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Solar Heating Systems

I'm not trying to nitpick, but careful with terminology.
Drain BACK systems are quite robust and trouble free, and as mentioned above, they don't need heat dissipation.

Drain DOWN systems are an embarassing relic of the past and no one even makes a system any more.

I know Dave already has a copy, but Tom Lane's book covers 80% of what a guy needs to get into solar. If that guy is an experienced boiler guy. Another 15% of what you need can come from the manufacturers of the panels and pumping equipment. If you're brand new to solar, the last 5% could come from a consulting engineer experienced in residential solar. Get a few systems under your belt, and you won't need him anymore.

Here's another great benefit of getting into solar...it's fun! Like a profitable hobby.
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments


  • Toddj_2
    Toddj_2 Member Posts: 9
    Solar Heating system questions..

    Hi with the recent spike in oil prices I have some questions about the feasability of solar heating systems for homes. Actually homes that are 1880's Victorian Duplex in Northern New England.

    1. Is solar and option really. I mean with short winter days does it make sense for solar heat?

    2. I remember reading somewhere awhile ago that solar heating systems require a large tank of hot water in cellar and therefore your basement needs to be deep and wide..any idea on minimum dimensions for that kind of system? Also any simpler systems that dont require this kind of tank?

    3. Are solar heating systems still photovoltaic?

    4. Can steam radiators be used as the heat source? Or is a solar heat system a sort of forced hot water system?

    5. Is there a way to get a cost estimation if all these other issues aren't an obstacle?

    6. Any good plain english non engineerese sites to glean more info that will discuss solar systems?
    Thanks for taking time to answer any and all these questions.

    Todd J
  • RadPro
    RadPro Member Posts: 90
    solar options

    The individuall should first adress heat loss in an 1880's house and any house for that matter.. Supplimental heating MAY make sense in areas of high sun year round preferably. Short winter sunny days dont give me much. Heating water takes time and clear sun for optimum results so of course spring-summer -fall ar the best. (and PV panels are electric generation) Paul
  • GMcD
    GMcD Member Posts: 477

    I like the Thermodynamics site for basic solar technology explanations and systems at http://www.thermo-dynamics.com/solar_boiler.html I'm sure there are many more and it is a quite popular and easy to install type of system for supplemental hot water heating for either domestic hot water or house heating, or both.

    To answer your questions directly:

    1. Yes, solar can work in most climates, here in my Pacific NW area, it's a challenge, but it can still work.

    2. Yes, solar requires some form of hot water storage as a buffer/storage system. Look at it like a battery - big collectors with a small tank = small collectors with a big tank. It's a matter of establishing a practical amount of hot water storage vs the area of the panels vs the climate zone and insolation at your location.

    3. Well- there are solar hot water panels and there are solar photovoltaic panels, two different animals. One system produces hot water, one system produces electricity. Same idea with photovoltaic panels: small panels with lots of batteries = large PV panels with smaller pile of batteries.

    4. There are some solar systems that can produce steam but those are really specialized and a bit esoteric for typical household uses. Solar water panels are predominately hot water generators.

    5. Cost estimates can be provided by a local solar panel supplier/contractor- do a google search for someone in your area.

    6. The Thermodynamics site above, or Thermomax at http://www.thermomax.com/ are good ones.

    Hope that helps.
  • jerry scharf_3
    jerry scharf_3 Member Posts: 419
    This would be way down my list


    You can do this to some degree, but it's way down the list. In simple terms, it's hard to store a lot of heat for a long time. With this, you can't capture the summer heat and save it for winter. So you're left with what each day or week brings for the sunshine. When you need it the most and are burning the most fuel, there is the least available.

    You also have the problem that unlike a PV system, it is harmful to the system to have generate too much heat at any time. You've got to move the heat somewhere. So during the hot summer days, you need to have a place to put that heat that it can be used within a few days. Doemstic hot water is a much more constant demand, and thus is in my opinion a better application for solar hot water.

    Like Paul said, fixing the building envelope is first on the list. Or maybe it's first, second third and fourth. Heat you don't lose is the best heat of all. It works in the winter, works in the summer, has nothing to break (except with a baseball) and no upkeep. It has the best ROI of any work that can be done relative to saving fuel. I'll bet that 120 year old house can be improved tremendously in terms of building envelope improvements.

  • jerry scharf_3
    jerry scharf_3 Member Posts: 419


    You know much more about this stuff that I do, but I always thought it was really bad to significantly oversize a solar hot water collecter relative to load. With PV, having no load on the panels during full sun does no damage. With hot water, having full sun and no load can have disasterous results. A small buffer will quickly fill up and then present no further load to the collecters.

  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    simple solution

    I've been pondering that "problem". Suppose you utilized a diff set-point device that triggered a solar driven pump to divert that excess energy to a zone where Btu's could be shed. If driven by PV, the pump would speed/slow in harmony with the excess. No harm, no foul, no grid-power use!

    I'm planning to size my system for 100%+ capacity on a cloudy day.

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  • GMcD
    GMcD Member Posts: 477

    The way I stated it was a simplification and I did not intend to infer that the "large panels/small storage tank" scenario was based on "oversizing" the panels relative to the load. What I meant was that if the solar panels are sized to the peak load with a small storage tank, it could be workable and provide the same net energy generation and storage as small panels with a large storage tank, generally speaking. I agree completely that "oversized" solar water panels can be a pain to deal with since a heat dump is needed to get rid of the excess energy somehow. Some of the Euro panels have exterior shades/shutters to modulate to prevent this. I hate more moving parts than are necessary though, and the simpler the system is, the better.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Load shedding

    Is load shedding necessary? I'm planning to use a drainback system in my area. If there is no demand for hot water esp in the Summer it would turn off and drain back. No stagnation temps and antifreeze contamination. What's the angles on this? WW

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  • Toddj_2
    Toddj_2 Member Posts: 9
    Complicated stuff

    Wow this is complicated stuff. I never even thought that you had to worry about times that the system could produce too much heat..I guess I thought the system sort of "shut off"... Never mind the worry about too little heat when I need it most.

    As far as building envelope..I definitely agree it is the place to start and as I have lived in this house several years I have worked on it...by reinsulating most of exterior walls from blown in crap to pink stuff...some new windows (have 10 done about 35 to go)....and just installed two new doors..the doors may make some of the biggest difference as one of the doors was a double door that was warped and didnt close right leaving quite the gaps..
    This year I also added insulation to the vent area (subject of an string on the wall here several weeks back with lots of great info you guys gave me)..

    I am always open to ways to save money. I keep hoping these high energy prices are gonna result in some significant tech breakthrhough such as heat producing windows (not just heat saving)..that is affordable, is self contained, etc, and affordable (i.e. get payback within 7 years or so)...
    I have shaved some serious oil usage off my bill on one side of duplex (from 1700 gallons (for my side) with new furnace and all the insulation to about 1300..and I hope the increased insulation and new doors this winter will do even more. I still have a ways to go..other side needs some more insulation and the furnace on that side (its a more traditional forced hot water system vs steam boiler on my side) is older (1957) so that will probably be done within next twelve months.. one step at a time I guess.

    So any additional solar ideas for an old house like mine is appreciated..and any heat conservation ideas as well

    Thanks Todd
  • Jay_17
    Jay_17 Member Posts: 72
    my experience

    We had solar panels installed for hot water in the late 70's, 3 panels, about 3x7 I think. The location is Connecticut, we had the panels aimed so that they took best advantage of the winter sun. We were a family of 4 with the usual appliances, though we tended to wash dishes by hand. The system had electric back up. As I recall the solar pump operated on an aquastat (separate loop to heat Xchanger in tank) and there was no issue with needing to dump heat when the tank was satisfied on a sunny day. I am not sure why it is a problem now.
    BTW, this system supplied us with most of our hot water for 20+ years and the electric rarely ran, well worth it in my book.
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    overheat issues

    The information I've read and seen (via posts) indicate there is an issue with overheating and boiling off the glycol solution if the energy is not dissapated - for instance: a family being away with no hot water draw for an extended period. Seems logical that repeated energy-capturing events would lead to overheating without use of stored energy (to me).

    I also have seen comments that drain-down systems can have issues with high panel temps and potential scaling as residual water droplets/moisture is evaporated.

    Seems to me that an alternative would be to move those excess Btu's off to an alternate spot where they can be dissipated & that doing so with a small PV panel for motor power would eliminate any parasitic energy use. No harm, no foul? If I'm installing a $7K to 12K system and a few hundred more dollars will provide overheat protection, that seems like a good investment (to me).

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  • Joe_55
    Joe_55 Member Posts: 62
    My $.02

    You can easily size a system for max on cloudy days By adjusting the collector angle steeper and also achieve better gain in winter months (I believe) Joe.
  • My big tank

    1500 gallons, seems to be the way to go. It's large storage dosen't overheat in the summer. it allows me to store heat instead of dumping BTU'S, like you have to do when a small tank is hot. The lower temps at the bottom of the tank sends cooler water up to the collectors, making them more efficient. I can harvest lower temperature hot water. We have had a week of rain, but I still have hot water, 100% solar domestic. you can't do that with a small tank. In Renewable Energy World, they talk about new insulations that use vacuum and phase change materials. It may be difficult to store hot water for a long time now, but people are working on it. It's the way to go. Bob Gagnon

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  • Constantin
    Constantin Member Posts: 3,796
    Hi Bob!

    Nice to see you again. Did you already have your tour? I misplaced the piece of paper you gave me, which is a shame.

    I like your system (large tank as a large battery) because it's simple and effective. With many of your collectors installed at steep angles, you should have few summer overheating problems. How is the system performing this winter? Are you collecting enough heat to help with the home heating?
  • ALH_4
    ALH_4 Member Posts: 1,790

    It's important that the collectors have the ability to maintain the storage tank at a usable temperature. Everyone's needs are different. Bob, how warm does your storage tank get in the winter?

    An alternative to making the tank large enough to handle full input during the summer is to cover some of the collectors during those months. A daily cycle that charges the tank during the day and discharges at night, and/or in the morning for domestic hot water production, is a pretty optimal way to go. We (mostly Dale) are working on a solar storage tank with custom copper finned tube heat exchangers right now. It's something similar to what Courtney and Dale did with the 13 Mile Sheep Ranch solar project. The heat exchangers may be something we will sell separately for use in a customer-supplied tank. It's not as simple as it sounds to create a tank that you can install and, for the most part, forget.

  • leo g_13
    leo g_13 Member Posts: 435

    First off say Hi to Dale for me.

    Have you looked at Tarm storage tanks? I haven't seen one personally, but they look mighty nice from the pictures.

    Here's an addy;


    Leo G
  • ALH_4
    ALH_4 Member Posts: 1,790
    Tarm Tanks

    Will do...

    Those tanks look like they would work well if there is enough room. I'll have to check into them more deeply. I haven't seen one either.

    We're attempting to manufacture something rectangular that would fit in a mechanical room against the wall. Hopefully it works out without being too expensive.

  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Atmospheric tanks

    Just a caveat that pretty much all early adopters can ignore: Evaporation is a real problem that must be solved effectively before this type of system can be mass marketed.

    One of the top 5 solar installation companies in these parts told me that they actually call every one of their customers once a year and remind them to top off the tank. Since many homeowners and renters won't even change a furnace filter, we need a better solution.

    Are there any high quality auto-fill devices that are fail-safe?
    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

    I have yet to see anything that's fail safe.

    A layer of insulation floating on top, or a layer of mineral oil can reduce evaporation. It's not completely maintenance free, but shouldn't take frequent maintenance.

    Large pressurized tanks are cost prohibitive. There really is no easy solution.

  • leo g_13
    leo g_13 Member Posts: 435

    > I have yet to see anything that's fail safe.


    > A

    > layer of insulation floating on top, or a layer

    > of mineral oil can reduce evaporation. It's not

    > completely maintenance free, but shouldn't take

    > frequent maintenance.


    > Large pressurized tanks

    > are cost prohibitive. There really is no easy

    > solution.


    > -Andrew

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  • Hi Con

    How is you evac. tube system working out? My solar tank provides enough heat to keep my basement well above freezing temperatures, and enough to heat my bed every night in the cold weather, and occasional space heating. It also provides 100% of my domestic- year round. the tank runs between 90-150 degrees, but I have a second smaller tank that gets the hot water first from the collectors, and I use the smaller tank just ot top off the domestic water, which runs through the larger tank first. The smaller tank heats up even on a partly cloudy day. you could cover them, but what if people forget? by covering the collectors you are leaving BTU'S on the table. Bob Gagnon

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  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Mineral Oil

    Mineral oil does work to an extent, but we found it wasn't a great long term solution. Since there's always a few pipes entering and exiting thru the top, the floating insulation won't seal.

    Turns out the only successful atmospheric tank systems we put in were for engineers. They'd keep an eye on things, and tweak and fill as required.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Pressurized Tanks

    We have gone exclusively to pressurized tanks, ganging several in series. Not the most elegant solution, but it alleviates the evaporation/maintenance issue....now we just have to deal with hundreds of gallons worth of absorbed air. Any thoughts?
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Ganging water heaters

    I'm heading this direction as well. For DHW and space heat, my current thinking is:

    1. Closed, Pressurized drainback solar loop. Ganged storage tanks are in this loop. 50 gal/collector min.

    2. DHW heat exchanger in the collector return line. The cold side of that HX is pumped to the DHW preheat tank. The DHW supply is piped in series, i.e., cold supply enters solar tank, then the backup tank.

    3. Space heating load pump pulls directly from the hottest solar loop tank, and returns to the bottom of the coldest tank. (Just the reverse of the collector loop, but the load loop shouldn't have the drainback provisions). Load pump supplies fan convectors on their own thermostats & zones. No HX between collectors and distribution system. No coordination required between solar distribution system and fossil fuel backup system. Just set the "solar" thermostats higher.

    4. 50 gal electric water heaters go for $219 at Home Depot. Pre-insulated, includes T&P relief, drain, nipples. Professional looking. Ganging ensures good stratification.

    5. In taller homes, a 6 gallon accumulator tank could be installed in an upper floor. This would allow a smaller, quieter collector pump.

    Hot Rod in the past has suggested propane tanks. They would work and save money, but you'd still have to insulate them and overcome the appearance of misapplication.

    I'm not sure if I understand your absorbed air problem. What are the symptoms?

    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Weezbo
    Weezbo Member Posts: 6,232
    did you catch the post by hot rod?

    the solar tank? now that i would say is where the smart money would be in my selection of stradgey.
  • Constantin
    Constantin Member Posts: 3,796
    So far, so good...

    ... once we got the thing purged and happy, I can hear it come on every day. However, given the huge trees around us, I imagine that it'll do better in the midst of summer (when the sun is higher) and in the midst of winter (when the leaves are gone).
This discussion has been closed.