DIY Solar Water Heater

All of the solar water heating schemes (shown below) prior to Feb. 2022 have been abandoned in favor of PV direct to the water heater resistive element.  The element in the tank measures 12.5 ohms, and it does not care if it is hooked to 240 volts ac, or the dc voltage coming from the solar panels.

The label on the solar panel shows open circuit voltage and short circuit current.  I connected a string of three 240 watt solar panels to the lower element of a 50 gallon forty year old water heater tank.  Using the label data of Power max. voltage and current, the source impedance of the panels is either 4.44 ohms or 3.85 ohms, and three in series would be a current source with an impedance of either 13.3 or 11.6 ohms.
The 4500 watt 240 volt resistance heater measures 12.5 ohms.
For maximum power transfer, my source impedance of 13.3 or 11.6 is close to the load resistance of 12.5.  Unfortunately, this is for best solar conditions around solar noon, when I can measure 80 volts dc on the 12.5 ohm load.  Voltage squared divided by 12.5 = 512 watts.
The panels are laying almost flat on the ground in an area of the yard known to have strong winds.  They are clamped to a hunk of 2" x 8" cedar using aluminum door jamb scraps, and tied to a steel fence post.
  The Panels are 240 watts, so 3 X 240 = 720 watts.  Therefore, 512/720 = 71% of possible power.  This could be improved by tilting the panels.
At first, the water in the 50 gallon tank only reached 95 degrees F, which my dear wife declared "not usable", but I found it almost comfortable.  In an effort to increase the temperature, I wrapped with tank in Fiberglass batting, held on with old elastic waistbands from worn-out skivvies. 

After several days of bright sun, the water temperature reached 125 degrees F, which is too hot for either of us, which means we diluted the water at the shower head with cold water.  We were both extremely pleased.  Dear wife requested that we not have to open and close the valve letting cold water into the tank, but when we left it open, the warm water was running out of the tank, and the temperature dropped.  So the valve remains closed except when we want to shower.

I am not using the built-in thermostat because it would most certainly burn out with the DC current.  Perhaps later in the season, longer days and more sunshine will heat the water too much.  In that case, we can turn on the water valve at the wall, and let the warm water travel to various faucets, or we can lay a rubber floor matt over one of the panels (if we are not home for several days, for example).  Or, being hot, we sweat more, and might enjoy showers more often.  Time will tell, but for now, it is working, and we are happy.

As with most of my "experimental schemes", a temporary set-up ends up as a permanent thing.  The idea was to see if it would work, so I found an aluminum door jam in our barn, aka "Menke Depot", and cut it into pieces, drilled some holes and screwed them to some wood spacers between the panels.   Cheap! 

See first photo for end result.  Three solar panels clamped to a plank, and tilted a bit with some concrete blocks, and the whole works tied to the fence so it won't blow away.

An old extension cord that we used for an electric corded lawn mower (until it was cut in several pieces) was salvaged and used for the hook up from the solar panels to the basement.  The solar panels were $29.50 + freight.  I didn't have to buy anything to make this work.  

Check the yellow label on the side of your electric water heater and see how much is costs to heat that tank full of water, and hold it at that temperature all year long.  (More than you imagine!)

 

Everything below is old data for history.

Collector for Solar Hot Water consisting of old fiberglass satellite dish on top of a Round Bale Feeder. There are 350 feet of hose in the top of the dish (minus the lengths running into the basement to the hot water heater tank.

The round bale feeder is covered with wire because it often serves as a temporary chicken or duck pen. The hoses (2) were purchased at Sam's Club in South Austin and each was either 125 or 150 feet long. When the hose is manufactured (or extruded) something is used that makes the water smell of “new hose”. Therefore, we used the hot water for washing clothes at first, and not for hot showers because we didn't know exactly what sort of chemicals were coming out of the hoses. This 'smell” eventually goes away. The reddish-brown hose is a hose that we removed from the garden and added to the collector to provide more capacity. 350-400 feet of hose in the dish works quite well. Sometime after 11 in the morning, when the sun is shining, and the wind is not blowing, the water in the hose will get warm. (We feel the hose.) If the water in the 50 gallon hot water heater is cold we start the pump in the basement, and start circulating the water from the bottom of the tank into the hose, and put the warm water from the hoses into the top of the tank. Our switch for the pump is on the computer table, and we generally run it for 15 min. ON and about 20 min OFF. (A tick-tock timer) Here is a picture of the Taco 006 115vac pump. It is pumping cold water from the bottom of the tank through a hose adapter out to the hoses. The top and bottom heating elements have been removed from this 50 gallon electric hot water tank. The threads in the tank are one inch, and next time I will probably purchase shorter one inch stubs. (There is not much material in the tank wall for threads, and the length I used has lots of leverage, so if someone steps on it, something might break.) When we are not using the collector, the faucets turn off the water so there is no pressure in the hoses. Here is a photo of the location of the hot water inlet at the location where the upper heating element used to be. I used a ball valve here because the faucet valve started dripping. In mid afternoon, this metal will be very hot. If the temperature of the bottom pipe is hot, then the water in the tank is warm enough that we will have to add cold water when taking a shower. (It is too hot..and almost FREE!) Once again, the 1 inch diameter pipe is too long. Here is a photo of the top of the tank. The tank on the left is used most of the year to hold the solar hot water. There are ball valves so we can select which hot water heater to use. The heater on the right has the bottom element removed, and the top element is connected to a timer. This timer was purchased at Home Depot, and it has a manual OFF/ON switch. If we have cloud cover and can't get any hot water from the sun, then we hit the switch a few hours before we need hot water. The upper element only heats water in the top portion of the tank, so if we have a need for lots of water (visitors), then the switch is left ON.

We are using the electric hot water heater in December, January, and February, because even though we have all the hot water we can use during the other nine months of the year, when the sun goes South, our hose water only gets warm, and not hot. During this time, we are running our wood stove, and there are pots and kettles on the stove with “almost boiling” water. We are totally convinced that everyone should heat their household water with solar energy. Future improvements include a computer to monitor differential temperature and switch the pump OFF and ON, and better solar collectors. (Perhaps tubes from China?) Also, the two tanks should be in parallel to double the capacity during the hot summers, and in series during the Winter, so one can act as a source of pre-heated (warm) water for the electric heater.

Other comments:

At first, the hoses were just stretched out in the yard, but grass grew over the hoses, so they were moved to the sidewalk. This was not a very good idea, because the cement sidewalk remains cold for a long time in the morning. Putting them in the dish was an effort to keep them off the cold ground, and also out of the wind. (The wind really cools the hoses.)

I have also experimented with putting some black metal shelving in the dish, and laying the hose on top of the black metal. I believe that made a slight improvement.

Someone suggested that I should cover the two hoses running into the side of the house with plastic 64 ounce or two quart juice bottles. (by cutting hose-sized holes in the bottom of the bottles)

Maybe I should also cover some of the hose in the dish with these juice bottles to prevent cooling from the wind.

Notice the heavy chains and cement blocks holding the dish to the top of the feeder? Someday, winds WILL blow it away! (It has seen some strong winds in the last three years!)

I also attempted to use a large coil of one inch black plastic tubing but was unable to insert fittings into both ends of it without some kind of cracking or leaking. Perhaps the tubing was too old, and had hardened up?

I bought the pump on ebay for sixty dollars, but now they seem to cost more. The hoses came from Sam's Club (another $60), and the hardware came from Home Depot and the local hardware store (less than $100).

Our house is all electric plus a small wood stove for heat. In June of 2006, Bluebonnet Electric sold us 410 KWH for $58.01 or 14 cents per KiloWattHour. The yellow tag on the hot water heater (4^th photo) is for a rate of 7.3 cents/KWH, so the $450 should be changed to $863. (annual cost) Way too much money! I should mention that we have a 6 gallon electric heater under the kitchen sink for dishes.

Ray Menke, Lytton Springs, Texas. December 2006

Thanks to Willie McKemie of Dale, TX for the satellite dish,

and the one-inch black plastic tubing which I couldn't get to work.

Wife comments:

I think we should paint the inside of the dish black to increase absorbtion of sun's rays. Then again, that may make it too hot- and it is hot enough as it is. We could also get a large piece of clear plastic to keep the heat in the dish, but then the hoses may melt- and that wouldn't be good.

These garden hoses are specifically not to be used for hot water, but the ones that are rated for hot water cost a mint. I'd like to see regular plumbing supplies used; either copper tubing or thin, flexible PVC tubing, painted black. That would eliminate the hose smell, (which lasted a long time), and any possible contamination from PCBs or other 'bad for the human body' stuff. Donna Menke

 

Update September 14, 2020

In February, apparently a tornado came though our place and the neighbor's yard.  They lost one outbuilding, a chicken pen, and most of a large tree.  Our water heating satellite dish blew far away, ripping the hoses as it escaped.  Several solar panels on the patio pergola were tossed upside down.  They were held down by the 220 volt connector cables, and did not break.  We decided to do without the dish, and eventually collected the hoses and laid them out on the ground on some of the galvanized roofing panels from the neighbor's outbuildings.  This Spring, the Taco 006 pump would not force water through the hoses.  Something was plugged, or the valves were corroded.  We decided to add a few more solar panels and use the other electric water heater on the switch.  Using only the top element, the heater draws 2400 watts for 1 hour or so, and lets say it cost me 3 kWh at my payback from Bluebonnet for excess power...ten cents for enough water for several people to use for showers, etc.   Ten cents, ten or fifteen times a month is something between $1 and $1.50.  That's about the cost of a good hose clamp each month, or a 1" valve once a year.  I would lose all that exercise from running up and down the basement stairs to adjust the valves, though.  So, the system is still there, and if repaired, the first step would be to drain the water tank and remove and inspect the valves in the lines going to the outdoor collector.  If the lose grid power, that may be the only way to get a hot shower, providing we have enough battery inverter power to run the Taco 006 Pump.

It did work fine for almost 14 years, and then my solar panels multiplied and now I always have excess power...the 3 cent stuff.