What Is a Solar Tower and How Does It Work?
Starre Vartan is an environmental and science journalist. She holds an MFA degree from Columbia University and Geology and English degrees from Syracuse University.
A solar tower, also known as a solar power tower, is a way to concentrate solar power to make it a more powerful energy source. Solar towers are sometimes also called heliostat power plants because they use a collection of movable mirrors (heliostats) laid out in a field to gather and FOCUS the sun at the tower.
By concentrating and collecting solar energy, solar towers are considered a type of renewable energy. Solar towers are one kind of solar tech (including parabolic trough or dish-engine systems), all of which can make up a concentrated solar power (CSP) system. According to the Solar Energy Industries Association, CSP plants in the United States have about 1,815 megawatts of energy capacity.
How a solar tower works
As the sun shines down on a solar tower’s field of heliostats, each of those computer-controlled mirrors tracks the sun’s position on two axes. The heliostats are set up so that over the course of a day, they efficiently FOCUS that light towards a receiver at the top of the tower.
In their first iteration, solar towers used the sun’s focused rays to heat water, and the resulting steam powered a turbine to create electricity. Newer models now use a combination of liquid salts, including 60% sodium nitrate and 40% potassium nitrate. These salts have a higher heat capacity than water, so some of that heat energy can be stored before using it to boil the water, which drives the turbines.
These higher operating temperatures also allow for greater efficiency and mean that some power can be generated even on cloudy days. Combined with some kind of energy-storage device, this means solar towers can produce reliable energy 24 hours a day.
Environmental impact
There are some obvious environmental advantages to solar towers. Compared to fossil-fuel burning plants like coal or natural gas plants, there’s no air pollution, water pollution or greenhouse gases typically created in the energy generation process. (There are some emissions created in the building of a solar tower, just as there would be in another type of power plant, since materials have to be moved to the location and built, all of which requires energy, usually in the form of fossil fuels.)
Negative environmental impacts are similar to other power plants: Some toxic materials are used to make the components of the plant (in this case photovoltaic cells). When you clear land for a new plant, the animals and plants that live there are impacted, and their habitat destroyed — though some of this impact can be mitigated by choosing a location that has minimal impact on local plants and animals. Solar towers are often constructed in desert landscapes, which by their very nature are somewhat fragile, so special care must be taken in siting and construction.
Some solar towers are air-cooled, but others use ground water or available surface water for cooling, so while the water isn’t polluted with toxic waste as it can be at other power plants, the water is still being used, and that can impact the local ecosystem. Some solar towers might also need water for cleaning the heliostats and other equipment. (Those mirrors work best to concentrate and reflect light when not covered in dust.) According to the US Energy Information Center, solar thermal systems use potentially hazardous fluids to transfer heat. Ensuring those chemicals don’t make their way into the environment in the event of a storm or other unusual circumstance is important.
An environmental issue unique to solar power towers is bird and insect deaths. Due to how the heliostats concentrate light and heat, any animal flying through the beam as it is transmitted to the tower will be burned or killed by the high temperatures (up to 1,000 degrees Fahrenheit). A simple way to minimize bird deaths is to ensure that no more than four mirrors are aimed at the tower at the same time.
History of solar towers
The first solar tower was the National Solar Thermal Test operated by Sandia National Laboratories for the U.S. Department of Energy. Constructed in 1979 as a response to the energy crisis, it still runs today as a test facility that’s open to scientists and universities to study.
The National Solar Thermal Test Facility (NSTTF) is the only test facility of this type in the United States. The NSTTF’s primary goal is to provide experimental engineering data for the design, construction, and operation of unique components and systems in proposed solar thermal electrical plants planned for large-scale power generation, according to Sandia’s website.
The first commercial solar power tower was Solar One, which ran from 1982 to 1988 in the Mohave Desert. While it was able to store some energy into the evening (enough for start-up in the morning), it wasn’t efficient, which is why it was modified to become Solar Two. This second iteration switched over from using oil as a heat-transfer material to molten salt, which is also able to store thermal energy and has the added benefits of being nontoxic and non-flammable.
In 2009, the Sierra Sun Tower was built in California’s Mojave Desert, and its 5 megawatt capacity reduced CO2 emissions by 7,000 tons per year when it was running. It was built as a model but was shut down in 2015 because it was deemed to costly to operate.
Outside the United States, solar tower projects include the PS10 solar power plant near Seville, Spain, which produces 11 MW of power and is part of a larger system that aims to produce 300 MW. It was built in 2007. Germany’s experimental Jülich solar tower, built in 2008, is the country’s only plant using this technology. It was sold to the German Aerospace Center in 2011 and remains in use. Other U.S. and European projects are detailed below.
In 2013, Chile put 450.3 billion into the Cerro Dominador CSP project, Latin America’s first solar tower project. It was begun in hopes of phasing out coal-fired power by 2040 and being completely carbon neutral by 2050. But delays due to a bankruptcy by the project’s funder, meant that by the time the plant’s construction was resumed, it’s technology had already been outpaced by cheap solar panels from China, and widespread adoption of renewable technologies. The that Cerro Dominador would charge would already be three times higher than what other renewables could provide. The project is now on hold indefinitely.
Deploying rotating PV arrays on cooling towers
Swedish researchers have proposed the installation of rotating and revolving PV arrays on the cooling towers of thermal power plants. While such projects are ideal in nations with limited land, installation costs are also cheaper than for ground-mounted or rooftop PV plants due to proximity to the grid, the scientists claim.
Image: zootalures, wikimedia commons
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Researchers from Sweden’s Mälardalen University have come up with a new rotating PV array concept for vertical deployment on the cooling towers of thermal power plants.
The proposed model is defined an “adaptive celestial motion-based solar PV system” that can rotate around its own axis and revolve around the cooling tower to follow the sun. The scientists selected three thermal power plants with cooling towers in China for a case study.
Surface area
The group explained that the best balance between power output and energy-harvesting efficiency is achieved when only one-sixth of the outer surface of the cooling tower is covered with PV modules, at a tilt angle of between 60° and 90°.
“In terms of elevation angle of solar panels, the studied system can always keep the solar panels as perpendicular to the solar rays due to the ability of rotating around its own axis,” it stated, adding that the area of space between the solar panels should account for 20% of the total solar array area.
For example, at the Wujing Thermal Power Plant, the solar array would occupy a total surface of 4,676.8 meters squared, assuming the deployment of 2,405 panels with power output of 365 W.
Four designs
Four different PV system configurations were proposed for such projects: with fixed solar panels on the cooling tower with an azimuth angle of 0° and a tilt angle of 15; with panels rotating on their own axis to adjust the tilt angle with a fixed azimuth angle of 0°; with modules revolving around the cooling tower to adjust the azimuth with a fixed tilt angle of 15°; and with rotating and revolving panels collaboratively adjusting the tilt angle and the azimuth angle.
“This is totally new design which integrates the existing … facilities without negative impacts of land-use and also close to the electricity demand sides,” research coordinator Jinyue Yan told pv magazine. “I had this idea one year ago and we have not seen a similar system in the market.”
Cost concerns
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Projects developed with these technologies at the three Chinese thermal power plants have capacities of 1.76 MW (Wujing), 3.52 MW (Datong), and 1.82 MW (Hami).
“The estimated hard cost is about 1 USD/W,” Yan said. “We estimate the costs of the installation is similar as roof PV power generation without costs for the land occupation. As system can be rotated, the efficiency can be higher than the fixed roof top PV power generation.”
The annual power yield and total power generation during a project’s lifetime is also higher with the rotating and revolving configuration, the scientists claim. The best return on investment, however, is ensured by the revolving configuration.
“The levelized cost of energy (LCOE) of the proposed photovoltaic system with the ‘fixed’ or ‘revolving’ configurations is lower than the local benchmark price of photovoltaic electricity in the three studied power plants, indicating the possibility of reaching grid parity,” Yan stated.
Cooling towers
Such projects are also cheaper to install than ground-mounted arrays or rooftop PV plants due to their proximity to the power grid.
“In China, there are more than 2,000 cooling towers of thermal power plants – thus, we predict that the cooling tower-based PVs has huge potential for bringing considerable economic and energy benefits in the future,” the research group said.
They describe their proposed model in A celestial motion-based solar photovoltaics installed on a cooling tower, recently published in Energy Conversion and Management and on the ScienceDirect website.
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Emiliano joined pv magazine in March 2017. He has been reporting on solar and renewable energy since 2009.
The Advantage of Declipse Technology
Shadows on a solar panel are a missed opportunity to capture solar energy. Declipse maximizes the energy that is captured by substantially reducing shadows.
Maximize Existing Solar Panels
Our material can reduce any shadows by 80-90%. This could allow current newly developed 3D solar tower technology from MIT to reach its true potential.
Solar panels and 3D Solar towers could be able to be spaced together much tighter when our Declipse material is present. You should be able to get more panels per acre by a lot.
Declipse Has Been Demonstrated To The:
Here’s the Impact Our Technology Could Make in the World
What You Need to Know About Declipse
Less Shadow Means Power
Shadows are detrimental to power output, even a small shadow caused by a branch, electrical wire or even a neighboring solar panel too close to another to cause a shadow cast over the second panel can decrease the overall output. Even a shadow covering only 3% of the solar panel can reduce output on panels connected in series (typical installations) by 25% and a shadow of 9% can cause a power loss of 54% as bypass diodes used in typical PV arrays connected in series reroute current around the shaded area of the solar panels.
These cause the overall voltage to drop. For just a single solar panel the drop in power output for a small shadow can be over 90%. Declipse can reduce shadows by 80% or more, thereby providing a solution to numerous location issues to limit the power loss due to those shadows.
A Missing Component Now Fulfilled
MIT recently developed 3D Solar Tower technology that they hope has the potential to increase global solar power generation into the Terawatt scale.
In 2015, the world total solar power output was just above 250 gigawatts. In 2018, solar power is somewhere in the 400-500 Gigawatt range worldwide ( a Terawatt is 1000 Gigawatts). The problem is that their plan is the shadow factor.
Hyperstealth has provided the solution for this. These 3D solar towers cannot be placed next to each other to replace flat panel solar farms as their shadows cause so much power loss on the surrounding towers that it is not a viable alternative, until Declipse came along!
By combining Hyperstealth’s Declipse technology with multiple 3DPV Solar Panel towers (3DPV Farms), the initial assessment by MIT researchers of the real possibility of Terawatt Generation may now be achievable.
Greenhouse Adaptability
Greenhouse owners lament about the loss of growing power due to shadows from irrigation and above infrastructure.
Our material should increase growing yields because our ability to reduce many of these shadows.
Power Entire Cities?
If you have seen the HBO Documentary, Happening: A Clean Energy Revolution, you know how the potential energy we can gain from the sun could power entire cities.
We believe that harnessing solar energy is critical for the future of our civilization and our ever-growing population.
Energy and Jobs
The Solar Energy sector creates more jobs in the U.S. than any other industry at a rate 17 times faster than the U.S. economy, based off one of the most recent census published in 2018 by The Solar Foundation. One in 50 new U.S. jobs is now in the Solar Sector. As countries worldwide commit to reduction of carbon emission and extra taxes are being added onto carbon based fuels, solar power is poised to fill in the need for clean, renewable, and carbon-free power.
With wind and hydro power confined to large government or corporate programs, solar power is unique when it comes to renewable, clean energy. solar energy can be incorporated by the individual homeowner. Another benefit is that any excess power captured not required by the home can be put back into the overall electrical grid, usually as a credit going back to the homeowner.
Could the individual homeowner also capitalize on the new 3D Solar Towers utilizing our Declipse technology instead of flat solar panels to improve their power requirements? Could it also potentially add extra credit for adding excess to the overall electrical grid and possibly reduce the time to pay off the initial investment to add solar power to the home? This is our hope.
This Solar Tower Can Transform Water, Sunlight, and Carbon Dioxide Into Jet Fuel
One plant could collect 100 MW of solar radiative power to produce about nine million gallons of kerosene per year.
- ETH Zürich professor Aldo Steinfeld spent 15 years developing a process to turn air into jet-ready kerosene.
- A mini refinery on the roof of the university’s Machine Laboratory conducted a successful test of the technology in 2019.
- The carbon-neutral process extracts carbon dioxide (CO2) from the air during the conversion process, as outlined in a new paper published in the journal Joule.
Aldo Steinfeld, a professor at ETH Zürich’s Department of Mechanical and Process Engineering, says his system for converting ambient air into jet-ready kerosene fuel using a solar refinery tower isn’t science fiction. It’s simply thermodynamics.
In a two-year proof-of-concept test atop ETH Zürich’s Machine Laboratory building in Switzerland back in 2019, Steinfeld’s mini solar refinery first showed how the process works, and laid the groundwork to scale the project. Both carbon dioxide (CO2) and water are extracted directly from ambient air and split using solar energy, as Steinfeld describes his work in a new paper, published late last month in the journal Joule. The result is syngas, a mixture of hydrogen and carbon monoxide, which is then processed into kerosene.
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“The design of the solar reactor, the cornerstone technology, was the most challenging,” Steinfeld tells Popular Mechanics. “We evaluated the performance of the solar reactor based on five primary metrics and experientially validated its stable operation and full integration in the solar tower fuel plant.”
The plant grew from mini status to a larger-scale test when the team operated a solar refiner at the IMDEA Energy Institute in Spain in 2021. It will only keep growing. “The solar-to-fuel energy conversion efficiency needs to be increased to make the technology economically competitive,” Steinfeld says. Already he’s working on optimizing the structure with 3D printing to improve volumetric radiative absorption, which leads to higher energy efficiency.
Supercharged Energy News
To help turn the research project into a commercial reality, Synhelion, a spinoff company from ETH Zürich’s Machine Laboratory, is already planning to commission the world’s first industrial solar tower fuel plant in Julich, Germany. In March, Swiss International Air Lines announced it will be the first airline to fly with solar kerosene.
Proving the concept was an “important milestone toward industrial-scale production.” Steinfeld says one commercial-scale solar fuel plant could collect 100 MW of solar radiative power to produce about nine million gallons of kerosene per year. He’d need about 2.3 square miles to make that work. The total land footprint Steinfeld says is needed to create enough solar plants to “fully satisfy global demand” equals about half a percent of the area of the Sahara Desert.
The thermochemical process comes via three conversion units, all in a series. First it captures the ambient air to extract CO2 and H2O before a solar redox unit converts the CO2 and H2O—solar radiation heats the chemicals—into a syngas, a specific mixture of CO and H2. The third step is a gas-to-liquid synthesis unit, which converts the syngas into liquid hydrocarbons, usable as kerosene in jet fuel.
“We have successfully demonstrated the technical viability of the entire thermochemical process chain for converting sunlight and ambient air into drop-in transportation fuels,” Steinfeld says. “The overall integrated system achieves stable operation under real conditions of intermittent solar radiation and serves as a unique platform for further research and development.”
The process is carbon neutral because solar energy is used for production and releases only as much CO2 as was previously extracted for production. If the construction materials of the solar tower plant are created using renewable energy, he says the entire process can produce zero emissions.
Steinfeld says focusing on aviation fuel can help reduce carbon emissions from one of the leading industries contributing to that pollution. “These emissions can be avoided by substituting fossil-derived kerosene by solar-made kerosene,” he says. “Note that solar kerosene is fully compatible with the existing infrastructures for the fuel storage, distribution, and end-use in jet engines, and can be blended with fossil-derived kerosene. Thus, solar kerosene can help make aviation more sustainable.”
Before You Go.
Tim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland.