Solar and wind are rapidly emerging as clean energy sources in the U.S., accounting for about 19% of energy generation today and potentially reaching over 40% by 2030. However, these renewable energy sources will depend on gas for decades to come. Solar and wind are variable renewable energy (VRE), meaning they only produce electricity when the sun shines or the wind blows. This variation can be predictable or unpredictable, such as cloud cover or wind droughts lasting weeks at a time.
Electric utilities are adding short-duration lithium-ion batteries to address daily and hourly variation, but these batteries only solve VRE deficits for a few hours at a time. Longer duration VRE deficits are another concern, as sustained periods of poor weather can lead to annual shortfalls as high as 20% of total grid production in a completely decarbonized grid.
To address VRE deficits, peaker plants, gas plants that run on a single cycle to power turbines for electricity, are used. These plants are less efficient than combined cycle gas turbine plants (CCGTs) and are paid to provide spare capacity, ensuring sufficient emergency power is always available. However, as VRE becomes a larger share of the overall grid, the impact of adverse weather events will become more pressing, and supply will become more variable. A grid with 40% VRE will need much more insurance to guarantee the lights stay on.
There are alternatives to gas-fired energy, such as hydrogen, hydropower, and compressed air. Hydropower is cheap to run, a mature and well-established technology, and its generators last for decades. However, there is no U.S. appetite for the dozens of huge new dams needed for this transition. Green hydrogen suffers from low efficiency, is expensive to make and store, and can cause serious emissions. Compressed air currently operates at about 50% efficiency, and electro-chemical batteries won't provide the combination of long duration, huge scalability, and low costs needed.
To make a VRE-dominated grid possible, natural gas must be used as insurance against VRE deficits. The function of gas power will change, as CCGT plants shift from producing baseload power to providing insurance against supply disruption. Eventually, we can hope to build a green grid with no emissions, with gas emissions eventually phased out altogether. To achieve this, a realist view of the near and medium term, a massive financial commitment to develop critical technologies, and a realistic understanding of the changing but still critical role of gas in a decarbonizing grid are needed.
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