Is High Voltage Direct Current (“HVDC”) an Answer to Wind Energy Transmission Woes?

Although there is a great deal of discussion about the need to harness wind energy to help in both replacing the carbon-based fuel sources currently used and to lessen our dependence on foreign oil, there has been less discussion regarding the need to build a new infrastructure to convey that power. The current electrical infrastructure is designed to move power from coal-fired power plants (and a few nuclear plants) to large cities. The possible size of new wind energy farms in the upper Midwest easily swamps the ability of existing transmission lines to carry that power. By some estimates the amount of power that needs to be moved from anticipated wind farms exceeds the existing infrastructure by a factor of four in any given route. This means that it will be necessary for some entity to undertake what could easily be described as the biggest regional infrastructure project since the Interstate system.

There are only two ways to convey this new source of wind energy and they are the same two methods debated by Thomas Edison and Nicholai Tesla in the 1800s : direct current (Edison’s choice) and alternating current (Tesla’s choice). Although Tesla won the argument and alternating current became the exclusive means by which utilities move electricity in the United States, High Voltage Direct Current (“HVDC”) lines offer several advantages over AC for the transmission of wind energy over long distances.

1. For long-distance distribution of electrical power, HVDC systems can be more efficient. As electricity is transmitted via a line, part of the transmitted energy transforms into heat and is wasted. HVDC systems suffer significantly lower thermal losses than the commonly used alternative current systems.

2. HVDC can carry much more power per conductor. This can be a substantial advantage when using a narrow right of way for a utility easement, as more power can be carried on each line. This also decreases the need for a wider tower array to carry the power.

3. HVDC lines can be placed closer together as they are not as susceptible to electrical harmonic interference. This is another feature of HVDC that works well with a narrower right of way.

4. Narrow right of way. The large AC projects currently in development may need in excess of 250 feet in width in order to build the large towers needed to support HVAC. Existing laws may not support that extra width. By utilizing HVDC, it may be possible to avoid the larger footprint needed for the tower structures. Instead of H-frame towers, HVDC can use single large steel pole structures.

There are a few disadvantages of HVDC systems that have been documented:

1. High cost of coversion. The main disadvantage of HVDC is the high cost of converting DC to AC. Therefore, it is anticipated that a HVDC utility line will have a limited number of converter stations, perhaps as few as two, one on each end of the line. For the transmission of wind energy, this may not be a major disadvantage as the market for electrical power tends to be in areas that do not generate significant amounts of wind energy.

2. Lack of existing knowledge and infrastructure. Long-distance HVDC systems have not been widely used in the Americas and there are no known and existing implementations of long-distance HVDC transmission in the America continents. However, a number of companies have announced intentions to use HVDC for electrical transmission lines, including several projects to deliver hydroelectric from Canada to New England and wind energy from Maine to Boston. Siemens is currently constructing a 5,000 megawatt (at 800 kilovolts) line in the Guangdong province in southern China. HVDC is widely used in Europe in undersea cables and is used by utilities to balance loads from disparate AC systems.

— James L. Pray

About James Pray

Attorney with BrownWinick Law Firm in Des Moines, Iowa.
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