By Robert Tarimo, Dow Electrical & Telecommunications
Demand management is growing more complicated for power utilities. Rising global and regional electricity consumption is speeding the need for investment in expanded or upgraded networks. Many utilities, additionally, need to connect renewable energy sources, which can be distant from power demand centers. They also need to pay heed to carbon footprints by minimizing losses during power transportation. To cap it all, the use of overhead transmission lines is not always an option. Resistance to overhead lines is increasing in many countries driven by urbanization trends and negative land value impacts. This slows down rights-of-way approvals.
Options outside of overhead transmission depend on location. Utilities in some regions have chosen a proactive path, while others have required legalities and politics with decision making. The Netherlands and Germany offer interesting insights that could be relevant in other countries, particularly in the U.S., where many of the same challenges now exist. These two densely populated European countries have contended with complex power transmission challenges for many decades.
European Transmission Practices
The Netherlands, a country of just 16.7 million people but with a population density of 397 people per square kilometer, chose underground cables for the transmission network. In February 2010, the Dutch government adopted changes to the Third Electricity Supply Structure Plan (SEVIII), capping the total length of the overhead transmission and distribution (T&D) network. These days, every new kilometer of aerial line must be compensated by changing a corresponding length at a different location from aerial into underground cables—a compensation principle. Regular evaluations determine if compensation impacts the implementation pace of new high voltage networks.
The Dutch approach is viewed as clear and consistent, overall, leading to the speedy implementation of many needed transmission lines. One downside is that some communities must tolerate more overhead lines than others.
Undergrounding was adopted by Germany as well, which has to meet the growing power demands of 82 million people across 357,000 square kilometers. The federal government recently approved a new energy policy to address this challenge. The policy includes the stipulation that the German grid must source 30 percent of its power from renewables by 2020, up from about 17 percent in 2010. Given that many of these renewable sources are offshore wind farms in the north of the country—a long way from some of the high population centers in the middle and south of the country—the new energy policy requires a 25 percent expansion of the transmission grid over the next ten years. That's the addition of 3,600 kilometers of extra high voltage lines to the German national grid by 2020.
Facing this and other longstanding transmission challenges, Germany adopted legislation in stages, starting with the German Energy Line Extension Act (EnLAG) in 2009. EnLAG accelerated the undergrounding approval process for four demonstration projects and provided clear guidelines on the use of underground cabling for utilities. It included a "200m/400m" rule to introduce physical boundaries to the application of underground cabling. Due to lack of clarity, EnLAG had mixed results. To resolve some of the legislation's shortcomings, the Bundesrat recently approved the NABEG policy. The policy requires utilities to underground any 110kV line if the comparative cost factor to an overhead line is not above 2.75. NABEG does not account for 380kV lines, but the industry anticipates the publication of appropriate 380kV guidelines in the near future.
For many European nations, Germany included, undergrounding will be an essential solution as countries push to connect renewable power sources to grids, including connections to offshore wind farms via submarine networks.
Relative cost is key to determination. Figure 1 shows the respective investment costs (without reactive compensation) of underground and overhead lines based on the experience gained by transmission system operators (TSOs). The bulk of the cost is civil works required for installation. Over the last 10 years, the range difference of investment costs between cables and overhead lines has been between three times and 10 times depending on voltage level and installation. Installation in tunnels can even be over 15 times more expensive. TSOs balance underground cable's extra benefits with underground cable's higher cost by partially undergrounding specific transmission network segments.
A concerted industry effort to clarify and resolve technical questions increased the use and legislative prescription of underground cabling. The cable industry association Europacable, for example, acted as a valuable information broker in Europe, developing and promoting the concept of partial undergrounding and producing a joint report with the European transmission organization European Network of Transmission System Operators for Electricity (ENTSO-E) to help legislators make informed decisions.
Overhead line technologies are expanding as well. European utilities can now evaluate new overhead technologies such as high temperature/low sag composite materials that can reduce power losses during overhead transmission and developments in towers that can minimize rights-of-way issues and the management of electro-magnetic fields.
Europe is adopting new approaches for transmission corridor maximization and reducing the losses incurred in the
transportation process. One of those options is overhead cable.
Figure 2 shows that HVDC cables, and overhead lines in particular, are solutions for cost-effective transmission over long distances. In the recent past, the introduction of extruded HVDC cables have a loss-efficient solution to transmit over long distances either underwater or underground.
The power demand challenges faced by Europe also exist in many other parts of the world. The U.S. is facing rights-of-way challenges that make connection to renewable wind energy sources difficult. The not-in-my-backyard (NIMBY) argument is being heard loud and clear in many American towns and cities. The challenge of overcoming intra- and inter-state grid connections is an additional challenge.
Solutions for the U.S. and other countries might be within reach if the global power industry defines power transmission best practices based on regional network experiences.
Robert Tarimo is Dow Electrical & Telecommunications' global HV marketing manager and is responsible for driving marketing strategies and application development globally. Reach him at firstname.lastname@example.org">href="mailto:email@example.com">firstname.lastname@example.org.