Leonardo Rydin Gorjão and Jacques Maritz
Cape Town - Power grids are the backbone of society’s electrical systems.
These large human-made networks provide electrical power to consumers worldwide, from the most minor households to the largest sprawling cities.
To generate this electrical power, power generators – conventional, like fossil-fuelled power plants, or renewable, like solar and wind power plants – are scattered throughout a power-grid system.
In the past two decades, power-grid systems have evolved tremendously.
Profound innovations surrounding solar and wind energy have turned what were once unprofitable energy sources into some of the most competitive power generation systems in the world.
In today’s world, most renewable energies, like photo-voltaic and wind turbines, are more cost-effective than all fossil and nuclear generation.
People and governments around the world now recognise the necessity of transitioning to renewable sources – not only due to their economic competitiveness, but also due to their low carbon emissions, which is inextricably connected to our ongoing attempt to mitigate climate change.
As more renewable energy systems enter a country’s “energy mix”, the more important it becomes to understand the impact of renewable energies in power-grid systems.
Power grids were created under an architecture wherein power flew from centralised and localised power sources as large conventional generators – usually located far from the larger cities, wherein most power was consumed.
These were not necessarily designed for small-scale, decentralised and distributed renewable energy sources scattered throughout the systems.
Yet the ongoing energy transition has now made it possible for consumers around the world to buy a solar panel to place on a rooftop and become self-powered.
In some cases, even independent from the grid.
Although this is a very positive outcome of the energy transition for society, we need to tend to the technical implications it brings to the operation of the power grids.
Operating a power-grid system, that is, monitoring, controlling, adapting, improving, and extending a power grid, is not a new task.
Power-grid system operators and governments have been doing so ever since power grids were first created.
What has changed is precisely the nature of power generation. As we transition to a “greener energy system”, we have to contend with its intricacies.
Most renewable generation types are intermittent. This means that their power output can vary very quickly and unpredictably. Moreover, it also means that the availability of power can be drastically different in a week from today.
Two very good examples of these involve solar and wind generation.
While the position of the Sun in the sky is well known, the movement of clouds is less so. This makes solar generation difficult to forecast.
Similarly, the nature of wind speed lends itself to changes over weekly periods: where today the wind may blow fiercely, in a week there might be a calm.
This does not need to be read as a drawback to the use of renewable energies. From a technical standpoint, the intermittent nature of renewable energies is an issue that we can and know how to tackle.
It is precisely here that science – from mathematics to physics, economics to engineering – enters the fray.
Let us take an example from wind energy. To understand the nature of wind movements we inherently delve into the realm of fluid dynamics. This is a topic that covers the aspects of the movement of fluids – which, in physics, also covers gases or, plainly, air.
It is also the domain where we deal with turbulence, and turbulence in and around wind turbines can have a significant negative impact on the turbines.
For one, under less favourable circumstances, turbulence can substantially reduce the power output of a wind turbine.
In the worst scenario, the fluctuations induced by turbulent wind can severely damage the blades of the turbine. Overall, understanding the nature of turbulence – one of many topics in physics – becomes crucial in power grids.
We similarly have a case for fluctuations of voltages and frequency in power-grid networks. These networks comprise all generators and consumers in a given country or area. From a physics standpoint, each element in this system works in tandem with each other, pushing and pulling depending on its energetic needs, yet they all do so in tight synchrony.
Deviations in such synchrony are cause for disruptions – and can lead in the worst case to total blackouts.
Within physics, we seek to understand what changes in each element cause the largest (negative or positive) impact on the power grid.
We seek to understand which faults or defective transmission lines could lead to a total blackout. Where most work is present to mitigate catastrophies, we can also use physics – the physics of power flows – to try to improve the quality of power delivered, studying how to reduce loads on already overloaded lines by adjusting the current power grid.
In this short article, we cannot cover all the domains in which physics can and does play a role in understanding and improving power grids –from fault detection, synchronisation, and optimisation, to developing control mechanisms and understanding fluctuations, to name a few.
We can, however, highlight that physics – as many other natural and social sciences – plays a crucial role in developing and improving modern power-grid systems.
Professor (associate) Gorjão is a researcher at the Norwegian University of Life Sciences and Dr Maritz is a senior lecturer at the University of the Free State