Estimates vary. This study [1] calls for ~1,700 TWh of storage globally (and proposes that synthetic methane be used for that storage, but this requires a way o

Estimates vary. This study [1] calls for ~1,700 TWh of storage globally (and proposes that synthetic methane be used for that storage, but this requires a way of separating and storing carbon dioxide out of gas turbine exhaust which doesn't yet exist). This study [2] calls for 3 weeks energy usage to reach 100% renewable energy consumption. A compromise of only 80% renewables would only require 12 hours. But that still leaves 20% unaccounted for. And even this more modest figure is still massive compared to what batteries can deliver. My numbers above weren't correct. The US consumes 4,000 TWh of energy annually [3] which works out to 11 TWh daily not 4TWh. half of that would be 5.5TWh, which is still more than 18 times the current global lithium ion battery production. Declining cost of solar does nothing if there's no way to store that energy. Daytime energy use is already saturated in many markets. This a big reason why German emissions have remained mostly flat for the last 5 years despite substantial increases to solar power. Energy isn't just a matter of installing X watt-hours of capacity. It's about delivering energy when it's needed where it's needed. Heat engines are the only way we know how to do this reliably (hydro and geothermal too, but those lose out on the "where" part). That's why the only country that have successfully gotten their electricity generation to mostly non-carbon sources without geographically dependent sources is France. They use heat engines, but with a non-carbon source of heat (nuclear energy). 1. https://www.sciencedirect.com/science/article/pii/S1876610214001702 https://www.sciencedirect.com/science/article/pii/S187661021... 2. https://pv-magazine-usa.com/2018/03/01/12-hours-energy-storage-80-percent-wind-solar/ https://pv-magazine-usa.com/2018/03/01/12-hours-energy-stora... 3. https://en.wikipedia.org/wiki/Energy_in_the_United_States#Consumption https://en.wikipedia.org/wiki/Energy_in_the_United_States#Co...