Never noticed until things go wrong, grid operators around the world work second-by-second to balance demand for electricity with supply.

That means keeping tabs on power stations, solar farms and wind turbines. It means watching the weather forecast to predict when people will turn the heating on and the TV schedules for when sports fans will open the fridge for a half-time drink.

As our sources of electricity change from fossil fuels to renewables, grid operators are changing the way they work too. “It’s a big technical challenge,” says Montana State University electrical engineering professor Rob Maher.

Under the old model, fossil fuels are burned in power plants. These are usually built close to where that electricity is needed, in cities or industrial hubs, and ramp generation up and down to meet demand. Vast amounts of coal, oil and gas are transported from mine or well to power plant by road, rail, canal and sea.

In the new world of increasing renewable penetration, where and when electricity is generated shifts. Solar panels are distributed across rooftops, while large-scale wind and solar plants are sited in windy and sunny spots, which may not be close to urban centres. As climate delayers love to point out, the sun doesn’t always shine and the wind doesn’t always blow.

The old ways were not perfect for energy security. Supplies of fossil fuels have been disrupted by frozen pipelines, blocked canals, terminals on fire, strike action, conflict and international sanctions. A mechanical failure at a conventional power plant can take a big chunk of supply offline.

Renewables are more resilient in many ways, but raise different challenges, calling for different solutions. With the G7 countries planning to completely decarbonise their power systems by 2035, flexible storage and grid upgrades are key.

Electricity storage

Part of the answer is to store the power from when the sun is shining and wind is blowing so that it can be used when they are not. Batteries can store energy in this way. That’s how your battery-powered remote control works without relying on any power station or solar panel.

Doing this on a large enough scale is a challenge. The International Energy Agency estimates that the world needs 585 gigawatts of battery storage by 2030 to reach net zero by 2050. Currently, it has 17GW.

According to Centre for Research on Energy and Clean Air analyst Xing Zhang, battery technology is currently “not mature enough to provide a base load of electricity to step up when needed”. The IEA says “a rapid scale-up is critical… to address the hour-to-hour variability of wind and solar”.

Another way of storing electricity is pumped hydro. This is where water is pumped from a lower reservoir to a higher reservoir when electricity is in abundant supply. It’s then released when electricity supply is low. It spins a turbine to generate electricity. This is how the US stores 95% of its energy and the department for energy says it’s “vital to grid reliability”.

Transmission lines

Variability can also be managed by connecting one grid to another. So, if the UK needs to buy some electricity because the wind isn’t blowing then it can buy some from France, where there may be an excess of power.

Grids are linked to each other through high-voltage cables called interconnectors. The UK’s has links to France, Belgium, Norway and the Netherlands and is building a new one to Denmark.

China has built thousands of kilometres of ultra high-voltage transmission lines to transport electricity from wind and solar farms in the west to where most people live in the east.

A recent Princeton University report found that the US needs to double the rate at which it builds transmission lines to fulfill the potential of its Inflation Reduction Act climate legislation.

Similarly, a report from the Center for Social and Economic Progress, found that India needs to build transmission lines to bring solar power from the west and wind power from the south to the rest of the country. This will be made easier, it found, by the fact that India has only one grid.

In February 2021, the US state of Texas showed what can happen when your grid is not connected. The US regulates electricity grids which are connected to other grids. To avoid regulation from Washington, Texan politicians decided not to connect their grid with others.

Then the weather turned unusually cold. Demand for power skyrocketed and energy infrastructure froze, causing power outages across the state and leaving Texans shivering in their homes. Because their grid wasn’t connected to the other states, they found it harder to buy in much-needed electric power.

While these outages were mainly caused by failures in fossil fuel infrastructure, the lesson was that an isolated grid is an insecure one.

Backup generators

As well as pursuing these improvements to the grid’s ability to handle renewables, many governments around the world are looking to non-renewable sources to provide backup power. This can be anything which isn’t weather-dependent and can be turned up and down by humans, usually by making their turbines spin faster.

There are options which don’t contribute to global warming including nuclear and geothermal power. Hydropower is vulnerable to drought, but as long as there is enough rainfall to keep the level of reservoirs up, can be dispatched on demand.

Polluting options include fossil fuels like coal, oil and gas. Their effects on the climate can be lessened, although not eliminated, with expensive carbon capture and storage technology.

Governments have justified a range of projects on the basis of backup power. According to Zhang, China allows renewables developers to build coal-fired power stations alongside their solar or wind farms for this reason, classifying the combined projects as green energy.

The idea is that the coal-fired power stations can run at a very low generation rate when their power is not needed, Zhang says. “But, to be honest, you can’t go too low”, she says, comparing it to turning the cooking gas down to the lowest setting and it going out completely.

In California, Governor Gavin Newsom’s administration has built gas plants and diesel generators for use as a last resort, when renewable production is too low to meet energy demands.

“They are essentially like big aircraft engines,” Maher says. “The advantage is that they can be throttled up and down very quickly. But if what your goal is is to have more renewables sources then relying on natural gas turbines is perhaps not the most desirable outcome. But right now, that’s kind of the way it has to be done.”

South Australia, on the other hand, is tantalisingly close to proving that a grid mostly powered by wind and solar can run without fossil fuel backup. The market operator cut the number of gas generators from four to two last year and is looking to reduce it to one.

While critics of renewables focus on what happens when the sun isn’t shining or the wind isn’t blowing, there is a flip side. When the sun shines hard and demand for power is low, grid operators can sell it cheap or even pay businesses or households to use it.

Increasingly, smart technology allows business customers and even households to play an active role in balancing the grid, through demand response.

“The most important thing is to think about the cost-efficient integration of renewables,” says E3G researcher Vilislava Ivanova. “You can do that most efficiently with flexible power systems and that allows the consumers, providers and network operators to manage demand better in the future.”

Demand response will be explored in full in the next article in our four-part series on the future of energy. Main image: Stephen Edmonds/Flickr.