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SSEPD: Shetland Tidal Array

SSEPD: Shetland Tidal Array

The Shetland power grid operates as an electrical island, with no interconnection to the main UK grid. There are vast renewable resources available, but the amount of renewable generation that can connect to the grid has been severely limited by network operation and stability constraints. These constraints are caused by various possible imbalances between generation and demand. Scottish and Southern Electricity Power Distribution (SSEPD), Shetland’s Distribution Network Operator, uses Active Network Management (ANM) to coordinate a range of Distributed Energy Resources (DER) on Shetland. ANM helps to better balance the grid, to overcome stability constraints, and to allow more renewable generation to connect. Shetland Array, a 500kW tidal array, is the third distributed generation connection to be managed by ANM.

Shetland Array is located in the North of Shetland, between the islands of Yell and Unst. The project is one of the world’s first in-sea tidal arrays. The tidal array will consist of five 100kW tidal turbines to be developed over two phases, with the first now fully operational and generating.

As with many Islands, power system stability is a major concern and this has prohibited the connection of additional DER. The possibility of sudden loss of power, either due to variable output or a network fault, means that it would not be possible to keep frequency within limits, which are already relaxed on Shetland. SSEPD needed to better balance the grid, by managing the output from the tidal array. The output of Shetland Array’s potential 500kW, will be managed by ANM, using a set of operating limits based on the constraints of the network.

SSEPD has implemented our ANM 100 product to schedule, coordinate, and control the tidal array.  ANM 100 continually monitors the 11kV and 33kV networks along with the output from all the distributed generation.

When network operation nears defined constraint conditions, ANM uses time-bounded, repeatable and fail-safe controls, to regulate export from participating generators and maintain the network within safe operating conditions.

The ANM system is integrated with SSE’s Serck SCADA system, PI data logging system, and data historians. This provides a real-time and historical outlook of the Network and all associated generators.

A private copper leased line is used to communicate data between Shetland Array and the Central ANM servers based in Lerwick.

Tidal arrays are a strong candidate for future development. They have the least environmental impact of available Tidal Power Generating Methods, and can be deployed to make best use of available tidal flow. This successful commissioning demonstrates that Smarter Grid Solutions can resolve integration and control issues with tidal arrays, in addition to our successful work with wind and solar generation.

By actively managing both local grid constraints and system-wide stability, through the real-time coordination of DER, energy storage, industrial demand and domestic demand - an estimated additional 8-12 MW of renewable energy generation can be connected to the existing Shetland grid through the tidal array. 8-12 MW represents a 200% increase in renewable energy contribution, and a reduction in CO2 emissions, through displacing fossil fuel generation.
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