renewables
As Europe continues to promote the greater integration of renewable power generation onto its grids, could they represent the final push needed to achieve a pan-European network modernisation?

European targets for integrating renewables are highlighting the need to upgrade the European grid infrastructure in order to permit effective balancing and bulk power transfer over long distances.

Paul Breeze

The EU has one of the most ambitious renewable energy programmes anywhere in the world. The target is to achieve a renewable contribution to the total energy supply of 20 per cent by 2020. This means that for the electricity sector, 35.6 per cent of power must be provided by renewable generation. The consequences of this programme for the electricity industry will be far-reaching – not surprisingly, with so much renewable electricity scheduled for integration, alarm has been raised in some quarters about system stability.

Speaking to The Guardian recently, Susanne Nies, head of the Energy Policy and Generation unit of European electricity industry association Eurelectric, warned about attempting too fast a transition to renewables. The integration of renewables must be managed carefully, she suggested – otherwise, Europe could experience increasing power failures: “The worst-case scenario is one in which we have a series of blackouts in Europe, and there would be a loss of support first for the utilities, but maybe also for the renewables.”

According to Nies, stability incidents have been rising across parts of Northern Europe. Loop flows have also started to appear in the European system. The transmission sector appears to have assumed that these problems are primarily due to an increase in wind and photovoltaic (PV) generation. There are clearly issues here, but closer analysis indicates these may not be as clear-cut as the most conservative voices within the industry suggest.

The warnings being issued today are nothing new, however. In the past, alarms have been raised repeatedly about how much renewable integration is manageable. According to Josche Muth, secretary-general of the European Renewable Energy Council, the German press was warning ten years ago that if the renewable contribution to electricity supply on the German system exceeded 3 per cent, it would break. But today, Germany has around 10 per cent of wind generation alone – and the system has not broken.

Meanwhile, in Denmark, 25 per cent of power is successfully supplied from wind. Even so, Muth stresses, the fears should be taken seriously. Firstly, it is important to distinguish what will be possible in the long term, and what is possible today.

One of the major issues surrounding the integration of renewable sources of generation is that the European grids as they exist today are strictly hierarchical. They were built to manage power from large centralised power plants that operate in a predictable and easily controlled way, and feed power outwards through transmission networks to customers connected to distribution systems. Intermittent sources of electricity such as wind and solar power, which often generate at the periphery of the system, do not fit comfortably within this particular infrastructure.

Even so, existing grids are proving to be remarkably adaptable. Muth quotes a recent International Energy Agency (IEA) study on reliable renewable integration, which found that Europe’s existing electricity grids should enable Denmark to accommodate more than 60 per cent of renewable generation, and the UK and Ireland to accommodate more than 30 per cent. Of course, European national grids are not all equally capable of accepting renewably generated electricity. But these figures suggest that with minimum change, the EU target should be achievable without significant disruption. That, however, overlooks another factor that must be taken into account: the level of interconnection of the EU’s individual grids. Meeting the 35 per cent target for renewables will require that renewable electricity be transported in bulk across Europe, which is not so easily achieved today.

Intermittency and bulk flow

For the EU, and for renewable integration generally, the problem appears to resolve into two principal issues: managing renewable generation intermittency and coping with bulk electricity flows from renewable generators. The solutions to these two issues are interrelated. For example, balancing intermittency can be helped by shifting power over long distances. Equally, both issues can be better tolerated with the use of greater energy storage capacity.

There is a consensus, nevertheless, that the most urgent issue relates to European grids, which are in need of significant upgrading and investment if they are to cope with the expected renewable integration.

Paul Wilczek, advisor to the European Wind Energy Association (EWEA) on grid and internal market issues, singled out two countries – Spain and Germany – where renewable penetration levels are already high and the operational challenges associated with this are clearly perceived. Germany is particularly important because of its high levels of both wind and solar PV generation, and because it is a large grid at the heart of the European system.

It is also in Germany that loop flow has become a particular issue, noted Wilczek. This problem – where power flows pass unexpectedly out of the German grid system and into a neighbouring grid instead of remaining within the country – is both annoying and unpredictable.

Loop flows are also symptomatic of the lack of Germany’s north–south transmission capacity. Much of Germany’s wind generation is located in the north. According to wind turbine maker Enercon, wind supplied over 40 per cent of the electricity consumed in several northern German states in 2010, and in one case, the figure exceeded 50 per cent. This demonstrates how much wind power a grid can absorb, but is also an indication of wind over-capacity in the region. It is imperative that excess wind power can be exported to other parts of Germany when it is available, but today the grid cannot cope adequately.

It was also in Germany that another issue — this time associated with solar PV — was identified, called the “50.2 Hz” problem. Germany’s grid connection regulations stipulated that generators connected to the low-voltage distribution network must shut down if the frequency exceeds 50.2 Hz. With large numbers of rooftop solar PV systems now installed across the country, the potential exists for several thousand megawatts of capacity to shut down suddenly. Not only that, but once the frequency drops below 50.2 Hz again, they may all immediately come back online, thus rapidly destabilising the system once more. New temporary regulations were introduced to combat this, allowing solar systems to shut down incrementally as the frequency rises above 50.2 Hz.

Modernising Europe’s grid infrastructure

Fixing the 50.2 Hz problem was relatively simple: fixing European grids is not. While Germany has an internal problem, many of the most vexing EU grid problems relate to interconnections between national grids and the way in which they co-operate. Symptomatic of this is the fact that today’s congestion management is generally carried out at the borders between EU Member States, which is where bottlenecks in the European system are often found. And, as Wilczek pointed out, some Member States such as the Baltic States are still isolated from the EU grid.

The European Network of Transmission System Operators (ENTSO-E) has recently produced a ten-year development plan for the network covered by its members (which goes beyond the EU itself). According to this report, around 80 per cent of the bottlenecks identified in 2020 are related directly or indirectly to the integration of renewables. Upgrading the EU grid to allow for the full integration of renewables is therefore clearly extremely important, but its significance is far wider than that. European leaders want to complete the EU electricity market by 2014. In principle, this will allow power to be traded across the region, and not simply within national or international boundaries. This should help reduce costs across the EU. But that is impossible without major upgrade work to improve interconnection.

In principle, a properly operating EU electricity market would allow wind power generated in the North Sea to be transported to supply southern Europe, and southern solar power to be exported to the north. However, without better interconnection, that is impossible.

Establishing a fully operating EU market with all the upgrading this entails is also important for energy security across the region. Renewable generation has a key role in maintaining that security, since it is both indigenous and unaffected by volatility in the fossil fuel market. It could therefore act as a hedge against rising coal or gas prices.

The importance attached to upgrading the EU grid is wide-reaching. But the process is also likely to be both costly and time-consuming. One investment cycle is now coming to an end, and a new one is required. Against the current economic backdrop of austerity and low growth within the EU, funding may prove difficult unless the demand within some states for growth-stimulating measures translates into Keynesian economic policies of state investment in major infrastructure projects.

Wind power
Wind power can supply up to 50 per cent of electricity in the north of Germany – a testament to the amount of wind power a grid can absorb Source: A. Majid

However, there are some measures that do not involve great cost, but allow improvement by optimising use of the existing infrastructure – for example, virtual power plants, more controlled forecasting and better demand response can help with managing the change to renewable generation without incurring large expense.

One of the most important areas for optimisation is establishing fully operational intra-day energy markets within EU Member States, of which only half have intra-day markets today, Wilczek pointed out. The closer the trading of electricity approaches real-time, the better renewable integration becomes. Intra-day trading encourages accurate forecasting of renewable output, when the margin of error is smaller. Establishing such markets requires no new transmission or distribution capacity, and can be achieved relatively cheaply. But once in place, they will make the operation of an integrated EU electricity market much more effective.

Looking to the future

Based on the present, the short-term integration of larger quantities of renewable power may proceed smoothly, or it may turn into a matter of crisis management, depending on how fast renewable capacity grows and what level of investment is available. No one now proposes that the EU target of 36 per cent of renewable electricity generation by 2020 is unachievable, provided the requisite investment is directed at the transmission and distribution infrastructure in time. So what are the prospects for the longer term?

Projections for EU renewable generation levels for 2030 and beyond vary, but in most cases show increased levels of integration, of up to 100 per cent during the second half of the century. Whether that is desirable remains debatable, but there are further measures that will at least make it possible. One of these is energy storage.

In principle, energy storage is attractive because it allows excess electricity from renewable sources to be stored for use when needed, effectively eliminating or at least reducing intermittency. BTU Cottbus has published figures that show that a major storm in 2008 contained the equivalent of 420 GWh of electricity that could have been stored if capacity had been available on the German grid. The total storage capacity on its 50 Hz grid is only 20 GWh.

The main issue with energy storage is expense. Pumped-storage hydro is the most cost-effective large-scale technology today, although it is difficult to make a case for constructing this type of large-scale storage plant in a liberalised electricity market. But two areas of Europe already have large hydropower capacities – Norway and the Alpine regions. With a fully integrated and operational EU electricity market, it would theoretically be possible for these two regions to act as energy storage centres for the whole of Europe. This would have to be economically attractive for the utilities operating hydropower facilities, and would require investment to convert some existing generating-only plants into pumped storage facilities, but in principle it is feasible.

Another potential source of large-scale energy storage is the battery-based electric vehicle. How that will develop depends on the market for energy-efficient vehicles and whether this moves towards hydrogen fuel cells or battery vehicles. But assuming the latter achieves a significant market share, appropriate Smart Grid technology would enable system operators to appropriate vehicles connected to the grid for recharging as temporary storage capacity.

With a large enough population of vehicles, the proportion connected to the grid at any one time could provide sufficient capacity to make this possible. In theory, this could provide all the storage capacity needed, and more, but it may take another 10 or 20 years to find out if this can be realised in practice.

From a balancing and integration perspective, the other major development for the future will be a European ‘supergrid’. Though this sounds grandiose, the supergrid is nothing more than a network of long distance HVDC transmission lines linking major sources of renewable generation with major load centres across the region. Single HVDC lines of up to 5000 km in length are already in use in China, according to Wilczek. But there is a need to develop an effective form of node technology so that HVDC lines can be interconnected efficiently. Otherwise, they can only operate as simple point-to-point links between AC networks. ENTSO-E views the supergrid as a long-term project for 2050 and beyond. However, others hope to see it built significantly sooner.

With timely intervention, both the short-term and the long-term integration of high levels of renewable generation on the EU grid appear technically feasible and practical. Unfortunately, timely intervention is not something that can be relied on, particularly under current economic conditions. Failing that, the future for the EU grid is likely to be one where necessity forces ‘reluctant change’ as renewable levels grow. This may lead to some short-term difficulties, but the predictions of impending doom that these might engender are unlikely to prove accurate, at least on current evidence.

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