Many people are familiar with solar photovoltaic (PV) or solar hot water systems. But in sunny spaces across the world, another lesser-known technology exists as a different way to take advantage of the sun’s energy: concentrated solar power (CSP). In this article, we’ll describe how concentrated solar power works, the types of CSP systems, and how the technology compares to solar PV.
What is concentrated solar power?
Have you ever tried using a mirror or magnifying glass to fry an egg on the pavement during a hot, sunny day? Conceptually, concentrated solar power works in a similar way. CSP technologies produce electricity by concentrating and harnessing the sun’s thermal energy using mirrors. At a CSP installation, mirrors reflect the sun to a focal point. At this focal point is an absorber or receiver that collect and store heat energy. Eventually, the heat is used to power an engine or turbine that is connected to an electricity generator.
CSP is used in utility-scale applications to help provide power to an electricity grid. Most of the world’s CSP systems are currently in Spain, but the use of CSP technology is increasing in other areas across the world. In 2018, the largest CSP plant to-date was being installed in Morocco – when finished, the plant will have a capacity of 580 megawatts (MW) and provide electricity to more than one million people.
Types of concentrated solar power
CSP systems come in all shapes and sizes, but most installations fall into one of four major categories: parabolic dishes, solar power towers, parabolic troughs, and linear Fresnel systems.
With parabolic dish concentrated solar power systems, mirrors are set up in a satellite-dish shape with a receiver mounted in the middle, away from the mirrors. Sunlight reflects off the mirrors and hits the receiver focal point, which typically has a heat engine mounted directly on it.
Two of the biggest advantages of parabolic dishes over other types of CSP systems are that they require very little land space and don’t need to be installed on a flat surface.
Solar power towers
Solar power towers have a host of mirror reflectors at the ground level, also known as heliostats. These heliostats run on a tracker system and will concentrate sunlight throughout the day, reflecting it to a single point at the top of a tower which hosts the receiver.
Within the receiver is a heat transfer fluid that will warm up, generate steam, and then power a turbine in the generator, creating electricity. Often times this heat transfer fluid is a molten salt, which can retain heat more effectively than many other fluids given its high heating capacity.
Parabolic troughs are the most common types of CSP systems used throughout the world. Long, u-shaped mirrors reflect sunlight towards a tube that runs along their center, parallel to the mirrors. Inside the tube is a heat transfer fluid that gets heated as sunlight is reflected towards the tube. Once hot, this liquid runs to a central power generator that will use the heat to produce electricity.
Linear Fresnel systems
Similar to parabolic troughs, linear Fresnel systems use rows of mirrors with a parallel absorber that carries a heat transfer fluid. The biggest distinguishing factor between these two technologies is that parabolic troughs remain stationary, while linear Fresnel systems use trackers systems on the mirrors to maximize the amount of thermal energy concentrated and reflected towards the absorber.
Concentrated solar power efficiency
The solar-to-electricity efficiency of a CSP system depends on many factors, including the type of CSP system, the receiver, and the engine. Most CSP technologies will have an efficiency somewhere between 7 and 25 percent.
To compare this to the electricity conversion efficiencies of other renewable energy technologies, wind turbines can achieve up to 59 percent efficiency, and hydropower systems can have efficiencies of up to 90 percent. When it comes to solar PV, the conversion efficiencies of solar cells are in a similar range as CSP; most solar panels available on the market today have efficiencies between 14 and 23 percent.
Concentrated solar power vs. solar photovoltaics
Though CSP and PV have similar efficiencies, there are few notable differences between them when it comes to applications, costs, and storage capacity.
Concentrated solar power systems require a significant amount of land with direct sunlight. Because of this, there are limited places to build these types of systems. CSP systems tend to be large, utility-scale projects, capable of providing a lot of electricity as a power source to the grid. They’re not used in residential applications, unlike solar PV.
PV is a lot more common because solar panels can be installed just about anywhere that the sun is shining. While utility-scale solar installations will require similar amounts of space that a CSP plant would, you can also install solar panels for your own personal use on your home in business without developing new, unused sunny land.
PV systems are also capable of generating electricity in more weather conditions than CSP. CSP technology requires direct solar radiation to operate. Because of this, the performance of a CSP system is more sensitive to cloudy weather, while PV systems will still generate electricity on cloudy days.
Solar PV is the less expensive technology, both in terms of installation costs and levelized cost of energy (LCOE). This is due to a number of factors, including ease of installation and hardware requirements. CSP is a newer technology that requires more specialized technology and installation practices, driving up the costs of these projects.
According to IRENA, CSP deployment by the end of 2016 was at 5 GW. For comparison, solar PV deployment by that time had reached 291 GW of installed capacity. Just as the price of PV has dropped as installations become more widespread, CSP costs are also expected to decrease in the future as the technology advances.
One major advantage that CSP has over PV is its storage capabilities. With CSP, the heat transfer fluid used to move the heat from the absorbers to the engine has high heating capacities, allowing this fluid to retain heat for a long period of time. Storing thermal energy with the use of thermal energy storage tanks is much easier than storing electricity. As a result, CSP is often dispatchable even when the sun isn’t shining.
Solar PV has a disadvantage when it comes to storage – while you can store solar electricity using solar battery technologies, it’s more difficult and expensive to do so at large power levels. This makes it a less feasible source of electricity to the grid come night time.
Look at your solar energy options today
CSP is only available for large, utility-scale installations, but that doesn’t mean you can’t benefit from solar power in other ways. Consider installing a solar PV system to cut down on your electricity bill costs, buying a solar hot water system to heat your water supply, or designing a property with passive solar in mind to keep your building comfortable all year round. If you’re interested in solar PV specifically, you can sign up on the EnergySage Marketplace to receive solar quotes from pre-screened, local installers. If you’d prefer to start out with a ballpark estimate of solar costs and savings in your area, try our Solar Calculator.