Garage heating - solar hot water?

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    Junior Member
    • Apr 2022
    • 3

    Garage heating - solar hot water?

    I built a large garage a few years ago.
    24' x 80' with 16 ft ceilings.
    I plumbed pex into the concrete floor. 2 x 4 loop zones.

    There is 2" of foam under and around the slab.
    The walls are 3.5 inches of closed cell foam.
    Ceiling is R40.

    I am located about 70 miles north of Detroit.

    Keep the shop from freezing in the winter
    Heat the shop to approx 65 degrees for a lot of the shoulder seasons, spring and fall. Understanding that this may vary depending on weather.
    Minimize operating costs to do this. I am willing to spend a bit more upfront for this as I feel that all energy costs will continue to increase, within reason of course. This isn't an unlimited budget. Would definitely like to see a ROI of this over the years.

    I do not have natural gas at home.
    So heating options are propane, oil, electric, or solar.
    It is not possible to tie PV solar panels to the grid here as I do not have 3 phase power.

    My intention at the time I started the garage build was to use vacuum tube solar panels to heat the water for the floor.
    Think type solar system with commercial panels.

    There seem to be conflicting info on this type of system online anymore.
    The stories of failed heat pipes or vacuum tubes, and maintenance required for them are making me rethink my options.

    This combined with some stories online that these types of solar systems are becoming obsolete and that PV and heat pumps may be a better option have me wanting to get some thoughts from this group.

    In my situation, what are your suggestions?

    Is a hot water solar option still viable?
    Tips for finding more robust vacuum tubes? Designing such a system for longevity?

    I am trying to research the PV panel and heat pump options.
    But, most of these seem to include grid tie feedback of the PV panels into the calculations.
    If I cannot grid tie, is this still an option? Are there examples shown online? Recommended vendors?

    Other suggestions?
  • J.P.M.
    Solar Fanatic
    • Aug 2013
    • 14943

    Whatever you decide as a means to heat the building, it's essential you get a fair idea of the heat load before choosing a heat source. Currently in the U.S. and usually, that number is expressed in terms of BTU per hr. of heat loss per degree of temp. difference between the desired inside temp. (65 F. ?) and the outside ambient. That loss is then multiplied by 24 hours in a day and then multiplied by the total degree days for 1 year. Also, it's usually necessary to get an hourly and/or daily design heat load by multiplying the hourly per degree heat loss by the max. design temp. difference between inside and outside.

    As for other suggestions, I'd incorporate more south facing windows and make (re)moveable insulation for them to take advantage of the passive solar heat and also the light they provide. If you do provide windows, paint the floor on the south side of the building a dark color and let the sun heat the concrete. BTW, how thick is the concrete ?

    I'd also consider spot or task heating so as to be able to keep the thermostat setting lower. I'd avoid propane or fuel fired bullet heaters as the building may be too tight to ensure adequate ventilation for combustion processes.

    Forget vacuum tube solar collectors. Poor quality and too many maint. issues.

    What's the roof like ? Mostly horizontal w/some slope ? Pitched ?

    If you do flat plate solar, consider a ground mount. If you put collectors on the roof, you'll never keep them snow free, and if on a horizontal roof, angled collectors will have wind design considerations with any such design most likely needing the services of a P.E. for wind design and most likely some real beefing up, especially when the bases of the collectors need to be 2 - 3 feet off the deck for snow clearance. Ground mount or on the roof, angle any such collectors at about 55 - 60 deg. to horizontal and face them south. And/Or, put solar thermal collectors on the non fenestrated portions of the south building wall. Do not eliminate south facing windows. They are more efficient at proving space heat via solar energy than are solar collectors.

    Overall, your area in MI is not very amenable for winter solar heating applications. What research did you do on solar availability before designing the building ?

    The concrete floor thermal mass and high insulation levels combine to give you a pretty good (that is long) thermal time constant (that is, lots of thermal mass/low heat loss) for the building and that's good because the building will lose and gain heat slowly, in effect acting as a good energy storage device, meaning the building will lose (or gain) heat slowly. But since irradiance levels pretty much suck from Nov. through about March or so, figure on conventional means of heating the building for those times.

    Welcome to the neighborhood.


    • bcroe
      Solar Fanatic
      • Jan 2012
      • 5203

      Your numbers look almost exactly the same as mine, except only 45
      feet long in the shop here at the northern border of IL. It is normally
      at 65 F, and at least well above freezing on the coldest days. I get
      air conditioning as a bonus in summer.

      This is accomplished with a 1.5 ton air to air heat pump, specifically
      selected as effective down to -25 F. Energy comes from a PV solar
      array, using a net metering contract with the Power Co. You do not
      need 3 phase for this. With the clouds and the short days, I cannot
      collect much energy in mid winter. In summer I pile up KWH credit
      with the Po Co, then take it back to stay warm in winter.

      Trying to heat directly off solar energy at these latitudes, with these
      clouds, is just about impossible. As it is, my house is a much bigger
      load, much warmer, and I do not buy any electricity either.

      There is my old propane furnace serving as backup, a gen set could
      run it for an outage. It has been many years since it last ran.
      good luck, Bruce Roe


      • KRCSWO
        Junior Member
        • Apr 2022
        • 3

        The problem is that my electric utility says they can not do net metering in an area without 3 phase power.
        So they won't let me setup such a system.


        • LucMan
          Solar Fanatic
          • Jul 2010
          • 626

          Is there 3 phase power available on your road? If it is you can upgrade to a 3 phase service. Single phase power will still be available for your use in the service panel.


          • KRCSWO
            Junior Member
            • Apr 2022
            • 3

            Originally posted by LucMan
            Is there 3 phase power available on your road? If it is you can upgrade to a 3 phase service. Single phase power will still be available for your use in the service panel.
            I do not have 3 phase power at the road. So, this upgrade would be VERY expensive as I would have to pay to bring 3 phase from approx 5 miles away.


            • SunEagle
              Super Moderator
              • Oct 2012
              • 15131

              Originally posted by KRCSWO

              I do not have 3 phase power at the road. So, this upgrade would be VERY expensive as I would have to pay to bring 3 phase from approx 5 miles away.
              If you decide to use solar to generate power for heating you may have to look into an off grid system. The problem is an off grid system can be very costly without much chance of any ROI due to battery costs. Still some people have done well with off grid but it requires a different life style then for those that are use to living with a grid

              If you already have a single phase grid connection you might look into running power from the home to the garage and install a split system like Bruce has done at his home and just forget about solar due to not being able to have a grid tie system and being so far North so solar becomes much harder to justify.


              • bcroe
                Solar Fanatic
                • Jan 2012
                • 5203

                It sounds to me like the Po Co is avoiding Net Metering except for
                industrial setups. I would wonder if what they are doing is actually

                I cannot run without Net Metering, because most energy is collected
                in summer, but most is used in winter. Just single phase, 200A
                240V service here. The heat pump could work without solar, as
                SunEagle says. Bruce Roe