Something solar for the handy and do’ers
Solar water heater, supplemental or main system.
This design is either supplemental to a hot water heater or as a main system for off grid use. The simplicity of the design will be inherent once construction is started.
1/2” copper tubing, schedule dependent upon budget. Get the best you can afford You will need roughly 30′ of it.
30 1/2” copper elbows
2 end fittings to change over from copper to flexible hose. Get the barbed ones to eliminate leaks down the road.
3/8” plywood. One 4X8 sheet is sufficient. (you may want to use 3/4″ plywood in some areas or depending on install location)
1/4” Plexiglass, a 2X4 sheet is sufficient.
One can of Ultra-flat Black spray paint.
One 15W solar panel (check the requirements for your pump, you may need more panel to power it.)
½ tubing and fittings to tie into the water heater lines.
Wiring for the pump
(Optional but recommended) a 1/2” back flow valve.
(there could be more, but this will get you in the ball park)
The beginning of the project is to build the solar collector. A 2X4′ box roughly 4-6” deep is more than sufficient. One side open set up so that you can install the plexiglass in it and are able to seal it up to retain any heat that you generate. Don’t worry about insulating it, the wood will be sufficient at this stage.
You will cut you pipe into 22 sections of 18” and 2 of 24” as well as 11 of 2” These you will assemble with the elbows to make a serpentine path for your water to travel through the collector. Assemble this and adjust as needed before you solder the joints. Both inlet and outlet should come out the same side of the box and this can be done on whatever side you deem best. I do not recommend coming out the bottom though as you will want to be able to tilt the heater to best collect sunlight as it traverses the sky through the seasons. Once the serpentine is assembled and soldered and pressure tested, paint the whole thing flat black. This will be mounted on points within the box roughly mid point between back plate and the plexiglass. Do this at various points but at no time should you touch either front or back. The only points touching should be mounts and where the pipe goes through the walls of the box(and these will be insulated/sealed) (Side note: You may want to install a valve on the outlet side; This will be for venting air out of the system for best performance. Not essential, as air can be vented in several ways even without that valve.)
The back wall of the box should be either black or reflective. An easy reflective surface can be done by painting that wall with resin/epoxy/glue and then pasting sections of aluminum foil on it. The walls can be treated the same way. The pipes MUST be blackened though. (I intend on setting up two boxes, one reflective, the other completely black and do some testing to see which is faster in heating. I have not done this yet, so can not say which is more effective.) (another way to blacken pipe (expensive) is to use a raw acetylene flame and soot the pipe. Its blackened at the atomic level (read: efficient) but is easily rubbed off. Use care in handling the finished product)
You will need to find your inlet and outlet pipe on your water heater. I have both ran to the main system of the house under pressure, and tap into inlet at two points to go out to the collector then return to the heater. From the pump I put in a back-flow preventor to keep the water from cooling off the storage tank at night. (Note: for best performance, have separate inlet and outlet points on the tank so that the circulation is truly isolated to the water within the tank. This may be more trouble than advantage, due to access to the tank wall and/or skills and tools needed) This is under pressure but you will be circulating only within the storage unit, so you pump does not need to overcome pressure. The pump will only run while sunlight is shining as it is self contained without a reserve power supply. (you can make this more complicated by tying into a power system and installing a thermostat but I won’t cover that here)
Fair warning. This system MUST have a pressure regulator on it (Such as the one on the water heater) This collector is capable of gathering a lot of heat into the storage tank and it must have a way to vent off pressure. It is capable of heating water far past boiling points. (pressure keeps it from boiling, but remove that pressure and the whole things goes critical. Vent before you burn) You can even put in a thermostat to shut off the pump to keep water from getting too hot in the tank but if you do, I would put a relief valve in the collector as it will overheat the water within the tubes if there is no flow through the pipes.
Now, a totally passive system can be made with a level regulator (float valve style) and a back flow preventor. Set up an insulated tank near the roof level, the pressure will be gravity to where you want heated water. The collector will have the inlet at the lowest point in the tank, and the outlet from the collector will drop in the top. (make sure to have an overflow and that the overflow vents somewhere OTHER THAN inside your dwelling) This works on the percolation action of water gaining pressure as it heats up. The water in the collector will heat up, expand and push itself out the top into the tank. As it does this, the collector cools off quickly, losing pressure and gravity will refill the empty space from the water from the bottom of the tank. The level in the tank is maintained by the pressured water via the float valve. The back-flow preventor also keeps the water from going the other route at night when the collector actually cools the water. (keep this action in mind for making ice without a freezer, It works!) Key points to consider in construction. The top of the collector should be no higher than midpoint of the tank. This keeps the weight of the water in the tank as a regulator for the percolation factor. Next: Large collectors work well for heat but not so much for the percolation, a smaller collector will not heat as much but cycles faster, therefor heating the water faster. Its a fine line on how much is too much or too little: you may have to experiment a bit. Third, the collector needs to be angled up from inlet to outlet for best operation. Again, experiment to find the best functional angle.
A simple water heater for an RV/travel trailer: get a section of copper tubing that is easily bent. Most are less than 1/2” ID This can be coiled up into a large spiral, the inlet of which is the outer edge and the outlet the center. You will need near 100′ feet for a large enough coil to work well. Paint the coil flat-black and mount on the roof the unit while feeding hose from your hot water heater to and from the coil. (mount directly to roof to cut reduce air flow around the pipes.) This is simplistic, but effective: Not recommended for locals with temps that drop below 400 F though. The advantage of this set up is near constant hot water on demand in normal average temperatures (during daylight hours of course). The downside is the space and quantity of materials required to achieve that.
Remember, There Ain’t No Such Thing As A Free Lunch (TANSTAAFL) Solar energy is a very good source of heat or electricity, but it has to be shining! Even a partly cloudy day means the difference in a functional system and a barely adequate system. Fully cloudy days will mean that you may only achieve lukewarm water or a trickle charge to your batteries. Ambient weather also determines performance. Lower mean temperatures will be reflected in lower output, and freezing conditions may ‘lock the system’ completely. The ideas listed above are really only ways to supplement what you have and potentially reduce your need for more power, at least for hot water. They will not eliminate it, unless you live in one of those mythical places where the sun is always shining 18 hours a day, and the temp never goes below 70. To use the first system as a ‘Main Unit’, storage is the key. You will want enough stored water to last through a couple of days, and you will want the insulation of that unit to be absolutely, top notch. More heat is lost through poor insulation, than in the process of heating that water. If you are using an old water heater as your storage unit, make sure to insulate the riser tube inside as well as supplementing the outside insulation as well. Reflective insulation is highly recommended. Make sure to flush the tank before use as well and you will want to do this annually. Heating water will cause some form of particle formation and those particles will gather at the bottom of the storage unit.(and in some cases, in the collector itself) These reduce the performance of your unit (and this applies to ALL water heaters! There is a reason they put that tap on the bottom of those things!).
A couple of thoughts; taking some of these ideas into consideration, they could be applied to other aspects as well. I can see using that percolation system as the key heater for radiant flooring to heat a small cabin in the winter. You won’t achieve tropical paradise, but you won’t be freezing your ass off either. Get creative, if it doesn’t work, figure out why not and fix it or cut the loss and try something different. (other than losing pipes in the flooring, there really would be no loss if the radiant flooring idea didn’t mesh.) Again, be creative, ya might surprise yourself.