What does the world’s largest machine do?

In February 7th, 1967, Homer Loutzenheuser flipped a switch in Nebraska and realized a dream more than five decades in the making. The power grids of the United States joined together, forming one interconnected machine stretching coast to coast. Today, the US power grid is the world’s largest machine. It contains more than 7,300 electricity-generating plants, linked by some 11 million kilometers of powerlines, transformers and substations.

Power grids span Earth’s continents, transmitting electricity around the clock. They’re massive feats of engineering— but their functioning depends on a delicate balance. Their components must always work in unison, maintain a constant frequency throughout the grid, and match energy supply with demand. If there’s too much electricity in the system, you get unsafe power spikes that can overheat and damage equipment. Too little electricity and you get blackouts.

So, to strike this balance, power grid operators monitor the grid from sophisticated control centers. They forecast energy demand and adjust which power plants are active, signaling them to turn their output up or down to precisely meet current demand.

By considering factors like the availability and cost of energy resources, grid operators create a “dispatch curve,” which maps out the order in which energy sources will be used. The grid defaults to using energy from the start of the curve first. Usually, the resources are ordered by price. Those at the start tend to be renewables because they have much lower production costs. Some grids, like those in Iceland and Costa Rica, run on more than 98% clean energy. But most dispatch curves contain more of a mix of carbon-free and carbon-emitting energy sources. This means that where your electricity is coming from— and how clean it is— varies throughout the day— as often as every few minutes.

Take the state of Kansas. Despite having plentiful wind resources, it regularly relies on carbon-emitting power plants. This is because wind energy is especially plentiful at night. But, this is also when there’s lower demand. So, Kansas’ is wind energy is actually regularly disposed of to prevent excess electricity from damaging the grid. And comparable scenarios add up to a big problem worldwide. Thankfully, dependence on renewables is rising. But power grids are often unable to make full use of them.

Many simply weren’t designed around intermittent energy sources and can’t store large amounts of electricity. Researchers are experimenting with unique storage solutions. However, this will take time and substantial investment. But hope is not lost. We have the opportunity to work with our existing power grids in a new way: by shifting some of our energy use to the times when there’s clean electricity to spare. Leaning into this concept, called “load flexibility,” we can help flatten the peaks in demand, which will place less stress on the grid and reduce the need for non-renewables.