Solving the major problem of renewable energy: intermittency

heating needs. Australia’s Outback solar energy resources are strongest in the southern summer, which is the northern winter. Therefore, Australia’s peak solar energy output is suited to meeting China’s winter heating peaks.”

This is not the only transnational grid either planned or under construction.

The release notes that a group of European companies and the Desertec Foundation envision that, by 2050, solar power plants in the Middle East and North Africa will satisfy 70 percent of the area’s electricity needs and 17 percent of the electricity needs of the European Union and some neighboring countries.

The solar energy would be transmitted across North Africa and connected to Europe across the Mediterranean Sea. Construction of the Desertec’s first 500-megawatt solar farm in Morocco is scheduled to start in 2012.

Ultrahigh-voltage DC power transmission
Pickard says, however, that  you can not ship power over extremely long distances through interconnected synchronous AC systems, because of stability problems. “What you get is sloshing inside the network area and sloshing will begin to take the network down.”

For long-distance transfer of bulk power ultrahigh-voltage (800 kilovolt) DC lines are needed, he says. These lines allow higher transmitted power with the same stability margins and lower losses.

The technical problems with these lines are not trivial, Pickard says, but they’re already being solved — in China. According to the authors of an article in the Proceedings volume on ultrahigh-voltage transmission, “China is constructing a number of high-power DC energy highways, superimposed on the AC grid, in order to transmit electric power from huge hydropower plants in the center of the country to load centers located as far as 2,000 to 3,000 kilometers away.”

Massive energy storage
Most schemes for the energy future, including transnational grids, also will require massive energy storage, some scheme to transform surplus grid energy into a different but conveniently stored form and then back-converted and returned to the grid when electric power is needed. Pickard calls them “granaries for electricity.”

By massive, Pickard means storage with a rated output power of at least 1 gigawatt and a rated storage capacity of at least 2 gigawattdays, enough to see a major metropolitan area through most emergencies.

Many of these storage schemes assume the baseload power would be supplied by concentrating solar power (CSP) systems. A CSP system uses mirrors to bring solar radiation to a hot focus that can then be used to superheat steam and run a turbine for power generation.

Surplus energy