Passive Solar Heating and Lighting
Using the power of the sun for heat and light is one of mankind's oldest technology pursuits. The Native Americans of Mesa Verde in southwestern Colorado designed their cliff dwellings so they would catch the warm rays of the sun in the winter and take advantage of the hill's cool shadows during the summer.
Today, buildings employing passive solar design take advantage of sunlight to heat and light indoor spaces through the same simple methods. Proper orientation of the building to the sun is a very important element.
Solar buildings typically have large, south facing windows to allow maximum light and thermal gain. The sun heats thermal mass - floors and walls made of dense, solid materials such as concrete or tile, during the day and gradually releases the heat at night.
Often, these passive solar heating features double as lighting sources, allowing natural light into interior spaces through the south facing windows, skylights and suntubes.
Of course, too much solar gain can be a problem. During the summer, passive solar design features can also keep buildings cool. West facing windows are minimized, and longer roof overhangs provide shade for windows when the sun is high in the summer, keeping thermal mass such as walls and floors darker and cooler. Open floorplans allow flow-through ventilation, reducing the need for electric fans and air conditioning.
Photovoltaic (PV) cells convert sunlight directly into electricity. These are the solar panels that are often used to power satellites, calculators, and highway warning lights.
PV cells are made of silicon semiconductors similar to those used in computer chips. When sunlight hits these materials, it knocks electrons loose from their atoms, which flow through the material to produce electricity.
PV cells are frequently built into panels that hold about 40 cells, mounted into frames that are usually about 2 x 4 feet. These panels are set up on unobstructed south facing roofs or spaces with maximum solar gain. Their output can be increased with the use of mechanical tracking devices that follow the path of the sun across the sky during daylight hours.
Depending on need, between 10 to 20 PV panels can provide enough power for a typical residence; for larger applications, such as electric utility generation or industrial purposes, any number of panels can be connected to form a single large system.
The performance of photovoltaics is measured in terms of their efficiency at turning light into electricity. Most modern PV cells have a conversion rate of about 15%, so about one-sixth of the sunlight hitting the cell is converted into power. Creating higher efficiency ratios for PV cells has been a subject of continuing research.
Solar PV concentrators are designed to focus sunlight onto a small space and generate power with greater efficiency. They must use tracking devices to keep the light aimed at a central area; the concept is to use small amounts of the expensive semiconducting PV material while collecting as much sunlight as possible. The lenses, reflectors and more sophisticated tracking systems make these more complicated and expensive, putting them out of the reach of typical residential uses. However, they can be cost-effective in larger applications such as industrial and utility-scale electric generation.
Direct heating of fluids by the sun can be effectively used for numerous domestic and industrial purposes.
Solar thermal systems are composed of two main parts - a solar collector and a storage tank. These collector panels appear similar to photovoltaics, but there are substantial differences. Thermal panels have a pattern of small tubes which circulate water or an anti-freeze solution through the unit. The tubes are attached to a black plate, which absorbs the sunlight and heats the fluid flowing through the pipes.
The fluid is usually transferred to an insulated storage tank, which can then be circulated for space heating or hot water generation.
Solar thermal systems can be either active or passive, but most are active systems. They use pumps to circulate the fluid between the collector and the storage tank, while passive systems are gravity fed or rely on the physics of water to naturally circulate when it's heated.
Additional information on solar
American Solar Energy Society
Smart Energy Living
Colorado Solar Energy Industries Association
Interstate Renewable Energy Council (IREC)
Million Solar Roofs Initiative.
National Renewable Energy Laboratory (NREL)
National Center for Photovoltaics.
Sandia National Laboratories - Photovoltaic Division.
Solar Electric Power Association (SEPA) (formerly the Utility PhotoVoltaic Group)
Solar Energy Industries Association (SEIA)
Solar Rating and Certification Corporation (SRCC)
Southwest Energy Efficiency Project
US DOE's Energy Efficiency and Renewable Energy Network
Western Resource Advocates
International Solar Organizations
This group coordinates the development and installation of photovoltaic systems in rural Honduras and the Dominican
By establishing renewable energy "village centers" that power computers, small businesses, and promote local culture, Greenstar creates social and economic opportunities for people in Jordan and India.
International Solar Energy Society (ISES)
Solar Electric Light Company. Consults, develops, and installs renewable energy systems in rural villages around the world.