The power tower: Perhaps its time is coming soon

The receiver sits atop a slender column, 40 stories above the desert floor. It glows like a giant, white-hot torch in the clear blue sky as it gathers limitless free energy from outer space. The energy is converted first into heat, and then into electricity, which is transmitted hundreds of miles across Earth – almost at the speed of light.

At the base of the column, a small team of earthlings performs low-cost, routine maintenance tasks. Occasionally, they look up at the receiver and marvel at its simplicity, its efficiency, its beauty. They chat about how it will render obsolete polluting, fuel-based electricity production from coal, gas and uranium.

This could be a scene from a futuristic science-fiction movie, but it’s not. It’s a description of Gemasolar, the world’s first commercial concentrated solar-power plant with a central tower receiver and a molten-salt thermal storage system, completed and brought online in 2011.

Located in southern Spain’s “sun belt,” the Gemasolar plant generates 19.9 megawatts of electricity, enough to power 25,000 homes. But that’s not the big news, because other solar-power plants have similar capacities. What makes Gemasolar a game changer is that it continues to produce a steady stream of electricity after the sun goes down – and until the sun comes up the next morning, re-energizing the system.

Here’s how it works. Gemasolar’s central tower is surrounded by a circular array of 2,650 “heliostats” (mirrors) that focus the sun’s rays on the receiver. Pipes inside the receiver are filled with common salts that melt in the intense, 900-degree heat.

The molten salts are circulated through a heat exchanger, where some of the heat is used to boil water that in turn drives a steam turbine that generates electricity. The salts, in a closed loop, are then returned to the tower for reheating.

But more salt is heated than is needed to drive the steam turbine, and the excess hot salt is stored in tanks and used to generate steam for up to 15 hours after the sun wanes and sets.

That’s a game changer because the big drawback of solar electricity has been its inability to provide “baseload” power, keeping up with demand as the sun begins to set and people return home from work and turn on their air conditioners and TVs and cook dinner. That’s when conventional power, mostly provided by coal-fired or nuclear power plants, comes on – and stays on until the next day.

But with Gemasol leading the way, reliable baseload-concentrated solar-power plants are beginning to crop up all over: in the American Southwest, Israel and, most importantly from a worldwide energy perspective, in Morocco and Tunisia.

Enter Desertec, the nonprofit foundation working toward developing “power tower” concentrated solar-power plants in the world’s desert latitudes, and transmitting the electricity wherever it’s needed.

The brainchild of a German nuclear engineer who, after the Chernobyl nuclear accident, decided that we must find a clean source of energy, Desertec has assembled an international consortium of investors and developers using three selling points: (1) Concentrated solar power with molten-salt storage works, (2) enough sunlight strikes the world’s deserts in six hours to power human civilization for one year, and (3) high-tension power lines can transmit electricity more than 1,500 miles with minimal power loss.

Based on studies by the German Aerospace Center – and backed by investments from heavy hitters such as Deutsche Bank and Siemens and the governments of Germany, France, Italy, Spain, Morocco and Tunisia – Desertec’s pilot project involves building concentrated solar-power plants in North Africa. The electricity will energize the host countries and transmit a portion of the power to Europe where it will enter a developing European super-smartgrid providing baseload backup for local wind and solar installations.

One plant is already under construction in Morocco and, in 2014, a larger plant that will produce as much electricity as two average-sized nuclear power plants will be built in Tunisia. Among the byproducts of the development: creating hundreds of thousands of jobs and cutting million of tons of CO2 emissions.

Concentrated solar power is already coming to America and, who knows? The day may soon come when you can turn on the lights without causing global warming at your ecological house.

Philip S. Wenz, who grew up in Durango and Boulder, now lives in Corvallis, Ore., where he teaches and writes about environmental issues. Reach him by email through his Web site, www.your-ecological-house.com.