[hirsin]

For some reason grid storage reporting always seems to use a power metric instead of storage metric, which makes no sense to me. I've seen this in a half dozen stories, and found that even the government reports do this. I think it stems from someone reusing a column to represent both storage and power across generators and batteries.

[danans]

> For some reason grid storage reporting always seems to use a power metric instead of storage metric

Grid scale batteries are used primarily for real time demand management, and therefore their most relevant property is how much immediate power they can output and for how long. If they were only described in terms of energy (i.e MWh) without separating the power and time components, then it wouldn't be clear how much immediate value they could provide to the grid.

It's analogous to how in an EV the max horsepower is determined in large part by the power output rating of the battery, but the range is related to the the energy capacity.

[ssl-3]

>their most relevant property is how much immediate power they can output and for how long.

You listed two properties there.

Only one of these two properties is present in a figure that is solitarily presented as "10,000 megawatts."

We can tell this because only one property is presented.

And because it is a very-clearly ambiguous and singularly-useless instance of a unit that sees frequently-erroneous use, we do not know if this singular figure relates to "how much" or if it relates to "how long."

It probably relates to one of them, I'd suppose.

However... we do know that it cannot relate to both things, as-presented. The singular property presented can't even be extrapolated to relate to both things.

[danans]

> The singular property presented can't even be extrapolated to relate to both things.

Both things aren't equally important.

The energy capacity of the battery isn't provided for the same reason that coal plants don't specify the size of their coal piles or hydro plants don't specify the potential energy storage capacity of their reservoirs.

Power is the most relevant property to the real time operation of the grid, and the specification of power (and not energy). The grid operators need to know how much power a battery (or other generation source) can provide, and for how long. That tuple <power, duration> what any dispatchable energy source ultimately bids onto the real-time electricity markets.

The energy storage capacity of a battery is a function of what energy market it is designed to fit into.

For example, a battery that primarily functions in the frequency regulation market (modulation of supply and demand every few seconds) doesn't need a lot of storage capacity, but needs high power output. In contrast, a battery that shifts supply over the course of a single day might need more capacity (4 hours).

From the grid operator's perspective, the storage capacity is an implementation detail of the particular power source, or at least a secondary consideration.

[icehawk]

> For example, a battery that primarily functions in the frequency regulation market (modulation of supply and demand every few seconds) doesn't need a lot of storage capacity, but needs high power output.

For ERCOT this is fixed as a hard requirement so there's no point in specifying the time-- it's all going to be the same. For example:

> Fast Frequency Response (FFR) – subset of RRS

> – Must be capable of sustaining its required response for at least 15 minutes (if necessary)

[ssl-3]

> The grid operators need to know how much power a battery (or other generation source) can provide, and for how long.

Sure do! They definitely need all both of those things! One thing, by itself, is definitely not enough information! Agreed. Absolutely!

But only one of those figures was presented here, and this here [waves arms around] is the context of the discussion.

And one figure is fewer than two figures, would you not agree?

[danans]

> Sure do! They definitely need all both of those things!

When a generation provider bids supply onto the grid, it doesn't tell the operator what the maximum storage capacity of its equipment is, it tells the ISO how much power it can output for a given time frame (or alternatively how much energy it can deliver during a timeframe).

That is different that the total energy storage capacity of the battery itself, which is what I think you asked for.

The grid operator usually pays more attention to the former when it comes to day to day grid stabilization, and especially so for batteries, because batteries today don't do long term energy storage.

[ssl-3]

Yep.

It's a measure that makes perfect sense for conventional electricity production: 10,000MW of aggregated coal generation can hypothetically produce 10,000MW more-or-less indefinitely, as long as it keeps being fed things like fuel, water, and maintanence.

But it doesn't make any sense at all, by itself, for energy storage: A net 10,000MW battery might be able to produce 10,000MW, but for how long can that output be sustained? Unlike a group of coal plants, it absolutely cannot do this indefinitely; at some point, that battery will become completely discharged.

It takes at least two figures to describe a working bucket of energy (whether that bucket is Lithium cells or pumped storage or whatever): The capacity (megawatt-hours is a fine figure here, and units like Joules also work), and the maximum input/output (and plain megawatts works fine for this part). Using only one figure doesn't really describe anything at all.

I don't know when or why we stopped doing this, but it's misinformative in a way that leads to a bad generalized understanding of the these concepts with the populace that is actually paying for all of this stuff.

[icehawk]

Its fine as long as the amount of time it can provide rated output is longer than it time it takes to bring replacement generation capacity on line.

I don't care how long my UPS will actually last as long the holdover time is long enough to cover the time it takes to deal with all of the foreseeable problems in starting up the backup generator.

[ssl-3]

I don't think that grid-scale batteries are working with consumers on the grid in the same way that your home UPS is with you in your house.

Perhaps most-obviously: Consumers who are suddenly running on grid-scale batteries have no idea that this is a thing that is happening. There's no signal for them to shut their stuff off -- automated, or not.

It's a whole different paradigm than your UPS under your desk is: With your UPS, your system(s) receive a signal that things are running on local battery, and you've elected to configure things to use that signal to order an automated shutdown.

But, again: That doesn't happen with the grid-scale batteries under discussion -- at all. You're comparing apples to dildos here.

(Which is not to say that grid-scale batteries offer new opportunities for power cuts, because the opposite of that is true. It is instead just to say that unknowingly using grid-scale batteries is nothing like monitoring a local UPS is.)

[icehawk]

> It's a whole different paradigm than your UPS under your desk is: With your UPS, your system(s) receive a signal that things are running on local battery, and you've elected to configure things to use that signal to order an automated shutdown.

The setup you described there wasn't the situation I was describing at all.

I was describing a situation where there is utility power, a UPS, and a standby generator. When the utility power goes out, the generator has to start, stabilize, and only then can the load be transferred off the battery.

The requirement is that the UPS meet this current power demand for longer than the generator start up and transfer time (the "holdover time" I was speaking about in the previous post.)

For things like frequency response the holdover time is a fixed requirement. ERCOT requires all energy storage resources be able to maintain output for 15 minutes.

[pixl97]

I mean during the great texas power outage natural gas plants ran out of fuel because of supply issues that were not typically supply issues it would be more honest if every power plant also listed it's on hand 'fuel battery'. Now I'm sure they may do this with ERCOT, but it's not something typically reported.

[ssl-3]

Why, sure. It would be good to know how long a conventional generator can keep running when everything around it has gone wrong. For coal, for instance, that might be represented by the mass of the piles of coal that are normally on-hand -- or by the electricity (in MW-h, say) those piles of coal should be able to produce. Having this information close by would seem to be a good thing for an organization like ERCOT, so as to be factored into their emergency playbook.

But that's still a different case than a battery, wherein: Even if everything is going right, using energy from a battery must eventually cause it to become depleted.

It's never like a coal plant that (ideally) consumes fuel at one end, and spits out electricity at the other end as a continuous process. A battery, in this context, can be in a charging or a discharging state, but it can never be in both of those states at the same time -- using a battery is not at all a continuous process.

[RecycledEle]

> I think it stems from someone reusing a column to represent both storage and power across generators and batteries.

It comes from idiots who can not math being allowed to participate in our society. We should correct this error.