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Solar windows

This is the simplest solar system since it is designed to allow the direct radiation from the sun to penetrate the interior through sun-facing windows. The windows, either in a house or apartment, act as collectors and the internal building materials become the heat store, radiating the accumulated heat at night or on cloudy days. To be effective, the sun- facing windows have to be larger than normal and you can add skylights or clerestories to allow light penetration into otherwise sunless rooms. All glass surfaces should be double or triple glazed in severe climates with, ideally, low-emissivity glass.

It is important that the internal sun- absorbing surfaces are effective as thermal-storage features. Materials such as heavy masonry walls and concrete floors are excellent, but you can give existing lightweight walls and floors more mass by covering them with additional plaster or thick ceramic tiles. You can also use water drums if the floor will support the weight. Although heat can be distributed around the home by normal thermal movement, fan- assisted circulation can help to reduce the amount of thermal mass required.

Adequate shading in summer is vital to prevent overheating, and insulating curtains, insulating blinds or shutters, and even plants can be both effective as shading devices as well as attractive features in their own right.

Solar walls

Rather than allowing the sun to heat the internal partitions and floor, you can build a special glass-covered thermal- storage wall on the sun-facing side of the structure. As the sun’s rays shine on the wall, generated heat is stored and circulated passively through wall vents into the living areas.

There are two types of solar wall: Trombe walls, named after Dr Felix Trombe, and water-container walls. The former are built of heavy masonry material, such as brick, stone, block, or earth, with a dark-coloured surface toward the sun. The wall can have window openings, with double or triple glazing fixed close in front forming a cavity between the two surfaces. It is possible to adapt most existing sun- facing masonry walls by painting the surface dark, covering it with glazing, and installing vents. However, in hot climates, such as in Australia and large areas of the US, you must provide summer shading.

Water-container walls use water drums or columns as heat stores instead of masonry. Water is more efficient than masonry as a thermal store but it is extremely heavy and needs regular maintenance to combat leaks and the growth of algae.

With both types, you either need to close vents or insulate the glazing at night and shade it in summer.

Sunspaces

Adding a sunspace to your home has become one of the most popular conservation features in recent years. Known also as a conservatory, solar greenhouse, solarium, or sunroom, a sunspace is an ideal area for a family room, growing plants, or to use as a solar heat collector. It is important, however, to decide what the primary use of the sunspace will be. It is really only successful when it is designed to fulfil one main purpose.

Working in much the same way as a solar window, the sunspace is basically an attached room built on the sun-facing side of a house with a large expanse of glazing. Also effective is a glassed-in balcony area in an upper-floor apartment. During the day the air warmed by the sun flows into the home by natural convection either through open windows or via special vents. At night, if the space is not being used as a living room or greenhouse for plants, you can close the area off and the temperature of the sunspace will then drop below that of the home.

If, however, you want to use it, either for recreation or as a contributor to night time heating, you will need to provide thermal storage and insulation to the glazing. Heat can be stored either in the heavy materials surrounding the sunspace or it can be transferred by fan during the day to a heat store.

To prevent overheating, especially in hot climates, you should incorporate roof vents or windows and, in summer, deciduous trees and vines can provide additional shade.

Sunspaces can contribute significantly to reducing heating bills, but in temperate climates recent UK research has revealed that the expense of installation is too high to be justified on energy-saving grounds alone. Less- expensive measures, such as solar windows, insulation, and draughtproofing, are much more cost effective. The popularity of sunspaces has more to do with their use as versatile, sun-filled living spaces, with a reduction in heating bills coming as a welcome extra bonus.

Active systems

In this system the sun heats glass- or plastic-covered metal collector panels housed in shallow boxes fixed in rows on a sun-facing roof. The absorbed heat is taken from these by passing liquid or air through or around the panels and is then fed into a thermal store under the ground floor. This store is either a rock bed for air systems or a water tank for water systems in hot climates. When you need the heat in the home it is distributed by water pipes or air ducts, assisted by fans or pumps. Alternatively, you can use a sunspace as the solar collector.

Depending on the climate, solar hot water systems can provide between half and three-quarters of a household’s requirements. In hot climates, the solar- heated water is stored directly in hot water tanks, but in cooler climates it is more usual to use it as preheated water for a conventional boiler.

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