Solar hot water

Solar hot water systems are quite common in some countries where a small flat panel collector is mounted on the roof and able to meet most of a household’s hot water needs. Cheaper flat panel collectors are also often used to heat swimming pools, thereby extending their swimming seasons.

Solar cooking

A solar box cooker traps the sun’s power in an insulated box; these have been successfully used for cooking, pasteurization and fruit canning. Solar cooking is helping many developing countries, both reducing the demands for local firewood and maintaining a cleaner environment for the cooks. The first known western solar oven is attributed to Horace de Saussure, a Swiss naturalist experimenting as early as 1767.

Photovoltaic cells

Solar cells (also referred to as photovoltaic cells) are devices or banks of devices that use the photoelectric effect of semiconductors to generate electricity directly from the sunlight. As their manufacturing costs have remained high during the twentieth century, their use has been limited to very low power devices such as calculators with >LCD displays or to generate electricity for isolated locations which could afford the technology. The most important use to date has been to power orbiting satellites and other spacecraft. As manufacturing costs decreased in the last decade of the twentieth century, solar power has become cost-effective for many remote low power applications such as roadside emergency telephones, remote sensing, and limited “off grid” home power applications. Though their cost is not yet competitive with conventional power and hydroelectricity, it has been declining steadily and is now within a factor of 2 in many areas.

Solar power plants

Solar power plants generally use reflectors to concentrate sunlight into a heat absorber.

• Heliostat mirror power plants use an array of flat moveable mirrors to focus the sun’s rays upon a collector tower. A vast amount of energy is transported from the tower and stored by using a high temperature liquid like sodium. This in turn is used to heat water for use in stream turbines.

• A parabolic trough power plant is another type of solar thermal collector. It consists of a series of troughs rather like rainwater guttering with a hollow tube running its length. Sunlight is reflected by the mirror and concentrated on the tube. Heat transfer fluid runs through the tube to absorb heat from the concentrated sunlight and is used to power a steam turbine.

• A Parabolic reflector power plant is rather like a large satellite dish but with the inside surface made of mirror material. It focuses all the sun’s energy to a single point and can achieve very high temperatures. They are often used with a stirling engine or steam engine to obtain mechanical power directly.

• A solar chimney is a power plant where air passes under a very large agricultural glass house (between 2-30 kilometres in diameter), is heated by the sun and channeled upwards towards a convection tower. It then rises naturally and is used to drive turbines, which generate electricity.

Solar chemical

There have been experiments to harness energy by absorbing sunlight in a chemical reaction in a way similar to photosynthesis without using living organisms but no practical process has yet emerged.

Energy Storage

For a stand-alone system, some means must be employed to store the collected energy for use during hours of darkness or cloud cover – either as electrochemically in batteries, or in some other form such as hydrogen (produced by electrolysis of water), flywheels in vacuum, or superconductors. Storage always has an extra stage of energy conversion, with consequent energy losses, greatly increasing capital costs. One way around this is to export excess power to the power grid, drawing it back when needed. This effectively uses the power grid as a battery.

Deployment of Solar Power

Deployment of solar power depends largely upon local conditions and requirements. But as all industrialised nations share a need for electricity, it is clear that solar power will increasingly be used to supply a cheap, reliable electricity supply.

North America

In some areas of the U.S., solar electric systems are already competitive with utility systems. As of 2002, there is a list of technical conditions: There must be many sunny days. The systems must sell power to the grid, avoiding battery costs. The solar systems must be inexpensively mass-purchased, which usually means they must be installed at the time of construction. Finally, the region must have high power prices. For example, Southern California has about 260 sunny days a year, making it an excellent venue. It yields about 9%/yr returns of investment when systems are installed at $9/watt (not cheap, but feasible), and utility prices are at $0.095 per kilowatt-hour (the current base rate). On-grid solar power can be especially feasible when combined with time-of-use net metering, since the time of maximum production is largely coincident with the time of highest pricing.