35 thoughts on “New Solar Thermal Panel Project From Hawaii!”

  1. Does the plastic pipe break down to a harmful substance. ? I think copper may be safer for drinking.

  2. The plastic pipes are used in irrigation and as such will not break down. Copper pipes of this length would have cost thousands of dollars. It could however have been down with copper, the plastic however works much better and is cheeper.

  3. Nice piece pf work Steve. Only drawback of course is that you have to wait till mid morning to have that shower :-). I trust you have tried additional storage for the project? I’d be most interested to hear how/if its come on.

    I have recently moved to New Zealand, and have been playing with something quite similar to your project for a short time now. It was refreshing to come accross your submission. Initially I want something to assist with heating a pool. Experiments so far look good, though I’m working on getting a permanent flow of warm water through the sunlight hours. At the moment the unit I’ve built can heat 10 gallons of water at 20 deg C to about 36 deg C in 60 mins of sunlight – though as you say, if the unit is left stable with no flow – the water will come out extremely hot. Will perhaps post the project when I make some more progress.



  4. Awesome, I wonder in cold climates if antifreeze (glycol) would work, or would it boil? you could make a heat exchanger out of an old fridge evaporator coil placed in a tank of water.

  5. VERY Inovative,, One possible improvement to get some storage without a pump, would be to take the center end of the pipe and raise it about two or three feet, run lines to top and bottom of old hot water tank, and presto , Thermal Convection. This would make a pyramid shape of the tubing (pipe) , and, as the water heated up , it would go to the top of hot water tank and displace the colder water in the bottom of tank, back to the inlet (outside of coil) Glass here in Canada is cheap, (free if you look hard), However, heavy clear plastic would probably work to cover coil. And The thin plastic thermal safety blankets make extremely good reflectors, Good to see others experimenting with solar etc’ ,, All the best from Canada Ehy !

  6. hello,

    i’ve made one but it doesnt work very well.
    is a plastic ore glass sheet realy nessesarely for the functionality of the solar heater??

    greetings from Holland

  7. Hello Maurice:

    If you live in a very sunny and hot place you might not need the glass top sheet, but I would say that without it you will suffer a very high loss in efficiency. The glass serves to trap the heat inside the unit, making it heat up faster and stay hot longer. Without the glass, any heat absorbed by the collector is going to radiate rapidly back into the air. Also the glass helps to keep wind from cooling the collector.

    I would say in Holland you may need an insulated box AND a glass top sheet in order to get good results. This project was made in a tropical place, your climate is a bit cooler and will require greater methods of heat trapping.

    Hope this helps.

  8. ok thanks a lot.
    (today it took me 4 houres to get 10 L of water from 15 to 50 degrees celcius, without glass ore plastic sheet) i will try with it.

  9. I’d be careful using polymer pipes, especially for heating. Leeching of hormone-disrupting chemicals is more common in higher temperatures, so I’d recommend using metal pipes and painting them black. Other than that, fantastic idea.

    Also, you might want to look into PV for your power needs, because it seems that electricity is quite expensive. And you obviously have the solar resources.

  10. We’re thinking of using a similar system to extend swimming time in our pool each end of the warm season. I reckon the best way would be to first make a layer of polystyrene boards for insulation, cover them with aluminium foil to reflect any IR heat, then coil the hose and cover that with glass, sealing the edges with strips of polystyrene.

    However, for aesthetic reasons, we’d prefer to use a dark green hose. Now, I realise that black absorbs heat more readily, but would the difference really be so great?


  11. rock on, Last year I bought about a quarter mile of irrigation tubing 1 inch thick outside diameter. I was going to use it gor a geothermal heat exchange, tube was oging to be burried underground. Could I use this polyethelene tubing for a large scale project like yours? Allothether the tubing cost me about 160 dollars. I think 1000 feet of 1 inch tube (inside diameter = .875 inches) pie r ^2 would tell me that each foot holds roughly 7 cubic inches of fluid. or .03 gallons. I could store about 40 gallons in that length I think. Only thing that bothers me is will the tube being exposed to uv light for so long render it useless after a while?

  12. I live in Belgium and even I can heat up water substantially with a similar panel (of course much more insulated and so on) but I can’t use the water that is heated for washing or drinking. This has to do with safety (legionalle etc) so I was thinking about other ways to use this hot water. Is there something else I can do with hot water? Is there a way to utilize the energy somewhere else or transform the energy to electricity?

    At he moment I have hot water but no use for it…help me make something out of this project. Thank you all in advance!


  13. Yavuz,

    This problem can be overcome by setting up a system that stores the heat you’ve collected or transfers it to the domestic water that is safe to drink. The fluid that circulates through the coil is reused and is in a sealed system. In colder regions it’s common to add ‘anti-freeze’ to this fluid as well.

    I’m not sure you will have the space, but here is an example. The hot liquid would be pumped through a coil in a barrel full of water transferring the heat to the barrel. The domestic water line would also pass through this barrel before it entered the normal heating system. This “preheats” the water, saving you energy and keeps the two systems completely separate.

    This addresses several of the criticisms of the design (and the earlier version) including the growth of Legionella, contamination due to Freon or lubricant in the lines, or the use of plastics not rated for potable water.

    It’s a more complex design that many commercial units have used for years, but it is a real improvement.

  14. I believe that all plastics photo degrade over time. Not sure if it will get in the water but it clearly best to use copper for drinking water. However how often do you grab a cup of hot water from your tap?

  15. That plastic tubing was not designed to run at high temperatures so be careful about mixing it with any water you plan on drinking. THere are some PEX tubing types that will safely work at elevated temperatures and may still be inexpensive. You could certainly find a way to use less tubing and absorb the solar energy with a metal plate. Try a sheat of maybe 0.04 aluminum simply painted with flat black paint and then silicone your plastic tubing onto the back side (perhaps one tube run every 3-4 inches). That way you could minimize the amount of tubing you need and so you could still stay in budget with something actually designed to run at high temperatures.

    Hawaii is a perfect example of a location where very simple and inexpensive solar heating ideas can work. Obviously this same design would not provide much hot water in NY or MN but in an area where temperature rarely go below 20 C and are mostly in the 30 – 35C range it could be quite effective. Now of course if you want to do something about your cooling bill then you will need a design able to run at much higher temperatures so that you can run an absroption chiller or stirling engine.

  16. just a few suggested improvements,keep using the glass covering as this will help in retaining the heat better, a thin piece of plastic is not a good insulator and would release the precious heat you are trying to capture. if you can paint the backing flat black, as this would absorb heat and not reflect it. also use a smaller diameter hose(perhaps 1/2 inch), this will give you a better heat transfer( more water moving along the hose wall), also allowing you to use more length of hose, giving you more hot water at a time.you can also put foam insulating tubing around the hose coming out of the solar collector the keep the water from cooling during delivery making the hot water last longer, and use a black colored hose as the feeder hose,this will pre heat the water before it enters the collector. as for a storage system you can use a 55 gallon drum or two, paint it flat black and wrap the outside with r-19 or better insulation and also paint the shielding flat black and leave it in the sun too.this will take a little plumbing know how but should be a snap for you to do. good job!!!!

  17. I’m in Boulder, CO, I have a small (8’X12′) greenhouse that does not hold heat in the winter, as such, I have had to use electric heat – very expensive!

    I have accumulated the following materials:
    A 15W 9-12V solar panel
    100″ of 5/8″ black poly pipe
    12V deep cycle battery
    a voltage controller
    an inverter (12V to 110V)
    a 50 gallon barrel
    Assorted ABS pipe, connectors, fittings & etc.
    Plastic “two walled corrugated” sheeting (left over from the greenhouse)

    My plan is to assemble a variation of the collector shown (utilizing the plastic sheeting on top) and mount it outside the green house (higher than the 50 gal barrel inside) with a small holding tank mounted above the coil – say 5 gal. The water will gravity feed from the holding tank through the coil and down to the drum.
    The solar charged battery will provide power through the inverter to the submersed 120V pond pump to pump water back up to the holding tank and the cycle will repeat.
    This circulation will, hopefully, heat the 50 gal. drum enough to prevent freezing inside the greenhouse.

    I still have some questions:
    How can I measure the heat of the water coming from the coil and how can I utilize this information to turn the pump on/off once I know? I can make a home made float switch to put in the holding tank to turn on the pump when it gets low but that doesn’t help with the heat measuring.
    Should I draw the water from the bottom of the 50 gal. drum (I think so) and at what level should the returning hot water enter the drum? The pump will be at the bottom of the drum.

    It has been awhile since I visited this site so I will go back to it over the next few days. Thanks to all of you out there struggling with their own versions of clean energy, you never know, perhaps one of use will discover the next generation clean, cheap power.

    He ho, he high!

    Pat – kramerllc@comcast.net

  18. “Electricity is 30 cents per kilowatt in Hawaii.” Wow. Electricity costs 8 to 9 cents in StLouis MO July 2014. (summer is coming so rates will increase for Time of Day charges)

  19. We are trying to get our 30′ round above ground pool going. I would like to see what people think is the best way to heat water for it. We have planned to get pvc pipe, paint it black and run it behind our pool. We will put tarps under it painting them black also. We are not sure how much it might take. Is there any other way that might help. We live in Kentucky. Thanks for any help.

  20. You could paint the concrete black to increase the heat absorption, kind of like a solar cooker works.

  21. Just a couple of things I would try – Line the bottom and sides with foam board insulation and paint the inside of the box black – may increase efficiency. Rather than hose, use PVC (painted black) inside the box. It is very easy to work with, cheap, and you can be more certain about the safety of the water.
    Alternately, in brewing, we use a wort chiller for rapidly cooling liquids. You can make one at home and it can be used in reverse – circulate the hot water from the hose into your copper heat exchanger in a larger reservoir of water in a food safe vessel then you keep the hose water separate from potable water at all times.
    Ahhh – or just google “Using a Closed-Loop Antifreeze System to Heat Your Water”.

  22. I use this system successful on North new Zealand. O
    I also constructed a frame over a small swim pool in a dome fashion covered in plastic .day time heats up night time heated swim pool. Also o pump the warm water though my green house to keep temp up at nite for melons o grow.

  23. To wanda of Kentucky. To heat yr swim pool build pvc pipe frame over yr pool in a dome fashion cover with plastic like we do for hot houses to grow melons tomatoes etc.you will have warm water for swimming most of the night..

  24. Great system and one I’ve considered using for some time. Does sound like you need to get yourself some sort of rain catchment set up rather than pay for water. Do you get a decent rainfall where you are?

  25. I live in Oregon. Our average temps. are cooler than HI. This system would be vastly improved by using a rigid box tilted toward the sun. Then you can plumb it so you have thermal circulation (take off at the top). Insulated, black painted, enclosed box is necessary.

  26. You live in Hawaii and are paying for water?
    Collect it yourself, store it, treat it with pool shock(yes this works).
    Save 420/year.

    Buy an electric water heater, the bigger the better. Add one or more additional fittings. Hook it up to your solar water heater and there you have 40-50 gallons.

  27. Hi. Make coil container box out of concrete, cement or even free brick (Fire proof). Change plastic coil to coper coil… Extend coper coil 4′ outside box for both inward and outward flow (this way connected hoses don’t melt). Cover with glass (Tempered Glas…)during summer and finito. The longer the coil the more water pressure aded. Durring winter burn with salvage, donated, or free landfill green waist and home burnables (thus tempered glass). Optional… lay yet another copper coil under copper water coil with tons of small puncture holes, connect coper line to a propane control valve, cap off coiled end. Propane is meant as back up winter “needs”, primary winter source is free green waist pre stocked from city disposal as well as trash burnables which saves a heapin ton on trash hauls.

  28. You.could.also.use.the.tubing.to.go.through.concrete.blocks.to.store.heat.to.release.at.night.time.But.all.great.ideas.keep.up.the.good.work

  29. How do you accumulate the hot water? How are you pumping the water? What’s the flow rate? It looks like a plan with a lot of potential but I have many questions. Is there a link to somewhere with more information on your design?

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