Maintaining grid reliability and stability is increasingly challenging as renewable energy resources are added to the power mix. Combining battery storage systems with gas turbine units can improve overall plant performance and ensure black-start capability is available, when needed.
Keeping the lights on has been the mantra from governments and utilities, particularly after several high-profile power cuts in the last decade. There has been much spoken about the reliability of the electrical network and concerns raised by the diminishing input from fossil-powered generation. This concern was raised again last year when a large-scale power outage struck South America.
In June 2019, a large-scale blackout affected Argentina, Uruguay, and Paraguay, leaving an estimated total of 48 million people without electrical supply. According to local supply company Edesur, problems with several 500-kV transmission lines disrupted the flow of electricity from two dams to Argentina’s power grid. It took more than 24 hours for electricity to start flowing again, highlighting the challenges of restarting a power grid in such a situation. Preventing these outages is one thing, but ensuring that power is restored as quickly as possible is equally important.
Black-Start Challenges
The procedure that network operators adopt to restore power in the event of a total or partial shutdown of the electricity transmission system is called black start. Most nations have a requirement that this black-start capability is built into the power grid, with certain generating facilities having specific black-start capabilities. Traditionally, power plants use small diesel generators to start turbines or to provide power references, such as voltage and frequency, to allow renewable power generators to reconnect. Another option is to use battery storage, such as forms part of Siemens’ Siestart system (Figure 1).
- Adding a lithium-ion battery energy storage system to a combined cycle gas turbine power plant offers several benefits, including black-start functionality. Courtesy: Siemens
Grid stability and reliability have always been top priorities for network operators, and will continue to be, but with the growth of renewable energy solutions on the grid, the challenges of maintaining that stability and reliability are growing. There is no denying that the growth of renewable energy is positive news for the worldwide fight against climate change; however, there are some other consequences of this growth that operators need to consider. When grid stability is considered, it must be recognized that both wind power and solar photovoltaics are highly dependent on the weather, which can lead to some variation, which needs to be balanced and compensated. It is a quite simple correlation—the higher the share of renewable energy sources, the harder it is to ensure stability.
However, as mentioned previously, grid stability needs support, otherwise there can be serious consequences, even in highly developed countries where significant blackouts have also occurred, such as in South Australia in 2016 or Argentina in mid-2019. It can and does happen, and it is really not an easy exercise to restart grids, once they are black.
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