concentrated solar thermal
Focusing the relatively dispersed energy from the Sun to produce electricity from steam is a high-tech way of capturing solar energy. Unfortunately, the places where concentrated solar technology works best—deserts—are the same places where a critical component, water, is limited and where impacts on wildlife habitat, including for endangered species, is sometimes inevitable.
Concentrated solar power (CSP) is different from PV systems in that it uses a series of mirrors to focus the Sun’s energy into one location where the heat is collected to make steam. Concentrated solar systems therefore produce electricity using the same mechanics as fossil fuels: Steam drives a turbine, which generates electricity. The most popular setup for CSP is called the “parabolic trough” system, which consists of long U-shaped mirrors that reflect sunlight onto a tube positioned above the array. The fluid (generally a synthetic oil) flowing through this tube is heated and is then used to turn water into steam. Concentrated solar power accounts for roughly one gigawatt of global electricity production, with much of the installed capacity located in Spain and the United States.
In CSP, the electricity generation process itself has zero emissions. There are emissions associated with the construction, maintenance, and decommissioning of the facility, but they pale in comparison to those from an average coal– or other fossil fuel–burning plant. But concentrated solar facilities do have a significant physical footprint (like any power plant) and require adequate transmission infrastructure to get electricity to consumers. Conservationists have opposed some CSP plants proposed to be built on U.S. public lands where their construction would negatively affect fragile desert habitat or endangered species. Proper siting on industrial brownfields near existing transmission lines would eliminate these negative impacts of CSP development.
Concentrated solar shares some of the shortcomings of solar PV-generated power. Since both rely on sunlight, they are intermittent sources of energy, which generally means that either natural gas or hydroelectricity must be used as a backup to offset the rapid fluctuations in power output from solar facilities. Additionally, cooling the steam produced at CSP facilities requires massive amounts of water, which is a scarce resource in the sunny, desert environments where CSP facilities are most efficient. On average, CSP plants consume as much water per megawatt of electricity generated as coal plants.