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Wind Power Variability and Impacts on Power Systems

A wind farm does not operate all the time; so backup capacity is needed when it does not and differences between forecast and actual production have to be balanced. Balancing and backup comes at a cost, as does building new infrastructure. These facts apply to wind energy just as they apply to other power producing technologies that we integrate into the electricity grids. But for reasons that are difficult to grasp, balancing and backup of wind energy is generally perceived to be problematic whereas balancing and backup for other technologies seems as easy as breathing. Certainly, most of the mainstream media does not find it interesting to report the complexities of balancing a constant supply of nuclear power or inflexible coal-fired power against the demand from millions of consumers, with their constantly changing and unpredictable demands for power.

There is nothing simple about operating a power grid. Delivering electricity to consumers is a logistical challenge larger than for any other product market. Transmission system operators (TSOs) are tasked with delivering an invisible product, which cannot be stored, to a customer that expects to receive it at the exact same second he discovers he needs it. Grid operation is just-in-time management in its most extreme form; when you think about it, it seems an unrealistic task for anybody to undertake. Nevertheless, European grid operators are simultaneously servicing 500 million fickle consumers with unpredictable behaviour every second of every hour of every day. They have done so for a hundred years with minimal supply disruption. If it was not for the fact that we experience it every day, we would say that it was impossible.

Just like an individual consumer, a wind turbine is variable in output and less predictable than most other technologies. However, from a system operations perspective, the supply behaviour of a single wind farm is just as irrelevant as the demand behaviour of a person. The collective behaviour of consumers and the collective behaviour of all generating plants are what matters. That has been the guiding principle of grid operation since its inception and is likely to remain so regardless of which technologies we use. If operating a grid is inherently difficult, we are fortunate in having system operators in Europe who understand what the rest of us find difficult to comprehend. Wind power is, admittedly, different from other power technologies and integrating large amounts of it in the existing power system is a challenge. But whatever the generating technology, the basic principles of balancing, backing up, aggregation and forecasting still apply.

Changes to the way we construct and operate the future European electricity grids are still needed if we are to meet one-third of Europe’s power demand with renewables within twelve years, as projected by the European Commission. But the challenge is by no means any greater or more costly than the one system operators faced when politicians thought that nuclear was the answer and expanded its share to 30 per cent of European demand in two decades. Today the answer happens to be wind, and of course the grid needs to be adapted to that new reality. It can hardly come as a surprise.

TSOs employ some of the most skilled people in the power sector. Nevertheless, they too need practical experience to acquire knowledge when new technologies are introduced in large amounts. European TSOs are gaining vast experience and knowledge about managing over 30 per cent wind power shares for long periods of time. In Denmark, a mind-blowing 140 per cent is sometimes managed.

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