$150 4'x8' Solar Panel
 

I was browsing over on BuildItSolar.com and found this. It is an awesome and simple design using PEX tubing and aluminum heat transfer plates. Simply unbeatable price!

Solar Collector using PEX Tubing

that thing is awesome! and you're right, you can't beat that price. do you plan on building one?

You betcha! I don't know when I'll get around to it though. Hopefully next summer.

My sunroom already has hydronic heat which is currently run off the hot water heater. I will be installing hydronic heat into my living room in the future as well. So, I really hope to build an array large enough to satisfy a descent amount of space heating needs.

Pex is not designed for outdoor use. It shouldn't be exposed to sunlight for significant amounts of time. It's simply not designed for it, it will degrade as most plastics do from exposure from sunlight. Look at:

PEX Products - FAQ

If your really looking for a cheaper way than say new cooper tubing might I suggest the grills from the back of broken refrigerators welded or brazed together, plus your water heater is then recycled instead of using a new oil based product.

This is the quote from the FAQ.


The thing is, in the design, the PEX is covered with either aluminum sheet or paint. The aluminum for sure is going to block any sunlight from degrading the PEX. The paint may not be the best blocker for sunlight, but its still not in direct light. That, or it could be covered up with something else (more aluminum perhaps).

I'm not saying the design is perfect. But, I do think you could make it totally workable and reliable.

Yeah, but if you look on at one of the links the same guys builds the same one with copper pipe for $190.00. So for $60 dollars more you get.

1. 15% more heating capability.
2. a lot less fuss (since copper is more durable and can withstand the heat and exposure).
3. A heater that we know will last a lifetime.
4. Uses a highly recyclable product vs. a one use product that isn't recyclable.

Seems like a no brainer to me, it's just $60.00, and with the increase in efficiency will pay it's self off just as fast if not faster. Really copper pipe isn't that difficult to work with. Solder is a pretty easy thing to get the hang of, and it's a very good skill to obtain for DIY's.

Very good point. I didn't think about the recyclability of it!

I think for the average DIYer, the attraction of the incredibly simple PEX collector is very nice. For someone who is willing to go a bit further, the copper/aluminum collector is probably the better choice.

oh and I didn't read the whole Pex write up, but last time I used Pex I had to rent a specialized crimping tool for $20.00, because to buy it would have been expensive (it was 2 years ago but I want to say $100 plus. I know it was more than $60 because I'll just buy the tool if it costs 3x or less the daily rental fee or less if I know I'm going to use it again later. And I've only replaced about 20% of my indoor plumbing in my 80 year old house.

This looks like a good idea if you use the copper pipe instead. It has me thinking about an oil or water closed system for the bedroom and back bath in my house (thermal storage.) A small pump to encourage flow based on temp differential and a valve to shut it off in the summer.

looks like a great idea.

Hi,
Right -- The PEX is all protected from exposure to UV.
The first layer of protection is the SunTuf polycarbonate glazing -- it has a very aggressive UV cut off built into the outer layer. They add this coating to protect the glazing itself, but it also protects the PEX.
The 2nd layer is the aluminum sheet that covers all of the PEX except the bends at the ends of the serpentine runs. The tubing at the bends is protected a couple coats of the same black paint that I paint the absorber with, but you could use a more bombproof protection if you are concerned about it.

On the PEX crimp tool.
I tried to make the thing so as not to require any special tools. Within the collector, there are not joints at all -- its just one continuous run of PEX. To make the connections for the supply and return, I used SharkBite push on fittings. These are really easy to use -- they literally just push on. They are approved for for residential water supply plumbing, even if hidden walls -- so, they should stand up to the almost zero pressure in a drain back system with no problem. The Home Depot in our area sells a good selection of them -- the only down side is that they run about $6 per fitting.
A 2nd small problem is that they don't fit all PEX -- I found that I had to take out the inside bushing in the SharkBite to make them work with the PEX-AL-PEX I was using.

The thing to read very carefully on the PEX collector is the cautions on avoiding high stagnation temperatures. I don't think that it should see temperatures higher than about 230F. I avoid these high temps on mine at stagnation by using a high tilt angle (about 70 degrees) -- this keeps the stagnation temps down in the summer because the sun is so high that the incidence angle is very large. This works out well for me in that it also increases winter collection (when the sun is low), and gets more benefit from reflection off the snow. But, if you can't live with the stagnation temp limitation, the copper alternative (that still uses alum fins) is only a few bucks more, and (as mentioned above) is more efficient. All in all, I think the copper collector is probably better for most people.

The solar heated water storage tank and plastic pipe coil heat exchanger actually end up saving even more money than the cheap collector, and they can be used with (just about) any collector.

Gary

Hey guys, the poster GaryGary I believe is the author of the builditsolar website. I invited him here to comment on the articles and projects we've been discussing from his website.

Welcome Gary. Glad to have you!

Hello Gary, thanks for the post and answers to some of our questions. I hope to hear more from you. :)

Hi,
Thanks for the welcome -- good forum.

If anyone goes ahead and builds the collectors, I'd like to hear how it goes.

Gary
gary AT BuildItSolar DOT com

I really like that web site :thumbup: BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution. It's what got me started on the hot air panel I have been collecting materials for. I was thinking of eventually trying a version of that hot water design. Since copper prices have dropped, it might be the material of choice. It would be neat to somehow tie it into the unused zone of my boiler to distribute the heat thru the house.

I would like to know what the heat output of this PEX solar hot water collector is, because I don't think it is going to be very high, real collectors are not that expensive compared to their life span and the space they take up.
I just like to see things that work, and work well, I've installed systems that were 7 3x10 panels (14sf less then 7 4x8' panels) and those 7 panels supplied 90% of the heat for a 2,000 sf super insulated house, and all of their domestic hot water, the other heat source was a small wood stove, they burned a pickup truck of sticks and twigs per year.

how fast does this heat the water? is it fast enough due a shower or mainly just washer, sink, and dishwasher?

The panel heats up a tank of water. You draw on that water just like you would a conventional water heater.

O ok. What would you recommend for the tank?

Most people tend to use an insulated 50-60 gallon tank with an electric heating element in it that can be used for back up, install a pressure releaf valve of course or it will not meet code.

Hi everybody!

This is my first post, so go easy on me.<EDIT>: it looks like Gary updated the original link June 11 '09, about five days after the last post in this thread.

I'm pretty sure the panel keeps draining back into a (thermal) storage tank, that has a 300' coil of PEX pipe submersed in it. The PEX coil is plumbed inline between the supply service and the hot water tank. When the collector is warming the water in it, it travels through in to the storage tank, and the seperate coil (with potable water) takes on heat from the storage tank, on it's way to the HWT.

I'm not sure if that's right, or makes sense, but here are a couple of pics from a link on the site mentioned above;

http://builditsolar.com/Experimental...DiagramDHW.jpg
PEX coil not to scale, lol. P is for pump and V is for Valve. The valves are there should he need to by-pass the solar collector.
http://builditsolar.com/Experimental...0567_small.JPG
The PEX in the tank with it's inlet and outlet connected to house plumbing.
http://builditsolar.com/Experimental...0569_small.JPG
You can see the white drain pipe in the middle of the picture, at the corner of the storage tank. The (cooler)water gets pumped from the tank bottom up into the collector, then drains (warm) into the top of the tank.

http://builditsolar.com/Experimental/PEXColDHW/Overview.htm

Thanks for the in-depth tour Gary. If I get some time in the Spring, I'll take a crack at this!

alg

I am a newbie to solar, I have been reading a lot and Gary's design really caught my eye. I live in Vermont with my wife and three daughters (teenage years are coming so hot water is going to be in short supply at my house). I heat my house 90% of the time with a Vermont Castings Defiant wood stove located in the basement next to my current hot water tank. I also have an oil fired boiler that I use for heating my DHW and base board heat. I am in the process of installing a secondary hot water tank that will feed the primary tank. The water in the secondary tank (80 gallon electric tank that will not be wired) will be preheated by circulating water through a heat exchanger on the back of my woodstove.

I had seen quite a few people that had put an exchanger inside the stove, but that just scared me, we lose power occasionally and I really did not want to come home one day and find pieces of my stove in the living room because it blew up.

So now you know a little about my setup, here is the solar question. Since I have a way to heat my hot water in the winter months with the woodstove heat exchanger could I use Gary’s PEX panel design to preheat my water in the summer months? I know it would have to be drained in the winter and I would probably move it into the garage. It would be considered a Direct Pumped System.

I know a couple of things would need changing, like the fact that I can’t use PEX-AL-PEX for potable water so I would probably use 1/2” PEX with elbow on each end. I would also have to put a pressure release valve and probably an air vent at the top of the panel where the water exits. I would utilize the same secondary tank and circulator so I think I am looking at about $300 to create the panel with enough pipe to bring it into the cellar. Any thoughts?


I had a couple of links to show examples but it would not allow me to post them, so if you have a question on my design please email me or post a reply. Thanks

Hi Trevor, if you will be circulating potable water through it I would recommend you use the copper style collector as normal pex wont hold up. you will need a temp differential controller(turns pump on when collector is hotter then the tank and off when tank max temp is reached) and a pump designed to circulate pressurised water (gerfundos?) when max tank temp is reached the pump stops running and the water just bakes in the collector(stagnate condition) and can get up to about 200* or more in strong sun, and I don't know about you but I have 80 psi water pressure and that would put me right at the 200* 80psi limit of standard pex. I think what would work good for you is batch heater as long as you drain it before the freezing weather or just build the $1k drain back system and not use the extra hot water heater. This is right off Gary's site:
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It is easily bent in to tight turns AND it retains its shape without spring back. This is a very nice feature.

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It has higher working and burst pressures than ordinary PEX.
The PEX-AL-PEX I used (Mr. PEX) is rated for 160 psi at 200F.
Standard PEX is rated at 80 psi at 200F, and 160 psi at 73F.

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It has better thermal conductivity that regular PEX -- this should result in somewhat better heat transfer from the aluminum fins through the PEX to the water.
PEX-AL-PEX 3.1 BTU/h-ft F for half inch tubing
PEX 2.6 BTU/h-ft-F for half inch tubing

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It has a much lower coefficient of thermal expansion than PEX, and is more compatible with the expansion rate of the metal fins.

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It may be somewhat more tolerant of freezing. It will probably withstand several freeze thaw cycles, BUT will NOT withstand continual freeze thaw cycles.

so regular pex would be less efficient and wouldn't be a good idea to subject it to such conditions. By the way I have seen the pictures of the blown up wood stoves and they all didn't put a pressure relief valve in-between the shut off valves and the heat exchanger

I have built half a dozen solar hot water heaters, active solar systems with no pumps. They all worked well, I built some in the late 70s and one a couple of years ago. Copper is the best but it will not tolerate freezing water. If you will be using a thermosiphon (no pumps) system and you are sure you will drain your system before the first hard freeze go with copper. Personally, I'm interested in pex and might build one to see how it holds up mostly because of the freezing issue. The last system I built for an organic farm (not for profit) and it keeps busting out either the line or a sweated fitting. Also, I use glass from discarded patio doors and build the collectors to fit them. They are free, often easy to find, easy to use and the most efficient. I used a fiberglass product called Calwall in 1979 which lasted 10 years but turned an ugly yellow, cutting down the efficiency, I'm sure.

Interesting ideas Miguel, and welcome to the site. :)