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Analysis: Danish surplus exposes grid challenges

DENMARK: For two hours on Friday 10 July, wind power generated the equivalent of 140% of national electricity consumption, surpassing the previous record of 135%.

Wind produced 140% of Denmark's consumption on Friday 10 July
Wind produced 140% of Denmark's consumption on Friday 10 July

The peak production was reached between 2am and 4am (CET). A combination of strong winds coupled with low energy demands in the early morning during the summer — when demand is typically lowest — contributed to the new record.

Looking at the figures over a longer period, there was a production surplus between 8pm on 9 July and 7am the following day. Wind production also remained at 80% of consumption for a further 12 hours through 10 July.

"It tells us that we are on top of the development in Denmark, where an increasing amount of the electricity is coming from wind," said a spokesperson for the Danish Wind Industry Association.

Denmark's electricity prices reflected the surge in power, driving down the day's average to €5.42/MWh — considerably lower than the 30-day average prior to 10 July of €19.50/MWh.

However, the event gave insight on how the northern European grid is facilitating exchange across borders, revealing a prominent challenge being faced in the region.

On the day of the record, Denmark's surplus was exported to Sweden, Norway and Germany — a net exchange of 6,010MWh.

Exceptional to this trend was a period of modest importing from Germany into western Denmark (energy zone DK1) amounting to 200MW between midnight and 6am on on 10 July, during the period of surplus.

Danish transmission system operator (TSO) Energinet explained the import was a response to higher than expected wind production in the north European region. This exposed a bottleneck in transmission that limits exchange capacity through the German-DK1 interconnection.

"Since reinforcements are needed in the German grid and on the Danish-German border, unforeseen wind power can become trapped in northern Germany creating an imbalance in the grid," said an Energinet spokesperson. "In this case the power couldn't move south, and so the German TSO, Tennet, asked for permission to export to Denmark".

In order to balance the import with its national surplus, Denmark reduced its own power generation, while exporting through its remaining interconnectors. The net effect optimised available energy and use of transmission lines, while adding energy liquidity into the Nordic market.

Energinet said during a counter-trade of this sort importing TSOs do not incur any financial costs, and facilities that agree to reduce production are compensated by the exporting operator.

A spokesperson for Tennet described the counter-trade as a "usual remedial action of TSOs to maintain system security on the basis of physical flow", adding that, in this case, "the intervention was necessary to prevent overloads on connected network elements".

Counter-trade is not an ideal solution to bottlenecks. Though it alleviates congestion in the short term, it does nothing to cost-effectively utilise renewable energy.

The increased share of wind will bring Denmark days of self-sufficiency. But it underlines the case for improved infrastructure to support exporting surplus energy.

Denmark is one of the most dependent countries on power imports for days when wind production is low. Such days are common: the day after the record was set, wind's share averaged just 8%.

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