Wind energy for grid support

The interest in renewable energy sources (RES) for the production of electric power became relevant with the oil shortages of the 1970s. In many countries, governments worked with industry to improve alternative energy technologies and in those days the concept of large commercial wind turbines started to catch on. With a rotor diameter of 10 m, the 10 kW wind turbine was a pioneer of the modern 10MW turbine (diameter of 190 m and hub-height of 125m). Nowadays, wind turbines operate in every size range from small turbines used for micro grids (battery charging, powering telecommunications, etc.) to hundreds of large-size wind turbines included in wind power plants of near-gigawatt-sizes.

The incentives for renewable energy and the commitment of developed countries to endorse global environmental concerns have led wind power generation to displace a significant amount of the power generated by conventional power plants. Figure 1 shows the growth rate of wind power capacity installed worldwide in the last 5 years. With regards to Europe, in 2017 wind energy (with an installed capacity of 160 GW) has supplied more than 11% of the European electricity consumption, avoiding about €9 billion of fossil fuel costs [1].

 

Figure 1: Statistics of capacity installed worldwide and annual growth [2].

Figure 1: Statistics of capacity installed worldwide and annual growth [2].

Whilst the ever-growing participation of wind power generation in the electricity production is necessary to decrease the dependency from fossil fuels, the increased penetration of sudden variations in the electrical power production due to the highly variable nature of the wind reduces the stability and reliability of the electrical grid.  Therefore, so far conventional power plants have been crucial for offering ancillary services in order to guarantee a reliable and stable power supply at any instant and time. However, a question arises: could wind power plants be capable of providing ancillary services? Yes, they could. The recent advancements achieved in controlling wind farms and the innovative wind turbine technologies ensure automatic and fast responses able to provide ancillary services participation, such as frequency support.

Frequency event is caused by the imbalance between power generation and consumption, in order to drive back the frequency at its nominal value the electrical power systems must improve (or reduce) the active power delivered into the grid. Nowadays, the participation of wind power plants in frequency support is already a requirement in some jurisdictions. Wind turbines are already widely used to provide inertial frequency support by releasing within milliseconds the kinetic energy stored in the rotating mass. However, the time-frame of a frequency event is much longer; typically almost 20 minutes are required to draw back the frequency at its nominal setting. In case of frequency drop, wind power plants must be capable of delivering for tenths of minutes extra active power into the grid, but if the wind turbines work at their maximum capacity frequency, support cannot be provided. With the envisaged further penetration of wind power generation in the electrical networks, some wind power plants could work in de-loading mode to reserve some power to provide frequency support.

In order to guarantee stability and reliability of the electrical grid, fast and high performance control strategies are required for wind farms. A proper wind farm controller should be fast enough to follow the rapid variations of the power demanded by the grid and sufficiently accurate to regulate the power generation of each turbine in the wind farm as such that the total power outputs meet the power demand. Within the INCITE project new wind farm control strategies are proposed in order to improve the capabilities of wind power plants to provide frequency support (and other ancillary services). As an example, the model predictive control technique (additional information regarding this technique can be found in Pippia's article) is used to build a wind farm controller, which ensures the tracking of the power demanded by the grid while providing frequency support only when the wind farm maximum capacity is over the power demand [3].

 

[1] Wind Europe: “Wind Energy in Europe Scenarios for 2030”.

[2] World Wind Energy Association:  “Half year Statistics 2017”.

[3] S. Siniscalchi-Minna, F. Bianchi, M. De-Prada, and C. Ocampo-Martinez “A wind farm operational strategy for primary frequency support optimization”, Wind Europe Conference and Exhibition 2017.

 

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