Advantages of solar energy
Solar energy is a renewable resource that is environmentally friendly. Unlike fossil fuels, solar energy is available just about everywhere on earth. And this source of energy is free, immune to rising energy prices. Solar energy can be used in many ways – to provide heat, lighting, mechanical power and electricity.
Passive Solar Energy
Passive solar heating and cooling represents an important strategy for displacing traditional energy sources in buildings. Anyone who has sat by a sunny, south-facing window on a winter day has felt the effects of passive solar energy. Passive solar techniques make use of the steady supply of solar energy by means of building designs that carefully balance their energy requirements with the building’s site and window orientation. The term “passive” indicates that no additional mechanical equipment is used, other than the normal building elements. All solar gains are brought in through windows and minimum use is made of pumps or fans to distribute heat or effect cooling.
All passive techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation. Solar heating designs collect and store thermal energy from direct sunlight. Passive cooling minimizes the effects of solar radiation through shading or generating air flows with convection ventilation.
Another solar concept is daylighting design, which optimises the use of natural daylight and contributes greatly to energy efficiency. The benefits of using passive solar techniques include simplicity, price and the design elegance of fulfilling one’s needs with materials at hand.
Passive Solar Heating
Passive solar heating of buildings occurs when sunlight passes through a window, hits an object, is absorbed and converted to heat. The most efficient window orientation for heat gain is due south, but any orientation within 30 degrees of due south is acceptable. Once the heat has entered the building, various techniques come into play to keep and distribute it. Even in the Canadian climate, the prevention of overheating in the sun space presents one of the biggest challenges.
To let the sun in, a ratio of roughly eight per cent window to floor area is recommended for south walls. Although this number may seem small, it is important to remember it comes from the floor area, which is much larger than the wall area. Again, the control of overheating is a significant issue.
Once the heat is in, a well insulated and air-tight building envelope helps prevent heat loss and allows the solar heat to provide more of the heating needed. A crucial component of the energy-efficient building envelope is the window system. Where common double-glazed windows let heat escape, high performance windows, with insulated frames, multiple glazing, low-e coatings, insulating glass spacers and inert gas fills, can reduce heat loss by 50 to 75 per cent.
High efficiency windows, together with R-2000 levels of insulation and air-tight construction allow passive solar heating to cover a large proportion of heating needs in many locations. With the heat contained, often a simple ceiling fan or a forced air furnace fan (furnace burner off, of course) is all that is required for heat distribution. Using building envelope upgrades alone, up to 25 per cent of a building’s heating requirement can be gained with passive solar techniques.
A helpful technique to control overheating and extend warm conditions in the sun space once the sun is down is the use of heavy mass materials in the walls and floors. Quarry tile or stone on floors in a mortar bed, and one wythe of brick or double layers of gypsum board on walls, will absorb solar radiation, smooth out the peaks of solar gain, and slowly radiate heat back into the room when the sun is gone.
Some solar homes use a centrally located masonry wood heater to store heat. The bricks and stones surrounding the firebox absorb the solar gain or heat from short but intense firings and slowly radiate it into the room.
The need for air-conditioning in homes can be greatly reduced or even eliminated by using passive solar cooling. When designing with passive solar cooling, heat from solar radiation and heated air is kept from reaching the building. Internal heat gains from appliances and occupants are minimised and exhausted by natural ventilation.
External solar radiation can be reduced by fixed or adjustable shading devices, providing shading by using vegetation or by using special glazing in windows. External shading devices can reduce solar gains by up to 90 per cent, while still admitting a significant amount of indirect light.
External heat gain can also be controlled by good insulation, reduced window size and by the use of reflective materials in the walls and roof. At the building design stage, attention should also be paid to cross-ventilation and the direction of prevailing winds, the source of cooling nighttime breezes.
In designing a building it is important to consider the optimal use of daylight. The term “daylighting” refers to using the overall light of the surrounding sky to illuminate building spaces, not just direct sunlight. In large commercial buildings, daylighting can significantly reduce energy consumption and provide a more comfortable working environment. Correct daylighting design will not only reduce costs related to electrical lighting but will also reduce the need for air-conditioning in rooms heated by light bulbs or ballasts.
A good daylighting system will consider the following elements: the orientation and space planning of the spaces to be lit; the location, form and dimensions of the opening through which the daylight will pass; the location of internal surfaces which may be able to reflect the daylight and the location of movable or permanent objects which provide protection from excessive light or glare.