[tuatoru]

What are you talking about?

The very first chart in the article is titled "U.S. Battery Storage Capacity (2015-2025)", but the vertical axis is labelled "gigawatts".

Storage capacity is not measured in gigawatts.

Edit: yes, batteries also have a power delivery rating, but that is not what is implied by "storage capacity".

[epistasis]

Are you saying that you can't measure battery power capacity? Why would you assert something weird like that?

Grid assets are measured by power, and power is a key specification of storage capacity.

Edit in response to your edit: the EIA, and in fact all the people who run grids and the grid storage, refer to capacity in terms of power, and when talking about "storage capacity" on the grid continues to use power because it would be nonsensical and silly to switch to a not-so-useful energy unit rather than power unit when power is the key metric for grids.

[tromp]

> Grid assets are measured by power

That seems of limited use without knowing for how long the power can be supplied. 1GW for 1 second is pretty useless. 1GW for a minute not much better. Most people would say that 1GW lasting a day is more storage capacity than 10GW lasting only an hour.

Wouldn't batteries optimized for power take the form of supercapacitors [1] instead?

[1] https://en.wikipedia.org/wiki/Supercapacitor#Comparison_with...

[nl]

"Seconds" of capacity might be useful for "primary frequency response" but not for any of the other functions listed in table 1 of https://www.nrel.gov/docs/fy19osti/74426.pdf. Primary frequency response is only seen as important in a limited number of markets in the US (see that table).

[epistasis]

It turns out that the resources that get deployed in the grid are useful ones rather than something that deploys 1GW for 1 second. So referring to the power capacity, and dispatching based on power capacity, is how to make decisions when operators bus into the grid. At any moment, a power source may trip off, or decide that the price they are being paid is not high enough to justify continued operation.

The grid is an amazing, absolutely massive, machine for matching power at the generation and load sides. Power, of both the real sort and the reactive sort, are the name of the game.

As far as optimization for power over minimal capacity, the best use case for supercapacitors might be frequency regulation, but batteries have proven to be superior for that particular use case, with a few fly wheels also taking part.

[nl]

Their terminology is defined here: https://www.nrel.gov/docs/fy19osti/74426.pdf

I think it is mostly use correctly. They genuinely are talking about "the total possible instantaneous discharge capability" when they talk about "storage capacity increasing".

I think this is because in table 1 of the linked doc they list where batteries help the energy market and most are capacity (as in power delivery capacity) limited, not stored energy limited (ie most of the uses are measured in "hours" of stored energy or less. In general it reads as the limiting factor is power capacity, not energy storage capacity).

I do think the graph in the linked article (https://www.eia.gov/todayinenergy/detail.php?id=54939) should use terminology consistent with https://www.nrel.gov/docs/fy19osti/74426.pdf though.

[heavenlyblue]

If you think of this as "the capacity of power we can generate at any given moment due to these batteries" then it makes sense. Just the same way as you would say "hydro power capacity"