Solar

bruce_21

Old cisterns don't necessarily hold water. I'd do a test before getting to far down the line.

Dobber

Putting Solar where the sun don't shine (much)

Just came from an EOS solar seminar. Nice looking product.
I bought a century home last year that is surrounded by trees. I was hoping to add solar to any place we looked at, but I wasn't going to be the deciding factor.I started thing about when I would want solar,obviously I would want it the most in the winter and the shoulder seasons. So although the trees will be there, the leaves won't be. So I'm going to get me some solar.
In the one cellar is a cistern.I would like to insulate it and use it for a dump and additional storage.Has anyone done this? How was it piped and controlled?

Thanks
Dobber

hot_rod

determine

the load and how much you hope to cover with solar. Low temperature systems are friendlier to solar. Then size the storage accordingly.

At a recent seminar the instructor told us to use a 50% reduction for output through trees with the leaves off? Sounds high to me, but he was an engineer! They sometimes estimate on the tall side, then again trees come in a lot of different sizes

Have fun with the project. Keep us in the "solar" loop.

If you have time tomorrow tune in to the Solar Webinar, that Siggy is presenting www.pmengineer.com to sign up. last I heard over 200 folks signed up for this timely webinar.

hot rod

Dobber

cistern

I was going to line the cistern with rigid insulation and then have a pool liner made. Need to find out what sort of temps the liner can take.

Dobber

Bob Gagnon plumbing and heating

Dobber

I would cut the trees down and plant shorter ones further away from the collectors, my neighbors let me cut their trees down and I planted white birch trees in their place, and I burned the wood in my wood stove cutting down on fossil fuels even more. I used heavy duty roll rubber roofing to make a liner for my solar storage tank and have seen some like this last for 20 plus years. Get the 20' wide roll so you have no seams, that could leak over time. Be careful about insulating the tank in the cistern, water saps a lot of heat away. I put my tank in the basement, it is only 8'X 8'X 4' high but it holds 1500 gallons.

Hot Rod, do you think using the low temp solar BTU'S for space heating would be a good way to harvest and use more solar energy, making them much more efficient? I wish I had a high speed computer to watch the solar seminar, I still have dial up. Thanks, Bob Gagnon

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Dobber

Trees

Bob
Unfortunately the tree in question is a 150 yr old oak that is healthy and beautiful. It is on my neighbors property, but even if it was on mine I wouldn't touch it. I would rather spend money on extra panels.

Thanks
Dobber

hot_rod

no question that lower

return temperatures to the collectors drive their efficiencies up. Pull any SRCC listing sheet,be it flat panels or tubes to see the output figures.

Page 12 of I-dronics 3, downloaable at www.caleffi.com, by the way, shows a graph for this.

The example compares a panel with 160F return, compared top one with 95F return. With same radiation numbers the 95F operating conditions presents a 43% efficiency. Compared to 16% for a higher operating system.

A solar panel is merely a heat exchanger, design it into a system where it provides the best performance and return on investment.

SDHW comes to mind, but low temperatue radiant sure is a nice marriage.

"How low can you go?" should be your motto for solar hydronic systems design

hr

Unknown

In fact, that is my exact motto for solar radiant design HR, where is my royalty check?????

siggy's seminar was a good one today too. nice overview of the tech and considerations with each. fun stuff!

Unknown

Siggy's webinar

What was Siggy's view on drainback vs. closed loop glycol? Is there anyway to view this Webinar after it's live stream?

As far the low operating temperature question, the problem is that to make 130 deg DHW we need water at least that warm. This is why I question high solar fraction designs. Smaller systems that can only reach close to 100% solar fraction in ideal conditions (mid summer) will have higher efficiencies than systems which have a more ambitious year round fraction. There is a real impulse to try and accomplish as much as possible with this technology, if our goal is sustainability we must give operating efficiencies the same consideration that we do with combustion devices. To deny this by saying that solar energy is free ignores the fact that is takes energy to build these systems. A system that operates at a higher efficiency will payback it's energy debt faster.

Low temperature heating does seem a good match for solar efficiency, but the inverse relationship of seasonal radiation and thermal loads is a big problem. Seems a waste to size a system for january insolation and then have so much capacity idle (or worse) in july. What were Siggy's thoughts on this inherent problem with solar heating design.

To the original poster I ask; does it make sense to invest in a low yield system that will be shaded in the best solar collection months? Would this capitol be more effective (environmentally) if used on building envelope or mechanical systems improvements? Solar is sexier than insulation but the later is more important. In my opinion it's silly to even consider an active solar heating system in a structure that does not exceed insulation standards by 50%. As I'v heard it said here "there's just is not that much heat to pull from a cold winter sky."

Leaves will be out soon, and were getting closer to the solstice so direct observation of your summer shading issues will be possible soon. I'v heard that as little as 4 hours of direct sun can be enough to justify a DHW system.

Rudnae

Well a little company called Viessmann....

I just got back from some excellent Viessmann training in Waterloo, ON where amongst other things we covered their take on solar. The problem with trying to use it for space heating is that we don't have a consistant year round load. That means that there is no single best position for the panels. If you pitch them high enough to catch more winter rays, then you lose out on a portion of the summer rays, and vice versa. What we should really be focusing on for efficency in these systems is year round loads that don't really change, like DHW or indoor pools. What makes a better dump load than a swimming pool? The problem with sizing the panels to heat your home in the winter is that they will have more load than you system can handle in summer. This means in a closed loop system that your glycol will be stagnating, heating up to very high temperatures with nowhere to release the energy. Over time this causes the glycol to break down, become acidic and chew up your piping, panels and other equipement subject to corrosion. The best bet if you really want to go with some solar and you don't really have the right area to put it in is a DHW preheat system. Just my 0.02.

Bob Gagnon plumbing and heating

Rudnae

There is a simple solution, simply install your collectors so you can tilt them according to the season. A steep winter tilt to capture the maximum low winter sun, about a 45 degree angle for the spring and fall, and you might leave it at 45 degrees for the summer, unless you have a BIG summertime load, if you did then you could go almost flat horizontal. This will keep the snow off the tubes, and you could tilt it away from the sun if you were going on an extended vacation.

Thanks, Bob Gagnon

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sol_2

angle of collectors

45 degrees is considered to low. What can happen in the summer is overheating the system. Generally people go around 60 -65 degrees in northern states and 65 to 85 in southern states.

UniR_3

Solar Powered Chiller

Have you looked into solar powered chillers for the summer?

Rudnae

Yeah, well..

Bob, I totally hear you there, adjust for the season right? Well I guess the main problem I have with that is that our end users hardly even want to adjust their thermostats any more, let alone the panels. I guess we'll just have to wait for an automatic / remote control panel array. Sigh. I wish that you could set it up with a tint that would get stronger as the summer goes on and thereby limit the amount of energy transfered. Kind of like those transition eye glasses.

hot_rod

that a big plus for drainback

the over heat stagnation issue, as well as freeze protection.

Use it or lose it, with large arrays and little summer loads.

Scott, really no reason you have to design to 130F on SDHW. even with a small panel raising the temperaturer from 55F to 90, 100, whatever, still lightens the load on the DHW production tank. It's rare to not have some sort of a back up system.

The beauty of thermal solar is the ability to go from mild to wild.

I've been building a demo system with a 3 square foot panel and a 12 gallon tank. I'm amazed to see that tank climb from 55 to 105F even this time of the year.

A system like that could be purchased for under 1 grand. plenty of power for a one person shower load.

Or install concentrated collectors and generate electricity for 25,000 homes.

Or anything in between.

Certainly solar thermal is not the perfect save the planet techonology. But it sure fits nicely in the scope of work everyone here is capable of selling and installing.

hr

siggy

drainback versus closed loop

Scott,

Happened to see your post. My personal preference has always been for drainback systems over antifreeze. Simple - reliable - been working on my house for 27 years. With proper design the same water that goes through collector can go through radiant floor circuits. Only heat exchanger is an internal coil for DHW preheating.

In June I'll be starting a new column in PM Engineer entitled Solar Design Notebook. It will be appearing every two months, and addressing some of the finer points in designing both types of systems. Always interested in solar topic questions you or others may have.

siggy

Paul Pollets

Solar

Hi John, liked your webinar on solar. Our staff watched and liked it. It was a good intro to the subject.

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Unknown

Nicely put HR,

Current economic trends will most likely propel a much deserved resurgence of this very Scalable alternative energy technology.

Marketing is important, but marketing is also part of the mess we are in. Marketing brought us the SUV, and snow melt mansions. The hypocrisy and naivet

Unknown

siggy, I look forward to your new column.

The common transfer fluid idea you describe is intriguing. Would the air space in a drain-back system present oxidation issues that would require all non-Ferris components and violate boiler hx warranties? A system optimized for winter collection (50 deg. pitch) but sized only for summer DHW loads could operate most efficiently in the winter by targeting the lowest temperature loads. Obviously dhw preheat represents the first step low temperature "sink" , however if this preheat tank is able to exceed 75-80 deg it could be more effective to target a Low temperature heating load than to continue raising the preheat tank.

Conceptually this is a good idea , but schematically it seems a bit difficult to accomplish. I'd like to see more on this.

Scott

Bob Gagnon plumbing and heating

Simple SolaRadaint Schematic

What do you think about doing it this way?


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Unknown

storage

Thanks for your input bob,

My personal inclination is to explore ways to avoid large storage tanks.

Perhaps this has to do with my interest in radiant monolithic slab foundations. Basically finding space for 1200 gallons of thermal storage, and ensuring that this tank is well sealed and insulated is a significant impediment to architectural flexibility. The other issue is that high quality large storage tanks are expensive (think embodied energy). The viability of alternative energy projects (and conventional energy sources) is largely determined by EROEI (energy returned on energy invested) in my opinion large thermal storage tanks present an impediment to achieving high EROEI.

To this end it is my belief that we may actually get more from the sun by asking for less. Thermal storage is required when we seek to ride out periods of low insolation, it's not uncommon in my area (during the winter) to go for a week or more with minimal direct radiation. We can both recognize what a large volume of water would be required to ride out these periods, even for a very energy efficient structure. I am not interested in 100% solar as I don't believe it's economically/environmentally justifiable. Yes someday (perhaps not so far from now) we will run out of oil and gas, but the best way to forestal this eventuality is through implementing as many high EROEI alternatives as possible. High solar fraction design may actually serve society less effectively than more modest use of the sun. Universal clotheslines usage could probably do more to offset non-renewables than active solar heating, EROEI is why.

In practical terms what I envision are thermal systems that recognize the use it or loose it limitations of this technology. Size the collector array and storage to cover 100% of summer DHW, tilt collators to optimize low sun angle (maybe 50 deg.) When heating loads develop, limit dhw preheat and divert load to heating, don't get to uptight about indoor feedback, Leverage the thermal mass of the slab even if indoor temps overshoot target to some degree. The pre-heat tank might actually be duel coil and the heating load could pull directly from this extra coil. The part that gets tricky for me is how to integrate the combustion input and not loose efficiency by raising return temps to collectors.

scott

mark D

solar

Solar has tweaked my intrest for as long as I can remember.
I would like some creative feedback as to making this a reality in my home. To off set the high usage of domestic hot water I am considering the instalation of an indirect waterheater and adding a 1000 watt electric element to run off of a small solar pv panel array. The indirect will need to be modified by a certified welder [me] and I think around $3500 in parts. The advantage to all of this would seem to be that in any weather we would be offseting our hot water usage and reducing the run time on my boiler. please give me any feedback that I might use to convice my charming wife. She thinks I am fixated on saving the planet!

mark D

solar

Solar has tweaked my intrest for as long as I can remember.
I would like some creative feedback as to making this a reality in my home. To off set the high usage of domestic hot water I am considering the instalation of an indirect waterheater and adding a 1000 watt electric element to run off of a small solar pv panel array. The indirect will need to be modified by a certified welder [me] and I think around $3500 in parts. The advantage to all of this would seem to be that in any weather we would be offseting our hot water usage and reducing the run time on my boiler. please give me any feedback that I might use to convice my charming wife. She thinks I am fixated on saving the planet!

Unknown

If you seek thermal energy from the sun PV is the wrong approach. Although electrical resistance is in essence 100% efficient at converting electrical energy into heat, converting sunlight into electricity is not. Most commercialized P.V technology is only capable of max. 15% conversion efficiency.

There are lots of factors which can effect the efficiency of solar thermal collector but assuming good location well designed system, and a fairly consistent matched load, this mature technology can deliver seasonal utilization efficiencies of 50%. in the summer operating efficiencies of 70% are possible. thats a lot less collector area on your roof to do the same work.

Save the PV for solar pumping, electricity is to special to "burn" in a resistance coil. Keep up the planet saving work, just make sure to get the most bang for your planet saving buck.

colin_4

Dedicated solar loop for radiant

When I installed the radiant floor loops in my house, I ran an extra loop between the normal heating loops from the boiler. The idea I had was to connect this loop to the upper coil of a dual coil IDWH, solar input to the bottom coil. Possibly bring this loop on 1st with a 2 stage heating T-stat if the tank is above a "certain" temp, possibly 110*f or so which would be hotter than what is required for domestic hot water. In this way the solar potential would always be used 1st, and the boiler temps would be un-affected. This is all theory since I have yet to install my panels. Any thoughts on this concept?

sol_2

solar

Colin,
Why not just put up solar thermal collectors? Back it up with a tankless water heater (like Takagi $900.00)unless up don't have gas or propane. just a thought

Larry Weingarten

Responding to...

...Bob and Scott and sharing some design thoughts with Mark: Starting with a really efficient building shell lowers the number of BTUs needed. I built my place with SIPS panels and a lot of caulk. If you can design a radiant system that can work on really low temperatures, solar can provide a larger fraction of the total needs. I built radiant into the walls and can keep the house at 70 with 80 degree water. When there are long overcast periods in winter, I use a wood stove and burn roughly 1/2 cord per year.

I've been involved in solar since 1978 and big tanks have always been a problem. Any steel fails and fiberglass doesn't hold up to hot water long term. Any thru wall fittings leak in time. For my place, I used a fairly inexpensive 1000 gallon PEX tank and brought all piping in through the top. The 1000 gallons act as the thermal mass of the house, an advantage being the mass moves wherever it's needed. I'll need to use a sump pump should it ever need draining. There are three gallons per square foot of collector, which prevents tank temps getting too high. Encouraging stratification in the tank allows it to behave along the lines of Bob's two tank system, which I see as something like counterflow heat exchange. For DHW, there is a coil of copper in the top of the tank to preheat.

Using high grade energy (electricity) to make low grade heat doesn't feel quite right, particularly as solar thermal is far more effective dollar for dollar at collecting energy than PV.

One degree heating water from 50 to 51 takes the same energy as a degree from 130 to 131. Solar works very well in that lower range. I'd let the boiler top it off when needed. I could ramble on, but this post is long already ;~)

Yours, Larry

Unknown

Larry, 30 meters is nice chunk of copper and glass. feel like posting a picture? Wood is a bit tabu with some folks on the wall, I grew up with wood, first energy crisis. It gets old trying to keep a farm house from freezing around here, but I have some fond memories of gathering wood with my unemployed father.

"We must face the prospect of changing our basic ways of living. This change will either be made on our initiative in a planed way,or forced on us with chaos and suffering by the inexorable laws of nature. "
Jimmy carter (1979)

Wood makes a nice supplemental heat source on cold morning. I hate smoldering wood though, almost to the point of knocking on peoples doors and telling them to let some air on that fire.

Bob Gagnon plumbing and heating

Integrating the combustion input

Have two separate radiant systems. Your conventional FHA,FHW, or radiant system tied to your boiler, and the solar is simply tied to a small separate radiant panel like a ceiling or wall near your living room couch, and maybe a wall or ceiling in the main bath. Most people do the heating only when 100% of the energy needed to heat the house is available from solar. That is the shoulder season, maybe only a few weeks in the fall and spring. the piping arrangement and controls for this are complicated and expensive. It may be less to simply have a separate radiant panel. I think it will be cheaper, simpler and less expensive, but it will also collect a lot more energy, There will be many days when solar could provide 25% or 50% of your heating needs, and with separate radiant panels, providing you with heat every sunny day during the heating season. In a super insulated house performance will be greatly improved. The large tank is necessary for this and it will allow you to use the low temp energy for the entire heating season making the panels more efficient by returining lower temp hot water to the collectors.

Thanks, Bob Gagnon

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Bob Gagnon plumbing and heating

Larry- tank questions

Would fiberglass tanks be a problem without the thru wall fittings? Who is the manufacturer of the PEX tank? How high is the temp rating and can you seal the tank tight to prevent humidity issues? And Scott remember wood is good. It's not for everyone but it can make a significiant contribution to reducing our reliance on fossil fuels. I know a guy that has a superinsulated house like Larry and he makes one or two small fires a day and ALL the rooms stay about the same temp. 1/2 a cord of wood a year is great. Remember wood is a renewable resource and the pollution from smoke isn't that bad it's mostly ash. It contains some carbon doxide but only the same amount of carbon doxide that the tree absorbed during it's lifetime- it is carbon neutral. The same amount of carbon would be released if the tree rotted on the forest floor.

Thanks, Bob Gagnon

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mark D

Thanks for the input, I guess that I still have a little bit of studying to do on saving the planet one home at a time. While many people dream of retiring and playing golf or touring the states in an RV I think of all the neat things I could do with a super built,insulated,designed off grid home. Guess I will look into solar panels for domestic hw and Heat as well.

Unknown

off topic (biomass)

Bob, I like the smell of wood smoke in october, I also sometimes like the smell of a freshly lit cigaret, but smoke is bad for you. Wood-fires that don't burn hot and clean are a meaningful source of air pollution.

I don't like to see much smoke from a wood stove, except while it's being lit. Many people's stoves are to big and they damper them down too much. I see alot of those new external wood boilers smoking like crazy. My jotul 602 is tiny.

I'm not sure if burning a mature living tree is better than letting it continue as a carbon sink. We can plant a new tree in it's place, but it will be decades before the saplings respiration can begin to compare to the canopy of the mature hardwood?

The log decaying on the forest floor provides food for a host of organisms, these organisms are built of carbon, Combustion makes only gas and ash. Decomposition is a bit different because some of this trees carbon will literally walk away from the decaying log. These bacteria fungi, and insects will remain in the biotic carbon chain and essentially out of the atmosphere to some extent.

Biomass will probably be an important future energy source, To characterize it as carbon neutral (while essentially true) might gloss over some limitations with this approach.

I'm not saying we should pass of on burning a nice fallen oak, but the rotting log has a value too,one thats hard to quantify in BTU CO2 metrics. All carbon is not equivalent, how did the building block of life get such a bad name.

scott