Concentrated solar power

Lore & Background

Concentrated solar power systems use mirrors to focus sunlight onto a receiver, converting it into heat that drives a heat engine—such as a Stirling engine or steam turbine—to generate electricity, or powers thermochemical reactions. A defining characteristic is the ability to incorporate thermal energy storage, often using molten salt as sensible or latent heat, which allows electricity production even at night, making CSP a dispatchable renewable energy source. This dispatchability is especially valuable in regions with high photovoltaic penetration, where demand peaks near sunset as PV output declines. The technology appears in several forms: power towers, like the Crescent Dunes project with 10,000 mirrored heliostats spread across 1,600 acres, and parabolic troughs, exemplified by the 354 MW SEGS complex in California. Range is limited but expanding; as of 2023, global installed capacity reached 8.1 GW, with operational plants totaling 6.6 GW and 1.5 GW under construction, including projects in China and Dubai. Habitats are typically arid, sunny regions with high direct solar radiation, such as deserts in the southwestern United States, the Atacama region of Chile, and South Africa’s Khi Solar One site. Historically, the first concentrated-solar plant was built in 1968 near Genoa, Italy, producing 1 MW with superheated steam at 100 bar and 500 °C, while the 10 MW Solar One tower in California (1981) later evolved into Solar Two (1995), which successfully demonstrated molten salt as both working fluid and storage medium.

Reader's Guide

Concentrated solar power is significant as a dispatchable renewable energy source, capable of storing thermal energy to generate electricity day or night. This makes it particularly valuable in regions with high photovoltaic penetration, such as California, where demand peaks near sunset—a phenomenon known as the duck curve. CSP competes with natural gas and battery-storage-backed photovoltaics for flexible, dispatchable power. As of 2023, global CSP capacity reached 8.1 GW, with projects under construction in China and Dubai. The technology uses four optical types: parabolic trough, dish, concentrating linear Fresnel reflector, and solar power tower. CSP's legacy includes early innovations by figures like Auguste Mouchout, Frank Shuman, and Professor Giovanni Francia, and its ongoing evolution aims to improve cost-effectiveness.

Did You Know?

• CSP can store energy as sensible or latent heat, for example using molten salt, enabling electricity generation at night.

The Thermal Engine at the Heart of CSP

Concentrated solar power works by directing a broad field of sunlight through mirrors onto a central receiver, where the concentrated light is transformed into intense heat. That thermal energy then drives a mechanical engine—either a Stirling engine or a steam turbine of the kind found in conventional fossil-fuel stations—to spin a generator and produce electricity. In some configurations the heat instead powers a thermochemical reaction. The same concentrating principle can also serve non-electric needs such as cooking or desalination. What sets CSP apart from photovoltaic panels is that the captured energy is stored as heat rather than as electrons, and that heat can be banked. By pairing the system with thermal storage—whether sensible heat or latent heat in a medium like molten salt—a CSP plant can keep generating power long after sunset. This dispatchability is the technology's defining advantage: it behaves more like a conventional thermal power station than like a weather-dependent panel array, capable of matching demand whenever it peaks, day or night.

The Dispatchability Gap and the Duck Curve

In regions where photovoltaic capacity has grown rapidly—California is a prime example—electricity demand tends to peak near sunset, precisely when PV output is declining. This mismatch, known as the duck curve, creates a structural vulnerability that dispatchable sources can fill. CSP, with its built-in thermal storage, slots naturally into that role, continuing to supply power through the evening and into the night. Yet the scale gap is stark: as of 2022, global PV nameplate capacity stood at roughly one terawatt, while CSP accounted for less than one percent of that, at just 6.8 gigawatts. By 2023 the CSP total had edged up to 8.1 GW, aided by three new projects under construction in China and Dubai. The NREL global database lists 6.6 GW operational and another 1.5 GW in the pipeline.

Design Diversity and the Commercial Rollercoaster

Most CSP plants worldwide rely on the parabolic trough design, though power towers and linear Fresnel reflectors also appear. The commercial history has been anything but smooth. The Ivanpah facility in California, built around the same period as Gemasolar, notably omitted thermal storage and instead relied on natural gas to preheat water each morning.

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