Addressing Power Intermittency and Long-Distance Transmission with High-Temperature Superconductor Technology
- Written by Jim Maguire
As energy demand increases and electricity is sourced from alternative resources, grid modernization is a must. Integration of renewable energy into a growing power system brings a host of new challenges, some of which can be addressed with high-temperature superconductor technology.
The electricity network was built for steady-source energy, like that from coal-fired or nuclear power plants. As the demand for clean, renewable energy increases, grid operators would like to see renewable power plants operate more like conventional power plants. This means providing a predictable, steady source of power and having the ability to stay on-line and support the grid in case of a disturbance.
Wind and solar power are clean, abundant and safe. But because of their inherently intermittent nature, incorporating large amounts of wind or solar power can lead to network quality and stability issues. The use of dynamic reactive compensation equipment allows electric utilities and renewable power plants to regulate voltage levels, support a stable point of interconnection, allow the generation to stay on-line during disturbances and ensure high-quality energy.
As intermittent renewable energy is increasingly brought into operation, the ability to store energy will be essential to high performance. However, energy storage systems should also include dynamic reactive compensation devices that can instantly respond to frequency fluctuations.
Another issue associated with renewable generation is the great distance between the best sources of wind or solar energy and the load centers, like those in major cities. At present, the inability of the existing transmission system in the United States to move electricity from resource-rich but often sparsely populated regions to large population centers remains a primary barrier to achieving renewable energy goals.
To continue to develop our renewable resources, the electric power grid must be expanded, reconfigured and modernized, in part, by taking a national view of the grid, rather than a regional one. This will enable renewable generation plant owners to offer their product to a larger, national market rather than their limited regional market and will allow them to obtain better prices and justify more investment in renewable development.
For example, a connected transmission infrastructure would enable wind power generated in Texas, or solar energy generated in the Arizona or New Mexico, to feed both California and Chicago. Transactions such as these simply are not possible today.
Moving electricity long distances is fraught with challenges, including the public’s objection to overhead power lines, limited rights-of-way and the inefficiencies of traditional technology. Nevertheless, major projects are being proposed to expand and modernize the grid in the U.S. and around the world for renewables integration. These include Tres Amigas in the U.S. Southwest, SuperGrid in Europe and DESERTEC, which would connect the grids of Europe, the Middle East and North Africa.
The traditional overhead transmission line, however, is not well suited to such initiatives. The challenges they pose may be handled more effectively with high-voltage direct-current cables, employing the "high temperature" superconducting materials discovered in 1987. When coupled with voltage source converters, such HVDC/HTS cables enable multi-terminal transmission over very long distances.
A single HVDC superconductor cable can carry tens of gigawatts of power. Such cables are much more efficient than any other transmission technology, have very high power handling capacity, generate no external EMF, and require minimal right of way for installation compared to conventional cables made with copper or aluminum.
The development of HVDC superconductor cables opens the prospect of installing transmission lines suitable not just for today but to meet the needs of the future as well. Indeed, direct current HTS cables invite comparison with fiberoptic cables, “dark fiber” having been installed on a large scale so as to be ready for forecasted data transmission demand. Advance installation of high-capacity HTS cables could avoid the time delays associated with siting publically unpopular overhead power lines.
Superconductor cable technology has promise in situations where conventional alternating current capacity is running into limits. Increasing capacity can be next to impossible because more right-of-way is unavailable. With their ability to carry several times more current than conventional cables, alternating current (AC) superconductor cables can be installed in existing rights-of-way, helping to reduce costs and mitigate environmental impacts.
Superconductor power cables for this purpose have already been demonstrated in the power grid and are now ready for commercial deployment. For example, on Long Island, New York, the Long Island Power Authority (LIPA) commissioned a 138kV superconductor power transmission cable system in the commercial power grid in April 2008. Capable of transmitting 574 MW of electricity and consisting of three single-phase HTS power cables occupying a one-meter right of way, the system has now been successfully operating for several years. The cable was supplied by Nexans, a worldwide leading expert in the cable industry, with AMSC serving as the superconductor wire supplier and prime contractor.
The way we generate, use and mange our energy is changing. From the point of generation through transmission and delivery, today’s grid needs to be more flexible, reliable and responsive. The modern smart grid will be a combination of technologies that can make our power supplies more efficient, more reliable and more resilient. These benefits ultimately will lead to positive economic paybacks and lower energy consumption and costs.