SSEPD: ANM saves SSEPD £30m by preventing grid reinforcement
In 2013 the Orkney Isles became a net exporter of electricity with 103% of annual electrical energy demand being met by renewable sources. The islands achieved this despite the limited export capacity of the subsea cables to the mainland and between the islands. Smarter Grid Solutions technology was used to maximise the utilisation of the existing grid assets and integrate considerably more distributed energy resources than would previously have been possible. The Active Network Management (ANM) system saved £30m in network reinforcement and allowed the renewable generators to connect many years earlier than would otherwise have been possible.
Given its location in the windy north-western corner of Europe, the Orkney Islands are home to some of the best wind, wave and tidal resources in Europe. Scottish and Southern Electricity Networks owns and operates the Orkney electricity distribution network, which is connected to the Scottish mainland by two 33 kV submarine cables. The subsea cables have a combined export/import capacity of around 40 MW. The demand for electricity on Orkney varies between around 8 MW and 32 MW. Applying conventional approaches to network planning resulted in a maximum secure hosting capacity for distributed generation (DG) of 28 MW.
To enhance the hosting capacity of the islands, a fast acting protection system was implemented to allow a further 20 MW of DG to be connected. This generation would immediately be tripped off the network in the event of an outage on either of the subsea cables. The grid connection rules in the UK require that connecting customers must fund reinforcements to the grid at their connecting voltage and one voltage higher. Additional DG connections beyond the 48 MW (28MW plus additional 20MW) would trigger the need for an additional subsea cable as well as multiple internal island network upgrades.
The minimum cost of a new subsea cable was calculated as £30m. The cost and timescales to implement the subsea cable meant that no individual DG developer would progress their connection application. With 48 MW of distributed generation already connected, the grid was therefore considered ‘full’.
The limitation on hosting capacity reflected a series of worst case conditions which rarely, if ever, actually occurred. Second by second, the electricity being consumed and produced on the islands varies. To release the latent capacity, Smarter Grid Solutions deployed an automated system to monitor the real time capacity of the grid and reduce distributed generation output only when the grid is actually under stress. This technology and method for managing electricity networks is known in the industry as Active Network Management.
The deployed system operates autonomously with sub-second processing and ensures that end-to-end control delivers repeatable responses to measured inputs within seconds. The system incorporates fail-to-safe functionality throughout, meaning that the failure of any individual component, communications link or lack of response from a managed generator results in a series of escalating control actions being initiated to ensure that the operating limits of the grid are never exceeded.
The ANM system has been expanded over time to incorporate a 2 MW / 0.5 MWh electrical energy storage device to help minimise curtailment while being available for other grid flexibility services.