How To Build a Solar Water Heater System

One of the biggest uses of electricity, gas and oil is the heating of water in the home, and in offices, schools and hospitals etc. Solar Water Heater is a very simple and efficient way to grab energy from the sun and use it. Solar water heaters concentrate diffused solar radiation into thermal energy. A solar water system consists of a solar collector and a storage tank.

The next step up in DIY solar water heaters is concentrated solar water heating. Concentrated solar water heaters are more complicated to construct and more expensive, however they can be very efficient and great fun to build. The key component of a concentrated solar water heater is a parabolic trough which focusses all of the light hitting it onto a pipe containing oil.

Obviously a large parabolic mirror would be extremely expensive, so some efficiency has to be sacrificed in order to bring costs down. The trough itself does not get very hot - primarily because it reflects away the suns rays rather than absorbing them - therefore it can be made simply of a thin layer of flexible material such as formica, MDF, or plywood. The inside of the trough must then be covered with a reflective material such as aluminiumised mylar, or aluminium flashing.

Bending the trough into an exact parabolic shape does not have to be very difficult. Basically two end support need to be made which are parabolic and the reflective sheet can then be fitted to them. Below is an example parabola with a focal point suitable close to the base of the trough. If you print this, or any other suitable parabola onto 2mm squared paper , you then just have the simple task of scaling up the parabola to the required size.
Every parabola has a focal point at which all light hitting the parabola is focussed. For our three dimensional parabolic troughl we have a line of focal points along which we position the pipe containing the fluid to be heated. Common motor oil is perfect for this job since it is made to be heated to very high temperatures, it is not corrosive, and it is cheap and easy to find. Antifreeze is another option which is often used in solar water heating systems.

Standard copper pipes must be used rather than the newer push-fit plastic pipes. Plastic pipes will melt at around 90 degrees, far below the the temperature which will be reached by the pipe in the solar collector.Painting it with black paint will increase heat absorption.

The oil is in a closed system with a small pump used to move hot oil through a coil in the hot water tank. As the oil passes through the coil it transfers some of its heat to the water in the tank before returning to the solar collector to be reheated. Twin coil hot water cylinders (tanks) are available, but it is sometimes possible (but difficult) to add a second coil to an existing standard cylinder.

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