batch solar water heater

homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
I'm starting a new project, I want to build a batch solar water heater, I been reading about how to build it, my question is, can it be done with a gas water heater core or it has to be electric?, does anybody had built one with a gas water heater core and had any trouble building it? any other alternatives?

thanks for any reply.;)


  • BB.BB. Super Moderators, Administrators Posts: 33,143 admin
    Re: batch solar water heater

    I have natural gas hot water heater too... Much of the heat of a gas water heater is lost up the center stack--so, to me it would seem that you should do this with an electric type water heater (which can have more insulation added--if needed).

    Electricity is expensive in California--so electric heat is not very desirable--and then I look at a tankless water heater (either as a boost heater for the electric heater or in-line with the hot water storage heater as a booster....

    Look at the cost of adding a new tankless heater (plus some of the issues with using a balancing valve on the shower--to prevent scalding--which seems to sometimes cause issues with stable hot water from a demand heater)...

    Then--I think about using the solar hot water as a pre-heat for my gas heater... but that seems like a less than ideal way of keeping my hot water hot -- still using natural gas to keep the natural gas tanked heater hot when I am not using hot water. Kind of misses the point of solar.

    And there are the maintenance costs (leaking pumps, tanks, etc.)... Vs a 12+ year life for a $400-500 tanked water heater as my only maintenance issue...

    Then I come back to how much I spend on gas for hot water ($20 a month)--and just walk away.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: batch solar water heater

    Are you talking about the kind of heater that uses a pump to pump water through a solar collector and circulate it in/out of the 'old' heater with the aid of a couple of check valves? I don't see why a formerly gas fired tank would be any different than an electric one, save the heat loss up the middle that Bill mentioned.

    Also an electric tank will have a built-in thermostatic switch which can be utilized to turn the pump on/off. You'd have to rig up something for a gas fired tank.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: batch solar water heater

    Do the batch types put the tank as the collector, on the roof, in a "sun oven", and you heat up a 30 gallon "batch" of water?
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  • Dave AngeliniDave Angelini Solar Expert Posts: 6,448 ✭✭✭✭✭
    Re: batch solar water heater

    The batch heater is the oldest type of water heater and it can be on the roof but is usually near a south wall on the ground. RV people do this so it is easy!

    If the OP is in Florida with a gas heater I would just go open loop to collectors. There is no good reason to go to electric and the extra loss in the flue is just made up with more collector area. For $600 you could use an El Cid pump from a 20watt panel controlled by an intermatic timer and warm temp thermistor and a rare freeze thermistor in parralel. Build a simple copper tubing collector and your in business. For $1K you could do this with pre-made panels for 2 people and save 80% on gas heating. Turn the pilot off for 9 months a year! Even get a tax credit and use a real controller to automate.

    This stuff is so easy compared to what I have to do in snow country where I use drainback for friends and at home. You should get started
    "we go where power lines don't" Sierra Nevada mountain area
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  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: batch solar water heater

    Thanks guys, yes, the solar water heater tank will be on the ground and water circulated as demand, the issue that I will have with a solar collector is storage, I may install a harbor freight pump to do some recirculation between solar collector, it uses a lots of power, is the marine type stainless steel 40 gallons per minute 100w 12v, those 20 w pumps El Cid, Grunflos are too expensive but relay with a thermostat it might do the trick, instead of a 30 gallons core I will go with one 50gal. plus one 40 gal., this way won't get to scalding point, my set up will be:

    1.- cold tap water line ball valve, T (run)branch to solar collector and (bull) existing water heater (return) recirculation pump.
    2.- 50 gallon collector to 40 gallon collector to ball valve to
    3.- cold tap (in) on existing electric water heater
    4.- from out (hot line) T (run)to house, (bull) to recirculating pump.

    any body have any suggestions on usin 50 and 40 gallons core? or it will be best to start with the 40gal. to prevent scalding?....I'm commited to make this project cost effective.

    any suggestions are apreciated.

  • BB.BB. Super Moderators, Administrators Posts: 33,143 admin
    Re: batch solar water heater

    Take a look at for a starting point.

    If you are in a sunny area, you should be look at (very roughly) 2 gallons per sq.ft of solar collector. And around 20 gallons of hot water per user per day...

    If the the water becomes dangerously hot--then you will probably want an anti-scald valve (mixes extra hot water with cold to temper to 120F-130F or so).


    PS: I am not sure you need such a large circulating pump...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: batch solar water heater

    Bill is right as usual: you don't need that big a pump. In fact too high a flow rate will limit the amount of heat the water can pick up while in the collector. Probably 3-4 GPM is plenty.

    Some plumbing plan:

    COLD water line -> check valve -> 'T' fitting -> 1). Water Tank IN & 2). Solar Collector OUT

    Water Tank OUT -> 'T' fitting -> 1). pump to Solar Collector & 2). check valve -> HOT water line

    The pump should be controlled by a thermostatic switch which will keep the pump running until the water in the tank is hot. A fancier version would have an over-ride to stop it pumping when there is no heat from the sun (very important for power consumption/pump life). Otherwise you'll have to switch it off manually every night, etc. You may need an addition Temperature/Pressure relief on the output side of the Solar Collector, just in case things get too hot.

    Is this making any sense? :p
  • homerramirezhomerramirez Solar Expert Posts: 102 ✭✭
    Re: batch solar water heater

    Yes, it does make a sense, by the way, I made a mistake with the recirculation pump specs, is 40 gallons per hr., 100w (8.3 amp.)@ 12v., 50 p.s.i. max. stainless steel marine grade, lift is 50 ft. from Harbor Freight, for $29.00, I'm well aware of H.F. products low quality but I'm trying to make this project under $75.00 with things already have.:roll:.... I'll install a tamper valve for safety, the 3/4 check valves are $10.00 at local hardware store plus some copper pipes, it seems to be an easy low cost proyect with greater return if nothing fails :roll:

    we already have a timer on our electric water heater, it comes on for 2 hrs. daily, from 6:00 to 8:00 p.m., with the solar batch collector I hope we do not have to turn it on during the warm seasons.

    Thanks guys for your advice.

    Homer :cool:
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