olar power seems to be taking a leading role in the global fight against climate change. And while photovoltaic panels are the first thing that comes to mind when thinking of harnessing the sun’s energy, there is yet another technology that is often overlooked - concentrated solar power.
Definition of concentrated solar power
CSP or solar thermal plants work by utilizing focused sunlight. They use sun-tracking mirrors or lenses also called heliostats to focus sunlight onto a receiver containing the so-called heat-transfer fluid (e.g. water, molten salts, glycol-based). The fluid heats up and transforms into steam, which rotates steam turbines generating electrical power.
Concentrated solar plants are commonly integrated with thermal energy storage (TES) systems. This combination can offer an uninterrupted and reliable energy supply, which is why this technology is generally used by the utility sector to provide electricity to the grids. The global total installed capacity of CSP projects currently stands at 6,800 MW.
CSP solar systems vs. solar PV systems
There are a number of reasons why photovoltaic installations are more widespread than concentrated thermal power systems. Firstly, they make fewer demands on the location, since PV modules can be installed pretty much everywhere there are considerable amounts of sunshine. Finding a location for CSP plants is a little more complicated. They require higher direct irradiance levels, that’s why a large share of them is installed in Sun Belt countries. In addition to this, they need access to a water source for cooling and washing the reflecting surfaces.
Another advantage of photovoltaics over concentrated solar power CSP systems is the lower initial investment. While PV modules can be easily installed by homeowners and businesses, thermal power options are suitable only for utility-scale applications. Building concentrated solar power plants involve huge upfront costs and getting financing for such big projects can be really difficult.
But despite the limitations of solar thermal energy, in some contexts, it turns out to be more cost-efficient than PV. One of the major advantages is greater storage opportunities. Thermal power is easier to store than electricity, as the latter needs less efficient and much more expensive batteries. As for CSP, a fluid stored in the hot tank can retain heat for up to 10 hours, which allows the plant to keep generating electricity no matter what time of day. This means thermal plants offer a dispatchable power source and can quickly ramp up their output in periods of high demand at the request of the grid operator.
There is one more considerable benefit: in contrast to PV systems, thermal power plants generate alternating current (AC), and hence they can feed electricity directly to the power grid. A simpler distribution process ensures increased grid stability than utility-scale PV projects and creates a more viable alternative to fossil-fueled generation. Therefore, supporting the solar thermal industry at a national level can speed up the shift from traditional energy to renewables.
Types of CSP solar power plants
There are four main types of concentrated solar power systems. Let’s take a quick look at how each of them works.
Parabolic trough plants use curved, trough-shaped mirrors focused onto a receiver tube. This tube is filled with fluid (most commonly thermal oil), which is heated and then sent to boil water and create steam to run steam turbines and generators.
Power tower systems are considered the most efficient. In these installations, flat sun-tracking mirrors focus the sun’s energy onto a receiver located at the top of a tower. A molten salt fluid is heated to about 600ºC inside the receiver and is used to produce steam, which, in turn, drives a generator.
Linear fresnel technology utilizes a field of mirrors set out in parallel rows. These mirrors are laid flat on the ground and reflect the sun onto a heat absorption tube above them.
Parabolic dish systems use a mirror similar in shape to a satellite dish. It directs sunlight onto a receiver mounted on a rotating structure to track the sun's movement. Parabolic dishes are valued for their scalability, as they are available in different sizes and capacities starting with 10kW.