SOLAR SITES AND LAND RESOURCES
Since solar energy conversion depends on solar intensity, solar plants are best sited in regions where there is a good level of insolation. For solar thermal plants, the regions of the globe where cloud cover is rare will offer the best locations. These are often the arid, desert regions of the world where land may have little other use. As a consequence of their nature, these regions are often distant from the major demand centers so transmission system extensions are likely to be necessary to exploit them. Some of the areas with good solar thermal potential include the southwestern United States, Rajisthan in India, the Middle East, North Africa, and the southern-most states of the European Union such as Italy, Spain, and Portugal. Typical space requirements for solar thermal plants are 2–5 ha/MW.
Solar photovoltaic power plants are less sensitive to their situation since they do not require direct sunlight and can operate effectively even with cloud cover. As a consequence, they can be used in a wider range of locations. Large, utility- scale, solar cell arrays capable of generating tens or even hundreds of megawatts of power are becoming popular, but most of the global capacity today is derived from rooftop-mounted solar cells. These units often supply power locally and col- lectively they represent one of the largest forms of distributed generation in oper- ation. Space demands for both rooftop and utility arrays of solar cells are similar, but rooftop deployment allows cells to exploit otherwise unused space. Utility arrays demand a similar area of land to solar thermal power plants.