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Analysis & Projections

Assessing HVDC Transmission for Impacts of Non‐Dispatchable Generation

Release date: June 27, 2018

Given the increase in renewable generation in recent years, it has become increasingly important to understand the manner in which operational challenges arising from intermittency may be mitigated with other technologies or operating procedures. One such technology is high-voltage direct current (HVDC) transmission lines. To help better inform the U.S. Energy Information Administration’s (EIA) long-term planning models and projections, EIA commissioned a study from ICF Incorporated, LLC (ICF) to assess the role that HVDC transmission lines may play as additional renewable generation sources become integrated into electrical grids.

More specifically, ICF was asked to review the extent to which they believed HVDC lines may mitigate challenges resulting from additional renewable generation, the advantages and disadvantages of using HVDC lines to transmit the electricity generated from renewable sources, and the potential costs of constructing additional HVDC lines in a formal analysis based on many sources of information.

To provide some background, electricity generated by renewable resources can be categorized into two types—dispatchable and non-dispatchable generation. Dispatchable generation sources include conventional hydroelectric, geothermal, and biomass. Non-dispatchable (or intermittent or variable) generation sources like solar and wind, however, depend on the resource availability, such as when the sun is shining or the wind is blowing. As a result, these technologies have limited capability to respond to generation dispatch signals.

The increasing deployment and penetration of non-dispatchable renewable generation from resources like solar and wind can lead to electrical system operational issues, which include under- or over-generation during times of high or low electricity demand. Such conditions could potentially require additional grid services to accommodate the associated fluctuations in generation delivered from these resources.

Power transmission lines facilitate the bulk transfer of electricity from a generating station to a local distribution network. The U.S. electric transmission network consists of around 700,000 circuit miles of lines. Most of these lines operate with alternating current, which is how power is typically generated and delivered to the end-use customers.

HVDC lines have typically been used to transfer large amounts of power over long distances. They are now being proposed as a way to move electricity generated from wind in high-quality wind resource regions to other parts of the country. If properly configured, direct current transmission could also help mitigate operational issues with wind and solar generation such as a mismatch in generation in relation to the need for increased ancillary services associated with renewable generation. This can be accomplished by effectively moving electricity generated from wind or solar resources from areas of high penetration to areas with lower penetration.

It should be noted that challenges associated with increased penetration of generation from wind and solar resources may also be mitigated using a variety of other technologies or practices, including smart grid technologies, energy storage, or other flexible generating technologies. However, the role that HVDC lines may play in mitigating some of the potential challenges imposed by the growth in non-dispatchable renewable generation on electric grids is an important consideration.

 

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