A quick glance at the US Department of Energy’s wind speed maps is enough to see that, in the US, wind energy is mostly where the people aren’t. The population megalopolises of the east and west coasts are thousands of miles away from the central states with high wind energy, challenging traditional high voltage alternating current (HVAC) transmission networks to overcome expensive and high loss transmission issues. Internationally, the same problem exists: How do developers make the most of untapped remote renewable resources?
Can the Solution Be HVDC?
High voltage direct current (HVDC) is a high capacity, long-distance transmission system with low losses. More expensive to build than HVAC power lines, an HVDC network becomes more cost-effective in the long run for distances of 400 miles or more on land and just 30 miles underwater. HVDC lines of 800 kV or more are commonly referred to as UHVDC (ultra-HVDC) As in the US, much of the world’s most valuable renewable resources are remotely located, and require long-distance transmission.
Delivering Energy with HVDC
(Source: Clean Line Energy Partners)
According to Navigant Research’s report Transmission System Upgrades for Renewable Energy Integration, global HVDC revenue is expected to grow at a compound annual growth rate of 9.5% from 2016 to 2025 and reach $12.7 billion by 2025. It focuses on HVDC’s application to renewables integration; the revenue figures do not account for HVDC installations for non-renewables transmission. The report also includes an in-depth analysis of the drivers, barriers, costs, and benefits of a HVDC system, a few of which are listed below.
HVDC systems can do the following:
- Connect distances of more than 2,000 miles
- Transmit up to 3 times more power than AC systems of equivalent voltage in a similar right-of-way
- Transmit the same amount of power as an AC network in significantly smaller right-of-way
- Interconnect grids over land and under sea
- Provide grid operators with greater control over power flow with minimal losses
If HVDC Networks Are So Great, Why Aren’t They Everywhere?
Despite the benefits of HVDC, financial and regulatory barriers limit the construction of new HVDC networks. Current restrictions on right-of-way permitting and heavily controlled costs have suppressed penetration of HDVC systems, but that may change now that there are several significant projects underway. A few of the most significant upcoming projects are the following:
- India-North-East Agra: The world’s first multiterminal UHVDC transmission link. The 800 kV, 1,073-mile link will supply enough power to serve 90 million people. Scheduled for completion in 2019.
- United Kingdom-Western HVDC Link: The world’s first 600 kV or higher subsea HVDC network, with 239 of 262 total miles underwater. It is scheduled for completion in 2018.
- Iceland-UK IceLink: This early-stage project will transmit power between Iceland and the UK. It will be 620-745 miles long, and will operate at 800 kV-1,100 kV. Estimated completion is 2027, and it will supply power to serve approximately 1.6 million homes.
Latest in HDVC
In early November 2017, the world’s first 1,100 kV UHVDC transformer passed its type test, confirming the design criteria and operating parameters of the unit. Designed and built collaboratively by ABB and Siemens, the transformer will be commissioned in 2018 for installation as part of the Changji-Guquan link. Spanning 2,040 miles (3,284 km), the link will set world records for voltage, transmission capacity, and distance.
Despite the high capital costs of HVDC, the benefits are clear, both for renewables and fossil fuel generation. The long-distance, high capacity systems can bring power to areas in need, deliver power from offshore wind farms to mainland cities, and reduce the environmental impact of transmission networks with smaller footprints. The commissioning of the Changji-Guquan link is a major step toward future intercontinental, long-distance, underwater, and over-land HVDC transmission systems, and it won’t be the last.