Yes, Words Can Have Multiple Meanings

I've been sick for a little while, and while it's not too bad, it has sapped me of almost all my energy. As a result, I was hoping to lie in bed resting and casually browsing the internet without any stress or need for coherent thought. That didn't work out. Instead, I wound up involved in an incredibly dumb argument.

It all started because of an unremarkable news article which discussed plans to install more battery storage capacity in the United Kingdoms electrical grid. Battery storage is primarily used for load balancing, where batteries are charged during periods of low demand so they can provide additional energy during periods of high demand. The use of stored energy for load balancing in electrical grids is commonplace and entirely unremarkable. When the article said:

Planning applications in the UK to install just 2MW of battery storage capacity in 2012 have soared since then to a cumulative total of 6,874MW in 2018. (92% of applications for storage projects are approved first time).

It should have been viewed as an innocuous statement the same as one might see in any of a hundred news articles. Instead, a number of "Skeptics" decided it was wrong. In fact, one decided it was not just wrong, but nefarious:

Why? Because they felt they get to dictate how the word "capacity" can be used. Yes, that's it. That's all this comes down to. According to them, when examining a battery, the "capacity" of that battery is the total amount of energy stored within the battery. And that's all "capacity" can mean. If you talk about "capacity" and "battery" at the same time, you better use "capacity" in that way or else.

This is nonsense. Words can, and often are, used in different ways depending on the context. When discussing a power plant or the individual generators within it, the most common thing to look at is its "nameplate capacity," or the amount of power it can potentially make. Power is the amount of energy that can be made/transferred in a particular amount of time. If energy were distance, then power would be speed.

Nobody disputes "capacity" is used in this way. The "capacity" of a generator will typically be the power it can produce. The "capacity" of a battery will typically be the energy it can store. As a result, "capacity" can be used to refer to power or energy. So what about a system which uses batteries to store energy like that described by the article?

Because the system involves batteries, we might want to know how much energy it can store, its "energy capacity." But because the system is used in the electrical grid for load balancing, we might want to know how quickly it can push that energy out onto the grid, its "power capacity." The result is the phrase "battery storage capacity" can refer to energy capacity or power capacity. To demonstrate this, here is a screenshot from a report by the Energy Information Administration (EIA), a government agency that collects, analyzes and disseminates information on energy issues:

This figure in the report is for the "U.S. Large-Scale Battery Storage Capacity by Chemistry (2003–2016)." The battery storage capacity is shown in two charts, one for "power capacity" and one for "energy capacity." The units for these are megawatts (MW) and megawatthours (MW/h). This same word usage can be found in numerous government reports, scientific papers, blog posts, etc. So when the article said:

Planning applications in the UK to install just 2MW of battery storage capacity in 2012 have soared since then to a cumulative total of 6,874MW in 2018. (92% of applications for storage projects are approved first time).

It should have been unremarkable. It was referring to power capacity (hence the units MW). The amount of power capacity given by battery storage systems is important because it determines how much of the electrical grid's load can be provided by them. It's not just battery storage systems though. There are a number of other energy storage systems used in the grid, such as pumped storage systems where excess energy from dams is used to pump water into an elevated reservoir to store it as potential energy (as it can be ran through the dam later). This is from the Wikipedia article on pumped storage:

In 2010 the United States had 21.5 GW of pumped storage generating capacity (20.6% of world capacity).[21] PSH generated (net) -5.501 GWh of energy in 2010 in the US[22] because more energy is consumed in pumping than is generated. Nameplate pumped storage capacity had grown to 21.6 GW by 2014, with pumped storage comprising 97% of grid-scale energy storage in the US. As of late 2014, there were 51 active project proposals with a total of 39 GW of new nameplate capacity across all stages of the FERC licensing process for new pumped storage hydroelectric plants in the US, but no new plants were currently under construction in the US at the time.[23][24]

The point is power capacity is a commonly used metric in the context of electrical grids. It shows up in pumped storage capacity, battery storage capacity, as well as other technologies. But some people simply won't accept that. No matter how many times I pointed people to sources like the EIA report, made by a government agency tasked with studying energy, some people simply insisted "battery storage capacity" could not refer to power capacity. They went so far as to say the government report was simply wrong in its terminology: Here are a couple examples:

With the exchanges happening on Twitter, especially with me being sick and exhausted, I am sure there were times I was less than precise/not completely clear in my remarks. However, I offered sources showing the terminology used by the article was normal, and nobody responding to me even attempted to offer anything showing it was wrong. It was just their say-so.

And no matter how poorly I might have phrased anything, it is clear people feel their opinion of how the word "capacity" can be used is so well based they could say official government reports are wrong in using it a way they disagree with. That is incredible. the EIA is arguably the most influential body when it comes to keeping up with energy issues. The idea the agency wouldn't know basic terminology of the topic it was covering strains credulity. If it were true, surely there would be tons of people who'd be willing to speak up and say so.

But no, it's just some random people on the internet. People who can't even seem to make a coherent argument. The person who responded to the figure of the EIA report saying "storage" should have been stricken followed it up with tweets like:

She said "storage" should have been stricken from the phrase "battery storage capacity" because, "Power cannot be stored." She then acknowledged "power capacity" is a real thing. Now, nobody had been claiming power capacity was the capacity to store power. The word "storage" was only used in the context of "battery storage." That is, systems which use batteries to store energy have a power capacity of X.

If she accepts battery storage systems can have a "power capacity," why would she insist the word "storage" should have been stricken from the header of a figure in the EIA report which referred to "battery storage capacity"? Even after acknowledging power capacity is real, she continued to insist the report was wrong in its terminology:

The article which started all this discussed plans to install new "battery storage capacity." I cited an EIA report's figure which showed "battery storage capacity" is a phrase used to describe both the "power capacity" and "energy capacity" of such systems. She responded by saying the report was wrong to include "storage" in the phrase "battery storage capacity." But consider what she argued a short while later, after I showed her Wikipedia's article on pump storage (as quoted above):

She acknowledges "pumped storage capacity" is a perfectly fine phrase. She acknowledges pumped storage capacity can refer to multiple things, such as power capacity and energy capacity. That situation is exactly the same as it would be with "battery storage capacity." But according to her, the fact I sometimes said "storage capacity" instead of "battery storage capacity" means I was entirely wrong.

Yet, how could that be? Her initial responses didn't say anything about dropping the word "battery" from "battery storage capacity." She started off by saying the word "storage" in "battery storage capacity" was wrong. That's the entire reason she said the EIA report was wrong. If the EIA was wrong for using the word "storage," then how was I wrong for saying "storage capacity" instead of "battery storage capacity"?

So exactly what was wrong with that article people condemned? Who knows. You won't find anyone criticizing it who will attempt to make a case showing it is wrong. They can't. The article's terminology is perfectly normal. But still, some people are determined to insist it is wrong. No amount of evidence or examples will make them change their minds. If you push the matter, this is all that'll happen:

Yup. That's Skeptics for you. Rant and rave about how wrong/stupid you are, and if you push back, block you so they don't have to hear what you have to say. Even if all you have to say is, "Hey, words can have multiple meanings."


  1. Unfortunately I can't read that article as it wants me to subscribe to do so. Can you share any excerpts that'd show why you linked to it?

  2. When I open the tweet in Chrome's incognito window (of course I've been blocked by you know who), and click on the tweet's link, it shows up. When I just click on the link (even in the incognito window), it doesn't. Shhhhhh, don't tell anybody.

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