Solar - Sunlight to Energy

There are many different ways the energy from the sun can be put to use. Plants turn sunlight into chemical energy using photosynthesis. Some ways we make use of this energy is by eating plants and burning wood. However, the term "solar power" means to convert sunlight more directly into thermal or electrical energy for our use. The two basic types of solar power are "solar thermal" and "photovoltaic".

Solar photovoltaic: This involves the generation of electricity from light. The secret to this process is the use of a semi-conductor material that can be adapted to release electrons, the negatively charged particles that form the basis of electricity.

The most common semi-conductor material used in photovoltaic cells is silicon, an element most commonly found in sand. All photovoltaic cells have at least two layers of such semi-conductors, one positively charged and one negatively charged. When light shines on the semi-conductor, the electric field across the junction between these two layers causes electricity to flow, generating DC current. The stronger the light, the greater the flow of electricity.

A photovoltaic system does not therefore need bright sunlight in order to operate. It also generates electricity on cloudy days, with its energy output proportionate to the density of the clouds. Due to the reflection of sunlight from clouds, days with a few clouds can even result in higher energy yields than days with a completely clear blue sky.

It's common practice these days to power small devices, like calculators, using very small solar cells. Photovoltaic is also used to provide electricity in areas with no power grid. We have developed a refrigerator, called solar chill that can run on solar energy. After testing it will be used by humanitarian organizations to help supply vaccines in areas without electricity, and by anyone who doesn't want to rely on the power grid to keep their food cold.

Architects are also using photovoltaic cells increasingly as a design feature. For instance, solar roof tiles or slates can replace conventional roofing materials. Flexible thin film modules can even be integrated into vaulted roofs, while semi-transparent modules allow for an interesting mixture of shading and daylight. Photovoltaic cells can also be used to supply peak power to the building on hot summer days when air conditioning systems need most energy, thus helping to reduce the maximum electricity load.

On both a large and a small scale photovoltaic can deliver power to the electrical grid, or stand on its own.

Solar Thermal Power Plants

Large mirrors concentrate sunlight into a single line or point. The heat created there is used to generate steam. The hot, highly pressurized steam is used to power turbines, which generate electricity. In sun-drenched regions, solar thermal power plants can guarantee large shares of electricity production.

From a current level of just 354 MW, by 2015 the total installed capacity of solar thermal power plants will have passed 5,000 MW, according to projections. By 2020, additional capacity would be rising at a level of almost 4,500 MW each year, and the total installed capacity of solar thermal power around the world could reach almost 30.000 MW - enough to power more than 30 million homes.

Solar Heating and Cooling

Solar thermal is using the heat of the sun directly. A solar thermal collector on your roof can provide hot water for your home, and to help heat your house. Solar thermal systems are based on a simple principle known for centuries: the sun heats up water contained in a dark vessel. Solar thermal technologies on the market now are efficient and highly reliable, providing solar energy for a wide range of applications, from domestic hot water and space heating in residential and commercial buildings, to swimming pool heating, solar-assisted cooling, industrial process heat and desalination of drinking water.

Domestic hot water production is the most common application for solar thermal today. In some countries it is becoming a common feature of residential buildings. Depending on the conditions and the system's configuration, up to nearly 100 percent of hot water needs can be provided by solar energy. Larger systems can additionally cover a substantial part of the energy needed for space heating. There are two main types of technology:

Vacuum tubes - The absorber inside the vacuum tube absorbs radiation from the sun and heats up the fluid inside, just as in a flat solar panel. Additional radiation is picked up from the reflector behind the tubes. Whatever the sun angle, the round shape of the vacuum tube allows the sun to reach the absorber directly. Even on a cloudy day, when the light is coming from many angles at once, the vacuum tube collector can still be very effective.

The flat panel solar collector - Basically a box with a glass cover which sits on the roof like a skylight. In this box is a series of copper tubes with copper fins attached. The entire structure is coated in a black substance designed to capture the sun's rays. These rays heat up a water and antifreeze mixture, which circulates from the collector down to the water heater in the basement.

Solar cooling - Solar chillers use thermal energy to produce cold and/or dehumidify the air in a similar way to a refrigerator or conventional air conditioning. This application is well suited to solar thermal energy, as the demand for cooling is often greatest when there is most sunshine. Solar cooling has been successfully demonstrated. Large-scale use can be expected in the future, as the cost of the technology is reduced, especially for small-scale systems.

Get active

Choose to be part of the solar solution. See the links bellow to learn more, or go to our Take Action section to find out what you can do to help.

Solar generation – Youth activist site.

Solar Generation report – Solar electricity for over 1 billion people, and 2 million jobs by 2020 (pdf)

Solar Living Institute

Real Good solar info page