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Comment by bcatanzaro | Hacker News Reader

Of all the non-metric units in use today, watt-hours has to be the worst. It causes so much confusion. A Pulitzer Prize winning institution reporting on our climate and energy crisis can’t get it right: “Over the past three years, battery storage capacity on the nation’s grids has grown tenfold, to 16,000 megawatts.”

Gigajoules were right there!

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Power plant generation is usually described in watts, because the amount is usually constant (barring solar and wind) as needed.

Grid scale batteries are treated as alternate supplies of energy, but yes, they are storage, and cannot indefinitely run at a constant output.

That's the confusion. Directly comparing them is not useful, except when describing a finite time span.

Gigajoules doesn't really help clarify the confusion, because it doesn't change that they're not directly comparable.

For batteries you need two measures at minimum: power (what you can get out when the battery is fully?/half?/?? charged) and energy. But there's more because a battery's power output might not be stable, and it might not be linear with remaining charge.

The article says "battery storage capacity" - the plaintext reading of this is referring to energy and they messed up the units. As per usual.

Don't stop reading there! The next three words are "on the nation's grids" (at least in the first occurrence of the phrase). When dealing with grids, capacity always refers to power measurements.

The journalists did not mess up anything, they are actually using the correct units used by people who run grids, build grid assets, plan grids, etc. The only people who are confused are those who don't know about grids, but know a few things about electricity in other contexts.

No, you're actually reading it wrong. Its a unit of power, not energy. You can follow the link on that line and see the EIA also using watts.

It's talking about the ability to supply power to the grid, not how long it can supply that power. It's arguable how useful a measure that is but they're certainly using it correctly. IMO they're also talking about it in a reasonable way- capacity and power are pretty closely related for batteries, and the ability to pick up demand is critical to handling instability.

It says "battery storage capacity". That is a description of energy.

> Of all the non-metric units in use today, watt-hours has to be the worst.

Watts are SI, hours are used all over metric countries. I don't see how watt hours aren't metric?

Watt-hours are inconsistent with the relatively standard meter-kilogram-second system. The joule is a watt-second and fits with MKS, but nobody is using that term for grid energy -- because hours are generally easier to work with.

I have, however, seen fellow laypeople regularly confuse power with energy (describing kW when they mean kWh and vis-a-versa) as OP thought the quote did. I'm not sure if sticking to kW and kJ would actually fix that.

Inches are metric as well in that definition. Just meters multiplied by a constant.

3600 seconds in an hour. 39.3700787402 inches in a meter.

Next you'll be telling me pounds are more convenient than kilograms.

The MW measurement for batteries is an important metric. The maximum power draw is important. If you only report one measurement it should likely be storage capacity (energy), but power is a close second.

It says "battery storage capacity". They're talking about energy and using the units for power.

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