“Black Start” is the process by which the National Electricity Transmission System (NETS) would be recovered following a total system collapse. This is a not uncommon occurrence in some regions of the world but thankfully) unheard of in the UK; that does not mean we should not plan for such an eventuality.
However, the current approach, which requires the constant availability of a thermal plant on hot standby, is costly in both environmental and financial terms (around £50 million annually).
The Distributed Restart Conference last week, led by National Grid and Scottish Power, presented an update on their programme which aims to demonstrate the potential for distributed (renewable) generation as an alternative means of providing this capability at a lower environmental and economic cost.
One speaker questioned the significance of this innovation, concluding that a cost of little more than £1 per household annually was hardly material. In environmental terms, the operation of an OCGT (rather than coal), if it was ever actually called upon to run, would also be trivial for the duration involved.
So, is that all there is to it? Is this project just a slightly cheaper or cleaner insurance scheme?
Before answering that question, it is worth considering the two innovative approaches being explored.
The first is to identify a single anchor generator with associated, manageable loads within a limited area, referred to as a “power island”, which would form the nucleus of a recovery process. Additional generators and loads are then added incrementally to expand the boundaries of the island. A number of these islands would be established and, as they expand, they eventually meet and are resynchronised to establish a unified grid once more. The most significant difference between this and the current paradigm is that rather than using a single (actually two) dispatchable thermal generator, a number of relatively small, renewable and distributed generators would be employed.
Although this might appear to be little more than a more environmentally efficient solution to the problem of black start, it also represents a significant contribution to the paradigm shift from a centralised energy system dominated by thermal (fossil) power plants, to a more distributed, lower carbon, sustainable system.
On its own it is a useful step in the right direction, but far more importantly it is a demonstration of the way in which, one by one, we are overcoming the obstacles to a fully renewable power generation system. It starts to tear down the myths that an energy system must have (mechanical) system inertia, it must have thermal plant on standby, it must have dispatchable fossil generation, it must have nuclear baseload…
And so to the second approach, the exploitation of microgrids.
A microgrid is a bounded system of generation, demand, storage and control, which is able to operate either connected to the grid or, in the event of grid failure, to disconnect and continue operation as an islanded system. The report acknowledges the potential role of microgrids as fixed power islands, capable of supporting the main grid as it recovers, but notes that there are relatively few microgrids at present in the UK.
However, microgrids provide a double benefit, for not only does a microgrid provide resilience (and many other benefits) to those who live within its boundaries, it also, at no additional cost, can provide resilience and other services to the wider energy system, including, perhaps, as the nucleus of a power island supporting black start system recovery.
What is next?
Following extensive theoretical evaluation and off-line analysis of potential case studies over the past twelve months, three real-life trials of the re-energisation process will be initiated on the SP Distribution and SP Manweb networks. We look forward to seeing how the commercial, organisational and technical challenges are overcome and to what extent the environmental and other benefits can be realised.
It is an area we will be following closely as part of our Local Energy Systems Research Service.