March 2009

Clean Solar Power is Here and There. But can it be Everywhere?

Ideas are taking shape in Europe, the Middle East and North Africa for a truly comprehensive, continent-wide energy landscape of the future. And some of the strategies coming out of planning bodies 'over there' deserve serious attention on the North American continent. They also deserve a more liberal and disinterested response from legislators and regulators at the local level than these officials have historically been wont to give. And that makes us wonder whether we can rise above the technical challenges involved, only to drown in a sea of regulation and self-interest.

The Trans-Mediterranean Renewable Energy Cooperation (TREC), an initiative of The Club of Rome non-governmental global think tank, has developed a concept known as DESERTEC, whose main elements include:

• Establishing large numbers of concentrating solar power (CSP) arrays in desert areas of the Middle East and North Africa (MENA);
• Transmitting power from these and other renewable sources throughout Europe, the Middle East and North Africa (EUMENA) via super-efficient high-voltage direct-current (HVDC) transmission lines.

(Solar Citizen reported on this concept in our May 2008 issue (Is Desert Solar Power the Solution to Europe's Energy Crisis?)).

The TREC group (now the DESERTEC Foundation) has calculated that an amount of electricity equal to the total present usage of the EUMENA region could be generated in this way if less than 0.3 per cent of the Sahara Desert was covered with CSP plants. And on a larger scale, the DESERTEC Foundation envisages a supergrid running from Iceland to the Arabian peninsula, from the Baltic to the west coast of Africa, in which offshore wind and wave farms, photovoltaic sites, tidal stream generators, biomass, geothermal and hydroelectric stations would unite with desert CSP arrays to meet the region's actual daily and hourly demands over an HVDC network of unprecedented size.

Graphic courtesy of DESERTEC Foundation

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Keeping Overheads so far Down, They're Underground

We automatically think, in this country, that if power needs to be sent from generating station A to a town rejoicing under the name of B, then some line joining the two points must be sown with large metal skeletons keeping high-voltage wires safely above our heads.

It ain't necessarily so. Thomas Blakeslee of Clearlight Foundation, writing in RenewableEnergyWorld.com, makes the case that using high-voltage DC instead of AC and burying the cables underground can cost the same or less than stringing them through the sky, for four reasons:

1. The electronic voltage converters required by HVDC grids (which are the kind we will need for the national backbone described in the above article) are no longer cost-prohibitive, thanks to falling semiconductor prices.
2. Costs for AC transformers, land and steel are rising dramatically.
3. DC transmission requires two cables, AC three.
4. Planning to bury cables along existing rights of way instead of proposing to mar landscapes with towers will likely avoid years of expensive legal battles with environmental and local citizens' groups.

Images courtesy of ABB

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NREL Testing New-technology Solar Trough

On South Table Mountain, Colorado, the National Renewable Energy Laboratory (NREL) is testing a parabolic trough--SkyTrough--that may make concentrating solar power more affordable at the municipal and utility level.

In trough-based systems, the highly reflective surfaces of the trough focus solar radiation onto a tube filled with a heat transfer fluid; the fluid then boils water to power a steam turbine and generate electricity.

The SkyTrough system, developed by SkyFuel of Albuquerque, uses a reflective skin layer attached to the trough. NREL and SkyFuel expect the design to work at least as well as the more traditional design that uses a delicate mirrored glass surface, while being less expensive to manufacture, transport and maintain.

The system tracks the sun's movement in two axes for maximum collection of radiation. Testing of the heat output of SkyTrough will extend through the spring and summer; details of the project can be found at the NREL web site.

See below for one current and very valuable application for products like the SkyTrough.

Electric Industry Examines Adding Solar Energy to Coal Plants

The kind of system described in the above article, connected to a steam turbine and generator, can serve as a power source at municipality scale or even at utility scale, with proper scaling. In fact, concentrating solar power (CSP) plants are already working hard in Nevada, in the Mojave Desert and elsewhere to supply electricity to the regional grids. But while such installations can eventually provide enough power to enable utilities to shut down older, dirtier coal-powered plants, and while the prospect of effective carbon capture and sequestration in new plants is still many years off, some utilities are looking to employ CSP technology today to help cut greenhouse gas emissions from existing coal- and gas-fired plants.

The Electric Power Research Institute (EPRI) is working with several power companies to evaluate the potential of adding CSP units to their plants: Dynegy in Kingman, AZ, NV Energy near Las Vegas, Tri-State at Prewitt, NM and Progress Energy in Roxboro, NC. The concept developed by EPRI involves building CSP units on land next to a power plant, and integrating the steam produced by these units into the steam cycle of the plant, either to reduce its fossil fuel usage or increase power output. This would lower the carbon intensity of the plant's power and help the utility meet state minima for clean energy production, where applicable.

"These projects will demonstrate a near-term and cost-effective way to use large amounts of solar energy at commercial scale to provide clean electric power," said Dr. Bryan Hannegan, vice president of Generation and Environment at EPRI. "These 'hybrid power plants' will combine the low-cost reliability of existing fossil power plants with the environmental benefit of renewables, and help companies meet federal and state mandates to reduce their emissions of air pollutants and greenhouse gases with renewable energy."