Wind and solar share of global electricity generation, 2050

But relying on variable energy sources for two thirds of global generation raises an obvious question: How do we keep the lights on when the wind doesn’t blow and the sun doesn’t shine?

While there’s no single (read: simple) answer, three key insights help us understand how to maintain a stable supply of power when relying mainly on variable renewable energy sources:

1) Solar and wind are key – but not the only solutions

The challenge is not just replacing coal and gas with solar and wind – it’s about building a new, smart, and integrated energy system.  And while solar and wind will play a significant role, the future green energy system will be based on a multitude of sources. Solar and wind will be complemented by energy sources such as hydroelectric generation, biogas, and sustainable biomass, as well as geothermal heat or even wave or tidal energy, to form a diversified mix of renewable energy. All these energy sources can be combined with pumped and battery storage, while hydrogen and Power-to-X solutions, which will make up an increasingly large share of power consumption, can run when energy is abundant and turn off when it's scarce.

All the above will be tied closely together, physically by expanded and interconnected regional grids, and digitally by automated demand-response applications.

2) Decarbonisation means electrification

Electricity and heating make up about one third of global energy-related carbon emissions. And while it’s crucial to mitigate emissions from existing power production, the remaining two thirds – transport, manufacturing, and construction – are just as important.

These uses must be decarbonised by replacing fossil fuels with electricity –also known as electrification – either directly, for instance through the use of electric cars or heat pumps, or indirectly by using electricity to produce green fuels.

Taken together, the energy needed for direct and indirect electrification outweighs the electricity we use today. In other words, we’ll need a lot more renewable power. In Europe, for example, power demand is expected to increase by as much as 150 % from approx. 3,200 to 8,000 TWh/y by 2050, according to studies by the European Commission.

But won’t adding even more renewable generation from wind and solar PV just increase variability challenges? Actually, no, as most of these ‘new’ types of electricity demand are far less dependent on when power is used, thereby adding flexibility on the demand side, which can balance the variable supply of energy.

For instance, electric vehicles can be charged at night or when power is available, serving as a ‘virtual battery’ in the grid. Heat pumps, while to a lesser extent, have the same capacity. And hydrogen-based e-fuels can serve as a flexible offtaker – and in principle as energy storage.

3) Connected markets create an even smoother supply

A final important part of a future energy supply based on high shares of solar and wind is long-distance transmission and interconnection. Establishing or expanding connections between price zones will, all other things being equal, improve resiliency by introducing more diverse sourcing options. But when viewed over a larger region, interconnectedness also helps offset variability caused by local weather patterns and increases predictability.