New Solar Thermal Concept Panel

[alex]

To make a long story short, I have built a solar thermal panel in my back yard. However, its a bit different then what I have seen elsewhere. My goal is to find a way to make a cheap solar thermal panels that can out compete current systems in efficiency. I think I may have a concept that could get there.

I have figured out how to make a solar panel out of nothing but plastic, insulted it, and keep it from melting. In short, the panel turns on (becomes black) when water is flowing and turns off (becomes reflective) when water is not flowing. The result, I think, is that solar thermal panels can be built from plastic since the panels will never overheat. This could mean a cost reduction of 80% over what I see currently.

I have a background in physics but I am by no means an expert in solar thermal. I have no practical experience with solar thermal systems whatsoever. The problem just seems to tempting not to work on. I would really appreciate any feedback from anybody out there.

http://www.particlepanels.com/

Blue Skies,

Alex

[Mike90250]

Very neat idea. I'm not sure why you get a descending flow on the back side.

Why doesn't the water pressure/flow trap all the particles at the top, or are they heavy enough to overcome the water flow, and stay distributed.

[alex]

Mike,

I know the answer to the second question. When the water pushes the particles up they hit against the wire mesh. That cause the resistance to flow to increase and the flow to slow down. That, in turn, causes less push on the particles, which fall down due to gravity. The result is that the panels self-stabilize at a working pressure that is just what is needed to keep the particles up.

As far as the circurlation, its really cool and I think related to emergent phenomean like the Bernard Cell.

However, its more complex because there is both tubulent and laminar flow and the liquid is not conserved (water coming in and out). There is a theory of dissipative systems that states that a natural system will configure itself for maximal entropy production (energy dissipation). If that theory is true, then these particle are organizing themselves for maximal heat transfer. I can sort of buy that explaination, because the turbulent flow seems to be mixing the particles, bringing the "cold" ones to the surface and the "hot" ones to the back. The water flowing past the particles in the upward turbulent flow extracts the heat and the laminar flow down the back efficiently cycles the cold water back down. Almost like a "living heat exchanger".

When I designed the panel I did not expect this sort of behavior at all. I figured the particles would spread out, but had no idea convection currents would set up.

[Jason]

Hi Alex,

I appreciate you registering here to share your project. It looks very interesting.

I emailed a few members who are knowledgeable with solar thermal, so hopefully they will pop in here to take a look.

Thanks again and I look forward to reading more about this.

[alex]

Thanks Jason. I look forward to any feedback, whatever it is. When I looked into how much energy we spend heating our homes and water and saw it exceeded our use of electricity, I got really motivated to think of ways to bring the cost of solar thermal down. Well, that plus every winter around this time I start to curse the gas company. I guess this is my way of venting.

[sundug]

Coroplast collector

I am working on a plastic collector design also, it is a refinement of this idea- http://www.iwilltry.org/b/projects/b...-water-heater/
using coroplast, the polypropylene sign and packaging material. See also-
Coroplast heat exchanger-

http://www.youtube.com/watch?v=470-rEXkNhA

I have had a PV pumped solar water heater on my roof for over 18 years, it is a closed loop, and uses propylene glycol antifreeze, which can be damaged by high temps. Since the PV powers the circulation pump whenever the sun shines, stagnation of the collector is not a problem. I have never had water temps over 165*F, since I sized the storage to collector area correctly. If we go away for more than 4 summer days, I cover the collector. I am on dial-up, and cannot view your video until I get to a hotspot. What type of plastic are you using? It looks like polycarbonate, which cannot take long exposure to hot water. Doug

http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm

[TekArt]

Plastics fabrication

I have read through the details of your design concept. I have a couple of concerns about the real-world practical design.

First you MUST use antifreeze in cold climates or the walls of the plastic channels with burst when frozen. I wonder how the higher viscosity of propylene glycol will affect particle distribution? Will glycol affect the plastic? Interact chemically with the particles?

I'm in Maine USA where temperature extremes range from -15F to 105F seasonally. A good commercial design should be able to withstand all conditions. I'm currently very happy with my "traditional" SunEarth copper collectors that I use to heat my building. But I have to drain them in the spring because I get too much heat. I routinely see fluid temperatures of over 220F in the spring and fall.

I have considerable plastics fabrication experience (museum displays) and the the fabrication of the manifolds at top and bottom will be very challenging and will need very careful thought. You really don't want to have a commercialized version to fail at the seams and create all kinds of property damage issues. This may be the biggest challenge in commercializing the design. So far you have tested with no pressure, but adding "real world" pressure and experimenting with pumped flow rates would seem to be the next step in testing.

Guy

[Mike90250]

> First you MUST use antifreeze in cold climates or the walls of the plastic channels with burst when frozen

I think it's a drain back system, with no water at night or bad weather.

[TekArt]

Well yeah, but drain back or not you have to design for all worst case scenarios!

Here in Maine a drain back system might turn on when the TOP sensor on the collector in a traditional copper collector gets substantially hotter than the storage tank. But with a plastic collector how do you measure that temperature? Without some thermal mass up there what gets hot?

Say you have a winter morning and it's 10F outside when the sun is up. The top corner of the collector may be warm enough, but the bottom where the fluid enters will get chilled very quickly in a plastic channel. Very different from a copper absorber that has already been warmed up in the sun. The thermal shock to the plastic will surely degrade it. Not to mention the copper piping to plastic transitions where thermal expansion coefficients will be very different. Hmmm.

Guy

[sundug]

Drainback vs closed loop

Drainback exposes the collector to high stagnation temps, assuming the differential controller shuts the pump down when the storage high limit is reached. If PV pumped closed loop is used instead, no such stagnation problem exists for the collector, which would be very advantageous for a plastic collector. Besides, PV pumped is the most efficient SHW system. Doug

There are pros and cons to each system, neither is the best in every situation. For example, many installations have the collectors out in the yard, where drainback is difficult if not impossible. Some collectors are not plumbed for drainback. Drainback requires more pumping power to repeatedly lift water to the collectors, which almost all the time means grid powered pumps. Since such pumps are performing more work, they wear faster than circulation pumps, as do the contactors controlling them. If a cloud bank passes over a drainback, it drains the fluid down, and then needs to add the energy back again when the sky clears, this can occur many times during the day. PV pumped systems will just reduce the pump speed to closely match heat gained in the panel, never requiring the considerable energy to lift a column of fluid. Being grid powered, drainback has parasitic losses requiring large differential settings compared to PV pumped. Most drainback systems are not set up for variable flow, PV pumping naturally provides variable flow. Because of these last two points, PV pumped is the most efficient. Don't take it from me, read what the experts have to say-

From Homepower Issue #126, Aug, Sept 2008 Article titled "Under control-solar water heating- SHW controllers" Page 60

"Parasitic loss occurs when energy is consumed or lost in order for a system to make more energy. <snip> In grid powered SHW systems, the pumps and controllers take a certain amount of electrical energy to operate. <snip> If the parasitic losses are greater than the solar energy being put into the SHW system, a net loss of energy results. In PV-direct DC systems, the pump energy losses are inconsequential because the energy from the PV module is there regardless, and at no cost. But in AC systems, a wider temperature differential is used to ensure that the parasitic losses are not greater than the solar energy gained. <snip> Since there is no utility generated parasitic power consumed with a PV powered DC differential controller, the turn off differential is lower-sometimes zero is appropriate if the pipe losses are negligible."
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This makes it clear that PV pumped SHW systems are more efficient because they have a zero degree differential, gaining solar heat whenever collector temps are above tank temps, while AC powered system differentials range as high as 18*F, to overcome losses caused by carbon based grid powered pumps. PV pumped systems also have the ability to moderate flow according to the amount of sun received, not just on or off like AC systems.Doug
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Subject: Most efficient solar water heater


Homepower Issue #121, Oct. and Nov. 2007 "Pick the right pump" article by Chuck Marken states on Page 86-

"Using a utility powered AC pump for your solar water heating system will give you a COP between 12 and 25, this is an excellent value compared to electric water heaters, which have a COP of 1. But the COP will never be as good as a DC PV powered SHW system. DC hot water circulation pumps have a higher COP than AC pumps because there is no traditional energy input if a PV module powers the system. If you use a solar-electric module to power the pump, your COP is infinite- you`re not adding any energy input. The sun provides it all, and you get something for nothing after the initial investment. PV powered systems are immune to utility outages."
"PV powered DC pumps are normally the optimal choice for a solar heating system except in high-head drainback and very large antifreeze systems."

[TekArt]

Excellent point SunDug! This is why I brought my solar powered Differential Temperature Controller to market. www.arttecsolar.com

There is an inherent mis-match between the performance of a PV and collector that necessitates the use of a controller. A PV powered pump can start too early in the morning and remain on long after the tank temperature has peaked unless you have an active control. My controllers are the only ones made in North America that operate from solar power. (forgive the plug!).

[sundug]

Differential controller

Hi Art!
I have bought two of your controllers, and have one one of the high temp models working on my system for years now. Thanks, Doug

https://www.builditsolar.com/Projects/SolarHomes/Doug/DougsProjects.htm

http://www.youtube.com/user/sundug69

[alex]

re: Sundug and TekArt

wow. Thanks for your comments! This is very helpful.

sundug: "I have had a PV pumped solar water heater on my roof for over 18 years, it is a closed loop, and uses propylene glycol antifreeze, which can be damaged by high temps. Since the PV powers the circulation pump whenever the sun shines, stagnation of the collector is not a problem. I have never had water temps over 165*F, since I sized the storage to collector area correctly."

The problem I see is that I want to use solar panels to heat my house (santa fe, NM). Thats were I would get a huge benefit. For me, space heating costs in the winter far exceed any other energy costs (other then gas for my car). The temperature fluctuations here are crazy. freezing one morning and 65 in the afternoon. Sizing the system for heating in the winter is a huge mismatch for summer hot water heating.

TekArt:
"First you MUST use antifreeze in cold climates or the walls of the plastic channels with burst when frozen. I wonder how the higher viscosity of propylene glycol will affect particle distribution? Will glycol affect the plastic? Interact chemically with the particles?"

Well, i was toying with the idea of a drain-back system. However, glycol is apparently chemically compatible with polycarbonate (but see sundug's comment about damage from hot water). I have no idea what would happen with very viscous glycol. Its challenging because the glycol's viscosity changes quite a bit as it gets warmer.

TekArt:
(1) "I'm in Maine USA where temperature extremes range from -15F to 105F seasonally. A good commercial design should be able to withstand all conditions. I'm currently very happy with my "traditional" SunEarth copper collectors that I use to heat my building. But I have to drain them in the spring because I get too much heat. I routinely see fluid temperatures of over 220F in the spring and fall."

Exactly!! That's the problem as I see it. I live in Santa Fe and, although I dont get temps quite that low, the variations are crazy. I would be happy with a modern commercial system too. However, I want to heat my house with solar panels and I don't want to spend $1,000 for each panel. What if the panels cost $200? How many people would start to use solar?

(2) "I have considerable plastics fabrication experience (museum displays) and the the fabrication of the manifolds at top and bottom will be very challenging and will need very careful thought. You really don't want to have a commercialized version to fail at the seams and create all kinds of property damage issues. This may be the biggest challenge in commercializing the design."

You are exactly right. Building a manifold that did not leak like a sieve was hard for me. (no plastics experience here, but im learning) However, I have since learned that I can bend the plastic to make the manifold, which would help. I also think that, in the hands of a true plastics engineer, a design could be built that was solid. (perhaps even one piece?) You are totally right however. The manifold is a big deal.

(3) "So far you have tested with no pressure, but adding "real world" pressure and experimenting with pumped flow rates would seem to be the next step in testing."

Well, I used the pressure from my main. Don't know what it is but it squirts a jet of water about 30 ft high. However, point well taken.

(4) "Here in Maine a drain back system might turn on when the TOP sensor on the collector in a traditional copper collector gets substantially hotter than the storage tank. But with a plastic collector how do you measure that temperature? Without some thermal mass up there what gets hot?"..."The thermal shock to the plastic will surely degrade it."

Very good points. This is actually one of my biggest concerns. Actually, another concern is that the mixture of particles at the bottom would be a big lump of frozen particle mud, so to speak. My "solution" here (the only one I have thought of so far) is to use residual heat stored in the heat exchanger tank coupled with some light sensors on the panel. The system would be able to tell if there is enough light hitting the panel to warrant starting, and it would also know how much heat was in the tank. It would use this heat to prime itself, melting the particle mud and getting everything started. [note that this requires one of the channels on the panel to be a bypass that would let the warm water flow around and over the particles.]

I have no idea about thermal shock to the plastic. Perhaps this is a deal-breaker. However, I remain optimistic. I will certainly look into it, and thank you for bringing that to attention.

sundug: "Drainback exposes the collector to high stagnation temps, assuming the differential controller shuts the pump down when the storage high limit is reached."

In this panel design, when the water stops flowing the panel goes from black to reflective, which would presumably prevent high stagnation temperatures.

[Jason]

Hey Alex, I'm going to move this thread over to the Solar Heating Discussion Forum if you don't mind

[Mike90250]

Automotive Mfg's have developed plastic tanks for radaitors, that handle frozen Alaska to 250F @ 15psi. So that 15 PSI will be about your limit. You could have a PV panel power the pump, but I think heat shock on the PC would be a minor issue. Also, if you control the speed/flow, so that the water only gains a little heat, you are not re-radaiting it out. Consider PEX tube, not copper.

Mike