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Solar Heating Ideas & Questions

Here's a quote from the Rocky Mountain News:

"Ron and Gretchen Larson, Golden

Those who know Gretchen and Ron Larson also know their passion: to experiment with ways to save energy.

Their latest experiment is annual cycle thermal energy storage.

What that means is a huge tank that holds 10,000 gallons of water. The tank gets heated by sunlight during summer, and the hot water is used in the cold winter months for various purposes. Besides the shower, laundry and other household uses, the hot water also runs through pipes under the floor and keeps the Larsons' home warm in winter.

The system needs fine-tuning, but Ron Larson is optimistic.

"We still got problems there . . . but it will work," Larson says.

Larson, who has a doctorate in electrical engineering, says his stint at the National Renewable Energy Laboratory in Golden made him more energy conscientious.

The Larson home on Lookout Mountain doesn't use natural gas - heating and cooling are done primarily by solar photovoltaic panels, although the couple has two backup wood stoves."

My point is that really smart people are working on this problem, don't work in a vacuum...
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments


  • Perry_3
    Perry_3 Member Posts: 498
    Solar Heating Ideas & Questions

    Something I have always had in the back of my head.... How would you make solar heating work for my house... If it could work; and would it be anywhere practical to build...

    Geothermal would not produce the required 140 F temps I needed (and I really need 145 F on the coldest days as I learned last winter).

    But, solar concieveably could supply 145 F or even much hotter. That could theoretically supply both heating and domestic hot water.

    Obviously, if you build a large enough collection field I can heat the house during sunny days even when it -20 F outside mid winter. But that would be a rather large collector field and I doubt practical.

    So, I always thought... what if you could store heat energy from the summer. Overall the collector area would shink down. Also, because you are storing most of the energy needed during the summer and fall... you have enough energy to handle the nights and even the occasional week or two of cloudy weather we get too (even in mid winter).

    I've known for a couple of years that the only way to store that amount of heat energy would be via phase change materials. But, how did I make it work for most of a years worth of energy and at high temperatures....

    Forced Air solar heat has used phase change materials for years to soak up heat during the day and release it at night. There are several companies that supply phase change materials that work in the mid 80's F to low 90's F.

    But how did I make it work for a hot water system. Not just how big would it need to be; but how did I get heat in and out fast enough, how did I prevent temperature stratification, etc.

    This morning I woke up with an idea on how to build the storage system (which I intend to keep to myself for now... Lets see if it is practical and works on paper firsr) Building a test model would be next (and not expected to be cheap either as a one time item). If it works - then you'll here a lot more.

    So I intend to poke away at the storage question (and yes I know it will have to be super insulated).

    However, an area I though was going to be simple looks to be harder to find the information than I thought.

    How much solar collector area for a given type of solar collector (Vitosol 300 as an example), would I need to gather 100 Million BTU's per year - assuming 1/3 cloud cover at my location in Wisconsin (figure 45 deg North latitude, as I'm about 50 miles south of that). Note the 100 Million BTU's was chosen as a representative number that was reasonably close to my natural gas usage.

    20+ years ago I had access to a computer program that would give an approximate answer (it assumed no heat gain on cloudy days).

    I figured it would be real easy to find such a program on the web. Well, either I'm looking for the wrong things on google or they are not that redily available.

    Does anyone have a good source for such a program. I'd rather spend my time poking on my design for the heat storage device (which may take a while - as I have to research a few things, and figure out a few other details in order to have a practical and functional device).

    Also, does anyone want to help out on the design of the rest of the system once I'm convinced I actually know how to build the storage device.

    Wouldn't it be neat to just tell the gas company that they can disconnect their meter (and stop charging me $180 per year just to have it); and never have to worry about heat again... (even if it cost $$,$$$ - which is what my new & relocated boiler cost me).


  • Jim Franklin
    Jim Franklin Member Posts: 170
    Drake Solar Village

    Have you checked out the Drake Landing Solar Village in Okotoks, Alberta (speaking of heating dominated climates...)? The system there is a district solar heating system using a closely spaced vertical geo-exchange well field to create a huge thermal mass of "dirt" to use as the main winter steady state stored energy source. Same principles apply to a single house or a whole suburb. The main issue is how to store the solar heat effectively, as you've begun exploring. Weblink to the Drake Solar Village info:http://www.dlsc.ca/how.htm

  • Perry_3
    Perry_3 Member Posts: 498
    Thanks for the link

    I had heard of this place (in general) but did not know of the link.

    I note that they are using forced air heat in their houses; and the houses were designed up front for solar heating (which also means good thermal insulation as well). They can probably effectively heat their houses on 90 F (32 C) water from their storage source. In my case I can't do that in cold weather.

    I readily admit that it may not be practical from any means to retrofit a system that would work on my house. I do not have the best roof areas for solar collection, I need hot water (145 F) available through at least mid April, ect. But, it is an interesting exercise to see what it would take. I had already understood that the main thermal storage would be burried in my back yard (or perhaps build a vault). I need to come up with something more efficient than dirt though for my existing house.

    I will admit - that with a house built from scratch - and one designed to use lower temperature water - that just using dirt would work well (although I'd probably trench and insulate arround it too). A large quantity of dirt has sevearl advantages: Cheap, not a disposal problem, and others.

    Even just using water would require the construction of a large tank which entails a certain cost - and could degrade over the years unless you used much more expensive materials.

    Use of materials other than plain water, dirt or rocks, would likly lead to a disposal problem in the future. Something that is an issue with many phase change materials.

    Anyway - I'll keep pecking away at the problem.

  • Andrew Hagen_2
    Andrew Hagen_2 Member Posts: 236

    F-Chart may be a useful program for your design.
  • Perry_3
    Perry_3 Member Posts: 498
    Hmmm.... I wonder if...


    You are right... This sounds exactly like the product I am looking for... and it is earily similar in concept to what I worked with when I was in college.

    Then I looked at where this company is located: Madision Wisconsin....

    When I was in college - in Madison - the University had a program that did something similar - but only at that time for flat plate collectors (all that existed then) and without some of the other current features of "F-Chart." It also only ran on a Mainfram and was written in a form of FORTRAN.

    I can't help but wonder if the writters of "F Chart" did not also play with that UW Madison program (if not start with it). I wonder if I ever met them as well...

  • Jim Franklin
    Jim Franklin Member Posts: 170
    Warm air heat

    Yes- that was an economic choice- you have to use an HRV to provide indoor ventilation anyway, and it was cheaper to put in a duct coil than string radiant systems in the homes. Still, a great example of a very low "free solar energy" district heating system, with the "active" central plant consisting of a couple of circ. pumps.
  • Perry_3
    Perry_3 Member Posts: 498
    Yes... Its the grown up version of what I played with in college

    I just recived the email on wondering if F-Chart came from UW Madison - as it seemed similar to the program I played with in college:

    "You are correct, F-Chart is a product of the UW Solar Energy Laboratory. It was developed as part of Sandy Klein's (now Professor Klein) PhD thesis."

    A little search work indicates that Professor Klein recieved his PHD in 1976. I went to college in the early 80's.

    For more information on the UW Solar Energy Lab...


    Heck, who knows. I might even had a clase by Professor Klien...


  • hot_rod
    hot_rod Member Posts: 18,195
    solar storage has been the million dollar ?

    for a long time.

    Water works well but the space, volume, and cost of insulation make it un-workable in most cases. At least for the amount of storage you would need.

    I currently have a 500 gallon "buffer" tank. At design conditions it only buys me a days worth of heat.

    Keep working on the concept Perry, it's certainly the missing link we all need.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    PV>solar thermal right now

    For my money, Mark Eatherton put this controversy to bed in Feb. 2007, (If you have net metering)
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Perry_3
    Perry_3 Member Posts: 498
    Not at all...

    Mark is just pointing out the problem I am trying to solve; and to quote him from that thread:

    "My feelings are that eventually, someone will come up with a cost effective seasonal thermal storage method/media that will make it all worth while."


    Without a reasonable storage method (a solar battery if you will) that can hold a lot of heat energy (weeks to several months) residential solar heating has some real issues that are hard to live with long term.

    There are always things that can be done to protect the system... but that adds cost and future maintenance as well. Why not put that cost into a large scale heat storage system.

    Now I'm not saying I have a perfect answer. My initial cut over the weekend is still not cheap for a modest amount of storage (and I have yet to get actual material quotes); but it is probably 1/2 the cost of what I had seen for ideas years ago. The first rough design item using my idea of Sat Am, to supply a 120F max water temperature heating system design would be about a 6 Million BTU stoage devide. This device would work as it addresses the issues of phase change materials and in my initial rough design the thing would probably last at least 100 years or more.

    I've come to realize that my house may not be practicle to do anything with due to its construction features (Heat loss, roof design & orientation, and amount of radiators).

    But, for a new purpose built house... the possibilities are endless...

    Now I have an alternative idea on construction that may cut the cost more - with some degradation of performance and life. That one I'll have to poke arround more on.

    Then we'll see what ideas come after that. This is not expected to be a fast process.


  • Uni R_2
    Uni R_2 Member Posts: 589

    GSHP makes use of a very inexpensive solar battery that holds a season's worth of heat. Connecting to the battery can be a bit expensive, but the battery is certainly cheap.
  • Perry_3
    Perry_3 Member Posts: 498
    10,000 Galons of water =

    About 83,200 Lb.

    To raise a lb of water 1 degree takes 1 BTU (the definition of BTU).

    So if you just use water - and need a 120 F system for the worst day, and heat the water to 200 F during the summer you would have a storage system that hold about 6.6 Million BTU's - in theory.

    That is thermal storage in its simplist form.

    I can also make some real good guesses at his problems with it.... Theory often doesn't work so well unless you deal with the real life realities about such a system.

    I'm trying to be a bit more complicated than that due to some advantages.

    Ground source heat pump is not a storage system and involves using a refrigeration cycle process that in of iteself uses a fair amount of energy. Also, many people do not have adequate land space for trenching a large field - or the $$,$$$ to drill a well field.

    The other problem ithe Ground Source Heat Pumps is adequate field size and earth temperature recovery. If a series of neighbors build such systems the ground temperature will continue to drop in the area and the system will stope working well.

    I'm looking to shortcut that by having something that you would either put in a vault or bury in the backyard (perhaps with the deck above it) that could store signifcant energy without many losses (i.e. that you could put energy back in - and would operate in the temperature ranges that your heating system would need - thus eliminating the need for the refrideration heat transfer cycle and losses).

    Currently soloar heating systems must have collector systems way oversized in order to handle the worst case winter. While it may never be practical to have a system with a collector size that would exaclty match over a course of a year the amount of energy needed. Perhaps the collector could just be twice that size with a suitable storage system. That brings the cost of the collector down substaintailly - which would offset - at least partially if not substaintailly - the cost of the storage device.

    Now my ideas may not work out (financially); but, at this point they are a lot more space efficient than just a huge tank of water (and that's not cheap either).

    But, I won't know until I play with a few ideas, and price out the cost of the components and estimated assembly cost.


  • ALH_4
    ALH_4 Member Posts: 1,790

    Perry, are you thinking of using phase-changing material for latent heat storage?
  • Perry_3
    Perry_3 Member Posts: 498

    Yes, Phase changing materials can save a lot of space over just plain water.

    Unfortunately, phase changing materials have issues just beyond their cost.

    They don't work well in a dedicated large mass. For example; wax (pariffin) is a reasonably good phase change material. But, you just can't fill a vat (or tank) with it and put in a heating and extraction coil. Wax is a good thermal insulator in and of itself - so that getting heat into and out of it is difficult if it is just a large mass.

    Breaking it into small mass units such that you have a good surface area to add and remove heat has been so far costly and has difficulties. Then how do you actually add and remove the heat and transfer it to circulating water; another difficulty. Very expensive methods are known to work.

    What I believe I have thought of is a different far cheaper way to appropriately separate the PCH into small enough units with fast enought heat transfer that would work with a water system. Now maybe I'm wrong and someone has thought of this before. But let me poke away at it. Maybee I've figured something out that no one else has.

    But the concept would be that it will be smaller than a simple tank of water and more effective than such a tank of water too. Not sure on the cost.

    On other factor that will need to be addresses is longevity. Since most houses last 100 years plus - the solar battery should also last that long as well. I can't imagine asking someone to pay the premium price that it will cost and then having key components start degrading and failing in 20 or so years. Especially since this would be buried in the back yard on in a vault extension of the basement, and any attempt to make it very servicable will add weaknesses that would allow it to fail faster.

  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    PCM drywall

    There have been rumors of microencapsulated PCM in sheetrock.
    Absolutely great idea, but I don't know much more
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • ALH_4
    ALH_4 Member Posts: 1,790

    How about immersing "capsules" filled with phase changing material in a tank of water or other liquid? I am not sure if this has already been done.

    Ok, here's another one. How about tubes filled with phase change material that drop vertically into the top of a rectangular tank? Some thin-wall stainless tube with welded caps and a flange for sealing to the tank. You could add or remove the "storage rods" as necessary.

    How about one more? Maybe a tank in a tank like a Triangle Tube Phase III indirect with the phase change material inside the inner tank and the fluid in the outer tank. Probably wouldn't be as efficient as the "storage rods".

    I have my doubts that seasonal storage is practically possible, simply because insulation becomes a huge issue. How do you keep the storage medium from losing its heat to the surroundings?
  • Perry_3
    Perry_3 Member Posts: 498
    A lot of information out there on this

    They have not had the best luck with it though.

    One of the key problems is how it works (in sheetrock, etc) Flooring has been more sucessfull in sun dreanched areas.

    For an example - let us assume that you would like your house to remain at 80 F; so you put in a PCM on the walls that phase changes from 78 F - 82 F (nothing exactly hits the target temperature due to impurities).

    On some days the sun shines hard on the walls - warming them up to 85 F; then at night the walls cool to 78 - and in the process release a lot of stored heat from the PCM material (and without PCM walls the room themperature would have dropped to say 70.

    But the next week the walls never get warmed up to even 78 F and their is no PCM benifit.

    A month later - and there is so much sun that the house heats up and the walls never drop below 82 - again no PCM benifit.

    So for PCM walls you really need to preset what temperature the room will actually be at - and have a good mechanism to heat the walls during the days and then cool the walls during the night.

    PCMs have worked a lot better in solar floor applications. But you are still stuck with the original design point on the PCM.

  • Perry_3
    Perry_3 Member Posts: 498
    If it were only that simple...


    Good thoughts. That is where most people start. When you get into it though - and a lot of details on exactly how the PCM material behaves... I don't believe verticle tubes would work well long term.

    Anyway, I could probably write for an hour or more on the details of how some of the PCM materials actually behave and how you have to figure out how to handle that behavior in a method that will last more than a few cycles - or will allow them to work most efficiently for you.

    Check my intial post on this thread for some of the issues involved. If only it were so simple...

    As far as how to keep the heat in the tank. Insulate like you've never seen anything insulated before - and that includes the bottom of your hypothetical tank (or my solar battery). Only problem is - that you need to insulate something that potentially has a support footprint of 500 - 2000 PSI. It can be done (and I know how), but - its not something that most people start out with. You also need to control heat losses from all fittings and connections.

  • ALH_4
    ALH_4 Member Posts: 1,790

    Now you have my curiosity piqued. I will have to do some research. IMO, the most exciting facet of hydronics is solar integration with a high efficiency heating appliance. The challenge of accomplishing this simply and relatively inexpensively is one that I do not feel has been completely met at this point, and storage is the primary challenge remaining.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,782
    It may be simplistic...

    ... but nobody's really been talking about load reduction. Last year, I used about 12,000 BTU/ square foot/year, which is roughly 1/10th the energy requirement of new construction. The passive house homes need to meet or beat 38,000 BTU/foot/year. That's total "imported" or "fossil" energy used for all loads, including plug loads. I see no good way to measure actual solar input. How much credit do windows or a clothes line get?

    As I get good sun here and radiant in walls keeps the house at 70* with 80* water, there is little or no heating load done with "imported" energy. I have a 1000 gallon tank, which acts as the mass for the house, which is distributed as needed for comfort. My point is that as energy use gets trimmed down, the need for seasonal energy storage diminishes. If the longest period of time you see no sun is a month, than you need a month's worth of storage, or two weeks of storage and some fire wood.

    There's been a lot of talk about "zero energy homes". The term changed to "net zero energy" when the concept proved easier to imagine than to actually live in. Plug loads can be offset by huge PV systems, but then the dollars per square foot cost to build shoots up and you need to use the grid as your battery.

    People have tried for a long time to store heat energy in large tanks and not met with real success as big storage has more surface area to lose heat from. A super efficient home, with redundant systems can solve the problem, just as theoretically a large heat storage system could, but the former approach has been demonstrated.

    If you've read this far, thanks for putting up with my stream of consciousness output ;~)

    Yours, Larry
  • ALH_4
    ALH_4 Member Posts: 1,790
    Reducing the load

    Larry, Do you think there is a way to get people to reduce their fuel consumption pre-emptively, or do you think it will take a major fuel price increase? My opinion is that it's going to take a fuel price increase.

    I do not think that seasonal thermal storage is practically possible, but reducing storage volumes for daily cycling would be very helpful. At the same time, I feel that our first line of attack should be solar domestic hot water rather than space heating.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,782
    Being an optimist...

    ... I think people would rather do the right thing, provided it isn't too difficult. Just as recycling isn't too hard for many people now, (or water conservation in my dry area) being aware of energy use necessarily will become the socially correct thing to do. This will take lessons from society along with self interest to be made to work, but staying on our present course can't work for long. It's likely that higher prices for energy will help to motivate the slackers.

    I just sat in on a two day meeting organized by ACI where about 100 really bright people (not me, I just watched ;~) tried to figure out how to reduce the energy demands of current building stock 70% to 90%. Ways were found. This conversion won't be easy, but it's doable given the public will to make it happen.

    As for solar space heating, once buildings are efficient, solar can easily do most of the job. Money is far better spent on efficiency measures first and then solar. I've read rules of thumb that it's three to five times more cost effective to go for efficiency first. Low temperature solar could be part of the solution. I've mentioned before that my place stays at 70* heated by 80* water. These low down BTHs are easy to capture most times of the year!

    Yours, Larry
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Electric heating

    "once buildings are efficient, solar can easily do most of the job."

    That's my point also. What's the easiest and cheapest (first cost) heat source? Electrical resistance. What's the easiest way to collect solar energy all summer? PV solar sent back to the grid where it's much needed.

    Historically the worst part of that scheme is the high cost of an electrical resistance btu. Now if you use off peak kwh's which are usually 3X cheaper, you've really got something. In addition, you don't have to try to store solar btu's for 6 months.

    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • solar today reported

    That in Europe almost twice as much energy is collected with solar hot water than PV and wind combined. That should tell you something. You don't have to store the energy for 6 months, you just have to have lots of collection, and enough storage to get through a week or two of clouds, then make more. Thanks, Bob Gagnon

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