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Forum Index : Solar : Solar hot water
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Russell Newbie  Joined: 16/08/2009 Location: United StatesPosts: 10 |
Im going to start building solar hot water panels soon. Wondering if any one has thoughts on hooking multiple panels up in series rather then parallel. It seems that all the info on the web has you hooking them up parallel.I think that if you took the hot water out of the top of the first panel and ran it to the bottom of the second panel the water would continue to get even hoter? |
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
You are correct in your thinking; series connections will in crease the temperature of the working fluid until . . . Sooner than later you will create two things: steam and pressure, neither of which will fare well in a flat-plate collector. First off, what do you want to use the heated water for? If you are intending to use it for "domestic" hot water, anything hotter than about 120 degrees F will have to be mixed against cold water or you'll burn your skin. If, on the other hand, it's steam you wish, there is a much better way. I've made copious amounts of steam from flat plate collectors in the past (I build small steam engines for a hobby), but I used a different working fluid, namely oil. Oil can be run and re-run through a SMALL single flat-plate collector all day long and the working pressure doesn't go up much at all. The oil is held in a very-heavily insulated receiver (tank) and when it's time for steam, a mist of water is passed over a heat exchanger that has some of that hot oil inside. If you choose to make steam and want help, respond here and I'll walk you through it, but BEWARE: Hot water will scald you; hot oil will KILL you. If you decide to run oil as a working fluid, several precautions must be adhered to or you're just asking for trouble. if you merely want an easy method to make hot water, again a working fluid of oil is as close to magic as you'll get, but let me help you before you wind up hurting yourself. Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Russell Newbie Joined: 16/08/2009 Location: United StatesPosts: 10 |
Thanks for the post MacGyver, Im just looking for hot water but I live in a place with a lot of overcast days and was trying to get the most of what I have to work with. |
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philb Regular Member  Joined: 05/07/2008 Location: United StatesPosts: 96 |
I am thinking the panels are hooked in parallel because all the water circulates into your hot water storage vessel. The water should get hotter as it makes several passes. Check out build it solar . If you don't get the info from the web, try emailing Gary. He is very knowledgeable. philb |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
I wish I knew how to make that quote-in-a-box thingy! Since I don't: "Im just looking for hot water but I live in a place with a lot of overcast days and was trying to get the most of what I have to work with." This being the case, the key to your success will be how well you are able to insulate your creation. First off, a flat-plate collector should be glazed with either glass or polycarbonate sheet (pricey!). Next, use foam insulation on all the pipes connecting your panel and the receiver and don't forget to insulate the receiver as well. I've had great success insulating receivers using about 3" to 5" of beach sand. This is the method I use to insulate hot oil receivers. Silicon is a fantastic insulator. If you mount the receiver at the top of the panel, it will naturally "thermo-siphon" and you won't need a pump. Remember to pull the cold off the bottom of the receiver and deliver the hot to its top! This design also lends itself nicely to not losing heat in that the heated water rises and won't flow down. If you're using a recirculating pump design, you have to make sure it's not pumping when the panel is in the shade or you will lose a great deal of your already-captured heat to radiation. All that means is the heat will "leak" out. Remember the rule: HEAT flows; cold doesn't. Heat flows from hotter to cooler. If I ever get around to putting up my new Web site, I'll do a complete blow-by-blow presentation of all this. Hope this gets you started in the right direction. Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Russell Newbie Joined: 16/08/2009 Location: United StatesPosts: 10 |
Thanks for the good info MacGyver, I have some nice large picas of glass for the panels, and found some good detailed plans on the net. I also picked up a circuit for the pump that senses the temperature of the panel and the temperature of the holding tank and only turns the pump on if the panels are hotter than the tank. I laid this circuit out for a stripboard and will put one together in the next day or two. I also found a circuit for a freeze detector that sounds a buzzer if the the temperature hit 32 degrees. I thought I could change this to run a pump to circulate water in the panels. Freezing not a big problem were I am, but it’s something to play with. |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Yup! Sounds like you're on the right track. While you're at it, a swing-check valve somewhere in the system will prevent accidental thermo-siphoning should Mother Nature throw you a curve ball. Also, try to remember to put an isolation valve each side of your pump and if you can, use unions between the valves and the pump. This way, you can take the pump out of the circuit for maintenance and not have to drain the whole thing. One last thing: Set the flat plate at whatever your latitude is if you're in the northern hemisphere facing due south. If you want to add a little more heat to things, you can use short mirrors to reflect early morning and late afternoon sun on the thing, but if it's glazed, this sometimes doesn't help much as the reflected light just reflects off the glazing and heads out into space again! Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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readyakira Senior Member  Joined: 17/07/2008 Location: United StatesPosts: 114 |
I believe parrallel is used to increase volume of heated water. In other wordsyou can get the water in storage hotter faster by moving more heated water rather then hotter heated water. like when guy wiring towers it is better to have more small wires then one stronger one. Don't you think Free/Renewable energy should be mandatory in new buildings? |
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| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
note here that evacuated tube collectors are far far better and cost peanuts, I bought a pair of low pressure collectors today off ebay that have 50 tubes each for $1000. this will collect about 90KW per day in summer, and 20KW per day in winter, almost enough to heat a house! I'll be using them to heat a pool unless someone else wants them for a few bucks for my trouble. Pity I'm in australia and postage would be a real killer here! Luck favours the well prepared |
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| gabbro Newbie Joined: 14/06/2007 Location: AustraliaPosts: 4 |
If you're using a thermosiphon type system you can't really put them in series as the hot water needs to keep moving upwards, hence why the reservoir is on top of the panels in most domestic systems. In these systems the water from the reservoir will normally pass through the plate a number of times anyhow, so I don't think putting them in series would gain you much anyhow. This site has some good info on DIY hot water with instructions on how to build a system using corflute for panels (which you can often find being chucked out after sporting events etc.) http://www.iwilltry.org/b/projects/build-a-simple-solar-wate r-heater/ |
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