Solar Water Heaters are making a come back as homeowners look for ways to reduce their energy bills.
Houston is not a bad place for a solar water heater. Laying down pipes on our roofs could get the temperature of the water within up to 120F fairly easily. The heat from the sun would come down on the pipe, and then you have the heat absorbed and radiated back up from the roof. I spent one summer day on top of Deerbrook Mall roof resetting circuit breakers for an air conditioning system, which had breakers that tripped at 135F. Still, we do have the cloud cover in winters; that is why I recommend a solar assisted water heater, rather than pure solar.
You may think of a solar panel powering an electric water heater when planning this installation, but I find a simpler set up becoming more popular with homeowners, which can be an easy do it yourself project. Have you felt the water rush through a garden hose that has been laying in the sun? The water can be quite hot. This is the concept behind the current wave of heaters.
Here are the steps to build a water heater using this concept:
Attach a black tarp to your roof. Tarps have eyelets where you could drive a screw through. Have a washer on the screw to hold tarp down.
Have PVC tubes run along the tarp in a square wave pattern. PVC is easy to work with, since the glue is applied with a brush in the can. You have to use a cleaner (sold near the glue) before applying the glue. There are pipe clamps for walls, which can be used to fasten the pipes to the roof. Important: any screw, bolt, or nail that penetrates the roof covering needs to be caulked with roofing caulk, so you do not get leaks into the house.
Run the pipes to your current water heater and attach. Depending on the size of your pipes, you may need to use a reducer. Most home lines a 3/4”, while most people use 2” ID pipes for the heater. When you connect one end of your heater to the cold water inlet, and the other end to hot water side. Water pressure pushes the water through your heater.
Cover your pipes on the roof with another black tarp. You are done.
I see two problems with this set-up. First, already mentioned, you do not always have sun to heat the tubes sufficiently for your home’s needs. Secondly, how much water do you need? Do you have enough space on a roof to build a large enough heater? A typical water heater for an average size home is 40 to 50 gallons. The volume of a cylinder (your pipe) would be equal to the radius squared multiplied by the value Pi (3.14) multiplied by the length of the pipe. Let’s say you use the 2”ID pipe and you want a volume of 40 gallons, you then need to calculate for length(the volume divided by Pi X radius squared). We need to convert gallons to cubic inches, before we plug values into our formula. One gallon equals to 231 cubic inches, so 40 gallons equals 9240 cubic inches. This gives us 2942.68 inches of pipe or approximately 245 feet of pipe. Quite a bit of pipe.
(Let’s go over some pipe terminology. ID stands for internal diameter, while OD stands for external diameter. For the volume of the pipe you need to base your calculations on the ID. “Sch.” stands for schedule, which is a reference to thickness of the pipe wall. Most pipe you will find for residential use will be schedule 40. Below you will see a reference to Type K,L,or M. These are designators to indicate what the pipe can be used for. At your home center, look for a phrase saying that the pipe can be used for drinking water or similar phrase. Refrigerant pipe is not acceptable for the water heater.)
I believe that you can resolve these two issues by creating an system that assists your current water heater. If you have a tank water heater, the tank will act as a storage device for your heated water. Water heaters turn on when the temperature drops. By pre-heating the water, you cause the heater not to turn as often. If you have a tankless unit, the first water rushing through the unit will be already heated, which takes care of the first water coming through the pipe that would have been cold till the pipe heats up. To achieve this assisted set up, you would hook up the cold water going into the heater to your solar water heater pipes. The output from these pipes goes into the cold water inlet of your water heater.
You could develop a more effective system with some adjustments. I wrote a post about making a solar oven. Take this concept, and think about running your pipes inside the oven. This oven could be built in a wooden box, so it would be more secure on the roof. Also, you may want to use copper pipes. Copper is a great conductor, so it will keep the heat well. To make this an easy project when using copper, use the push connectors which bite into the pipes, so you do not need to use flux and a blow torch. I believe one brand name for these connectors is called Sharkbite. When using copper, check that the pipe is a Type K, L, or M, or that the pipe is suitable for use for drinking water.
I hope that this gives you an idea of how to create your own solar water heater. I have been experimenting with the copper and PVC in the oven, and I have had good results. I was thinking about experimenting with PEX tubing too. I am about to use copper myself, < !– google_ad_section_start –> with the Sharkbite connectors for my assisting solar water heater< !- google_ad_section_end ->. I think that a solar oven of about 2’X2′ would be a good size to pre-heat the water before it goes into the tank heater.