On April 30th the Orange County Campus of Durham Tech hosted a Sustainability Fair focusing on Solar Energy. When most people think of solar energy they think about generating electricity from the sun. Who isn’t at least a little bit fascinated but placing a panel out in the sunshine and having it make electricity? While I am strong supporter of solar electricity, the benefits and compelling simplicity of solar hot water need a little more press. So let me give that a try.
I’ll start with solar electricity. Solar cells make electricity through the photoelectric effect. To get the photoelectric effect you start with a semi-conductor, which is just what it sounds like, a material that sort of conducts electricity but not very well. The most common solar cell is made from silicon which is mixed with the proper amount of two other elements, boron and phosphorous. (It also matters where in the cell you put the boron and the phosphorous). When sunlight strikes the solar cell (the UV rays in the sunlight to be precise) it causes the some of the electrons which are in the region with the phosphorous to migrate to the region with the boron. Having a higher concentration of electrons in one part of the cell compared to the other creates voltage. By connecting a circuit from high voltage side to the low voltage side of the solar cell you cause the excess electrons from the side of the solar cell with the boron to flow through the circuit to the side with the phosphorous. On the way through the circuit the electrons can turn on a light, run your radio, or charge up a battery so the electricity can be used later.
Here in Chapelboro, we are blessed with plenty of sunshine, and at a cost of around $25,000 you can outfit your home with a photoelectric system which should provide for most electricity needs for an energy conscious family of four. Smaller sized, solar electric systems for remote locations with lower energy needs can be much less expensive. In the interest of full disclosure, in addition to my family’s house in Chapel Hill, we have 16 acres of land in Orange County which we are converting (slowly) to a small sustainable farm. I am currently installing a small solar electric system (125 amps) to run some small appliances there e.g. a light for my chicken coop. I’ll cover that project in a future blog.
While photovoltaic systems spark the imagination, if you want to consider an investment in solar technology for your home I suggest that you look into solar hot water. Once you start to learn more about solar heating for your water you are going to be amazed why more people have not installed a system. All over the world, from 1000’s of years ago until now, people have been and are successfully and efficiently heating their water with sun. There are a number of designs for the system, but all are based on allowing the water to pass through tubes or a tank where the water is heated directly by the sun. Here in Chapelboro there are very many days during the year where sunshine can provide all of the hot water you need for your family. If you already have natural gas in your house, you can install an in-line water heater after your solar hot water system to add heat as necessary to maintain your water temperature on cloudy days. (I really like this type of hybrid systems of new and old technology and am planning a future blog on these types of systems) If you have a swimming pool that you heat for part of the year and do not have a solar water heating system, stop reading this blog now and go buy one.
It takes a lot of energy to heat water and heating of water is the basis for the standard unit for measuring energy consumption, the British Thermal Unit (BTU). One BTU is the energy required to heat one pound of water from 39 to 49 degrees Fahrenheit. Generally speaking the water heater in your house accounts for about 30% of the energy consumption. You can begin to see the appeal of a solar water heater from a simple energy balance.
The cold water from your tap is not cold because it’s refrigerated; it’s cold because it runs through underground pipes. All year long once you get at least 2 feet underground the temperature is around 50 degrees F. Your water heater brings the temperature of the water up to 120 degrees, a temperature rise of 70 degrees. Now imagine the simplest solar water heater you can think of, just a tank sitting on your roof, no glass, no fancy UV-absorbing paint, just a tank. Instead of sending the 50 degree water from the ground straight to the hot water heater, you send up to the tank on the roof and let it warm up to the temperature of the air around it and by having the sun shine on it. On a warm summer day in Chapelboro the water will easily warm to 85 degrees. Now you supply this warm water to your hot water heater and it only needs to raise the water temperature by 35 degrees to get to 120. Since the temperature rise is only half what it was before, the energy consumption is cut in half as well. In many parts of the world if you look around you will see black tanks sitting roofs of houses and buildings to take advantage of this free energy. It seems that only here in the U.S. would we so casually ignore this free resource.
If you upgrade your simple tank system by building one a number of green house type structures with water pipes treated with special paint, for much of the year you can heat the water to above 120 degrees. In this case you actually need to install a temperature gauge and a mix valve to add cold water to the outlet to prevent scalding someone in the house. In our climate a solar water heater can reduce the energy consumption for water heating by over 60% on a year-round basis. I was thinking of reviewing some of the typical designs for solar water heaters, but this blog is already getting a bit long. If you are interested in more information we have many experienced and reputable companies right here in Chapelboro who can provide you with the detailed information and install one for you.
If you want to get a taste for solar water heating try this experiment for fun. Find a glass contain at least one half gallon in size with a lid. Paint the outside black with spray paint. Put some water in it, but leave at least 25% of the container empty to allow for expansion of the water. Put it in your back yard on a sunny day, let it sit for an hour or so and see how warm it gets. I’d love to hear what temperature you reached.
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