Inertia and the Unintended Consequences of More Renewable Power Deployment
The following is a Q&A session with Chris Kimmett, Commercial Director at Reactive Technologies. The subject is inertia and the unintended consequences of more renewable power deployment, mainly wind and solar technologies.
Q: What is grid inertia, and why does it matter?
A: Inertia is the physical force created by large, spinning pieces of metal such as turbines in hydro, gas, coal and nuclear power plants, which act like a stabiliser for the grid and allow it to ride through short term issues. A good analogy is that its like a steam train which once moving will carry on in the same direction without much input.
Renewable energy sources like wind and solar power are non-synchronous, meaning they don’t generate inertia and as a result power grids around the world have dealt with decreasing levels of inertia as the prevalence of clean energy generation has increased. To continue with our analogy a little further, they are more like a motorbike with a greater need for fast balancing actions to keep the grid on track. With declining inertia, electricity networks have become more volatile and required increased investment to avoid increasing the risk of power outages.
2020 has seen some substantial drops in electricity demand and as a result a higher percentage of renewable energy sources on the grid. As demand ramps down, fossil fuel generation is often the first to drop off the grid given its high marginal cost relative to renewable sources. But due to the intermittent and non-synchronous nature of technologies like wind and solar, this shift has meant that many power grids in then US are experiencing the lowest inertia conditions they have ever experienced.
This presents regional transmission system operators with a challenge of maintaining grid stability in a situation few have experienced previously.
Q: How do you measure inertia – and what can you do with those measurements?
A: Power grid inertia has previously never been accurately measured, and was instead estimated based on various assumptions. As we move towards a much more dynamic energy system, these assumptions are becoming less reliable, putting grid operators in a difficult position. Noting the proliferation of renewables on the grid and a lack of reliable, real-time data, Reactive Technologies developed a platform with National Grid UK.
By using an ultracapacitor to send tiny pulses which are picked up by sensors throughout the system, the measurement system, GridMetrix, can detect the level of inertia at any given moment. That information is then analysed in the cloud and sent to the system operator’s control centre in real time.
Understanding and measuring inertia allows grid operators to bolster system security and avoid blackouts, minimising risk of faults and reduce balancing costs. Real-time visibility of critical network conditions will also help to facilitate the energy transition by empowering TSOs to make key commercial and operational decisions faster, safer and more cost-effectively. Without it, system operators may be forced to cap renewables integration or curtail output in lieu of fossil fuels.
Q: How does inertia impact grids in the United States?
A: Recently, the United States has seen renewable electricity generation overtake coal for the first time during the pandemic. This has accelerated the need for ISOs and RTOs to improve their understanding of network conditions and how to manage them, given the issues that increased renewables penetration can cause for grid stability. This is particularly important for many regions in the US, especially those with ‘islanded’ grids in Hawaii and Texas, unconnected to any others, as well as those states that have implemented ambitious plans for carbon emissions targets or 100% renewables generation such as California or New York.
Q: Does inertia measurement make it possible to achieve a 100% renewables grid?
A: Inertia measurement will become a crucial component of allowing system operators to achieve a 100%-renewable grid and sits alongside a broader package of measures and technologies that will need to be implemented. These include the introduction of new sources of synchronous inertia in the form of condensers or “artificial” or “synthetic” inertia from utility-scale battery storage to help balance supply and demand on the grid. It allows TSOs and regulators to understand the way their systems operate so that they can build and adapt them to a future with higher renewables integration. TSOs still need a strong toolkit of both technological and regulatory solutions – from higher energy storage adoption to innovative market design theories. However, without fully understanding network conditions, grid operators won’t be able to take the steps necessary to integrate renewables safely, cost-effectively and reliably.
Chris Kimmett is Commercial Director at Reactive Technologies.