How Long Will Natural Gas Be A Bridge Fuel?

In a previous article, I addressed the reality that natural gas is already serving a bridge fuel between a past powered by coal and a future powered by renewables.

Today, I want to discuss the factors that will influence the length of that bridge.

Coal is a source of firm power, which means power that is guaranteed to be available when needed. This contrasts to wind and solar power, which are intermittent. They are available when the sun shines and the wind blows.

That means that intermittent power sources require much more installed capacity than do firm power sources to produce the same amount of electricity over time. The capacity factor — that is the amount of power produced divided by the power that would be produced if the power source was producing at full capacity at all times — is around 90% for nuclear power, 70% for geothermal power, and 50-60% for coal-fired and natural gas-fired power. But annual power factors for wind and solar power are in the 25% to 35% range.

This has two implications. One is that wind and solar power must have around double the installed capacity of firm power sources like coal to produce the same amount of electricity over time. But because these intermittent sources can sometimes see output fall dramatically, they must also have significant backup power supplies available.

Opponents of using natural gas as a bridge to a renewable future argue that batteries can fulfill this backup role. They see the role of natural gas as simply filling a balancing role for renewables in times of extreme mismatches between supply and demand. It is probably true that this is the long-term solution, but cost-effective battery technology isn’t quite ready to assume this role on a massive scale.

That’s why natural gas has become a bridge. But how long might that bridge be? We can look back at trends since 2000 and extrapolate with a thought experiment.

The U.S. generated 2.0 trillion kilowatt-hours (kWh) of electricity from coal in 2000, 611 billion kWh from natural gas, and about 6 billion kWh from wind and solar power.