Solar Power
Most countries in the world will be facing serious energy shortages in the near future. High energy consumption and the ever-increasing world population will force residents of many countries to confront the critical problem of dwindling domestic fossil energy supplies. Current dependence of the majority of countries on oil has important economic costs and portends future negative effects on national and international security and the economy. There are many other ways of using modern technology to make the renewable and other alternate energy technologies work for us. One of the key renewable energy technologies is photovoltaics.
There is more than enough solar radiation available around the world to satisfy a vastly increased demand for energy. The total amount of energy irradiated from the sun to the earth’s surface is enough to provide for annual global energy consumption 10,000 times over. If all this electricity were to be generated by means of PV systems with a modest average electricity output of 100kWh (electrical) per square meter per year, a total solar capture area of 150 x 150 km would be required. A large part of this capture area could be situated on roofs and walls of buildings, and would not therefore occupy extra land area.
Photovoltaic systems have a number of merits and unique advantages over conventional power-generating technologies. PV systems can be designed for a variety of applications and operational requirements, are modular, easily expandable and transportable. Energy independence and environmental compatibility are two attractive features of PV systems. PV systems can be used for either centralized or distributed power generation. The fuel (sunlight) is free, and no noise or pollution is created from operating PV systems. In general, PV systems which are well designed and properly installed require minimal maintenance, have long service lifetimes and are very reliable.
Solar Electricity
Electricity can be generated from the Sun in several ways. Photovoltaics (PV) has been mainly developed for small and medium-sized applications, from the calculator powered by a single solar cell to the PV power plant. For large-scale generation, concentrating solar thermal power plants have been more common but new multi-megawatt PV plants have been built recently.
Energy Storage
Storage is an important issue in the development of solar energy because modern energy systems usually assume continuous availability of energy. Solar energy is not available at night, and the performance of solar power systems is affected by unpredictable weather patterns. Therefore, storage media or back-up power systems must be used.
Solar energy can be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems.
The Solar Two, the largest of its type solar facility in the US, built in 1981 by the Department of Energy near Daggett, California, used this method of energy storage, allowing it to store 1.44 TJ in its 68 m³ storage tank with an annual storage efficiency of about 99%.
Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid. Net metering programs give these systems a credit for the electricity they deliver to the grid. This credit used to offset electricity provided from the grid when the system cannot meet demand, effectively using the grid as a storage mechanism.