How to Use Solar Energy for Your Home


The sun is the source of all energy on earth except for geothermal and nuclear energy. Even fossil fuels are the product of ancient solar energy. We can feel this energy very directly when we sunbathe and are warmed by the sun. We are also using this direct energy all the time in our homes as it warms the fabric and as it enters through windows and becomes trapped by the green­house effect (in its original meaning). This use of solar energy is called passive solar energy as no mechanism is used to enhance or collect it. Active solar energy uses special collectors, of which there are two main types: fluid collectors which heat a fluid circulated within them, and photovoltaic cells which convert light energy to electrical energy. Both these active ways of harnessing solar energy are dealt with first.

Solar Energy

Active solar energy – Solar water heaters

There have been many different types of solar water heater installed in Britain. However very few of the early models worked with any degree of satisfac­tion, and many members of the public have been sold systems that cost hundreds and sometimes thousands of pounds which resulted in no appre­ciable reduction in their overall energy expenditure. In Britain it is only worth using the most advanced and efficient systems to take particular advan­tage of the summer sun to provide hot or warm water, so that the main boiler can be turned off. The far south of the country will provide considerably better returns than the far north. Where the total amount of heat collected is small, the most successful method of using this heat is to preheat the water in the hot water cylinder, so that less energy is expended to bring it up to the required level.

The way the most advanced existing solar collectors work is to collect the heat in vacuum tubes similar to those used in fluorescent light fittings. This reduces the heat loss considerably. In some of these heaters the back of the tube has been silvered so that light and heat are focused on to another long thin blackened tube containing water or oil at the centre. Others simply use an absorbing metal plate with the liquid similarly running down a tube in the middle. This second type is more suitable for overcast skys and so is most commonly used in Britain. The heat in the inner pipe is transported away by a liquid medium to a calorifier or heat exchanger, usually inside a hot water cylinder or in a pre-heating cylinder.

A second type of collector, which is more commonly used, is the flat plate collector, consisting of a metal absorber plate to which tubes containing the heat transfer fluid are bonded. The absorber plate is placed on a layer of insu­lation and the whole is put in a box with a glass or plastic lid.

If you have a large enough area of these collectors it is possible to obtain all your hot water needs during the summer and a considerable proportion of your autumn and spring needs. This will depend on your having a suit­able roof, or equivalent inclined location, facing roughly south with enough area to take the number of collectors you require for your needs. The main problem is that to install a really efficient system is still relatively expensive. Generally, the most energy-efficient plan is to complete all your energy conserving measures first before investing in solar water heating. However, if electricity is your only means of heating, then fitting solar panels makes sense.

Orientation and mounting of collectors

The optimum panel size for an average household is about 4 square metres: a larger panel area will of course provide more hot water but not so cost-effectively. It is important when mounting a collector to watch for obstruc­tions such as buildings or trees; the panel should ideally face no more than 45 degrees from due south, i.e. south-west or south-east, but not beyond. For optimum solar collection over the whole year it should be tilted at an angle of about 35 degrees to the vertical. Care should be taken with the mounting of the panel so that the weight is taken by the rafters. A low power pump is used to transfer the heat from the panel to the hot water cylinder and a differential temperature controller is used to turn the pump on when sufficient solar heat is available to heat the tank. It is important that this is properly installed, as otherwise much energy can be wasted. Neither building regulations consent nor planning permission is usually required but it is worth a phone call to check with your local authority. However, in a conservation area, planning permission is likely to be needed.

Photovoltaic cells

Photoelectric cells are based on a wafer or ribbon of semiconductor mate­rial, usually silicon. One side of the semiconductor material is electrically positive (+) and the other side is negative (-). When light strikes the posi­tive side of the solar cell, the negative electrons are activated and produce an electric current. When a group of solar cells are connected, a solar module is created which then produces a higher voltage than just a single cell. The cells are encapsulated under transparent material and the total electrical output is determined by the number of cells that are connected together within a module. Modules can be further linked in a panel to form a solar array.

Solar Energy

The efficiency of most standard crystalline silicon cells is about 13%, which means that 13% of the energy in the incident light is converted into electricity. A photovoltaic device converts fight into DC (direct current) electricity. They have become common in powering calculators and watches that require very small amounts of current and have proven to be reliable electrical power producers in thousands of terrestrial and space requirements. There are contin­uing developments in photovoltaics with many possibilities for future devel­opments in domestic energy applications. It is conceivable that windows them­selves, or even south-facing walls and roofs, could become solar cells.

For the present, however, the same can be said of photovoltaic cells as for solar water heating—that for the equivalent expense you can probably save far more energy by undertaking other energy conserving measures first. Their expense precludes them from being a first priority installation in most people’s homes. Their use at present is particularly appropriate in isolated situations where small amounts of power are required.

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About the Author: Justin Belden is a freelance web & graphic designer with over 15 years' experience. He is also an Avid member of the Design/Development community and a Serial Blogger who loves to help people by sharing interesting and informative tips and trick related to computer and technology.

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