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.
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.