A new JRC lead-authored report on transmission network planning highlights that a radical change in coordinated network planning and operation is needed to accommodate market liberalisation and the increasing integration of renewable power sources.
The key issues to obtain a reliable and effective European grid are integrated strategic planning and cross-border coordination. In the US, studies by the Electric Power Research Institute (EPRI) also highlight planning’s central role to accommodate high levels of variable generation from renewable resources.
The importance of electricity transmission grids – the backbone of the European Union’s and United States’ economies – is higher than ever. These networks are getting older, are confronted with complex market liberalisation processes and have to host increasing amounts of renewable energy sources.
Furthermore, in order to address the challenges of energy security and climate change, transmission grids need to become more interconnected and ‘smarter’ by seamlessly integrating a wide range of users (generators, consumers and/or other grids).
In the European Union (EU), electricity grids are included among the low carbon energy technologies assessed as part of the strategy to achieve the energy and climate change policy targets (which include a 20% reduction of CO2 emissions and a 20% share of renewables in overall EU energy consumption by 2020; this translates to 30-35% of electricity consumption covered by renewable energy sources).
According to SETIS, if the maximum potential is realised, the electricity grids could avoid up to 30 Mt/year CO2 in 2020 and 60 Mt/year CO2 in 2030 in the EU. The corresponding maximum cumulative CO2 emissions avoided for the period 2010 to 2030 would be up to 600 MtCO2.
The importance of better planning
Existing transmission planning methods commonly make use of a worst-case scenario approach: power flow analysis is performed for a small number of cases selected by experienced network planners. With the increased uncertainty and the many assumptions necessary for the analysis, the need to include more combinations of load, (renewable) generation and international exchange is becoming essential and a probabilistic approach to deal with such uncertainties is needed.
The way forward…
In particular, the planning criteria for expanding the transmission and distribution grids (which could be compared to the main arteries and the capillaries in the human body) have to be rethought, and more robust methodologies for network planning must be pursued.
Current transmission and distribution systems, both in Europe and in the US, "do not talk to each other". It is therefore critical to improve the two-way interactions between electricity transmission and distribution. Recent disturbance and disruption events in Europe (for example the disturbance on the 4 November 2006 which originated in Germany and then spread all over the continent), clearly call for this type of improved coordination. One of the causes of the disturbance was in fact the inadequate monitoring and control by transmission operators of small sized generation units installed at distribution level. The uncoordinated action during the disturbance worsened the situation and introduced a risk of more severe instability.
Such disturbances prove that, without properly coordinated system interfaces between transmission and distribution, and real time information exchange (e.g. concerning generators connected to the distribution network), the consequences of a power disruption at the distribution level may also be suffered, if not amplified, at the transmission level.
… in the EU…
The recent JRC review of existing methods for transmission planning and for grid connection of wind power plants presents the state of the art in this field and points the way for future developments. The report’s findings and recommendations include:
* Transmission planning must change drastically to accommodate market liberalisation and increased integration of wind energy and other sources of renewable power.
* Grid expansion should focus on achieving better coordination between Transmission System Operators (TSOs) through integrated strategic planning and cross-border cooperation.
* Transmission planners should take a smarter approach to integrating ‘variable’ power sources such as wind power, solar energy, hydro and wave, which do not generate consistent levels of power (e.g. by balancing the variable power with storage technologies).
* TSOs should prioritise the emerging challenge of integrating the future transmission system (hosting large-sized generation, both conventional and renewable) with smart distribution grids (embedding dispersed small sized energy sources and storage).
* A more harmonised and market-based framework is required to overcome planning and regulatory differences at national level, and to realise the potential synergies between offshore energy projects and cross-border trade in electricity.
…and in the US
On the US side, the Electric Power Research Institute (EPRI) has contributed to various studies on the topic, and has a specific research programme for the integration of renewable energy in the US transmission grid. Its key conclusions largely match the results of the European research:
* Planning methodologies must change significantly to accommodate high levels of variable generation from renewable sources. A particular focus will be the challenge of moving renewable energy long distances from its source point (e.g. offshore wind farms) to centres of demand (e.g. cities and factories).
* More comprehensive planning approaches, from the distribution system through to the bulk power system, are needed. These must take full account of the uncertainty factors associated with variable generation.
* Deploying different types of variable resources (wind, solar, etc) to take advantage of complementary patterns of energy production and advanced control technologies such as storage and flexible power control devices (e.g. FACTS, Flexible Alternating Current Transmission System) show significant promise in managing variable generation characteristics.
* More efficient storage and smarter technology will be needed to accommodate high levels of variable generation (e.g. plug-in hybrid electric vehicles).
* Integration of large-scale variable generation in grids may ultimately depend on larger pools of generation becoming available, and on increased demand from users.
* Technical issues related to grid code compliance and the potential for control interactions must be addressed.
In summary, although there are intrinsic differences, between the EU and US power systems, both infrastructures are facing similar challenges towards planning future power grids capable of effectively hosting and seamlessly integrating a large and diversified number of low carbon energy technologies.