So far, concentrated solar power (CSP) “has been a tale of two countries, Spain vs. the U.S.” That is how the International Energy Agency sums up the beginning of the story of CSP, also know as solar thermal electricity. The first plants came online in California in the 1980s, and still run today. Instead of capturing energy from the sun’s light and converting it directly into electricity like photovoltaics do, they rely on the core technology of conventional fossil fuel generation: steam turbines. The difference is that rather than using coal or natural gas. CSP uses solar radiation as its primal fuel-free and clear of carbon.


CSP plants rely on immense amounts of direct sunshine—direct normal irradiance (DNI). DNI is highest in hot, dry regions where skies are clear, typically between latitudes of 15 and 40 degrees.


Rather ironically, the recent success of solar photovoltaic (PV) has limited the growth of solar thermal electricity. PV panels have become so cheap with such speed that CSP has been sidelined; steel and mirrors have not seen the same price plunge. But as PV comes to compromise a greater fraction of the generation mix, it may shift from a damper to a boost. That is because CSP has the very advantage photovoltaics struggle with and need: energy storage. Unlike PV panels and wind turbines, CSP makes heat before it makes electricity, and the former is much easier and more efficient to store. Indeed, heat can be stored twenty to one hundred times more cheaply than electricity.


… Even without molten salt, CSP plants can store heat for shorter periods of time, giving them the ability to buffer variations in irradiance, as can happen on cloudy days—something PV panels cannot do. More flexible and less intermittent than other renewables, CSP is easier to integrate into the conventional grid and can be a powerful complement to solar PV. Some plants pair the two technologies, strengthening the value of both.

Compared to wind and PV generation, the major downside of CSP, to date, is that it is less efficient, in terms of both energy and economics. Solar thermal plants convert a small percentage of the sun’s energy to electricity than PV panels do, and they are highly capital intensive, particularly because of the mirrors used. Experts anticipate that the reliability of CSP will hasten its growth, however, and as the technology scales, costs could fall quickly. Efficiency of energy conversion is also projected to improve. (Technologies currently under development are already proving it.)


Human beings have long used mirrors to start fires. The Chinese, Greeks, and Romans all developed “burning mirrors” – curved mirrors that could concentrate the sun’s rays onto an object, causing it to combust. Three thousand years ago, solar igniters were mass-produced in Bronze Age China. They’re how the ancient Greeks lit the Olympic flame. In the sixteenth century, Leonardo da Vinci designed a giant parabolic mirror to boil water for industry and to warm swimming pools. Like so many technologies, using mirrors to harness the sun’s energy has been lost and found repeatedly, enchanting experimentalists and tinkerers through the ages—and once again today.

IMPACT: CSP comprised .04 percent of world electricity generation in 2014. Despite slow adoption in recent years, the analysis assumes CSP could rise to 4.3 percent of world electricity generation by 2050, avoiding 10.9 gigatons of carbon dioxide emissions. Implementation costs are high at $1.3 trillion, but net savings could be $414 billion by 2050 and $1.2 trillion over the lifetime of the technology. An additional benefit of CSP is that it can easily integrate energy storage, allowing for extended user after dark.

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