Desalination of brackish water is done in the United States in order to meet treaty obligations for river water entering Mexico. Several Middle Eastern countries have energy reserves so great that they use desalinated water for agriculture. Saudi Arabia's desalination plants account for about 24% of total world capacity. The world's largest desalination plant is the "Jebel Ali" Desalination Plant (Phase 2) in UAE. It uses multi-stage flash distillation, dual-purpose and it is capable of producing 300 million cubic meters of water per year.
The traditional process used in these operations is vacuum distillation — essentially the boiling of water at less than atmospheric pressure, and thus a much lower temperature than normal. Due to the reduced temperature, energy is saved.
Solar energy
Solar energy is the transformation of heat, the energy that comes from the sun. It has been used for thousands of years in many different ways by people all over the world. The oldest uses of solar energy is for heating, cooking, and drying. Today, it is also used to make electricity where other power supplies are not there, such as in places far away from where people live, and in outer space.
It is becoming cheaper to make electricity from solar energy. Because the Sun always gives heat and light, solar energy can be considered a renewable energy and an alternative to non-renewable resources like coal and oil.
Solar energy is used today in a number of ways:
After passing through the Earth's atmosphere, most of the Sun's energy is in the form of visible light and infrared light radiation. Plants convert the energy in sunlight into chemical energy (sugars and starches) through the process of photosynthesis. Humans regularly use this store of energy in various ways, as when they burn wood off fossil fuels, or when simply eating plants, fish and animals.
Solar radiation reaches the Earth's upper atmosphere with the power of 1366 watts per square meter (W/m). Since the Earth is round, the surface nearer its poles is angled away from the Sun and receives much less solar energy than the surface nearer the equator.
At present, solar cell panels convert, at best, about 15% of the sunlight hitting them into electricity.
The dark disks in the third diagram on the right are imaginary examples of the amount of land that, if covered with 8% efficient solar panels, would produce slightly more energy in the form of electricity than the world needed in 2003.
Many technologies have been developed to make use of solar radiation. Some of these technologies make direct use of the solar energy (e.g. to provide light, heat, etc.), while others produce electricity.
Solar power plants convert sunlight into electricity, either directly using photovoltaics (PV), or indirectly using "concentrated solar power" (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics converts light into electric current using the photoelectric effect.
Solar cooking uses the Sun as the source of energy instead of standard cooking fuels such as charcoal, coal or gas. Solar cookers are an inexpensive and environmentally sound alternative to traditional ovens. They are becoming widely used in areas of the developing world where deforestation is an issue, financial resources to purchase fuel are limited, and where open flames would pose a serious risk to people and the environment. Solar cookers are covered with a glass plate. They achieve a higher temperature by using mirrors to focus the rays of the sun.
The Sun may be used to heat water instead of electricity or gas. There are two basic types of active solar heating systems based on the type of fluid — either liquid or air — that is heated in the solar energy collectors. (The collector is the device in which a fluid is heated by the Sun.)
Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air collector." Both air and liquid systems can supplement forced air systems.
Solar cells can be used to generate electricity from sunlight. It is a device that converts light energy into electrical energy. Sometimes the term "solar cell" is reserved for devices intended specifically to capture energy from sunlight, while the term "photovoltaic cell" is used when the light source is unspecified.
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. A large no. of solar cells are combined in an arrangement called solar cell panel that can deliver enough electricity for practical use. Electricity produced by solar panels can be stored in rechargeable solar batteries, which is then drawn upon when required.
Photovoltaics
Photovoltaics (PVs) are arrays of cells containing a solar photovoltaic material that converts solar radiation or energy from the sun into direct current electricity. Due to the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaic arrays has advanced considerably in recent years, and costs have dropped.
Solar photovoltaics are growing rapidly, from a small base, to a total global capacity of 130,000 MW at the end of 2013. More than 100 countries use solar PV. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building.
Photovoltaic solar panels come in many different voltages. The most common are 12 volts, 24 volts, and 48 volts. Like batteries, multiple solar panels can be connected together to produce higher voltages, for example, two 48 volt panels connected together would produce 96 volts. The inverter, batteries, and solar panels in a system are usually all of the same voltage. The advantage of a higher-voltage system is that thinner wire is used, which is less expensive and easier to pull through conduit. The disadvantage of a higher-voltage installation is that electric shock and arc flash become more of a hazard, so installations above 48 volts are usually only found in solar power plants or commercial buildings.
A photovoltaic installation typically includes an array of solar panels, an inverter, rechargeable batteries (for use at night), a charge controller (a device that prevents the batteries from over-charging), two GFCI circuit breakers (one before the inverter and one after), and interconnection wiring. There is sometimes also a transformer after the inverter, which can power 240 volt heavy appliances such as a clothes dryer or oven. The transformer is often part of the inverter and can't be seen. Everything past the inverter (or transformer if there is one) is set up like a normal utility-fed installation (breaker panel, lights, outlets, switches, etc.). If there is no transformer, only 120 volt devices may be used. Installations without a transformer must be labelled as such on the breaker panel to alert future electricians that 240 volt appliances can not be installed. Some installations have direct current (DC) lighting and possibly DC appliances. The advantage of this is that for DC loads, the losses in the inverter are avoided. These installations will have a separate DC breaker panel connected before the inverter. For safety reasons, DC wiring cannot be run in the same conduit as AC wiring, and DC outlets must not accept an AC plug and vice versa.