Every hour enough sunlight reaches the Earth’s surface to meet the world’s energy demands for a year. How do we harness it?
So why are we still blasting mountains flat for coal, hydrofracking for natural gas, fretting about nuclear waste, and plunging pipes miles deep from floating oil rigs? Despite common arguments that renewable energy technology simply isn’t ready to carry our nation’s electrical load, the technologies exist to capture and convert plenty of clean energy—like solar and wind—into electricity. The holdup is in transmission and storage. The best places to catch the wind’s energy aren’t generally near cities, where demand is the highest. And as solar naysayers always like to remind us, the sun doesn’t shine at night—and many places have frequent cloudy days. If we could solve this problem, we could use existing technology—the photovoltaic panels and concentrated-solar-power plants and wind farms we already see spreading around the country—to convert enough clean energy into electricity to satisfy our nation’s thirst for juice.
Here’s a survey of projects and potential technologies that could do the trick.
Transmission:
Atlantic Wind Connection
Announced by Google and the transmission company Trans-Elect this past October, the Atlantic Wind Connection is a transmission “backbone” that would stretch for 350 miles from a point off northern New Jersey to a point off southern Virginia on the mid-Atlantic continental shelf. It would connect 6,000 megawatts of wind capacity—enough to power 1.9 million households—to high-demand areas on the East Coast.
National Interest Electric Transmission Corridors, or NIETCs
Let’s call them transmission superhighways, as they would do for electricity what our interstate system did for cars and cargo trucks. American Electric Power, a major utility, and the American Wind Energy Association have partnered to map out how these high-voltage wires—19,000 miles of cutting-edge 765-kilovolt transmission lines—could allow the United States to get 20 percent of its electricity from wind. The cost to replace our unstable, piecemeal grid that hasn’t evolved much since Edison’s time? Sixty billion dollars.
High-Voltage Direct Current
HVDC is the building block of any high-tech, modern grid, and a technology essential to both of the projects above. Alternating current might have won the early 20th-century war of currents, but because of some technological advances in converters, direct current is now able to carry higher voltages, and HVDC is proving to be cheaper and to suffer less “line loss” (the loss of energy as it travels through the wires) than long-distance transmission on AC lines.
Storage and Transmission:
Smart Grid
Our current grid is dumb—a blind system of transmission lines and converters that funnel electricity one way from big centralized power plants to our factories, streetlights, shops, and homes. Regardless of demand, it ushers the same amount of electricity from source to end user.
The smart grid, however, would be a web of clever, high-tech components—networks, microprocessors, and digital sensing technologies—that would be as flexible as it was intelligent. Computers would let the utilities predict and manage system-wide demand and capacity, with batteries and other storage mechanisms—plug-in hybrids, for instance—ensuring that there would always be enough power to handle consumers’ needs. Power from distributed (ideally carbon-free) sources like a rooftop solar panel or a wind turbine on a ranch could feed into the grid without causing breakdowns. A smarter grid is a necessary hybrid solution for both storage and transmission.
Storage:
Molten Salt
Concentrated-solar-power plants use mirrors to focus the sun’s rays on a small point, where the intense heat drives a steam turbine and produces electricity. Concentrated solar has incredible potential for providing “baseload” electricity supply, on the same scale as medium-sized coal or nuclear plants. But when the sun goes down, the turbine stops spinning. Unless, instead of focusing the sun’s radiant heat on water or oil (as is the convention), it’s used to heat up molten salt. Molten salt holds its heat for hours on end—right through the night—and that heat can gradually be siphoned off to create steam, turn those turbines, and produce electricity at any hour. This is no pipe dream. The world’s first molten-salt CSP plant is up and running in Italy.
Compressed-Air Energy Storage
Compressed-air energy storage uses energy from wind farms at night—when the wind is blowing the strongest and steadiest—to pump air into underground storage chambers. When demand for power rises again in the morning, the pressurized air is released to spin a turbine and produce electricity. The system has been used for decades on a city-wide scale, taking advantage of cheaper “off-peak” electricity rates at night to compress the air. But it’s still pretty inefficient, and hasn’t been well connected to any large-scale wind farms. Yet.
Side note: Using solar energy to pump water up to an elevated reservoir and releasing it down through a turbine generator is a similar method that has been around for decades, with some systems around the world producing as much as 1,000 megawatts for several hours.
Fuel Cells (Plus a Chemical Catalyst)
In what’s being described as a breakthrough in solar-energy storage, MIT scientists have developed a process that uses the sun’s energy and a chemical catalyst—cobalt metal, phosphate, and an electrode—to split water into hydrogen and oxygen gases. Later, these gases can be recombined in a fuel cell that will generate enough electricity to power your house through the night.
Thermo-Chemical Solar
Score another one for MIT. A group of researchers there has figured out how to capture solar energy in the configuration of certain molecules—fulvalene diruthenium is currently doing the trick—storing the heat in the form of a fuel, which can then be moved, transported, or carried around, and released anywhere, anytime. Researchers describe it as a rechargeable heat battery that can repeatedly store and release heat gathered from sunlight. The released heat can reach 392 degrees Fahrenheit, which is plenty hot enough to boil water and spin a turbine. As of now, the rarity and cost of the element ruthenium is keeping the technology from spreading, but there’s confidence that more abundant and cheaper replacements can be found.
Batteries
You know that batteries store electricity. And you’ve probably noticed that they aren’t yet capable of keeping even your MacBook running for more than five hours. In fact, there are projects under way right now to develop grid-scaled batteries capable of holding 32 megawatt-hours’ worth of juice (that’s enough to keep a lightbulb burning nonstop for nearly four years). The lithium-ion battery is the most talked about for massive, grid-stabilizing storage, but there are plenty of other players in the battery battle, including highly efficient sodium-sulfur, nickel-hydrogen, and vanadium.
Flywheels
Flywheel technology is well known. It involves spinning a large mass on a magnetic bearing; the rotational energy is stored as inertia. But recently, some utilities have been advancing the technology to help balance electric loads from peak to off-peak hours. Each flywheel can be connected to a motor that either takes current from the grid to spin the wheel faster or takes momentum from the wheel and converts it into electricity that flows back into the grid. When supply is high—say, at a wind farm at night—the wheels will spin faster, but when demand rises, the energy from the wheels can be sucked back into the grid.
illustration by Matthew Lyons
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