What is concentrated solar? Solar Power Plants (Power Towers)

This is how concentrated Solar Energy is Captured

For many people, the concept of solar energy brings images of hundreds of photovoltaic (PV) panels spread out on rooftops or occupying large community fields. And while this is mostly true, there are other interesting technologies in this field that don’t get the hype despite having considerable potential. One of these is concentrated solar power (CSP).

CSP uses mirrors to generate electricity. That sounds impossible, but probably because it’s a grossly oversimplified explanation. To better understand CSP, you have to dig a little deeper. 

Table of Contents

What is concentrated solar power?

Concentrated solar uses mirrors to reflect and concentrate solar energy on a specific point (receiver). During the process, the solar energy from the sunlight is converted to thermal energy (heat). The heat is then used to power an engine or spin a turbine to generate electricity. 

3rd Century Death ray concept is now being used to produce Energy

Concentrated solar power(CSP) is a pretty clever concept that works and carries significant potential for the future of renewable. It’s also been around for much longer than many people realize; plants have been operating for the past 15 years in the United States. Today, the Solar Energies Industries Association(SEIA) estimates that roughly 1,815 megawatts are in operation within our borders. 

There are four approaches to concentrated solar technology; parabolic trough, parabolic dish, power tower, and linear fresnel systems.

Parabolic trough

These systems use large curved mirrors to focus solar energy onto a receiver tube running down the center of a trough. Within the tube is a high-temperature heat transfer fluid like synthetic oil. The oil absorbs the sun’s heat energy and is heated to temperatures higher than 750 degrees Fahrenheit.

Parabolic troughs are curved not like regular Flat Solar Panels

It then passes through a heat exchanger, where it heats water to produce steam. This steam is used to drive a steam turbine to generate electricity.   

In a parabolic trough system field, the mirrors are arranged in hundreds of parallel rows on a north-south axis. This allows them to track the sun from east to west. 

Power tower

A Single Power Tower Collects Solar Energy from reflectors below

This system uses computer-controlled mirrors (heliostats) to track the sun’s movement and focus solar energy on a receiver at the top of a tower. The concentrated thermal energy then heats a transfer fluid to temperatures over 1000 degrees Fahrenheit, used to produce steam. The steam then runs a central power generator for electricity. 

Molten salt is the thermal fluid typically used in power tower systems. Because it retains heat efficiently, it can be used to make steam immediately or stored for later use. This allows for peak electricity generation on cloudy days or even a few hours after sunset. 

Linear fresnel systems

Linear Fresnel uses a Horizontal Beam-like collector on top of the reflectors

Commonly referred to as Compact Linear Fresnel Reflector (CFNL), these systems are similar to parabolic troughs. However, they use long parallel rows of flat mirrors in place of curved mirrors. 

These mirrors focus sunlight onto an elevated receiver with a system of tubes flowing with water. The concentrated solar energy boils the water past its boiling point, producing high-pressure steam that generates electricity in a steam generator. 

Parabolic dish systems

CSPs have the energy collector directly in front of the parabolic dish. FYI this is not a Satellite Dish TV

These use mirrored dishes to concentrate sunlight onto a receiver mounted at the focal point. Each dish resembles a backyard satellite, only larger. It can rotate along two axes and uses a tracking system to follow the sun. 

Unlike other concentrated solar technologies that use steam turbines, the receiver in parabolic dishes is integrated into an “external” combustion engine. The engine has thin tubes with a working fluid, like hydrogen, heated to temperatures as high as 1200 degrees Fahrenheit. This heat causes the gas to expand and drive pistons that turn a crankshaft to generate electricity.

Concentrating solar power plants

Concentrating solar panels can be found on almost every continent. However, most of the world’s installations sit in Spain, accounting for around 42% of all CSP projects. With a capacity of 510MW- enough to provide power to 1.1 million people- Morocco’s Ouarzazate Solar Power Station is the largest CSP project in the world.    

Today, the United States has 52 concentrating solar power plants. The largest of these is the Ivanpah Solar Electric Generating System in California’s Mojave desert, with a capacity of 392MW

Other large-scale CSP projects include the Mojave Solar One in Los Angeles, Solana power plant near Arizona, the Crescent Dunes project in Nevada, Genesis Solar in Blythe, California, Nevada Solar One, Kimberlina Solar Thermal Power Plant in California, Sierra Sun Tower in California, Martin Next Generation Solar Energy Center in Florida, and Stillwater Solar Geothermal Hybrid Project in Nevada. 

There haven’t been any new concentrating solar power projects in the country since 2016. This is probably because CSP is only feasible in large-scale power plants, and establishing one is easier said than done. Nevertheless, the SEIA lays out the following requirements for a viable CTP project. 

Massive financing

Being a utility-scale energy generating facility, establishing a CSP plant is a relatively expensive affair. There are a couple of reasons for this, the chief being that current CSP technologies are still regarded as somewhat experimental. And with experimental technology comes a lot of R&D and slower commercialization, leading to high financing costs. 

Fortunately, CSP is following the same trend as PV technology; it’s getting cheaper. As of 2020, the cost per kilowatt installed was 4,725 U.S dollars. This is a pretty comfortable 50% drop from the 10,588 dollars it cost to install the same amount in 2011.

Large parcels of land

True to the nature of utility-scale projects, concentrating solar power also demands large areas of land. This is because they are most efficient and cost-effective when built in sizes of at least 100MW. The SEIA estimates that the average CSP plant requires 5 to 10 acres of land per MW. That’s quite a lot of space.

High solar radiation

Concentrated solar power requires as much solar radiation as it does space. The sun’s energy must not be too diffuse; otherwise, the project would waste financial resources and valuable real estate. Thus, renewable energy experts use sunlight’s direct normal intensity (DNI) to determine how CSP viable an area is. And as you would expect, the Southwest stands out as the region with the most potential.  

Access to water resources

Due to its reliance on thermal energy to produce electricity, CSP systems require a lot of water for cooling. And although other techniques are being tried, water cooling remains the primary way to cool CSP components. This presents serious challenges in water conversation. Small amounts of water are also required to clean mirror surfaces.

Convenient transmission access

Concentrated solar plants must also be sited near a transmission grid, preferably outdated and stressed by prevailing energy demands. This siting of a CSP plant in areas where new transmission is urgently needed creates a ready market for the electrical energy produced. 

The Southwest U.S also stands as an ideal candidate under these conditions. 

How efficient is concentrated solar power?

The energy efficiency of CSP systems ranges between 7% and 25%, depending on the type of system, engine, and receiver. Compared to other renewables like hydropower, wind turbines, and Solar PV cells with efficiencies of 90%, 59%, and 23%, respectively, CSP is not the most efficient of energy sources. However, more research leading to innovation and better technologies could see the efficiency of concentrated solar rise.  

Is concentrated solar power any good?

Concentrated solar power is an innovative idea that probably has massive potential. It may have a position in our renewable future, but how big of a role it will play in that future tends to split opinions. To give you a better understanding of this, let’s take a look at its advantages and disadvantages. 

Pros of Concentrated Solar Power

The biggest advantage of CSP lies in its renewability. It uses the sun’s energy to generate heat, and we can never exhaust the sun’s heat. Also, concentrating solar power doesn’t emit carbon dioxide, making it a lot kinder to the environment than fossil fuels. 

Operating and maintaining CSP plants is also much simpler than maintaining nuclear or hydro-carbon-based plants. This makes the operating costs of concentrating solar power relatively cheaper compared to these sources. 

Compared to solar photovoltaics (PV) and wind power, CSP provides a more continuous source of electricity. This is especially the case with plants that use molten salt as the thermal fluid; molten salt can store energy for later use, making it more reliable and predictable. 

It’s also easier to integrate CSP systems into existing steam-based power plants, like those running on fossil fuels. So, it can supplement these energy sources and even replace them if CSP technology gets good enough. 

Cons of Concentrated Solar Power

CSP is very expensive to set up and run. This is because it requires special materials with special properties, like molten salt, which is difficult and costly to source. 

CSP requires a lot of acreage to operate, making it highly unsuitable for populated areas. There is also the question of the opportunity cost of the land being used to establish concentrated solar plants. 

Environmental concerns

CSP also carries environmental impacts that can’t quite be ignored. For instance, power plants need a lot of water for cooling, but they are often situated in arid areas where access to freshwater is scarce. This has raised many eyebrows, especially in places like the Middle East and North Africa, where the demand for freshwater is on the rise. 

CSP plants are sometimes set up on lands with environmental value. Such lands are home to endangered flora and fauna species, often killed or forced to migrate by the sudden change in their natural habitat. 

Another environmental impact involves the toxic substances emitted by CSP plants. These include biphenyl, which produces harmful dioxins when burnt at high temperatures, and the greenhouse gas nitrous oxide. Materials used to establish concentrated solar plants are also not recyclable. 

See our related article where we break down the Top 17 Environmental Issues. Some of these issues may surprise you how they affect our planet.

Verdict

Concentrating solar power is not the cheapest nor most efficient of renewable energy sources. It might even be safe to say that it lurks behind PV, wind energy, and nuclear power in terms of technological development and adoption. But due to efforts from large-scale utilities and the National Renewable Energy Laboratory, it remains a decent and promising renewable energy source.