Renewable energy production potential and energy demand do not often match up geographically or temporally, and no amount of flexible load or demand response can overcome this completely. For example, on a winter night in a polar vortex, there is no sunlight to produce electricity from photovoltaic panels. Asking people in the Upper Midwest to turn off their heat and risk frozen pipes isn’t a great solution. Fortunately, energy storage can solve this and similar issues.
When looking at future storage needs, the issue is not short-term energy storage, measured in hours; rather, it is saving energy from late March until it is needed in November. In the first nine months of 2020, California had curtailed more than 1 terawatt-hour (1 million kilowatt-hours) of energy. And in May 2020 alone it was 318 gigawatt-hours, according to California ISO. On May 20 alone, over 2 GW of solar was curtailed from 9 in the morning until 5 in the afternoon, a massive amount of renewable power potential lost. Solar today is 20% of California’s power supply and is scheduled to become 50% of total energy used in the state by 2045. The marginal value of solar — and the curtailment of solar — will increase as the percentage of intermittent supply increases in a nonlinear fashion. This means that by the time solar reaches 50% on some days, curtailment could be as much as 80% of possible production. Storage, rather than curtailment, is needed. And extended periods of storage would be even more valuable.
There are many types of energy storage, from pumped hydro and hot sand to ice-based thermal storage. Among the many types of storage, two that are very different from each other stand out as having the potential to have a massive impact on how the energy infrastructure evolves. One, lithium-ion batteries, is all the rage for vehicle propulsion and now is being touted as a way to store energy for everything else. The other is hydrogen.
Until 2018, batteries appeared to have a clear field for future transportation and electrification, storing excess renewable energy until it was needed. In the past few years, something has happened that may shift the tide. Hydrogen, dismissed by most parties in 2018, has seen investment in research and development that has increased the efficiency and lowered the cost of hydrogen-based energy significantly. The leading hydrogen production processes today are on par with some other battery round-trip efficiencies, and the cost per kilowatt-hour stored is much less for the production of hydrogen than for other batteries. The capital investment for capacity in kilowatts is still higher for hydrogen than batteries, but it too is being reduced. Holding hydrogen in existing underground storage is cheaper than batteries, and the life of an underground storage facility is decades longer than most batteries. Some salt caverns have been in use for underground gas storage since the 1940s.
A number of barriers exist both for battery technologies and hydrogen. This paper examines the barriers for each technology and compares them with the state-of-the-art answers for both technologies. At this time, neither technology is a clear winner or loser, but the scale is tipping from batteries clearly having the upper hand to hydrogen becoming a viable alternative.
There are hundreds of types of batteries and at least 16 ways to produce hydrogen. Some of the batteries and the methods of making hydrogen are ”greener” than others. All of the methods and batteries differ in detail, so the comparison has been generalized here, though detailed comparisons have been made by the author to develop this generalization.
To illustrate the two options, green hydrogen from renewable power — specifically polymer electrolyte membrane (PEM) electrolysis — and lithium-ion batteries with a 811 nickel- manganese-cobalt (NMC) cathode composition (80% nickel, 10% manganese, 10% cobalt) were selected as the generic technologies in Figure 1.