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"The US has about a fifth of he world's total pumped water capacity of 100 megawatts of power."

A typo surely? 100,000 megawatts...

The many ways of measuring energy stored is maddening when you try to figure out how to compare. British thermal units, barrels or tonnes of crude oil equivalents, cubic feet or meters of natural gas, and so on. No wonder journalists gets the basics wrong. The same is true in economics. Today a story is floating around the internet that the inedible Apple is worth more than Chicago, a classic failure of comparison of a stock with a flow, as well as earnings with revenues.

Not being a physicist I like watt-hours, perhaps because i fancy a future based on electric power, with most storage turned into electrons eventually.

Talking stocks and flows do you know of this? The human flows of the planet graphed: http://ivarref.github.io/bp-diagrams/?country_code=BP_WORLD&mode=total
China: http://ivarref.github.io/bp-diagrams/?country_code=CN&mode=total


No mistake. Power stations on the grid, solar panels on the roof, fuel cells and secondary storage batteries are rated in terms of the power they can supply (watts). There is a constant balancing of load and capacity and power is the relevant measure. For standby or stored power the next important metric is the ramp curve - how quickly a station can supply or shed power - measured in megawatts per minute for gas turbine generators and megawatts per second for faster sources like flywheels. The shape of the curve is very important and known by the humans and computers that balance the grid. Of course cost comes into the game and varies widely depending on the source type and demand. For storage like pumped hydro or batteries the time it can run - the amount of energy it can store in MWh - is of important, but complicated and varies widely depending on technology and load. It's understood by the operator, but is not as important as power capacity,

Sort of like cars and horsepower/kw and gallons/kWh of fuel


According to the DOE there is 168 GW of pumped hydro in the world. Wiki source: https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

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