Monthly Archives: June 2008

Solar water heating

Now it’s sunny and hot on most days, and the solar water heating system is working well.   The house was designed from the start to use active solar power as well as passive solar gain.  It was important from the start to find a site with southern exposure.  The lot faces about 25 degrees east of south, not quite optimum;  zoning restrictions meant that there was little option to turn the house on the lot so that it could face due south, but at least we have basically a good orientation, and a site that slopes to the south too.

Solar energy these days usually means photo voltaic (pv) or photo-electric installations.  The glassy silicon arrays generate electric power when stimulated by the sun’s radiation.   Grants are available in many states, and were at one time in Pennsylvania.  With grants paying 50% of the installation, photo voltaic can be cost effective.  But since I would have had to foot the whole bill, it was not worth installing pv even with the 30% federal tax credit.  This is the popular type of solar power for homeowners right now, and it can contribute low-carbon alternative energy;  with wider use, it will no doubt become cheaper.  Rising utility rates will also make it more cost effective, and in the future I hope to install it.

Time-tested low-tech solar water heating however is more cost effective right now, and can have a payback I calculated of maybe eight years.   I installed three panels with an area of 30 square feet.  Hot water is heated in a separate storage tank via a heat exchanger, and the heating liquid – which has to be a glycol mixture with anti-freeze to provide frost protection – is circulated with low voltage power from a small photo- panel.  this is cost-effective because only a very small amount of electricity is needed, and it eliminates more complex controls.  The sun shines and the pump runs, basically.  The heat exchanger which heats the hot water tank is a Butler wand, which can be retrofitted to an existing hot water tank as well as used in a new system.  It is one of the most cost-effective ways of providing solar hot water.  The heated water goes into the hot water heater tank, where is is further heated as needed by the regular water heater. 

 I had intended to combine the heating “wand” in the same tank as the regular water heater.  It did not work due to the type of tank I opted to use, without my realizing it.  So now we have nearly 100 gallons of hot water storage.  Since the sun does not shine every day, it is usually good practice to have a greater than usual capacity for the hot water.

The whole system cost about$3,000 installed, and I got back I think $800.00 in energy credit.  Apart from buying the components, I had to pay a crew to help install the panels on my high roof, and the plumber to install the tank and piping. 




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