Menus Subscribe Search

Did Archimedes Solve Our Energy Crisis?

• April 08, 2008 • 6:15 PM

Sticking solar concentrators where the sun shines could potentially generate phenomenal amounts of electricity. But the perfect technology doesn’t yet exist.

Mirrors and lenses properly shaped can concentrate the benign rays of the sun into a powerful flame, something people have known for at least 2,500 years. In the 1500s, for example, in one of his notebooks Leonardo da Vinci suggested boiling water for a dye factory with the heat generated by a curved mirror four miles in diameter! Though the mirror was never built, Leonardo’s mentor, Andrea del Verrocchio, used a much smaller one for soldering.

In the 1800s, concern grew over steam engines’ prodigious appetite for fuel. Once they consumed all the coal in Europe, as some people expected, what would industry do? “Reap the rays of the sun,” replied one man of science, who went out to build a dish-shaped mirror that focused sunlight onto a boiler to help resolve what he believed was the impending demise of fossil fuels.

By 1914, Scientific American reported the first economical solar-powered engine operating in Egypt, which had at the time little in the way of accessible fuel but plenty of sun. A few years later, this same region was tapping its plentiful oil, as was North America. No one worried too much about energy from then on, and interest in solar power faded.

The Need Returns

With oil now at record prices and the knowledge of the harm burning fossil fuels can cause, solar-powered engines once again generate a lot of interest.

Advocates for the technology — “solar thermal energy” — have calculated that they would need less than 1 percent of all the world’s deserts to power the entire globe. They have quite a task ahead of them to achieve this goal, although the world’s only long-term operating solar thermal plant, built 22 years ago in California’s Mojave Desert, points the way.

The plant consists of long rows of curved trough-shaped reflectors that follow the sun throughout the day. They focus sunlight onto an absorber — pipe surrounded by glass — located above each trough. As a fluid, usually oil, passes through, it heats to around 300 degrees Celsius. The extremely hot oil collects at the power plant, where it heats liquid water into steam that then drives a turbine. The plant so far has produced 11,000 gigawatt-hours of electricity, worth almost $2 billion, and is expected to continue producing electricity until 2035.

It’s eerily similar to an Egyptian solar plant built 94 years ago. Trough reflectors’ long-standing record of reliable performance has allowed confidence in the technology for new entrants, one of which, Acciona’s Nevada Solar One, has just come on line south of Las Vegas. The plant, the largest built in the world in the last 17 years, is rated at more than 60 megawatts and is now the third largest in the world.

Ironically, the founders of the plant — actually a series of plants — in the Mojave Desert say experience has taught them trough technology’s limitations. They now embrace a different approach — “power towers” — to produce electricity from the concentrated rays of the sun.

More than 250 years ago, Comte de Buffon, an 18th-century French experimentalist, focused 124 flat mirrors on a model ship in Paris and burned it, anticipating power tower technology while demonstrating that Archimedes indeed could have burnt the Roman fleet, as some ancient writers claimed (but modern scholars disproved).

A modern power tower consists of a tall tower surrounded on all sides by rows of flat mirrors. On top of the tower sits a central receiver, through which molten salt moves. The flat mirrors follow the sun’s path to always focus sunlight onto the receiver. In this way, the molten salt gets much hotter than the oil heated by trough concentrators. The super-heated fluid creates steam, again to run a turbine. Excess molten salt goes to a storage tank which, according to plans, would allow the plant to operate continuously, something no other solar-electric plant can do.

Advocates for power towers argue that they can produce electricity cheaper than the trough technology for five reasons, some based on costs (flat glass used for the mirrors is simpler to build than curved mirrors required by troughs, and less concrete and steel is used) and some on mechanics (less heat is lost during operation as there is less piping, higher temperatures allow for the use of more efficient steam turbines, and the molten salt storage allows for 24/7 operations).

Trough advocates retort that no commercial power towers of any size — a power tower built by Spain’s Solucar outside Seville produces about 11 megawatts — have yet been built. A joint Spain-Dubai venture plans to spend more than $1 billion to build three commercial power towers expected to go on line by 2012.

The least developed of solar thermal power devices, the solar-fired Stirling engine, also has its roots in the past. In 1872, the Swedish-American technologist John Ericsson built a prototype: A curved mirror focused the heat of the sun onto an exposed cylinder, causing the air inside to expand to push down a piston; inrushing cold air pushed the piston up. The piston continued to move as long as the heat of the sun continued to bear down on the cylinder.

Today’s proposed device relies on hydrogen as the medium whose change in pressure due to heating and cooling cycles drives the pistons inside the engine placed at the focus of a dishlike reflector. Its modularity and higher efficiency give it an advantage over competing technologies, but unlike troughs and power towers, the Stirling cannot store solar energy and requires specially built engines.

Lots of Juice, Couple of Issues

Solar thermal power plants, unlike solar water heaters and photovoltaics, require direct sunlight to operate. Such conditions consign them to arid regions usually distant from population centers. Transmission lines specifically dedicated to such plants must be built, at a current price of $1,000 per megawatt per mile. Required cooling towers call for large amounts of water at times scarce in environments otherwise ideal for the technology. (Air can be used but is more costly.)

The key advantage to solar thermal plants, Stirling engines excepted, is that they use the same electrical-generation equipment as do most other power plants. The only difference is the fuel. Instead of fossil fuels or nuclear, solar thermal plants’ heat source is the sun — free, readily available and clean burning. Compatibility with other thermal generators allows for hybridization with other fuels so the plants can run continuously, eliminating downtime when the sun is not shining.

Plans exist for the deployment of at least five gigiwatts of solar thermal plants worldwide by 2010. Under the right economic conditions, experts estimate that, in the American Southwest alone by 2030, enough solar thermal plants could be built with the capacity of 80 gigawatts, greater than all the current conventional electrical generation plants that serve California.

John Perlin
An international expert on solar energy and forestry, John Perlin has lectured extensively on these topics in North America, Europe, Asia, and Australia. Perlin is the author of A Forest Journey: The Story of Wood and Civilization as well as From Space to Earth: The Story of Solar Electricity. Perlin mentors those involved in realizing photovoltaic, solar hot-water, and energy-efficiency technologies at the University of California-Santa Barbara, and coordinates the California Space Grant Consortium as a member of UCSB’s department of physics.

More From John Perlin

A weekly roundup of the best of Pacific Standard and PSmag.com, delivered straight to your inbox.

Recent Posts

July 25 • 4:00 PM

Flying Blind: The View From 30,000 Feet Puts Everything in Perspective

Next time you find yourself in an airplane, consider keeping your phone turned off and the window open.


July 25 • 2:00 PM

Trophy Scarves: Race, Gender, and the Woman-as-Prop Trope

Social inequality unapologetically laid bare.


July 25 • 1:51 PM

Confusing Population Change With Migration

A lot of population change is baked into a region from migration that happened decades ago.


July 25 • 1:37 PM

Do Not Tell Your Kids That Eating Vegetables Will Make Them Stronger

Instead, hand them over in silence. Or, market them as the most delicious snack known to mankind.



July 25 • 11:07 AM

The West’s Groundwater Is Being Sucked Dry

Scientists were stunned to discover just how much groundwater has been lost from beneath the Colorado River over the past 10 years.


July 25 • 10:00 AM

Shelf Help: New Book Reviews in 100 Words or Less

What you need to know about Bad Feminist, XL Love, and The Birth of Korean Cool.



July 25 • 8:00 AM

The Consequences of Curing Childhood Cancer

The majority of American children with cancer will be cured, but it may leave them unable to have children of their own. Should preserving fertility in cancer survivors be a research priority?


July 25 • 6:00 AM

Men Find Caring, Understanding Responses Sexy. Women, Not So Much

For women looking to attract a man, there are advantages to being a caring conversationalist. But new research finds it doesn’t work the other way around.


July 25 • 4:00 AM

Arizona’s Double-Talk on Execution and Torture

The state is certain that Joseph Wood’s death was totally constitutional. But they’re looking into it.


July 24 • 4:00 PM

Overweight Americans Have the Lowest Risk of Premature Death

Why do we use the term “normal weight” when talking about BMI? What’s presented as normal certainly isn’t the norm, and it may not even be what’s most healthy.


July 24 • 2:00 PM

California’s Lax Policing of the Fracking Industry Has Put the Drought-Stricken State in a Terrible Situation

The state’s drought has forced farmers to rely on groundwater, even as aquifers have been intentionally polluted due to exemptions for the oil industry.


July 24 • 12:00 PM

What’s in a Name? The Problem With Washington’s Football Team

A senior advisor to the National Congress of American Indians once threw an embarrassing themed party that involved headdresses. He regrets that costume now, but knows his experience is one many others can relate to.


July 24 • 11:00 AM

How Wildlife Declines Are Leading to Slavery and Terrorism

As wildlife numbers dwindle, wildlife crimes are rising—and that’s fueling a raft of heinous crimes committed against humans.


July 24 • 10:58 AM

How the Supremes Pick Their Cases—and Why Obamacare Is Safe for Now

The opponents of Obamacare who went one for two in circuit court rulings earlier this week are unlikely to see their cases reach the Supreme Court.



July 24 • 9:48 AM

The People Who Are Scared of Dogs

While more people fear snakes or spiders, with dogs everywhere, cynophobia makes everyday public life a constant challenge.


July 24 • 8:00 AM

Newton’s Needle: On Scientific Self-Experimentation

It is all too easy to treat science as a platform that allows the observer to hover over the messiness of life, unobserved and untouched. But by remembering the role of the body in science, perhaps we humanize it as well.


July 24 • 6:00 AM

Commercializing the Counterculture: How the Summer Music Festival Went Mainstream

With painted Volkswagen buses, talk of “free love,” and other reminders of the Woodstock era replaced by advertising and corporate sponsorships, hippie culture may be dying, but a new subculture—a sort of purgatory between hipster and hippie—is on the rise.


July 24 • 5:00 AM

In Praise of Our Short Attention Spans

Maybe there’s a good reason why it seems like there’s been a decline in our our ability to concentrate for a prolonged period of time.


July 24 • 4:00 AM

How Stereotypes Take Shape

New research from Scotland finds they’re an unfortunate product of the way we process and share information.


July 23 • 4:00 PM

Who Doesn’t Like Atheists?

The Pew Research Center asked Americans of varying religious affiliations how they felt about each other.


July 23 • 2:00 PM

We Need to Start Tracking Patient Harm and Medical Mistakes Now

Top patient-safety experts call on Congress to step in and, among other steps, give the Centers for Disease Control and Prevention wider responsibility for measuring medical mistakes.


July 23 • 12:19 PM

How a CEO’s Fiery Battle Speeches Can Shape Ethical Behavior

CEO war speech might inspire ethical decisions internally and unethical ones among competing companies.


Follow us


Subscribe Now

Do Not Tell Your Kids That Eating Vegetables Will Make Them Stronger

Instead, hand them over in silence. Or, market them as the most delicious snack known to mankind.

The West’s Groundwater Is Being Sucked Dry

Scientists were stunned to discover just how much groundwater has been lost from beneath the Colorado River over the past 10 years.

How Wildlife Declines Are Leading to Slavery and Terrorism

As wildlife numbers dwindle, wildlife crimes are rising—and that's fueling a raft of heinous crimes committed against humans.

How a CEO’s Fiery Battle Speeches Can Shape Ethical Behavior

CEO war speech might inspire ethical decisions internally and unethical ones among competing companies.

Modern Technology Still Doesn’t Protect Americans From Deadly Landslides

No landslide monitoring or warning systems are being used to protect vulnerable communities.

The Big One

Today, the United States produces less than two percent of the clothing purchased by Americans. In 1990, it produced nearly 50 percent. July/August 2014

Copyright © 2014 by Pacific Standard and The Miller-McCune Center for Research, Media, and Public Policy. All Rights Reserved.