Author: Thomas Sattich
The role of electricity grids for decarbonisation is largely explained by the fact that storage of electricity is difficult and costly: Power generation therefore needs to follow changing load in real-time in order to keep main voltage and grid frequency stable. The power transmission infrastructure is one of several ways to optimise this system, with interregional power lines providing system operators with the flexibility needed to keep the network stable despite local load changes (ECF 2010:70): The larger, the more flexible and diverse a power pool is, the better network stabilisation works.
Renewables greatly increase the need for flexibility (see below); a densely intermeshed and smart electricity transmission grid is therefore widely believed to be one of the preconditions for the achievement of EU’s decarbonisation target (Fürsch et al. 2013:642): European power grids need to be adapted to increase the capacity for flexible reactions to momentary load changes caused by renewables, otherwise further decarbonisation will be impossible. This is common knowledge. The question is, however, where exactly the increase of renewables will require adaptations, what kind of adaptations will be necessary, how the EU could intervene, what measures have been envisaged and/or implemented, and whether these are effective and sufficient. In order to answer these questions, the following section aims to determine the complex relation between the integration of (intermittent) renewables and (cross-border) power transmission infrastructure; moreover, the necessary reorganisation of the European grid is highlighted.
Electricity transmission networks and decarbonisation
Decarbonisation poses a double challenge for the European power transmission infrastructure: First, the availability of the energy carrier co-determines the location of power plants; the switch to renewables will thus change the distribution of power plants and the geography of the grid. Second, the product of electricity generation changes with decarbonisation; in contrast to carbon-based systems, where standardised units of coal, oil or gas make the power system partially independent from meteorological effects, many renewable energy plants depend on changing elemental forces such as wind and sun. Grid modernisation will thus be required to stabilise power supply.
The changing geography of the European power grid
Due to the relatively low energy density of most renewable energies, decarbonisation requires large territories such as wind parks; these will thus have to be developed and interconnected. Moreover, most renewables cannot rely on modern transport systems to bring the energy carrier to the plant, but solely on the electricity transmission infrastructure to bring their product to the consumer. And as the renewable energy sources required for power generation are a) distributed unequally , and b) typically to be found in remote regions, decarbonisation will result in a highly unequal distribution of generation sites.
Power transmission infrastructure will have to cover the growing transmission distances in order to bring the electricity to the consumer. There are, however, differences between the various forms of renewables: While wind, solar and tidal power will be highly concentrated in geographic areas that do not coincide with consumption centres, biomass can (partly) be transported to, and used in the power generation infrastructure in place. Where new transmission lines are necessary will hence greatly depend on the regional energy mix.
The impact of intermittent renewables on the grid
The changing location of generation sites has strong implications for the future shape of the European power grid. The same applies for the changing product of power generation: According to the International Energy Agency (IEA) and the European Commission, network balance is in jeopardy where intermittent renewables such as wind and solar power exceed five per cent (Commission 2012:8). Until that margin the existing power pools are flexible enough to counterbalance fluctuations in network frequency and voltage caused by changes in wind, solar and ocean energy.
Where, however, intermittent RES exceed this number, additional measures are required to provide the system with enough flexibility to absorb network fluctuations. In this regard the European power system is close to a paradigm shift: In 2011 intermittent renewables already amounted to 35 per cent of RES-generated electricity in 2011 (9 per cent in 2002), and seven per cent of all electricity generated (Eurostat online data). It can be expected that this number will climb to 49.7 per cent of RES capacity until 2020 (ECN 2011b:14, see Fig. 1); if current trends continue intermittent RES will hence account for a total of 17-20 per cent of European electricity (ECN 2011a).
The EU’s power sector is thus headed towards an era where the characteristics of intermittent renewables will increasingly determine the logic of power generation, transmission and consumption. Increasing the flexibility of existing power pools and their transformation to a smart and flexible system of power generation and consumption is thus the key to the sector’s further decarbonisation, and – in the long run – a complete switch to renewables.
With its capability to integrate otherwise isolated regions, and thereby to increase the capacity to keep growing network fluctuations under control of system operators, the power grid has a vital role to play in this adaptation. The need for more flexibility in particular areas and more interconnections with other parts of the European power grid depends, however, on the specific regional energy mix: Because the ability to control energy input and output largely varies between different forms of RES, not all parts of the network will be in need for the same level of interconnection.
The reorganisation of the European power grid
In order to continue the decarbonisation of the European power sector, electricity networks need to be reorganised. Two different dimensions can be identified in this regard: New infrastructure to cover the power sector’s changing geography and adaptations necessary to compensate growing network fluctuations caused by intermittent renewables. On both dimensions the European power grid has to be adapted to the requirements of renewable energies, if decarbonisation of the European power sector is to be continued.
This need for grid modernisation concerns also all parts , levels and sections of the grid, and can thus be described as universal. Ideas and plans for the reorganisation of the European grid are hence far-reaching, and include the construction of regional (North Seas Countries’ Grid Initiative), continental (the super-grid) and even transcontinental networks (Desertec). The varying characteristics of different RES technologies will, however, also pose specific challenges for particular sections of the power grid, depending on the particular energy mix in a given region.
In this specific context, cross-border transmission infrastructure is of particular importance, as it is badly developed, with generally low Net Transfer Capacity values: Exchange between the different national systems stagnates between 7 and 10 per cent (ENTSO-E online data; see also Commission 2007e:175). Most member states can therefore be described as largely self-sufficient in electricity supply (Eikeland 2011:14); today’s power transmission infrastructure hence rather prevents free flow of electricity in Europe, and thus a rational distribution of RES generation units and the ability to balance network fluctuations caused by renewables.
About 80 per cent of the bottlenecks in the European power system relate hence to the integration of renewables (ENTSO-E 2012:56). Increasing exchange capacity along national borders is hence a precondition for further decarbonisation of the European power sector. The aim of the reorganisation process should be the creation of a flexible and smart power pool of European size, where all power plants jointly balance the disturbance of one power station, regardless of its location (Battaglini et al. 2009). This has been regarded a convincing and economically viable possibility for better network stabilization (Booz&Co. 2013:86-87). Filling the gaps in the European cross-border grid infrastructure can therefore be interpreted as largely untapped options (Booz&Co. 2013:86-87) for near complete decarbonisation at moderate costs (Haller, Ludig & Bauer 2012:288).
But even though cross-border transmission capacity is generally low in Europe, it nevertheless largely varies along European borders, with well integrated parts on the one hand, and gaps and bottlenecks on the other. Thus, the question arises, where grid development is required and where the necessary adaptations are most urgent. The per area generation of intermittent electricity is helpful in this regard (see Fig. 2), as it reveals sharp differences between member states in their approach to renewables: Whereas some countries show only a moderate density of intermittent renewables, and intend to keep their numbers limited, other countries decided to integrate large numbers of these plants into their national systems (ECN 2011a). This will result in largely varying need for interconnectors with neighbouring countries.