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Pushing out more power on Europe's grids

Researchers at the European Wind Energy Association (EWEA) are saying that a series of grid demonstration projects lasting three years has proven significant, tangible cost savings that can now be put into use by transmission system operators (TSOs) across Europe and beyond.

Wind companies and Transmission operators worked together in the Twenties grid programme (pic:NKT Cables)
Wind companies and Transmission operators worked together in the Twenties grid programme (pic:NKT Cables)

The six projects, looking to improve management and monitoring of power across networks, can help TSOs make better use of power from wind projects and delay the need for costly grid upgrades.

The Twenties grid programme was initiated by the European Commission (EC) in 2009 to find ways to enhance the grids across Europe in anticipation of the mandated 20% of energy supply from renewable sources by 2020. "There was a need to improve the way the EU grids are managed," says Jacopo Moccia, EWEA head of policy analysis. "To prevent a major bottleneck, we need to integrate this growth of renewables into the system."

The overall project had a budget of EUR56.5 million - more than 50% provided by the EC - and involved over 20 organisations, including TSOs and wind-turbine manufacturers. Each of the six demonstration projects claims to have proven that its technologies can enhance and transfer more power across existing networks.

Spanish TSO Red Electrica ran the Flexgrid project, installing a fibre-optic line along 40 kilometres of its overhead power cable between Fuendetodos and Maria de Huerva in northern Spain. Spain already has a high level of wind energy and other renewables, and with a network that has only one large connection, with Portugal, it has to manage its own supply and demand. By necessity, its grid is already well managed, but the operators know they need to continue to improve how it is used.

Using these fibre-optic lines, the TSO was able to measure the temperature at two-metre intervals every ten minutes, and accurately calculate the maximum power it could push through without the cables overheating and compromising the security of supply. Without this technology, TSOs are obliged to estimate when overheating may occur and curtail the power on the grid well in advance. A conservative figure of the additional power it can run on the same cables is 10-15%, says Vicente Gonzalez Lopez, head of research and development and EU projects at Red Electrica.

On windy days when power is more plentiful and the prevailing wind can also cool the cables, the additional power can reach as high as 25%, the study concludes. In a second Twenties project, Belgian TSO Elia looked at the same technology across cables at a regional level.

By installing new management software to the 91 offshore wind turbines at Horns Rev II in the Danish North Sea, TSO Energinet.dk continued to operate some of the project through storm conditions. By more closely monitoring the machine and the weather at each turbine, and by altering the pitch of the blades, the operator could selectively ramp down or shut down turbines when required, while other turbines continued to generate power. The additional checks allowed the TSO to continue running some turbines in winds of up to 32m/s - higher than the usual maximum of 25m/s. During the test period, Horns Rev II maintained generation of 100MW capacity for five hours when the 209MW site would previously have been closed down.

Reducing need for reserves

By reducing the power output across the site on a more gradual basis, the test indicated a reduction in reserve power requirement of up to 50%. "If you look at how much capacity is planned in the North Sea in the next 15 years, that is a huge amount of other capacity that is no longer needed in reserve," says Moccia.

Other projects include a virtual power plant run by Dong Energy, which aggregated the information from a number of small generators such as wind farms, and delivered it to the TSO as one power plant. This allowed the TSO to better manage the flow of power, reducing congestion and the need for reserve power.

Voltage control and secondary frequency regulation was investigated by Iberdrola, which showed it is possible to predict the wind energy it will deliver and how it is going to affect the frequency and voltage across the grid. The final project, led by RTE France, tested the potential of direct-current cables, creating conditions for their use with a new offshore grid and how it will connect to shore.

"A lot of the Twenties project is about squeezing as much as we can from existing power systems. Of course we will need improved grids across Europe, but we can do so much more with what we have, and that will bring down the cost," says Moccia.

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