Solar power is a viable alternative to fossil fuels as a source of energy. But it needs cost reductions and new ways to store electricity in order to assert its supremacy over coal, natural gas, and oil.
Passive solar space heating, Trombe walls, and other absorptive materials help reduce energy costs. Solar panels that convert sunlight into electricity are also improving in efficiency and affordability.
1. Low-E Glass
Low-E glass has a special coating that reduces the amount of radiant heat allowed into a home or office. The coating is invisible to the eye and consists of metallic oxides that are able to reflect thermal radiation (heat).
This spectrally selective filtering helps keep your room cooler in summer, decreasing energy usage and costs. It also prevents harmful ultraviolet (UV) rays from entering your home or office and potentially bleaching out your carpet and furniture.
These specialized coatings are produced during the float glass manufacturing process and fused to the glass ribbon. Typically, these coatings have a visible light transmittance of more than 80 percent and a solar gain coefficient that is less than 0.25.
While the concept behind low-emissivity (low E) coatings on glass dates back to World War II, it was not until the mid 1980’s that R&D efforts were focused on developing and demonstrating the commercial viability of the technology. This eventually lead to the development of windows, doors and skylights with this energy-efficient glazing option.
To maximize the energy efficiency of low-E glass it should be combined with argon gas in an insulated window unit. This gas is injected between the panes of glass and works to keep warm air from seeping out in winter and cool air from penetrating in the summer.
2. Thermal Mass Materials
When properly used, thermal mass can be a key part of a solar-responsive building. This material can store a large amount of heat energy and help keep indoor temperatures stable during the day and night without using air conditioning systems, thus reducing the use of fossil fuels.
Thermal mass is any solid or liquid material that can store a lot of heat and can be released over time. Common examples include concrete floor slabs, masonry brick walls or rammed earth (in naturally ventilated buildings). Water is another good example of a material with high thermal mass since it can absorb and release heat over long periods of time.
The key to making thermal mass work is to integrate it into a building where it can be exposed to low-angle winter sunlight and protected from heat loss at night. The mass should also be insulated to prevent overheating in summer. It is important to understand the different heat transfer properties of a thermal mass material, as some materials have high specific heat capacity but require a lot of energy to change their temperature, while others are poor conductors of heat but have a low specific heat.
It is therefore important to select a thermal mass material with an appropriate balance of these characteristics. In general, concrete and masonry walls have a high thermal mass, but they take a while to warm up from a cold start. Timber framed walls, on the other hand, have less effective thermal mass but can warm up quickly and maintain their temperature for longer.
3. Overhangs
Roof overhangs keep the glare and heat of direct sunlight off windows, and are instrumental in keeping rainwater away from walls and foundations. They also provide a buffer zone for your home during storms, reducing pressure on the walls of the house and minimizing wind damage.
Roof overhangs can be built in a variety of shapes and sizes, from simple and fixed to elongated and even curved. Some are built from solid materials like wood and metal, while others are constructed from lightweight awning-like materials such as fiberglass or vinyl. They can be designed to work in conjunction with windows, allowing the sun to penetrate deep into the room for heating during winter, but shielding it from summer overheating.
Overhangs can also be used to shade east and west-facing glass, though this is less effective because the sun is lower in the sky at these times. It is important to consult a design professional for advice on the appropriate size and shape of overhangs for your specific climate and building type, as different solutions are needed for cold and moderate climates compared with hot and tropical ones.
4. Shading Screens
Shading screens are a flexible solution to solar heat gain that can be used as part of a comprehensive approach to passive design. They reduce sunlight and glare without reducing natural light, which increases occupant comfort and can help to maintain healthy indoor temperatures. They also enable natural ventilation by releasing hot summer air to the outdoors, which helps to control energy costs in climates with large diurnal temperature swings.
Shade screens consist of dark, tightly woven mesh that goes outside your window frames and reduces glare and UV damage while preserving the view. They are available in a range of shading percentages, from 5% to 50%. They can be fixed or adjustable to accommodate changing climatic conditions.
Insulated window coverings are a type of window treatment that reduces energy costs by insulating against both heat and cold. They can include shades, blinds, shutters, and curtains. They can be operated manually or with automated systems that adapt to changing sun angles and illuminance levels.
Passive solar design can be enhanced by strategically placed vegetation, such as deciduous trees that allow winter sun through their bare branches but block direct summer sunlight with their leaves. Trees and shrubs can also serve as shading for walls and windows. In addition to lowering cooling costs, they can block wind, assist in cooling by transpiration, improve indoor air quality by filtering pollutants, and enhance the visual environment with pleasant filtered light.