Intermittent weather-dependent sources of electricity need backup storage to compensate for gaps in production. Elon Musk has promised that Solar + Powerall batteries ensure that your home will never lose power. In this episode, returning guest Mark P. Mills breaks down the concept of energy storage, the physical requirements and limitations of our current storage technologies, and what to expect in the future.
Batteries will play an important role in the future of the grid and will continue to improve. However, the laws of physics and chemistry dampen some of the magical thinking that surrounds batteries, putting limits on their efficiency and energy density as well as demanding dramatic increases in mining if lithium-ion batteries are chosen for grid-scale storage.
In a purely wind/solar grid, storage must be able to bridge days-long periods without sun or wind, which occur several times per decade in North America. Currently, all the grid-scale lithium battery storage in the U.S. could keep the country powered for just 20 seconds.
This contributes to the economic reality that battery storage is unlikely ever to be cost-competitive with the storage of fossil fuels. While wealthy nations may be able to afford to go further down the path of a "green energy" transition, these costs will be prohibitive for poor countries. The fragilization of the grid and the crises of reliability that are beginning to impact states with a high penetration of wind and solar, like California, are beginning to create some of the characteristics of a third-world grid, such as a skyrocketing demand for gasoline backup generators (learn more about Nigeria's backup generator situation: https://www.energyforgrowth.org/memo/the-love-hate-relationship-with-self-generation). This is an impending disaster for a state pursuing an "electrify everything" agenda. 
An outcome of the high costs and impracticality of using batteries to back up intermittent generation is that grids with high renewable penetration have built parallel generation portfolios: one low-carbon, and the other, in the absence of abundant hydro or nuclear, dominated by fossil fuels. 
The renewables portfolio spares some fossil fuels, but it doesn't displace the need for maintaining fossil generators to run when it's not windy or sunny. This is why Germany, despite spending 500 billion euros on renewables, has kept 70% of its coal-dominated fossil fleet and is continuing to build natural gas infrastructure such as the Nordstream 2 pipeline.
Dr. Keefer and Mills also reflect on the timescales of innovation and the (un)likelihood of achieving ambitious 2030 decarbonization goals; the concept of "energy Lysenkoism"; the geopolitics of China's energy policy; and Mills' forthcoming book, The Cloud Revolution.
Mark P. Mills is a senior fellow at the Manhattan Institute and a faculty fellow at Northwestern University’s McCormick School of Engineering and Applied Science, where he co-directs an Institute on Manufacturing Science and Innovation.
Apologies for connectivity issues throughout the interview that garbled some of the audio.