Sunward Solar Hot Water

[jbeall]

Hi All,
Is anyone here familiar with Sunward Solar Hot Water? It's a solar hot water system. Sounds interesting, it's the cheapest "packaged" solar hot water system I'm aware of (but maybe there are others I don't know of).
It's way more expensive than a standard hot water heater, but if it works, it may pay for itself over the long term... anybody here have experience with Sunward, or another solar hot water system?
Thanks!
-Josh

[rreidnauer]

What seems common (and counter-intuitive?) with renewable energy "packages" is, they are always expensive. You can almost always do better sourcing the individual components yourself. (I guess you are paying a "convenience" premium for "packages") Second, these are flat-plate collectors. I don't recommend them, especially if you live anywhere there is less the 98% sunny skies. They suffer from two problems which reduce their efficiency. First problem, the flat glass front. Almost every photo on their website reflects the problem, literally!!! Notice the glare on the panels. That is reflected light that never gets collected. It's not bad if the sun is directly in front of the panel, but as angle increases, energy absorption decreases exponentially. Second problem, the collector itself. It's just black tubing under glass. The problem occurs when a cloud or any form of shadow reduces light input. Heat energy of the fluid being pumped through the panels is actually radiated back out of the panel. There are supposed coatings to help reduce this from happening, but it can't be avoided. Essentially, when a cloud passes by, you go negative production.
I strongly recommend evacuated tube collectors. They suffer neither of the problems of flat-plate collectors, as they are able to collect energy at an angle as efficiently as if directly forward, and being that they are vaccuum tubes, heat energy can't be released back when shaded. (that, and the fact that the fluid never enters the collector tubes to start with) Efficiency all around is higher. Though be warned! Fluid MUST be continuously circulated though evacuated tube collectors while exposed to sunlight. Due to the nature of their design, stagnation temperatures can exceed 400F.
The rest of their system is basically the same as my own I'm putting together. So parts and costs. What do you need and what is it going to cost? Well, this is a breakdown of what I have.
2 - American Solar Works ASW-52B collectors. (old model no longer available) I paid $650 each through a Craigslist ad placed by importer/distributor.2 - El-SID 10PV 10 watt, 3.3 GPM direct solar, magnetically driven circulator pumps. I paid $200 each1 - 50 watt polycrystalline solar panel (used, brand unknown) I paid $254 shipped off Ebay7 - Weksler 152FC 40F - 260F 1/2"NPT thermometers. (Bought new on Ebay for $25.50 shipped. So low the seller didn't want to sell them until I pressured him to complete the sale)And, what I still need:
1 - ART-TEC DTC-1 Solar powered temperature differential controller (costs $110 w/ sensors)1 - liquid to liquid heat exchanger. (I haven't chosen one yet, but probably a flat plate <$100)1 - expansion tank (<$50)1 - pressure relief valve (<$10)2 - 80 gallon water tanks (can be simple storage tanks or water heaters. Way cheaper option than solar storage tanks with built in exchanger) Price? Probably around $450 ea, versus a solar storage tank w/ internal heat exchanger at $1500+ each. Pipe and fittings. (I'll probably use copper pipe salvaged from my previous job for non-potable portions of the system)

[rkissinger]

Hey Rod, sorry in advance for these stupid questions, I am totally ignorant on the subject of solar hot water. Is it realistic to use solar heated water in a radiant heating system? Also how do you address freezing in the winter? Thanks

[rreidnauer]

. . . . is the one not asked.
Yes, you can do solar hot water home heating. It just takes more panels and more storage tank volume. I think when I was calculating how many panels would be needed for home heating alone, I came up with 12 of the type I bought, for my 1,800 sq.ft. home. (I didn't even calculate tank volume since it was already too pricey for me to further consider)
Freezing concerns are handled in one of two ways. You can either do a "drain-back" system, where water is pumped up to the collector, but pipes are pitched back to a vented storage tank indoors, so when the pump stops, all water drains out of the system and back to the tank. It has two drawbacks. First, you need to run your temperature sensor wires all the way out to the collector(s) to tell the system when it should start pumping. This can also cause some erratic cycling of the pump during the night to day transition. Second issue, you need more powerful pumps to lift the water to the height of the top of the collectors and still maintaining sufficient flow.
The second type is a closed loop, heat exchanger system. In this system, there is a separate loop that goes from the collector(s) and a heat exchanger located near the storage tank. This loop is filled with a non-toxic glycol solution, so it never freezes. The other loop goes from your storage tank, to the heat exchanger. Here, you don't have those problems mentioned earlier. Because the loops are filled completely, there is no head pressure. (fluid pumped up is balanced by fluid returning back) and small pumps can be used. Also, because the glycol loop can be pumped continuously, (as long as the sun is shining on the solar panel) you can place your temperature sensors right at the heat exchanger. Then only the tank loop gets switched on and off (by the temperature differential controller) whenever the collector loop is hotter than the tank temperature.
The second is the system I prefer. It can easily be powered by one small photovoltaic panel, and is completely self-contained, fully automated, and nearly maintenance-free. (change glycol annually/biennially)
Here's basically what I'm doing:
http://img.photobucket.com/albums/v328/titantornado/Solar_Hot_Water.jpg

[jtellerelsberg]

. . . Second, these are flat-plate collectors. I don't recommend them, especially if you live anywhere there is less the 98% sunny skies. They suffer from two problems which reduce their efficiency. First problem, the flat glass front. Almost every photo on their website reflects the problem, literally!!! Notice the glare on the panels. That is reflected light that never gets collected. It's not bad if the sun is directly in front of the panel, but as angle increases, energy absorption decreases exponentially. Second problem, the collector itself. It's just black tubing under glass. The problem occurs when a cloud or any form of shadow reduces light input. Heat energy of the fluid being pumped through the panels is actually radiated back out of the panel. There are supposed coatings to help reduce this from happening, but it can't be avoided. Essentially, when a cloud passes by, you go negative production.
I strongly recommend evacuated tube collectors. They suffer neither of the problems of flat-plate collectors, as they are able to collect energy at an angle as efficiently as if directly forward, and being that they are vaccuum tubes, heat energy can't be released back when shaded. (that, and the fact that the fluid never enters the collector tubes to start with) Efficiency all around is higher. . .

Rod, the theoretical arguments for evaculated tubes makes them sound definitively better than flat plates, but in actual practice they turn out to have pretty much the same performance. As evidence that flat plates work just fine, even in a climate with plenty of clouds and snow and the whole bit, see these results for side-by-side systems in Ithaca, NY: http://goo.gl/JQBj0 . You can play with the graph displays to compare different bits of data collected by the installer. The graph I link to shows "total thermal energy produced" by each system for the most recent year. In all but 3 or 4 of the 52 most recent weeks, the flat plate system outperformed the evacuated tube system by this measure--not by a lot, but by a little.

(As a side note, your second point about radiating heat out when there is a cloud passing by doesn't look quite right to me. Radiation of heat occurs through a vacuum perfectly easily, so evacuated tubes can't avoid that. What the evacuation does is create insulation that prevents convective or conductive heat loss, but the only way they could slow radiant heat loss is with a reflective radiant barrier--which would prevent any sunlight from hitting the heating tubes in the first place.)

-Jonathan

[rreidnauer]

Yes, you are correct. I should have said that the flat-plate collectors convect off heat when shaded, not radiate it.

I didn't get a chance to look at those side-by-side specs yet, but it does have my interest. Thanks for the link.

Sent from my Samsung Galaxy using TapaTalk 2

[Steve Wolfe]

I’m still not convinced. From what I understand the reverse transfer of heat in a flat plate or vacuum collector is minimal during a sunny day. However during the night or cloudy days with below freezing temperatures the reverse heat transfer from the transfer medium, (water/glycol) will occur much faster on flat plates versus vacuum tubes. The terms “Radiate’ and “Radiation” are very different. Both heat and radiation can radiate as radiate describes something emanating from a source. Radiation is light and easily passes through a vacuum. Heat will not transfer through a vacuum, at least in any amount that you or I could measure. The reason is there are no atoms or particles in a perfect vacuum.

To simulate particles, put 10 dominos standing up on edge and one inch apart. If the first domino falls in the right direction each succeeding domino will be pushed and fall down. But if you removed the second, third and fourth domino to simulate a vacuum, movement or energy transfer will stop after the first domino falls toward the vacuum as there is no other domino or particle it can push to continue the transfer of energy. It is possible that a miniscule amount of energy may occur due to vibration.

Jonathan, that link you posted is a great link with lots of comparative data. But after comparing specs on the two systems used in the side by side test it appears the data was based on flat plate with a collection area of 64 s.f. whereas the vacuum tubes had about 32 s.f. The guy that did the test and data collection stated in his summary that he did not select the collectors based on each having similar s.f., but on equal system cost!

If my research is accurate the flat plate systems required 2X the collection area in order to perform as well as the vacuum tubes. Based on this I still believe that per s.f, vacuum tubes are much more efficient. If I can spend the same $$$ and consume one half the area for installation, it looks like I would go with vacuum tube collectors.

[LogHomeFeverDan]

Ok conceptual question. Do we not have the technology to keep a body of water hot enough for home use for extended periods of time? I'm thinking like 100 gallon "thermos"? What I'm saying is, the challenge with hot water for the home is the need to keep reheating it. Even in NC where our land is located, I would think the sunlight hours would be sufficient to heat enough water. Isn't it a matter of keeping it hot? or am I just too naive?

[rreidnauer]

I suppose that's true, except you don't account for actually using hot water.

Sent from my Samsung Galaxy using TapaTalk 2

[StressMan79]

But the second u use any hw, cold replaces it. Best to use it 4 preheating.