Gasifier / Solar Sweet Spot?

[VeggieFarmer]

I’ve been poking around the Boiler Room for the past few weeks and have been impressed by the amount of knowledge and willingness to share it.

Here’s a question that’s been on the edge of several threads that I’d love to discuss straight out: if you’re using a wood gasifier (with water storage) to run a radiant heating system and dhw, is it worth adding a loop with a few solar hot water panels? Is there a “sweet spot” hybrid between solar and wood?

The theoretical upside seems clear enough – you could shut off the boiler for half the year and reduce your overall wood chores. But there would seem to be downsides: can solar panels get hot enough to run dhw by themselves; will the panels actually displace a significant amount of wood; if the solar system is sized large enough (6-8 panels) to make a dent in the winter season, will it require a substantial summer heat sink; is the expense of all the additional plumbing really worth it?

At present I heat a 3,700 sf old farmhouse (insulated reasonably well) using 6 cords of wood (burned in two newer non-cat woodstoves), 270 gallons of oil (fha ancient backup furnace), and 670 gallons of propane (dhw plus radiant heat under 700 sf of living space.) I also heat a 800 sf greenhouse (March to May) on 200 gallons of propane.

My plan this summer is to convert to a wood gasifier plus storage tank to run everything, including the greenhouse. My wood is free for my labor, but given that I’m already cutting and splitting 6 cords under the current system, I’m concerned about how much more wood chores I might be taking on. Hence the theoretical appeal of adding some solar. Any perspectives? Is there an optimal price/complexity/thermodynamic tradeoff point between gasified wood and solar?

 

[Eric Johnson]

Welcome to the Boiler Room, VeggieFarmer. Organic, I presume?

I'm glad you've found the site interesting and even happier to learn that you're considering a gasifier. Those of us who have them, really seem to love 'em.

One of our members, nofossil, has a solar component to his system, as do a few others, I believe. So I'll let him answer your questions, other than to say that the answer is probably "yes."

 

[slowzuki]

Solar works really well on big tanks and radiant heating temps, very poor for radiators etc needing high temp water. A solar collector can really help in shoulder seasons to reduce wood consumption and could replace a lot of wood burning in warmer winter spells. Of course this depends how far north you are.

 

[sled_mack]

I've been considering the same question. I think if you are going to have a storage tank, it's a reasonable thing to do for eliminating any costs over the summer for DHW. At least that's my thought so far.

We go snowmobiling during the winter, so anything that will help add heat to the storage tank when we are gone is a great thing. The big IF - If the sun comes out when I need it to

Everything I've read points to evacuated tube style solar systems to get the required temperatures. My idea is to install more racks than I need at first and only partially populate them. Start with enough for DHW in the summer at minimum, then add more each year as the funds are available. With this style system, you could remove the excess tubes in the summer to reduce the amount of dumping heat that will happen. This is only practical if they are easy to get to. Otherwise, maybe cover them with a tarp or something.

As I said, just thoughts and ideas for now. I'd like to hear other peoples ideas and comments as well.

 

[leaddog]

I'm kicking this around also, but the thing I'm wondering is where You get the evacuated tubes. The ones I find here in the US are really high. I've googled them and there is a ton of them made in china and exported but by the time they make it here it seems that they get really expensive. I've been kicking around the idea of importing a container as I'm sure that you could sell the excess very easily but I'm not sure what is all involved. How would one find someone that is importing things? It seems like you should beable to make somekind of deal. These things are really taking off in the rest of the world but every one I talk to here says there isn't a market here. Well not for 10 to 12 thousand but when you can get the BIG 58x1800 tubes for less than $700 per 30 tubes then you are talking. I have the tank, piping is CHEAP, and I have the bronze taco pump so it becomes very doable. (broken link removed to http://www.wksolar.com/p08.htm)
leaddog

 

[Nofossil]

If you have storage and use it to heat or preheat your DWH, then solar makes a lot of sense for the summer months. I'm set up to use solar from last frost to first frost, and wood the rest of the year. Here in Vermont, the sun doesn't shine enough in the winter to make solar worthwhile, so I just drain the panels around mid-October. I use a bit of oil at the end of the season. By September, the sun angles are getting low.

I'm WAY too cheap to use evacuated tubes. I'm getting 175 degrees off of simple glazed panels. Don't know why you'd need more than that.

I've got a writeup on my site - link is in signature below.

 

[sled_mack]

Nofossil,

I read your write up. Nice setup.

Obviously, your experience contradicts what I have been told by many solar panel places. Even places that only sell flat glass panels tell me the efficiency drops way down once the outlet temp reaches 140. Most told me I could never get 160 out of them, no matter how many I had in series. I should know better than listening to sales people by now....

I can't use my tank for pre-heating domestic like you do. My tank is in the boiler shed. So, I've got to get the tank hot enough to make my DHW. If I can't, the project is a loss.

I also really like the gravity setup you have. There is no way I can pull that off, either.

Instead, I'm thinking of installing the panels on a platform so they are higher than the tank. Then, having the pump started by sensors on the panels such that the pump will pump water up into the panels and back to the tank when the panels are hot. Once the sun goes down, the pump stops and everything drains back to the tank. Obviously, my tank is not pressurized. Several places sell gravity drain systems like this.

Since you have some experience with this, I'd like your opinion on a setup like this. Any thoughts or comments from someone who has done this are worth a lot compared to a salesman on the phone.

Also, I'm not that familiar wiht flat plate solar panels. Is there anything about yours that would make it more efficient or capable of higher output temps then any other flat plate exchanger? I have no objects to flat plate, and no real preference to evacuated tube, as long as I can find one to do what I need it to do.

Thanks.

 

[Eric Johnson]

That's interesting. My folks recently bought a house with solar hot water and heat (in Wisconsin). It's an older setup, so I'm guessing there are no evacuated tubes. Huge panel. Dad reports that today, which was cold and clear, he was getting 175-degree temps in the collector. Once the pump kicked on they cooled off for awhile, of course, but I suspect that's true of any collector, evac. tubes or not.

 

[leaddog]

I have seen a report that said there wasn't that much difference in heat output between the two during the study as the flat plate would melt off the frost and start heating where the tubes might be frost covered and because there wasn't any heat loss they would stay frosted or snow covered. That was done about 3 years ago so I don't know whats been done since. The other way you can get high heat is with a concentrator. There are several projects doing that and there is some commercial co. starting to put them out. Old satellite dishes make good starts and then you use reflective mylar. The problem with them is you need to track the sun but temp of 1200f is possible. I think that with in 5 years there will be a big push toward solar again.
leaddog

 

[sled_mack]

Eric,
That's good to know. I'll have to do some more digging on this.

I would expect the temp to drop for a while when pumping starts, then level out again.

To keep it in perspective, I'm trying to eliminate the use of 150 gal of fuel oil each year. Not a ton, but we know for certain the prices are only going to go up. And, I expect wood will get more expensive, and possibly harder to get in the future too. Anything I can do to eliminate some fuel usage will save some money now and a lot more later on.

Question is - will the price of things like solar panels go up with demand or go down as more people make/sell them? I'm guessing up. Any efficiencies of mass production will get pocketed as profit.

 

[Eric Johnson]

I suspect as the price of copper continues to rise, along with all costs associated with manufacturing and shipping, costs will rise. Of course, if consumer electronics are your model, then prices should drop as efficiencies increase=who knows?

 

[atlarge54]

Solar is a tough nut to crack. When you need it most the amount of daylight is least available, not even allowing for cloudy days. I built a pole barn with six large windows on the south face, with a 3ft. overhang no sun in summer and full sun in winter. When the sun was out in the winter there was some really nice heat gain (est.20K BTU hr.) I think to get a net benefit passive solar with movable insulation to block heat loss during no sunlight holds the greatest promise. When looking for glazing check out patio door replacement panes approx. 76"x34" double pane tempered. They cost me $80 each in 1985. Last Jan. I broke one and paid $77 to replace it and it's an in stock item.

 

[Nofossil]

Nofossil,
Obviously, your experience contradicts what I have been told by many solar panel places. Even places that only sell flat glass panels tell me the efficiency drops way down once the outlet temp reaches 140. Most told me I could never get 160 out of them, no matter how many I had in series. I should know better than listening to sales people by now....

That's part of the reason I did the site. I got lots of advice and information that turned out to be dead wrong, and not just from salesmen. It's amazing how often the things that 'everybody knows' just ain't so. One piece of data beats a thousand opinions.

Since you have some experience with this, I'd like your opinion on a setup like this. Any thoughts or comments from someone who has done this are worth a lot compared to a salesman on the phone.

This can work, and it can work very well. However, you really want a variable speed pump because the ideal flow rate varies considerably depending on sun angle and cloud cover.

Also, I'm not that familiar wiht flat plate solar panels. Is there anything about yours that would make it more efficient or capable of higher output temps then any other flat plate exchanger? I have no objects to flat plate, and no real preference to evacuated tube, as long as I can find one to do what I need it to do.
Thanks.

No, my flat plates are just a thin copper plate with six or eight lengthwise tubes formed in them. Cheesy aluminum box, minimal insulation, single pane glass. By the way, I get 135 degrees off the plastic pool heater that's just lying on the ground! It cost all of $140.

In my never-so-humble opinion, the evacuated tube folks confuse efficiency per square foot with efficiency per dollar. If you can get 5 times the square footage at half the efficiency for the same money, you're way ahead of the game. In most cases, there's more than enough space and not more than enough dollars available.

I'm hoping to see aluminum flat plate glazed collector panels. Copper is too spendy now.

 

[mikeyny]

I built my solar dhw system a few yrs ago. I just posted pics in the GREEN ROOM. I used epdm roofing rubber for the heat sink in place of the copper sheet. Since the rubber is already black it works fantastic. A full roll 10 by 50 ft of epdm .o45 thinkness is about 200 bucks give or take. I used scrap pieces left over from a job. One roll could make a few panels. I have an oven thermometer inside the panel and it gets over 350 degrees in the air space in the panel behind the glass. They really are easy to build. I didn't use any scientific data or methods to build mine. It would be nice if there was a better spot on my house to put it. But I can't complain about the performance.
Mike

 

[sled_mack]

Nofossil,
What ever I do, it will be near my shed, not my house. I'll be cutting down some trees to make a clear spot (too bad it's all pine). You bring up a good point about efficiency and cost per area. I have lots of space.

Mike,
I saw your pics over there. Looks nice. From reading solar mfg sites, I was thinking making my own was out of the question. Now I'm thinking it is possible. And maybe even practical.

I saw someone posted a link to some solar DIY projects on the green page, too. I'll have to check those out. I'm starting to feel really encouraged by this. Now it's a question of deciding what I want to do and being able to get it done in time. Based on my current work schedule, I won't be able to do more than read about it till late April. I'd rather take my time and do it right, than rush into it and waste money doing it twice.

 

[solarguy]

If you are thinking about adding solar to your water storage system, you do not want to connect your solar system to your wood boiler heat storage. The 2 systems run at different tempertures,
you'd never get any benefit from your solar system.

Also, a low temperature radiant heat system is the balls for a solar application, I'm talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical "staple up system" that operate at 140 to 160 degrees.

Solar energy will work w/ fan coils because you can run 105 degree water thru a fan coil.
Solar will not work with baseboard.

 

[ISeeDeadBTUs]

it's funny how once you get started [saving money by spendinf money] it gets exciting and we keep looking for more toys!! :cheese:

My somewhat sketchy plan is to put one vac-tube collector on my roof (my theory is this will cut the radiant heat gain during the summer on my dark-colored steel roof) and go with a small storage tank (more of a buffer tank in the Viessmann scheme) and a dual coil DHW tank. I think I want to be able to heat with either the GW, the inside oil, or the solar (depending on supply) and be able to heat either the buffer tank, the DHW tank or the oil boiler (depending on demand).

But since the recession that has been coming for a while (I'd like to find a way to profit on the sale of sand . . .the place where most politicians and those who listen to them have had/still have their collective heads) is going to cut into my purchase decisions, I need to make sure I maximize payback. That may mean only a buffer tank and a dual-coil DHW tank come spring so as to enable GW use for summer.

All just thinking out loud at this point, but GroundHawg day is less than 10 days away already!

Anyone know if the Elton-Striebel (sp?) stuff is any good? Has anyone checked out (broken link removed) ?

Jimbo

 

[Nofossil]

My simplistic view of solar:

Spring / summer / early fall: Sun angles good, wood boiler not running, solar is good. Solar is for domestic hot water, but I store solar output in my big storage tank (DHW tank is way too small). I reach tank temps over 150 degrees in the big tank with my el cheapo solar panels.

Winter: Sun angles bad, temps below freezing, snow on panels, wood boiler running, solar is pointless. I heat everything with wood and drain the panels. No antifreeze, no fuss, no bother.

I don't use solar for space heating.

Each spring and fall there's a transition ceremony.

 

[ISeeDeadBTUs]

Can the 'top' of a vac - or "el cheapo" style - panel be mounted with a motorized screw so that as the sun angle changes the panel is kept perpendicular to the incoming rays?

 

[verne]

Is it possible to hook up the solar panels to pressurized storage? The back of the barn storing boiler and tank is facing south. the roof will be dark grey, but the grade does drop off so maybe thermo syphoning?

 

[sled_mack]

Here is what I'm trying to figure out: Everyone says solar can not make high temp water. But why? As the storage tank gets warmer, the water going to the solar panel is warmer. My thinking is that the solar panels should raise the water temp x degrees based on a given day. If the water going to the panel is 90 degrees, the output will be 90 + x. If the water going to the panel is 140, the output will be 140 + x. Is this true or not?

Obviously, I expect the hotter you get some efficiency will be lost and you won't get the full heat gain. But I don't think it should drop to zero. I expect it to be noticable, but not enough to defeat the original purpose.

It cost me $450 to fill my oil tank for this winter. That was DHW over the summer, heat in the shoulder seasons, and heat anytime we were away for more than 4 days last winter. If putting in solar is only going to be able to eliminate DHW over the summer, then I have to question if it is worth it at all? It would have to be really cheap at that point.

My house has quite a mixture of heat devices - staple up radiant, staple up with thin plates, baseboard, and cast iron radiators. The outdoor reset modulates the water temp between 110 and 150. If the solar can make water hot enough for DHW, then it should be able to make water hot enough for heating during the shoulder seasons. The question becomes having enough solar to keep up with the quantity of water required.

We've had some really cold but sunny days here this week. Opening the shades gets the house well up over 72 deg with the thermostat set for 68. If the sun can do that for my house, I'd like to try to capture it for my storage tank, too.

I know the angles are a problem. But I think the panels could be mounted such that they are adjustable. It will take some thought, but it should be possible.

 

[sled_mack]

Can the 'top' of a vac - or "el cheapo" style - panel be mounted with a motorized screw so that as the sun angle changes the panel is kept perpendicular to the incoming rays?

My thoughts exactly. Except my panels will be closer to the ground, so I was not thinking motorized. Either a lead screw of some sort, or use a small portable jack and pin/bolt the slide where you want it. Cheap and easy from the ground. I wouldn't want to do that several times a year on a roof!!

 

[slowzuki]

(broken link removed to http://www.sunearthinc.com/Evacuated%20Tubes%20v.%20Flat%20Plate%20Collectors.pdf)

Ok the chart in this compares them nicely.

 

[Grover59]

Also, a low temperature radiant heat system is the balls for a solar application, I'm talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical "staple up system" that operate at 140 to 160 degrees.

I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.

Steve

 

[sled_mack]

Also, a low temperature radiant heat system is the balls for a solar application, I'm talking about temperatures in the 85, 90 to 100 degree range. The problem is most of those radiant systems are expensive to install when compared to typical "staple up system" that operate at 140 to 160 degrees.

I plan on installing staple up radiant heat, and the reason is so that I can get to lower temps with my storage tank, I was under the impression that staple up with the aluminum plates would work with lower temps, so long as you insulate and use the shiny deflector stuff.

Steve

I did my first radiant floors over 10 years ago. Staple up with no plates and foil insulation. A few years ago I did staple up with thin plates.

Thin plates work better than no plates. Since half my house already had staple up with no plates (and I didn't want to replace it) using thin plates on the later areas kept the heat transfer rates close to the same.

If you want to use staple up and low temps, you need to use thick plates. These are generally extruded aluminum. There are a few staple guns that will put them up with the right staple. Or, you can drill them and use short screws to hold them up.

Everything I've read says that the reflective insulation is a bit of a joke. Once it gets dusty, it's ability to reflect goes way, way down.

There is a lot of variance in staple up applications. If you want to use low water temps you have to plan ahead for it - thick plates and good insulation are a must.