Building Solar Thermal Collectors

[(unknown)]

Hi All,

I'm a newbie to the forum but thought I'd share and collect some ideas for a project I'm working on.

I'm piecing together a solar thermal collection system to offset the cost of water heating in my home. The system is intended to suppliment hot water only and not be tied to heating of my home.

I started by putting together a small 1' x 10' copper tube/plate collector. Roughly sixty feet of 1/2" rigid copper tubing spot soldered to a 1' x 10' copper sheeting in a 2x4 frame. It's insulated with 1" foam board below and covered with a scrap sheet of aclar film stapled and taped around it's edges. There is also a temperature sensor clamped to one of the pipes via a hose clamp.

http://home.comcast.net/~rossfree/solar/solar10.jpg

http://home.comcast.net/~rossfree/solar/solar9.jpg

http://home.comcast.net/~rossfree/solar/solar12.jpg

My heat storage was a 30 gallon ice chest. I drilled a couple of holes in it's side and plumbed it to the collector. There is a small pond pump in the ice chest and when turned on it simply circulates the water from the ice chest through the collector and back into the ice chest. A second temperature sensor was placed in the ice chest.

http://home.comcast.net/~rossfree/solar/solar11.jpg

Control was by way of a PIC processor and minimal circuitry. With a simple program, the pump was turned on whenever the collector was 10 degrees F above the storage temperature and turned off when the collector was only 5 degrees F above. It also kept track of how long the pump was running during the day.

http://home.comcast.net/~rossfree/solar/solar6.jpg

I live in southern New Hampshire and put this together back in early April. The daytime temps were running in the low 60's but with sunshine I could raise the water temperature 20 - 25 degrees in a given day. With three days of sun I got the storage temperature up to 153 degrees F. Not too shabby. And at that temperature I would loose at least 10 degrees at night from cooling through the icechest. The ice chest only has about an inch of insulation around it. If I took the time to improve the insulation around the ice chest, I'm sure I could have hit 180 degrees... no problem. At that temperature, I would have started worrying about the plastic softening.

At one point, I came home and the display read that the temperature of the ice chest was 79 degrees and the collector was 210 degrees. I could hear the pump running and knew it couldn't be right. I figured the electronics got fowled, being uncovered and exposed to the elements. I reached down to feel the copper pipe protruding from the collector and got a surprise. It burned me good! It didn't dawn on me how it could have gotten so hot with the pump running until I opened the ice chest. The pump had popped off of the tubing and was not circulating water through the collector. Sitting in the sun with no circulation, the collector had hit over 200 degrees! HELLO! So I reconnected the pump to the collector and turned it back on. While it circulated water, I put my hand underwater in the ice chest to feel the water entering from the collector and... duh! ...burned myself again! Ha!

I can be not to brite sometimes.

When the pump comes on, it only runs for about 30 seconds. In that amount of time, cooler water has replaced the warmer water in the collector and brought the temperature below the 5 degree cut-off temperature. Average run-time during a sunny day was less than 45 minutes. That equates to about 1/2 penny cost per day based on $.12 / kilowatt hour.

I'm happy to report a very sucessful small scale test.

Enough for now. I'll share the beginnings of my larger 330 gallon system soon.

http://home.comcast.net/~rossfree/solar/solar1.jpg

http://home.comcast.net/~rossfree/solar/solar2.jpg

http://home.comcast.net/~rossfree/solar/solar3.jpg

Ross

[BurksFallsMan]

Ross: Sounds good and I would like to try something like that. Do you nhave the schematic for the controller and what kind of  pump and where to get it ? Can I run on 12 Volts since I do not have utility power?

Good work !!!

Wilson --   e-mail:WFGonzalez2@cs.com

[Ross]

Hi Wilson,

I'm no electronics genius but have a couple of genius electronic buddies in my back pocket.  :-)  When I'm about to blow something up I check with them and after some "tut tuting" they straighten me out.

I don't have a schematic for you at this time but the whole thing can be built for a hundred bucks and done in a few hours. I am also sure someone could do it cheaper. I designed around a PIC processor because I was toying with it for other projects and it gives you infinite possibilities with programming.

For instance, I am already aware that I will need to place an upper limit on my system because of the low density polyethelyne(sp?) tanks I'm going to use for my home system. I'll just do that in software so that the pump won't come on if it reaches a pre-determined temperature. I have three of the 110 gallon tanks that I show in my pictures for a total of over 300 gallons of heat storage. My final system will use the PIC and I'll place a display in our kitchen so I can see its progress.

I'm rambling.

To answer your question, yes you could use a 12vdc pump. It could easily be turned on and off with a relay actuated by the PIC processor. The pond pump you see in the pictues is a $35 ebay pick up. Ebay is great for such stuff. Be sure to determine the maximum head pressure your pump will see before purchasing one. The test system on my deck places the pump, storage and collector at nearly the same height. If the collector were six feet above the storage, the system would have to be "primed" with a larger pump before the pond pump could be used.

When I have a schematic together I'll post it here.

Hope this all helps!

Ross

[thunderhead]

As a simpler design, couldn't you run the pond pump off a small PV panel?  When the sun shines, the water circulates - and when it doesn't, it doesn't?

Just my $0.02...

[TomW]

thunderhead;

Elegant solution and the one I use for my little window air heater made from aluminum dryer vent a pc fan and a little panel.

When the sun shines the fan blows air through the flat black painted duct zig zagged across the window. Works super and 100% solar.

Cheers.

TomW

[wooferhound]

How to Build a Solar Hot Water system...

http://www.jc-solarhomes.com/how_to.htm

[Ross]

Yes you can do that. But the sun shines early in the morning and late in the afternoon... and if the system runs all the time, at some point you will be sending hotter water back into the collector that the collector temperature effectively increasing your losses by some degree. If you only run the pump when the collector is hotter than the storage temperature then your in good shape.

Still... simple is good and what you have suggested would work,

[R Love]

 If it is possable to set your panel below your storage perhaps you could go with thermal syphon and go with 0 controls also in NH you might want to think about a closed -loop panel with a heat exchanger, installed in your potable water tank, and the loop filled with RV antifreeze-- Just a thought

 R Love

[jimpep]

Ross:

I have had good luck with used flat plate panels(dystars). My first set was about 100 SQ feet for $800.00. Ironically right after pick up, 2- 8x4 pannels were in the paper for free. One of my buddies picked them up with everything needed except for the tank and piping for free.No muss or fuss. There is lots of used stuff out there. People don't understand them so they get rid of them. In many of the cases I know about they are attached to water tanks with electric backup which is tabu nowadays. In my case ,with an 80 gallon stone lined solar tank, check valve, controler, expansion tank, circulator, guages, pipe, air scoup, air purger, glycol, valves and wood framing materials ran me about $1700.00. I'm figuring payback in 5 or 6 years. I'm guessing my elctric bill is an extra $10 to $15 a year for Taco pump. It ran me a bit more than I wanted but I think you could probably find used panels for free. I'm in Northern Vermont and I heated 80 gallons of water to 155 degree F yesterday(6-5-4). I hit 150 F on a certain day in April.My top temperature was 169 last year when I installed it but it was uninsullated until October. I picked up another free 22 square foot collector last month but I'm not sure how I will incorporate it yet. Got to love free energy. Good luck on your projects.Cool setup.

Jim

[Ross]

Hi Jim,

Your system sounds great! It's right in line with what I'm trying to do. I'm finding it irritatingly expensive to build collectors but don't have the foggiest idea how to find any used ones in my area.

The last couple of pictures I posted showed a plastic tank. I got that and two others at Bayhead Corp. down the street from where I work. The tanks were scheduled for scrap because of minor imperfections (slightly bowed, rust marks on first shot, etc...) and I was able to pick them up for $50 each. Not bad for 330 gallons of storage. They have no openings in the bottom so that raises my comfort level on possible leaks. From all of the reading I've done on the subject I needed a little over 200 gallons of storage. This may be a bit of overkill but I doubt it will hurt any.

I intend to put two coils in each tank. One heat exchange coil for the collectors and a second heat exchange coil for pre-heating house water. That's a lot of coils at about $30 each but it will allow me to use a minimum of glycol or antifreeze in the closed loop collector lines. It also allows the tanks to be unpressurized. I'm a bit concerned about the plastic getting too hot but will monitor them closely for the first few weeks of installation to get a better feel for their durability.

I'm interested in how you went about insulating your tank. I intend to put about two inches of foam board insulation around the three tanks I have and then fill inbetween with a new glass-less blown-type insulation. The only possible leaks will be at the solder joints to the coils and they will all be above the tanks for easy inspection. I will hinge the top foam-board insulation for easy access.

All of the other components you listed will likely be in my own system.

I would love to see your system some time. Your not to far away for a nice day's drive.  :-)

rossfree@comcast.net

Thanks for the input!

Ross

[jimpep]

Ross:

I got the used panels from Solar Works Inc. in Montpelier Vt. 802-223-7804. I know they have many used panels still because I was down there a short time ago. Talk with Todd Wells ..he is their field service guy. You could tell him that I gave you his name. They just moved their used panels to a smaller warehouse on route 2 just outside of Montpelier. My Daystars are 47" by 81" . The width includes some 1" copper fittings. Some have a hose barb and some don't. You can have less space between the panels if you don't have to deal with sweating on  1" hose barb fittings. They have 8' by 4' flat plates also among others. I'm not sure about their current prices. I bought my tank new and already insulated. It is a Vaughn S80SR solar series model water heater that I got a break on.It comes with the exchanger, an aquastat and a electric element which I don't use. It was a bit more than I wanted to pay but it has good features including a per hour drop of 1/2 a degree it claims. It seems to be right in their performance stats.I'll see if I can post pictues. Don't give up on free panels..there are many out there. There are some ideas on open loop systems in cold weather areas in I believe what was called "HOMEPOWER MAGAZINE" .I believe I got the link here. That is where I got the schematic for my closed loop system if I remember right. Good luck on your projects.

Jim Pepin

[jimpep]

[jimpep]

[jimpep]

I have a tempering valve in there for warm days which I can turn on. This is pretty much all of my setup.

Jim

[Ross]

Hi Jim,

The pictures are great. I appreciate the number. Will check it out. My budget is tweaked right now. Need to rob a bank or something... too many hobbies, not enough money!

It erks me that my house isn't pointed in the right direction. I have a full dormer on the back of my cape which I plan to use for the panels. But all roofs face east/west. So I intend to place the panels on the dormer and angle them south somewhat. I've looked up numbers for best solar collection at New Hampshire latitude and will likely need to angle them at almost 45 degrees. That means that if they are large panels, they will tend to shade eachother unless they are well spaced. The temporary panel I made for testing would seem to be about right for that reason (it was unintentional).

I have layed out a sheetmetal frame in CAD and am considering getting quotes to have the pieces made by a local sheetmetal shop. In quantity the price might be right.

I'll be installing the tanks in the comming few weeks. Once that's done I can concentrate on the panels.

Ross

[jimpep]

Ross:

They say the angle is always your latitude. I'm at 45 deg here so that's my pitch. You can go for more or less but when you run the numbers you always end up losing if you deviate from it. Example: what you gain from a higher pitch during winter doesn't stack up against what you lose in the other parts of the year by making the adjustments.My panels are dead South. When we built I set it that way for that reason. It seams like you would be able to fab some Pressure Treated brackets to get your pitch correct and angle correct to South.

Good Luck

Jim