solar hot water system

Pfirth Registered Users Posts: 1
Hello. We have several small older low income houses on a walk in lane in Hawaii. Water is heated by electricity which particularly in Hawaii is expensive and inefficient as I'm sure you all know. I would like to at least provide solar water heating for our tenants but there are currently no programs or tax deductions and everyone pays their own utilities.

As the temperature is in the low 80's year round with ample sun and all the roofs are corrugated metal I thought of a very simple low cost system that would use the existing electric water heaters as storage tanks and backup systems. Cold water would be drawn from the lower part of the tank through a cpvc pipe to the grid which would attach directly to the metal roof. The section of roof under the grid would be painted black and an inexpensive UV resistant clear acrylic sheet would attach above the grid and to the roof. Metal roofing repair tape would seal and insulate the acrylic sheet from air circulation. The grid could be constructed from cpvc which has a fairly low melting point or PEX if the temperatures got too high. Copper would probably be better, but I'm trying to keep it low cost and low tech. The heated water would then circulate down to the middle of the tank via a small electric circulating pump run by a simple temperature activated controller. An additional pressure relief valve would be located close to the grid outflow. This would in effect be a pre heat system but because of the consistently warm climate and already existing components should be inexpensive, practical and relatively low maintenance.

Any thoughts on this idea would be most appreciated.


  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: solar hot water system

    Simple 4X10 commercial made collectors are fairly low cost and can be oriented better to take advantage of the solstice angles. this does lend itself to DIY as well.

    Lots of good ideas here:
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: solar hot water system

    My opinion, certainly worth a try. Try one unit first of course to see how it works out. Seems almost criminal to be using electricity to heat water when free solar heating is there for the taking. I built my own solar water heater over 10 years ago, provides all I heed Spring, Summer and Fall. Directly heats the water, very simple, no heat exchanger or pump involved. The collector is mounted lower than the tank, so the water circulates naturally when the collector gets hot, by convection. A 60 CDN gallon electric tank, with added insulation, stores the solar heated water. The electric is not hooked up at all. In Winter of course the collector must be drained to prevent freezing where I live.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,490 admin
    Re: solar hot water system
    BB. wrote: »
    If you want a do-it-yourself kit... This one appears to be hard to beat:

    Solar Guppy has many years experience with a system from them and has been pretty happy. It does require proper maintenance to keep running well and to prevent problems (like freeze damage).

    There have been a few threads here that link back to several extensive home projects--right down to installation photos, and documentation of mistakes and corrections...

    Link 1
    Link 2
    Link 3 (also sells battery based Differential temperature pump controller).

    Follow the off-forum links. The several projects/websites highlighted are very educational.

    And this one is a bit more low tech home made heating system. Also very interesting and informative.

    Between the two above links, they probably give the best detailed explanations of how to do a major home heating/domestic hot water project that I have seen.

    The second one is, by itself, probably not practical for a city home system--but both give great ideas of the scope of such projects.

    Any of the solar thermal are plumbing projects--If you are into Do It Yourself, then the maintenance will not be too bad for you.

    However, if you are not looking forward to becoming a union plumber--You might look at the Geo Spring and similar Heat Pump based hot water heaters. They are around 2-3x more hot water for the same amount of electricity (vs a resistance based heater) and you can get some "free" cooling and dehumidifying with them too if installed in a weather sealed room/basement.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: solar hot water system

    I would shy way from any plastic in the collector, for two reasons. First, plastic is a much poorer heat conductor than. Opper, or steel or aluminum. Second, plastic will degrade in direct sunlight, ( and in fact PEX must be UV protected or it will quickly fail) and it can give off nasty chemicals as it heats too hot, and or it fails.

    A simple flat plat collector, made up of plywood, scrap steel, discarded patio door tempered glass is very cheap to build and works pretty darn well. The last one I built was ~ 24 sq ft, with perhaps 150' of 1/2" copper pipe puts out enough hot water in the summer for several people. I would talk to some local suppliers, installers to get some ideas.

    That said, since you have no freezing issues, the system gets all that much easier to build.