Solar Thermal Plate Collectors

Hello -

I have the opportunity to buy a lot of 15 solar thermal plate collectors for $2k (~ $130/piece) They are black chrome 3x6 collectors from the 80’s, drain back design and still appear to be in pretty good shape.

These would ideally be for some combination of an indoor hot tub, radiant floor heat and DHW in a 500 sq ft house in Northern New Mexico.

Does this strike you guys as a good deal? I have to transport them quite a ways so I’m trying to make an informed decision.

I know a lot of the net zero home guys says it’s a better bet to use PV and a heat pump these days, but that’s for a new install and definitely less eco than recycling old panels. I also like warm floors!

Any help would be much appreciate. I’ll be posting on the planned build shortly!

Thanks so much for everyone's excellent feedback! I quote Frank's detailed response for future viewers:

frank li wrote:
I have been repairing and installing solar thermal hydronics for 14 years and rarely see a failed collector that is made of metals and glass.

I have installed seveal systems with used collectors, including my own and dozens of systems featuring new collectors, flat plate and evacuated tube. The tubes do perform better in very cold ambients, but this is michigan and when a person has a 30 plus year old flat plate system that fails or needs to be re-installed and fired up after a re-roof, it is common to hear that they couldnt possibly consider, not fixing or replacing it, it saves too much money!

That is from long time owners who originally had them installed and from people who moved into them.

If you do a pressure test on them and they hold air, they are likely good for another 40 years!
Look for corrosion and sediment coatings on the inside of the waterways. If the ways are clean and not corroded, they are a great deal at that price.

Collectors (4x8 and 4x10) were going for $250 from AAA solar at new mexico last time i checked.
A new Steibel Eltron or Heliodyne will cost you $1200 to $1400 each plus shipping, $900 or so for the smaller 3x6.

I have seen 150 deg F fluid flowing in flat plate collector loops under less than full sun and below freezing outside, overcast, not so much, but the colder the storage temp falls, the higher the scavenging of heat from the collector, so you will at least pre-heat on most days.

Just like pv, expect 5-10 percent energy output under moderate gray sky, and almost nothing on heavy overcast days, occasionally.

Location matters. And a reverse cycle chiller type heat pump will start at around $3500 for a high quality machine, you would still need storage, distribution, circulation, control, pv panels, wiring, mounts, integration materials like power electronics, transfer switching, etc. Depends on what you have for energy systems existing too.

One of the cool features i have seen are heat pump systems that use a transfer from pv to 240vac.
Of course you could just run it off of your house inverter, but some systems do not want to have much additional loading or pv capacity without renovation or upfit.

Still, heqt pumps are great solutions where appropriate.

http://www.hotspotenergy.com/air-cooled-chiller/

http://www.hotspotenergy.com/solar-air-conditioner/

The cool thing about hydronics is being able to integrate multiple sources of heat to storage and distribution.
There are relatively few components to a hydronic system and service intervals for failure are 15-20 years or more. Much of the system parts are common to the plumbing industry leaving collectors and controllers as specialty items.

Wood/biomass, electricity, gas and direct solar thermally produced heat can all be added to liquid storage easily and distributed from in a manner that allows new inputs and outputs efficiently.

Storage is easy and lasts 30 years or more. Very long lived if you have stainless, possibly lifetimes.

Pv prices are going back up... soon they will be back to 2007-2008 prices, is my guess.

270 square feet of collector surface is quite a few btu on any half sunny day as long as you have a low temp loads. Perfect for domestic hot water, space heating with radiant hydronics embedded in mass and keeping a hot tub heated with the least amount of fuel. Depending on what insolation (sun availability) and coldest temps and wind factors of course.

If those collectors look good inside and out, and the insulation and backing are in good shape, they are worth 10's of millions of btu per year for dozens of years on most of north america.

Th main problem with solar thermal is that it doesn't work worth a damn when it's cloudy, or at night, etc.

You could try to overcome this with some kind of thermal storage system, perhaps even a phase-change type of storage.  But this get's expensive fast.

I can't really say if the price is good or not.  
If they are in prime condition then they might be worth $130 ea, but I'd be suspicious of leaks, etc.  That is one of the main reasons they remove these systems.
If you're handy you could build panels for less than that, although they would be slightly less efficient than the black chrome panels.

As stated above you don't remove something that works. 130 seems steep. I see them come up in the classifieds locally for $50. I would not go for it I'd rather install evacuated tubes or the new solar collector heat pump setup. I might incorporate them into a ground array with storage so I could keep an eye on them. Good luck. Interested either way.

That is a very good deal

Solar Thermal collector panels are very under-regulated. It is hard to get solid comparative data from one panel to the next. UL [Under-writer Labs] has not tested many of these.

I have 10 collector panels from Stiebel Eltron.

btw, Photovoltaic panels do not work well on a cloudy day. Solar Thermal panels work great on cloudy days.

Hmmmm, sounds like mixed feelings.

I would think that if space was not a limitation, I could make them make the same capacity for cheaper. The only problem is with construction of a house about to begin, finding the time is going to be tough.

I guess there’s really two considerations. One is whether solar thermal is really worth it at all in this day and age. I’ve read both sides. The other is whether buying 40 year old panels at this price point is wise.

I think the math favors PV+heat pump, except that we are really fixated on this in-ground hot tub, and I’m not interested in heating it with electricity or propane, so that leaves wood and/or solar thermal. The hot tub would also serve as the water storage and therm mass. I am also attracted to the idea of warm feet in the winter.

As for the panels, I worry about leaks as well. That said, this guy has worked in solar his whole life and says he bought these for a project that never happened. I’m not sure there is any way to look for signs of leakage (discoloration, etc.) but that would be big bummer. The guys swears these panels don’t degrade, but in my experience all metal corrodes and degrades with time, so that makes me a bit suspicious.

Galen Young wrote:
btw, Photovoltaic panels do not work well on a cloudy day. Solar Thermal panels work great on cloudy days.

That's not been my experience.  My solar thermal collector doesn't produce any useful heat when it's cloudy/overcast.

There is also the delta-T issue, even on sunny days, if it's really cold out then flat plate collectors don't produce enough heat to be useful.  
PV on the other hand works BETTTER when it's cold out.

Final consideration, what are you going to do with the huge amounts of heat produced by 15 flat plate collectors during the summer?  With a PV array you could run an air conditioner if needed.

Note: it is possible to use heat to create cold. Absorption coolers come to mind.  However, last I checked nobody make one small enough to use for cooling a house and they are rather complicated to build.

Hot tubs are lovely, but unless you are going to toss the water after each use, they involve some nasty chemicals and a fair amount of work balancing said chemicals.
However, a single use system sounds intriguing.  I've been considering this myself.  Use the water once, allow it to cool and then pump it back through a slow sand filter into my rainwater tanks.

Hydronic systems can work quite well with a heat pump (providing both heating and cooling).  

Another possibility I'm considering is a hybrid system that uses BOTH solar thermal and PV.  Have a few plate collectors that feed a small (300 gallon?) tank, then use the tank to feed the input side of the heat pump.  This way even on cold/cloudy days you could still get enough heat to be more efficient than an air source heat pump.
Bonus, the same setup could work with nigh sky radiant cooling during the summer to provide a cold sink to feed the heat pump.

Galen Young wrote:That is a very good deal

Solar Thermal collector panels are very under-regulated. It is hard to get solid comparative data from one panel to the next. UL [Under-writer Labs] has not tested many of these.

I have 10 collector panels from Stiebel Eltron.

btw, Photovoltaic panels do not work well on a cloudy day. Solar Thermal panels work great on cloudy days.

My experience is much the same as Galen's.

I have been repairing and installing solar thermal hydronics for 14 years and rarely see a failed collector that is made of metals and glass.

I have installed seveal systems with used collectors, including my own and dozens of systems featuring new collectors, flat plate and evacuated tube. The tubes do perform better in very cold ambients, but this is michigan and when a person has a 30 plus year old flat plate system that fails or needs to be re-installed and fired up after a re-roof, it is common to hear that they couldnt possibly consider, not fixing or replacing it, it saves too much money!

That is from long time owners who originally had them installed and from people who moved into them.

If you do a pressure test on them and they hold air, they are likely good for another 40 years!
Look for corrosion and sediment coatings on the inside of the waterways. If the ways are clean and not corroded, they are a great deal at that price.

Collectors (4x8 and 4x10) were going for $250 from AAA solar at new mexico last time i checked.
A new Steibel Eltron or Heliodyne will cost you $1200 to $1400 each plus shipping, $900 or so for the smaller 3x6.

I have seen 150 deg F fluid flowing in flat plate collector loops under less than full sun and below freezing outside, overcast, not so much, but the colder the storage temp falls, the higher the scavenging of heat from the collector, so you will at least pre-heat on most days.

Just like pv, expect 5-10 percent energy output under moderate gray sky, and almost nothing on heavy overcast days, occasionally.

Location matters. And a reverse cycle chiller type heat pump will start at around $3500 for a high quality machine, you would still need storage, distribution, circulation, control, pv panels, wiring, mounts, integration materials like power electronics, transfer switching, etc. Depends on what you have for energy systems existing too.

One of the cool features i have seen are heat pump systems that use a transfer from pv to 240vac.
Of course you could just run it off of your house inverter, but some systems do not want to have much additional loading or pv capacity without renovation or upfit.

Still, heqt pumps are great solutions where appropriate.

http://www.hotspotenergy.com/air-cooled-chiller/

http://www.hotspotenergy.com/solar-air-conditioner/

The cool thing about hydronics is being able to integrate multiple sources of heat to storage and distribution.
There are relatively few components to a hydronic system and service intervals for failure are 15-20 years or more. Much of the system parts are common to the plumbing industry leaving collectors and controllers as specialty items.

Wood/biomass, electricity, gas and direct solar thermally produced heat can all be added to liquid storage easily and distributed from in a manner that allows new inputs and outputs efficiently.

Storage is easy and lasts 30 years or more. Very long lived if you have stainless, possibly lifetimes.

Pv prices are going back up... soon they will be back to 2007-2008 prices, is my guess.

270 square feet of collector surface is quite a few btu on any half sunny day as long as you have a low temp loads. Perfect for domestic hot water, space heating with radiant hydronics embedded in mass and keeping a hot tub heated with the least amount of fuel. Depending on what insolation (sun availability) and coldest temps and wind factors of course.

If those collectors look good inside and out, and the insulation and backing are in good shape, they are worth 10's of millions of btu per year for dozens of years on most of north america.

Frank - wow! What an incredibly thorough response! Thank you so much for taking the time to write all that up. I will keep this information on hand throughout our remaining planning and build. I think I will embed your response in my first post as well. It's a really great point about combining heat sources using hydronic systems. I've been intrigued by the same benefits myself.

Peter (& Frank) - I too am very intrigued by the combined heat pump / solar thermal setup. The guy with the panels actual has an air-water heat pump he'd throw in for $300, but it's a 3.5 ton unit and older so probably lower efficiency. I don't need more than a 1 ton. That has actually been the issue for me in general. All the air-water or water-water heat pumps seem to start at 24k btu (2 ton) and are significantly more expensive than air-air (I assume because of much lower demand, economies of scale). That makes it hard to justify. Cheaper I'm afraid to just have a separate backup air-air heat pump than tie them together for my purposes.

I do however love the idea of adding a wood fired boiler (forced air with exhaust gas through the embers as per the new high efficiency designs) tied into the solar thermal. Whenever it's really cold or time for a soak, fire that puppy up.

Unfortunately, I have decided to not purchase these panels on the grounds that solar thermal is likely one of the final steps in the building process, and the risk of damage in transport, theft during storage, and tied up funds makes it impractical despite being a good deal for a number of identical panels. I did notice other panels for sale in the Denver area, so I would still love to pursue this when the time comes.

If anyone else is within driving distance of Phoenix AZ and has a need for a system, I can get you guys in touch!

Thanks so much everyone - I will be posting a link to a thread specifically on our planned build momentarily...

Here are some window units. The outdoor mechanicals usuall only require a couple small holes to get the indoor end placed in the area you need. Not sure if that helps...they say air conditioner and will heat and cool.

http://www.hotspotenergy.com/DC-air-conditioner/

http://www.hotspotenergy.com/hotel-air-conditioner/

https://www.pioneerminisplit.com/

The Pioneer mini-split heat pumps are pretty impressive, and really cheap.  I have the 22 SEER 12,000 btu model that is currently heating my whole house.  The weather has been too cloudy for the past few days for my solar space heater to run, looks like that will change today.
The overnight temps dropped down below freezing last night, hitting a low of 27F / -2.8C.  For most of the night the heat pump was only drawing 250-300 watts,  about 2 hrs ago that jumped up to 400 watts (still below freezing outside).

I'm tickled as all get out by how efficient this unit is, especially considering it cost less than $800.

Thanks so much for the links to those heat pumps! I am definitely going to check them out!

I have started a thread on our actual build: https://permies.com/t/77046/sq-ft-Passive-Solar-House

Many, many thanks for all the help!

just had a post from this morning about low temperature heating.  I did not deal with storage, but would not do the solar thermal without lots of heat storage.. The cheapest way is still to store the water in a large well insulated tank.   The second point is to move the emisser of the heat away from the floor and into the ceiling or walls.  Go very light weight construction. pex al pex with heat spreaders on top of 2 inch poly that is aluminum on both sides and then lay that ontop of osb.  you can pretty much use any finish to cover your emitter.   One can play games with the thermo panels.  but a simple pv panel to drive a pump to a drain back system is easy.. Put one circuit from the panels into a large loop of pipe. 2 inch by 100 ft  so plenty of time for the flow to run and heat the water in the tank.. Playing with phase change materials is less efficient than just plain water..  Then run another similar length of pipe that is connected to your hydronic heating  and or domestic water.  I would personally run two circuits so that there is no intermix between the hydronic heating and domestic water..   Plumb the domestic water thru a water heater so as long as the heat is sufficient that heater rarely will ever cycle.  The only real power needed is for the pumps.  They certainly do not draw anything near to a heat pump.  The cost of a heat pump is not cheap by any means.    

As to 130 per panel.. cheap enough. but I would take a compressor and some fittings so you can check to see if they are holding pressure.