1. Concentrated Solar Power

Last year, renewable energy technologies like wind and solar were the fastest growing new sources of electricity in the U.S. — and though the recession has slowed down expansion, green power is still set to take off under President Barack Obama. But if America is ever going to truly run on renewable energy — less than 12% of U.S. electricity currently comes from alternatives sources, and most of that from older types like nuclear and hydro — we'll need to embrace next-generation technologies.

When most of us think about solar power, we picture the silicon panels that dot our greener neighbors' roofs, converting the sun's rays directly into electricity. But there's another, simpler type of solar power that uses massive mirrors to focus the heat of the sun, creating steam that can drive electric turbines. The advantages of concentrated solar power (or solar thermal, as it's also known) is that utilities can build commercial-scale plants that could potentially replace fossil fuel-powered plants for a lot less money than what it would take to install thousands of distributed solar photovoltaic panels. The 354-megawatt (MW) Solar Energy Generating Systems plant in California's Mojave Desert is the largest such solar installation in the world, and last year the Spanish company Acciona built a new 64-MW plant outside Las Vegas. The vast, sun-soaked desert of the American Southwest has tremendous solar thermal potential — by one estimate a single, massive plant 100 miles on each side could supply enough electricity for the entire country. Granted, that's a big patch of land — but it's not much to power a nation.


2. Tidal Energy

Anyone who has been caught in a nasty undercurrent knows the power of the tides. And just as windmills can covert the physical energy in a breeze into electricity, tidal turbines can do the same for the motion in the ocean. The engineering principle is no different — the steady currents found in coastal of water like Canada's Bay of Fundy turn the rotors of an underwater turbine. But tidal streams are far more predictable than wind, which means utilities using tidal don't have to worry about unexpected still days. The cost of putting equipment under water and concerns about the impact on the marine environment have kept tidal experimental, but that's beginning to change. Verdant Power recently completed a successful trial in New York City's East River, and the UK-based Marine Current Turbines is preparing for a 10.5 MW project off the coast of Wales.


3. Smart Grid

Our electrically-powered TVs and iPods might be state-of-the-art, but the grid that brings that juice to our homes is barely 20th century. The U.S. electrical grid is antiquated, prone to breaking down and terribly wasteful. Utilities don't even know there has been a power outage until customers pick up the phone and call them. But we could achieve tremendous energy savings — and emit less carbon — if we marry the electrical grid to the networked power of the Internet, in a concept called the smart grid. Intelligent, networked electrical meters could track exactly how much electricity we're using, and adjust our rates and usage patterns automatically for maximum efficiency. A smart grid would lessen demand overall, allowing for intermittent alternative sources of power like wind and solar to be more easily slotted into the electrical supply. Bits and pieces of the smart grid are already taking shape — Obama's stimulus package includes $11 billion for the development of a nationwide smart grid — and utilities like Xcel are starting test projects in cities around the U.S.


4. Offshore Wind

Wind power is great — it's perfectly clean, it's relatively reliable and it can be scaled up quickly. But there are downsides. For one thing, to get to scale, wind farms have to grow and grow, and land is often at a premium. But put wind turbines just offshore, in the water, and you can take advantage of plentiful space and stronger winds. Increasingly, utilities are doing just that, especially in densely populated Europe, which lacks wide open plots of land like the American Great Plains. Offshore wind farms began in the North Sea in Denmark, and can now be found in the Baltic and off the coast of Britain. Though construction and maintenance costs tend to be higher for offshore turbines than land-based ones, offshore wind benefits from lower transmissions costs, since many major cities sit on the coast. There is no offshore wind farm yet in the U.S., but the controversial Cape Wind project near Nantucket Island is moving closer to approval.


5. Algae Biofuel

Biofuel from food plants like corn is simply a bad idea — it does little to reduce carbon emissions, and drives up grain prices. Advanced biofuels from cellulosic material — plant waste and wood — are better, because they don't compete directly with food, but they still need reasonably fertile land in which to grow. Algae — microscopic plant-like organisms that feed on carbon and produce oil that can be used to make fuel — don't have that problem, and that could make them the perfect biofuel. Algae can be grown on waste land in plastic tanks called bioreactors, with little more than sun, heat and water — and the water can be salty, which leaves freshwater for food crops. Even better, algae could efficiently absorb the carbon being put out by fossil fuel power plants, producing a biofuel that is close to being carbon neutral. Algae biofuel is still some way from commercialization — a gallon of the stuff costs as much as $20 — but the technology is progressing. One start-up, Algenol, has plans for a 100 million gallon a year facility in northern Mexico's Sonora Desert.


6. Carbon Capture and Sequestration (CCS)

Environmentalists dream of the day when all of America's electricity will come from the sun, wind, water and other truly renewable sources. But the unavoidable reality is that fossil fuels like coal are deeply embedded in our energy system, and we'll have to use them for years. That means we must figure out a way to inexpensively capture the carbon released by burning fossil fuels and sequester it into the ground. Currently there are no utility-scale Carbon Capture and Sequestration projects, and there are still outstanding technical challenges — like ensuring that the captured carbon remains buried in the ground for centuries into the future. But a few experimental projects are underway. Notably, the Swedish utility Vattenfall opened a 30 MW pilot plant in September than can capture the carbon burned from coal, although the company hasn't yet found a place to store what they collect. We'll need similar projects soon, and on a global scale, if we want to have any hope of denting carbon emissions.


7. Geothermal

Jules Verne knew it — the center of the Earth is packed with heat energy. Humans have been using underground thermal springs as a source of hot water for centuries — just visit an onsen resort in Japan. But geothermal energy can also be used to make electricity, by taking the ultra-hot water found beneath certain parts of the Earth's surface, converting it to steam and then using the steam to drive an electric turbine. Right now geothermal energy is mostly used in countries with unusually active volcanic surfaces, like Iceland, where more than a quarter of the country's electricity comes from geothermal sources. But you don't need volcanic eruptions to make use of geothermal energy. Geothermal heat pumps can generate carbon-free heating and cooling nearly anywhere in the world. And the U.S. has significant geothermal potential for electricity as well: the government estimates that geothermal could provide up to 10% of the country's electrical supply.


8. Lithium-ion batteries

As we wean cars and trucks off gasoline and other fossil fuels, battery technology will become increasingly important. Until recently, most larger-scale batteries were made using nickel and cadmium, but they were heavy, and lacked the long life needed to properly power cars. That's shifted in recent years to lithium-ion batteries, which can be made much smaller, with a superior weight-to-energy ratio. Your laptop, iPod and cell phone all use rechargeable lithium-ion batteries. The hope is that the same kind of technology will finally begin to make electric cars a reality, by producing batteries that can run a car for 40 miles or more per charge, but which won't take up the entire backseat. Tesla Motor's all-electric Roadster runs on nearly 7,000 lithium-ion cells, while General Motors's innovative plug-in car, the Volt, will be using 400-lb. lithium-ion batteries from the Korean company LG Chem. Right now lithium-ion batteries still aren't cheap enough to make electric cars truly economically viable, but the hope is that as projects like the Volt reach scale, the price will drop dramatically.


9. Concentrated Solar Photovoltaic (CSPV)

Some renewable energy ideas are complicated — it'd take a PhD to explain the biochemical ins and outs of cellulosic ethanol. But others are simple — like concentrated solar photovoltaic. If you've ever used a magnifying glass to focus the sun's light and burn an unfortunate ant, you've got the gist of it. CSPV plants uses mirrors or lenses to concentrate the sun's light on an array of solar PV panels, vastly increasing the amount of electricity that can be produced. It's a cheap way to multiply solar power; instead of producing lots of expensive PV panels, you can get the same amount of electricity with relatively cheap mirrors. Only a few CSPV plants are in operation, including a 500-kilowatt test plant from the company SolFocus in Spain, but more are on the way. One of the most innovative ideas comes from a start-up called CoolEarth Solar, which uses thin-film plastic lenses, blown up like a balloon, to cheaply concentrate the sun's rays.


10. Nuclear Fusion

The white whale of energy, scientists have been hyping the potential of nuclear fusion since, oh, the first hydrogen bomb was dropped over the Marshall Islands in 1952. It's easy to see why: nuclear fusion powers the sun, and it holds out the possibility of near-limitless electricity, without pollution. But decades of research have gone by and scientists remain incapable of creating a sustainable fusion reaction that could be used to create reliable power. That could be changing, however. Construction has begun on the International Thermonuclear Experimental Reactor (ITER), a $15 billion project that will rely on magnetic fields that are 100,000 times stronger than the Earth's to create the conditions necessary for viable fusion. The plant is scheduled to be switched on in 2018 — assuming everything goes right. Nuclear fusion remains a long shot, but if the world is going to avert climate change, we'll need some luck, too.


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