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In Q1 2024, wind power in the UK reached 2.53 billion kWh, or 39.4 percent of total electricity generation; together with solar power generation of 180 million kWh, renewable energy generation reached 2.71 billion kWh, or 42.2 percent of total electricity generation!
New energy sources not only create problems of grid connection and peaking, but as their proportion rises, they also pose another, more subtle problem - that of grid stability. So how is the UK addressing this issue?
Modern power grids carry alternating current, and carrying this current requires a certain frequency to be maintained (usually 50 / 60hz). And its stability is maintained by grid inertia.
Conventional power generation turbines can be seen as devices that generate inertia. As the number of new energy sources continues to increase, these turbines gradually become smaller and smaller, resulting in less and less grid inertia. In countries with a high proportion of new energy sources, maintaining grid stability becomes an important issue.
The UK has two main approaches to this problem.
In March 2022, the UK's National Grid began construction of a synchronous phase regulation plant in the north of Scotland to provide the inertia required by the grid via a pair of steel flywheels. Each flywheel weighs 194 tonnes and rotates at 500 revolutions per minute.
A second phasing plant will be built near Liverpool. Its flywheels will have a slightly smaller mass but will be capable of spinning at 1,500 revolutions per minute. Both plants will provide 2 percent of the inertia required by the UK grid, equivalent to that provided by a conventional coal-fired power plant.
Subsequently, National Grid will build two more synchronous phasing plants to enhance grid stability.
In addition to new synchronisation plants, it is also possible to convert existing coal-fired power stations into synchronisation facilities. In 2021, National Grid converted a gas-fired power station in north Wales. The converted plant no longer generates electricity, but instead provides inertia to the grid.
Another method is to use grid-forming inverters to provide inertia.
Photovoltaic energy storage is DC. Wind power, although AC, needs shaping to be delivered to the grid. The current method is to remove the irregularities through an inverter before connecting to the grid. Inverters work in a passive mode, called "grid following". They adjust the frequency of the output current according to the set grid frequency. This is fine when there is a small percentage of wind power, but as the percentage increases, it becomes unfeasible.
However, it is possible to design inverters as "grid-builders", which stabilise the grid by simulating the mechanical inertia of the output. The use of "grid-built" inverters will allow more new energy to be consumed.
Grid-built inverters are not yet being used on a large scale and have only been tested on a small scale, but in January 2022, the UK energy regulator Ofgem signed off on a technical standard that will drive the deployment of grid-built inverters on a large scale. Julian Leslie, Chief Engineer at National Grid UK, predicts that large-scale grid-built inverters will be deployed within two years.
New energy is a major trend, and the UK's problems and ideas for solving them are worth learning more from. Standing on other people's shoulders, we can bend the road to overtake the car, and the latecomer to the top!
