount of real work for creating usable steam or what-not. Those plexiglass covers look opaque and need to be replaced if you want to maximize captured energy. Using the collectors without the covers will allow them to get dirty and water spots which will affect reflectivity.

Good luck and have some fun.

TnAndy

Re: Water heating: parabolic trough solar collector

Thanks.....got a buddy in the glass biz, so I'm working on some tempered glass to replace the plexiglass.

If I can just get a 50-75 degree rise out of the water at a few gallons/min, I'll be quite happy.