Sustainablog

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Scientific American has a thought-provoking proposal in its January 2008 issue. The magazine proposes a massive, far-reaching plan to get solar power generating 69 percent of America’s electricity 35 percent of our total energy by 2050, thus replacing all of our foreign oil needs and slashing global warming emissions. Below are some of the highlights of that “solar grand plan.”

Technology

The American Southwest would be the home of massive amounts of solar power needed for this clean energy conversion. Specifically, two types of solar power would be employed: Photovoltaic (PV) cells and concentrated solar power.

According to the solar grand plan, 30,000 square miles of PV cells would provide 3,000 gigawatts (GW) of energy. The “30,000 square miles” part made me flinch, but already existing solar installations indicate that the land needed for each gigawatt-hour of solar energy in the Southwest is less that the amount of land needed to run a coal plant and mine the fossil fuel for it.

Concentrated solar power would supply about one-fifth of the solar energy in the plan. Concentrated solar power uses long metallic mirrors that focus the sun’s rays onto a pipe filled with fluid. The fluid is heated and runs through a heat exchanger that produces steam that turns a turbine. Nine plants like this already exist in the in U.S.

Storage

The solar grand plan recommends compressed-air energy storage for PV energy: Electricity from the PV plants compresses air and pumps it into empty underground spaces like caverns, abandoned mines, aquifers or depleted natural gas wells. The air can be released on demand to turn a turbine and make electricity, aided by burning small amounts of natural gas. Compressed-air technology has been used in Germany since 1978 and in Alabama since 1991.

To store the concentrated solar power, pipes could be run into a big insulated tank containing molten salt that would retain the heat. At night when the sun isn’t shining, the heat could be extracted to create steam. Of course, the salt doesn’t retain heat indefinitely and so the stored energy would have to be tapped within a day. The first commercial installation with this molten salt storage technology is being built in Spain and has seven hours of storage, so this technology would still have a ways to go.

Transmission

Our existing grid of AC power lines isn’t up to the job of efficiently carrying solar power from the Southwest to consumers around the country (it would lose too much energy over that distance). Rather, the plan proposes a high-voltage, direct-current (HVDC) transmission backbone for the nation.

Studies have shown that an HVDC line loses less energy than AC lines over long distances and are less expensive to build. The lines would end at converter stations, where the power would switch over to AC and then be sent along already-existing regional transmission lines. About 500 miles of HVDC lines already exist in the U.S. and companies are eying them up for their renewable energy projects: Southwest Power Pool of Texas is designing a system of DC and AC transmission for a wind farm in Texas and TransCanada proposed 2,200 miles of HVDC to carry wind power from Montana and Wyoming down to Las Vegas and beyond.

Cost

The cost of this plan is admittedly large, as any major change in the nation’s infrastructure would be. The plan estimates $420 billion in subsidies are needed from 2011 - 2050 to fund the infrastructure and technology advances to make solar power more cost-competitive. Economies of scale and continued efficiency milestones will also help:
A report by the Solar Task Force of the Western Governors’ Association found that concentrated solar power could cost 10 cents per kWh or less by 2015 if four GW of plants were constructed.

The cost would be well worth it. The writers argue:

The infrastructure would displace 300 large coal-fired power plants and 300 more large natural gas plants and all the fuels they consume. The plan would effectively eliminate all imported oil, fundamentally cutting U.S. trade deficits and easing political tension in the Middle East and elsewhere. Because solar technologies are almost pollution-free, the plan would also reduce greenhouse gas emissions from power plants by 1.7 billion tons a year, and another 1.9 billion tons from gasoline vehicles would be displaced by plug-in hybrids refueled by the solar power grid. In 2050 U.S. carbon dioxide emissions would be 62 percent below 2005 levels, putting a major brake on global warming.

The biggest obstacle to the solar grand plan may not be the money or the advances in technology, but rather the political will to get it done. And while I personally appreciate and recognize the need for grand plans to demonstrate how we can get this done, I question whether solar power is really the best technology or if it’s being billed as the silver bullet answer to our energy problems. At the same time, the arguments for efficiency and a modern transmission system are on-target. Whether our clean energy future employs a majority of solar power or is a mix based on the local resources of the region (solar in the South, geothermal in the West, wind in the Midwest, etc.), our obsolete electric grid and advancements in storage capacity will be crucial for expanding other renewable energy systems.

The amount of sunlight the earth receives in 40 minutes is enough to power the globe for a year. With the 250,000 square miles in the U.S. Southwest suitable for solar power plants, a large amount of this resource must be a part of a 21st century system.

Scientific American Magazine