Power Conversion Technologies for Large Scale Renewables Integration: Reviews and Prospects of ICEF 2016 Concurrent Sessions
Large shares of renewable electricity pose major challenges to the power grid: One is that renewables are to be produced where wind potentials exist and space for harvesting solar radiation and biomass is available. Unfortunately these renewable resources exist often in remote areas far from power load centers. As a consequence, a growing share of renewable electricity depends on long distance electricity transport. The ICEF session addressed solutions such as High Voltage Direct Current (HVDC) transmission lines and other power conversion technologies.
Dr. Bo Normark from the Royal Swedish Academy of Engineering Science gave a deep introduction into the two most advanced HVDC-Technologies, the Line Commutated Converter (LCC) and the Voltage Source Converter (VSC). In both cases the electricity transmission losses over distances of 700 km remain below 5 % and the costs are competitive. The LCC concept is particularly applied in Asia because it offers rather high power ratings. The VSC concept is more common in Europe, due to its ability to provide ancillary services.
Dr. Johannes Henkel from 50Hertz, one of the four German Transmission companies, explained that his company is presently not investing into new power transmission lines but instead applies a sophisticated management of its grid infrastructure in order to accommodate a 50 % share of intermittent renewables. Instruments such as a temporal curtailment of renewable generation in case of grid bottlenecks are applied, because grid investments are faced with strong opposition from local population and are therefore delayed by many years.
Dr. Yoshiro Owanado from the Fukushima Renewable Energy Institute and Dr. Atsushi Nishioka from Hitachi explained how the long distance transport of renewable electricity will be managed in Japan. One solution is offshore HVDT cables along the Japanese coasts. According to the two experts, the costs of offshore HVDC are higher than those of onshore HVDT lines but the investment risks are smaller and the realization time shorter.
During the lively discussion it became clear that the transmission problems in Japan and in Europe are similar, but the proposed solutions are different. This is well explained by differences between the power grid systems, the degree of vertical integration and the political grid regulation. The good news is that advanced HVDC technologies are available and competitive. But there are also challenges. One is the weak acceptance of new onshore grid lines by the local population; the other is the undecided question how to manage supply side risks of HVDC lines with transmission capacities above 10.000 MW.
In the future HVDT investments may become instrumental for reaching a net zero CO2 electricity system. For this purpose the transmission lines need to become part of an intercontinental super grid. On an intercontinental scale, wind is always blowing somewhere. If renewable capacities in different continental regions are connected in a proper way by a transcontinental grid, these generation sources can provide electricity similar to baseload power plants so that traditional fossil power plants are no more required. The implementation of such a visionary concept crucially depends on improved international stability, confidence and cooperation.