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Old 03-10-21, 12:29 AM   #1
jeff5may
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Default Cheapest most effective solar thermal system ever

Due to a few armchair conversations with the masses, I've decided to build a few of the cheapest, most effective solar thermal collector panels ever. Here's the plan:

I did some research online and with a few (real) people that have been operating thermal collector panels for a few years. I've decided not to mess with antifreeze or highly pressurized rigs. This leads me towards a drain back system.

Low wallet dent/ high eco recycle factors also apply here. Something like a higher performance version of a flat plate plastic pool heater is the object here. I've got an endless supply of 3 foot wide storm windows and corrugated metal roofing also.

I have a fence about 100 feet long at the north side of the property that runs really close to due East - West that would be a good place to put the array. The spot would get total solar exposure until about 3pm, then the shadow of the house creeps down the fence row. Decreasing exposure until about 6pm when the shadow reaches the back corner of the fence.

The corner of the house nearest the fence is where the heat pump is located, so there's an ample chase to run plumbing above the basement drop ceiling that's somewhat isolated/insulated but accessible as well. That corner of the house is where the master bath (ground floor) and the basement bathroom are located. Behind the basement bath, there's a little equipment closet with a sump pump on it's own 20 amp breaker. Probably room enough for a 50 gallon water heater and more plumbing.

As of now, I'm open to suggestions. Main purpose of the system is to decimate my electric bill. Heat domestic bath and shower water, and keep the basement warm. Not trying to build a massive insulated aquarium in the basement. If I need a big heat store, it'll be an ibc container sitting next to the heat pump.


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Old 03-10-21, 05:57 PM   #2
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Looking for a suitable design, I found one on builditsolar. They call it the MTD collector, short for modified trickle down.

https://www.builditsolar.com/Experimental/MTD/MTD.htm

There seem to have been two guys (Richard and John) collaborating on a few different versions of the basic design. John has some YouTube videos up describing a few of them. I like this idea because it uses a variety of materials for the actual absorber, that all seemed to work good enough to heat water up above the 150 degF range. It uses polyiso "Rmax" boards for rear insulation and mylar sheet for a waterproof membrane. Pretty much "zero pressure" drain back operation.

John built his panels out of light gauge galvanized steel "stud wrap" channel, that's dirt cheap. My local Menard's has them in multiple sizes for between 3 and 6 dollars each per 10 foot stick. So between the stud track and insulation, I can probably build a 10 foot long (probably a little shorter, due to the Rmax being only 8 ft long) enclosure for under 50 bucks.
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Old 03-10-21, 06:12 PM   #3
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Nice project. I have considered doing this in a closed-loop fashion to heat my fish water.
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Old 03-13-21, 09:35 PM   #4
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Nope, not trying to do a copper skeleton and roll form or solder or both. If it was going on a roof, if it was meant to last 50 years, if I had a big budget... Maybe. Too high speed high cost for my "meager" purpose. For fish or swimming pool duty, the plastic micro channel heat soakers are very bang for the buck. I had some and they don't bust when they freeze if you don't touch them.

Anyhow, I went shopping at menards and came home with 3 pieces of 3-5/8 track, 2 pieces of 1-5/8 track, and a sheet of polyiso Rmax board. 1 inch was 20 bucks, half inch was 10 bucks, and 3/4 inch was 13 bucks, so I got 3/4 inch. Grand total of about 34 bucks. I had a chat with hotrod / ratrod builder buddy, and found a few suitable watertight back things for the wet collector part: plastic store sign panels. Pretty close to the same thing as gas station signs without the number brackets. He had two that were long and skinny: smaller was about 2 ft x 10 ft, larger about 3ft x 15 ft. Good enough for prototype duty. We're still negotiating on price, but I may be able to get them for sweat.

I found a water pump on FB market for 10 bucks also. 12 volt RV duty, 3 gallons per minute with a built-in pressure switch. Previous owner took the pressure switch apart and couldn't put it back together. Go figure. Rigged it to my truck battery and jumped the switch contacts to verify no moving parts gremlins in the actual pump, and it spit out some moisture. Yee haw! Thanks, see ya, zoom! Flojet model 03526 looks up easy on the net, dude had a Ziploc bag full of guts and fittings for the pump body, so whenever I can carve out some time I've got just about everything I need to get something made.

Another possibility: it's fake spring here. All of the pilgrims are getting rid of their old hot tubs. For some more sweat and some beers, I could probably score one for free. I absolutely NEED another hot tub. One if those appliances you either love or hate and I love 'em. It would make a great heat dump for all the extra summer output.
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Old 03-21-21, 04:26 AM   #5
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We finally got a clear day that wasn't windy. I got the small one about whipped together today. A buddy had a bunch of wood shelving this week, and I grabbed half a truckload of it from him. So the back of the panel is gonna be 5/8 x 12 inch slats of particle board. He had solid wood, but I traded it to hotrod guy for the plastic store signs.

Next layer up is the polyiso, then the plastic sign collector, top is gonna be classic single storm window pane in aluminum frame. Yes, they'll butt up fine, I just have to remove the spring loaded latches and pins from the corners.

All this sandwich is wrapped in the steel stud channels. The small collector absorber is gonna be corrugated galvanized steel roof, painted BBQ grill flat black. Paint was a toss up between engine paint and BBQ paint. Engine paint can said use primer and don't eat it. BBQ paint said wire brush, rinse, dry, spray. Non stinky, non poisonous. Hopefully that means no off gas after the initial dry and bake cycle.
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Old 04-27-21, 03:49 AM   #6
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Interesting experiments, Jeff.

What is the latitude of your location?

What elevation angle do you plan to install the panels at?

If the panels have any tilt to them, you could consider to look at the area in front of them. You write they are mounted on a fence, right? So if there is a somewhat reflective surface in front of the panel, you should get extra performance out of them.
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Old 05-23-21, 03:40 AM   #7
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Sorry, life and my schedule got in the way. Got everything done with the smaller one except the glass. The particle board I used was a little swollen in a few places, so the glass won't fit inside the channels. I got some galvanized drip edge angle to top mount the glass. It's been sitting for a while.

Osolemio,
I'm in Kentucky, not far from Fort Knox. Latitude is about 38 degrees North. I believe I will be angling the collectors at about the same angle back from vertical to get consistent output about 8 months of the year, and maximize the winter exposure. I picked up a bunch of landscaping timbers from a renovation this month.
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Old 08-08-21, 03:45 PM   #8
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Finally got a weekend off and threw the little collector together. I did a worksheet on the solar electricity handbook dot com website for solar irradiance and it said 52 degrees back from vertical was optimal for year round. So the uphill side is that, the downhill side is 48 and change to get even flow from my header pipe. Made a quickie fence mount and put water in it this morning. Hose water was around 70 degF. It's about 4:30 pm and the thermometer reads 118 degF. Yayyy!

No automation yet. I found a little mag drive aquarium pump that only has about 4 feet of head pressure and filled up a Rubbermaid tote until the water just made it to the far side of the drip pipe. Earlier, the pipe was sweating hard, condensing water vapor from the hot air atop. Now that the reservoir has heated up, only the center pane of glass is fogging up.
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Old 08-08-21, 03:56 PM   #9
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The garage and the basement workbench are both wrecks from hiding everything in sight. This is the month that every distant relative from around the universe decided to come visit. All of the microcontroller stuff and digital measuring instruments are buried under and behind the stuff that didn't make the house look spotless.

I'm running the water pump nonstop today off the extension cord that usually powers the pool filter. Weather underground says it's 88 degF out now, and the uninsulated reservoir has 15 gallons of water in it, plus maybe a quart to get the flow where it needs to be. The reservoir temperature is being measured with the pool thermometer. If I gather any more heat, it'll go off scale at 125.

So, not too bad for peanuts. I used one sheet of polyiso and two stud channels, plus a can of flex seal on this one. Everything else was freebie recycled junk. Somewhat maybe billable materials: black duct tape and an old light duty garden hose, leftover garden hose ends and copper sweat fittings.

EDIT: Being the hopeless tinkerer, I couldn't help myself. I slapped a layer of Mylar over the glass to see if it would help retain the heat. Just a little test, and it worked! I drove the pool thermometer above 125. Yayyy, that'll definitely preheat bathroom water.

Next up, the bigger, lighter Mylar version. I'll be using a gutter style drain for that one. A garden hose is barely big enough for the little one to not clog up or overflow. If two aren't enough, I've got a lot more fence area available.

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