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Gasifier / Solar Sweet Spot?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by VeggieFarmer, Jan 22, 2008.

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  1. Grover59

    Grover59 Member

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    Ok what I was going to do is make my own plates with aluminum flashing, these things tend to be expensive already made what do you recommend?

    Steve

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  2. sled_mack

    sled_mack New Member

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    Those would be thin plates, and essentailly what I used the second time around. There are mfg's that produce pex and matching plates. They are extruded, and average about .100 inch thick. Not something you can form yourself. Expensive - yes they are. But if you want to get you water temps down you really don't have much choice.

    Sorry for the thread hijack. I'm still interested in hearing more about solar setups!
  3. Nofossil

    Nofossil Moderator Emeritus

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    Back on topic...

    Adjusting the angle dynamically can greatly improve solar panel performance - ideally, track the sun east-west each day, and adjust north-south over the course of the year.

    Here's where my practical side kicks in. As anyone who's visited my site knows, I'm not afraid of complexity. However, my sense is that if you wanted to double your output, it would be easier to simply double your square footage rather than build and maintain a sun angle tracking mechanism. Kind of the same issue as the evacuated tubes - seems like a more expensive way to increase your output. I suppose there's a kind of logic if you start with the premise that you need expensive and exotic panels. They cost so much that it makes sense to put in place a complex system to get the most out of them.

    There would be a case to be made if you couldn't attain high enough temperatures to be usable, or if you needed to use the panels when the sun angles are really bad. However, there's no question that even the simplest and crudest panels deliver usable temperatures for all but the coldest seasons.

    By the way, an entire day's solar output in the summer is the same as one hour's output from my wood boiler, and I have the smallest boiler I could find. Going to a lot of effort to harvest solar heat during wood burning season doesn't seem worth it to me.

    I have a 4' x 20' extruded plastic pool heating panel feeding three glazed panels plumbed in parallel. Typical performance is 100 degrees entering the bottom of the pool heater panel, 135 degrees entering the glazed panels, and 170 degrees delivered to the storage tank. Flow rates can only be inferred, but they are in the range of 0.5 gpm.

    In response to an earlier question, it's true that your output temperature will increase as your input temperature increases, but panel losses increase as well, and there will be an equilibrium temp at which panel losses match solar gain. It's about 140 degrees for my unglazed plastic panel lying on the ground. Don't know what it is for the gazed panels - probably around 230 or so. I do know that they will boil water. The problem is that solar panels are really good at absorbing energy, but they're equally good at radiating it out into space. Since the temperature of space is really low, they dump a lot of heat back out through the glass. On a cool clear night, the black panels will have a thin layer of frost even thiough the air temperature never reached freezing. Radiational cooling is not your friend, but it's unavoidable.
  4. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Ok NoFo, you got me wondering . . . Seeing that the dog and I dispise the heat . . . care to postulate on radiational cooling? I have often wondered if pex stapled to the underside of my roof (Grey standing seam steel sheds snow and water. . .but NOT the sun's rays) could be used as a DHW pre-heater in summer, with a positive side effect of attic cooling?
  5. Nofossil

    Nofossil Moderator Emeritus

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    Do I interpret this to mean that you're now sleeping with the dog?

    Pex stinks at heat transfer to/from air, and I'd worry a bit about condensation if you were running cold well water up there. However, solar hot water panels on the roof definitely reduce attic temps. Your pex idea would work a bit, but I don't think you'd make much of a difference unless you could thermally couple the pex to the attic air. Clip-on aluminum flashing fins would help a lot in this case.

    If I can find a source for aluminum sheets with formed-in tubes, I want to place a couple on the ceiling of my main living space and a couple on the north facing side of the roof. The idea is that the panels on the roof will cool by radiation (the north sky temp is well below 0 degrees in te summer) and the cool water will thermosiphon through the ceiling panels, cooling the living space. I'm curious to see how many BTU/hr/sqare foot you would get.
  6. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Stiebel Eltron Solar Panels Look like about $1k per panel when you include mounting hardware. Obviously this doesn't include plumbing, pumps/controllers, nor a tank.

    Total surface area sqft 29.06
    Net effective surface area sqft 26.91
    Collector output range Btu 0-6826
    Max. temp. F 410 C 210
    Typical transfer flow rate Gal / h 13-80
    Working operating pressure PSI 50.7
    Max. operating pressure PSI 80.7
    Tested to pressure PSI 160
    Pressure loss PSI 0.44
    Dimensions inches 87 15/16 x 48 1/8 x 3 1/16
    Weight without heat transf. fluid lb. 106
    Recommended mounting angle 10 - 90 degrees
    Plumbing connections 3/4 inches
    Frame anodized aluminum, seawater resistant
    Absorber copper, titanium-nitrite-oxide coating
    Thermal insulation rock wool
    Eta Optical 78.5 %
    Light transmission 92 %
    Heat transfer fluid non-toxic polypropylene gycol solution

    But what would you expect with a 6.8 BTU collector? My house is in Upstate NY and faces North, so would a WAG of 10Am-2PM (southfacing roof) @ 6k make for a best case scenario of 24k BTU per day? If I am thinking anywhere near reality, one collector should be plenty for two people. Figure for the lack of sunshine, fire the GW as needed. Let's say a week of straight solar collection, how much storage would be needed? I am thinking 160 gal dual exchanger $2.4k would be enough, as long as we set up over-heat controls. Then I am thinking after we run it for a year, add another collector on a west-facing roof (2PM- 6PM for another 24k BTU on a perfect day) as needed.

    Viessman seems to want a buffer tank too, but I cant see where they make anything over 80 gal???

    Tell me what I'm missing??
  7. Nofossil

    Nofossil Moderator Emeritus

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    You need to look at average sunlight - lots of days aren't sunny. If you haven't read through my page on solar hot water, it might make sense to look at the data. I've attached a graph below that shows panel output temps over the course of a (rare) perfectly sunny day. Peak output doesn't happen for very long, and the average over the best 4 hours is considerably less.

    I have three glazed panels that are in the same general size range as what you describe, and another 80 square feet of pool heater. I think I could supply our needs with two of the pool heaters at $140 each. Max temp is only 135 degrees, but lots of surface area means lots of BTUs.

    I know that you're willing to burn wood, but that might not seem so attractive come August.

    24,000 BTU/day seems a bit low, but reasonable if you're really careful about hot water use. With a family of five using low-flow shower heads and front-loading washing machine, we're somewhere around 65,000 BTU/day.

    Attached Files:

  8. leaddog

    leaddog Minister of Fire

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  9. mikeyny

    mikeyny Feeling the Heat

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    take a quick look at my solar setup. I posted in the green rm. No scientific data, just free hot water. My bill went from 80 to 100 therms down to 15 to 25 per month. It is only a savings of about 60 to 70 bucks a month. Seems hardly worth doing until you add it up over 4 yrs of doing nothing but going to bank with that dough. As I have said before my favorite saying "shut up and do it". (Not really meant to offend anyone,, buttt).
    Mike
  10. VeggieFarmer

    VeggieFarmer New Member

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    CT River Valley, Vermont
    Very helpful thread. The consensus seems to be that some amount of solar is worth it for augmenting wood, especially when sized to handle the summer dhw load. But really going for it with solar - say 8 panels or more to try to make a dent in the winter space heating - is throwing lots of money down the hole of diminishing returns. At least in climates like VT and NY, it's more efficient just to cut an extra half cord or so to feed the beast.

    Let me add one wrinkle - our farmhouse came with two flat-plate collectors on a glycol loop to the dhw heater. (A pretty standard-type installation.) I was planning on moving this loop to the proposed wood-boiler storage tank. Would having an existing four-season solar rig change anyone's approach? Would you try to extend your solar season beyond the frost-free months? NoFossil - I notice from your site that you're still burning some oil in the shoulder seasons to bridge from solar to wood. Could this bridge the gap?
  11. Nofossil

    Nofossil Moderator Emeritus

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    The bridge is because the sun angles are too low and / or there are too many days without sunshine. I shut down the panels last fall on the same day I started my first fire. Last season I was still dialing it in, and the glazed panels didn't come online until sometime in May, if I remember right. The fall shoulder is probably what this coming spring will look like. Perhaps there will be years where there's a gap between frost-free and wood boiler seasons, but it's pretty small if it exists at all. Four season panels would certainly reduce the oil demand during the frost portion of the shoulder seasons, though they probably wouldn't eliminate it.

    My freebie glazed panels had heavy corrosion from some antifreeze solution that had been used in them. Don't know if it was glycol, but I've heard that it can be corrosive under some conditions. For that reason and because I'm still chasing little leaks in the pool heater portion, I'm staying away from glycol.
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