Most techniques for generating electricity from heat need high temperatures to achieve reasonable efficiency. Solar thermal energy is a form of energy and a technology for harnessing solar energy to generate thermal energy or electrical energy for use in industry. This high-temperature heat can be stored, thus allowing electricity to be generated on demand which is an important advantage of this technology.The first installation of solar thermal energy equipment occurred in the Sahara desert approximately in 1910 and was a steam engine without a kettle and fire but with a mirror system for sun light collection to heat water for the needed steam pressure.Thousands of tracking mirrors, known as heliostats, directly concentrate sunlight onto a boiler filled with water that sits atop a tower. When the sunlight hits the boiler, the water inside is heated and creates high temperature steam. Once produced, the steam is used either in a conventional turbine to produce electricity. The Ivanpah Solar Electric Generating System is the biggest solar thermal power plant in the world located in the California Mojave Desert with a planned gross capacity of 392 megawatts (MW). It deploys 173,500 heliostats, each with two mirrors, focusing solar energy on boilers located on three centralized solar power towers. The Ivanpah Solar Electric Generating System consists of three solar thermal power plants on a 4,000 acres (1,600 ha) producing clean, reliable solar electricity to more than 140,000 homes. It cost $2.2 billion. The construction began in 2010 and lasted about 4 years.