Before long, it will be cheaper to build new wind and solar plants than continue running coal-fired power stations in every major market worldwide. The idea of a fully renewable electricity grid is no longer a pipe dream. But as energy utilities race to decarbonise, they’re heading towards a new problem. As electrical systems are becoming more dynamic – with electricity generation more spread out and decentralised across many sources – it becomes harder to balance supply and demand, risking blackouts. And fossil fuel powered turbines provide a way to balance the system that renewable generation doesn’t. Fossil fuel power plants use steam from burning coal, oil or gas to turn a turbine connected to a generator, producing electricity. The electrical power taken out by the grid must be matched by the power put into it by the turbines, but demand rises and falls throughout the day. As the steam power input takes a little while to increase or decrease to match demand, there can be an imbalance. All the rotating parts in the turbine and generator effectively store kinetic energy. When there is a sudden increase in electricity demand, there will be more energy being taken out of the system in the form of electricity than coming in from the steam power. When this happens, the rotating masses in the turbine and generator slow down, giving up some of their energy. This allows time for the power supplied by steam to increase to match electrical demand. But as large amounts of renewable energy generation are introduced to electrical grids and fossil-fuelled plants close down, the system loses this short-term storage provided by the huge spinning rotors of the power stations. This means that grids run on renewable energy would struggle to balance supply and demand throughout the day with backup energy. It all comes down to what we call inertia, the process of slowing down how quickly things can change. The buffer energy stored in fossil fuel power stations provides inertia, buying time for the system to adjust to match supply and demand. Renewable-based grids don’t have the same levels of this buffer energy built in.
The Conversation 23rd March 2020 read more »