Five things you need to know about: the return of direct current
How the idea of channeling direct current electricity using circuit breakers could give rise to supergrids.
- What is it?
In the early era of electrification, the distribution of electricity by direct current (DC) ruled. Thomas Edison’s first electricity utilities in the late 19th century used DC, but Westinghouse Electric Corporation championed alternating current (AC), developed by Nicola Tesla, which transmits more power more efficiently over longer distances than direct current. Edison did his best to smear the new technology, developing the electric chair as a means of demonstrating the danger of AC and going as far as to electrocute dogs and an elephant, to further illustrate its danger. But to no avail – AC’s superiority was evident and it was soon widely adopted.
- Why the renewed interest in DC?
DC has been used since the 1950s to transport electricity at high voltages over distance. In the right application it is more economical and efficient, and suffers fewer power losses. But conversion equipment at terminal stations (transforming high voltage direct current (HVDC) back to AC) is complex and costly, and controlling the flow of power where there are multiple terminals in an HVDC-only network is tricky.These drawbacks have limited HVDC to specific and relatively simple applications that, for example, transfer power between nations using undersea cables or carry power from China’s remote hydropower schemes. But companies including ABB, Alstom and Siemens are competing to show that a much wider application of HVDC is possible. These companies believe an application with new circuit breakers and powered by renewables can be developed. ABB was the first to demonstrate an HVDC circuit breaker in late 2012.
- What are the applications?
The potential prize for HVDC is moving power around far-flung and complex power networks. This could link renewable energy generated on a continent-wide scale from solar in North Africa (as proposed for the Desertec initiative, for example), to onshore and offshore wind turbines in Northern Europe into one grid. Some claim HVDC could one day be the backbone of a largely renewable supergrid across Europe, something the EU has proposed funding for. Germany is already building three HVDC lines to handle the massive growth it is pursuing in wind and solar electricity generation.
- What do the critics say?
Skeptics warn that progress is likely to be slow due to the massive investments required. A Pike research study estimates the proposed projects up to 2020 alone will cost more than US$200b to finance. They highlight the high costs of renewable energy generation, the setbacks suffered by the Desertec project, following strategic disagreements between Desertec Foundation and its partner Dii GmbH, and funding constraints as serious limitations to the rollout of HVDC. Advances in other areas, such as the increased abundance and use of natural gas and the vast potential for greater energy efficiency, could also threaten the economic rationale for such schemes.
- So is it the future or just ani che technology?
There’s little doubt that HVDC will continue to be rolled out by most utilities, but the costs and complexity mean an HVDC supergrid is some way off. Innovation doesn’t stand still, however, and advances in key areas that reduce equipment costs, aid development of IT tools and control algorithms, could one day make the case for supergrids irresistible.
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