> "In South Africa, for example, the total amount of energy produced from solar systems in 2019 was thought to be about 500 megawatts"
This is annoyingly common with journalists and also a very clear tell that they don't have any idea what they are writing about.
Maybe in a few years the writer will understand that it's tricky to store energy in a cost-efficient way and that energy isn't the same as power.
Or perhaps they won't.
Either way, in late 2024, this low level of understanding is pretty tiring.
The writer "has been the the recipient of a 2017 National Association of Science Writers reporting award for coverage of air pollution in Detroit, and a finalist for the 2019 Livingston Award for a series on water politics at the Texas-Mexico border. At The Atlantic, she covers climate change."
The writer's CV doesn't mention any education at all.
500 megawatts would be 4.4 terawatt hours per year. That's in the ballpark of what they actually did produce in 02019, according to https://en.wikipedia.org/wiki/Energy_in_South_Africa. So the journalist seems to have actually been correct in this case, although it's a bit like saying "the distance covered by the runner was 12 miles per hour", when it would perhaps be more appropriate to say that that was the runner's speed rather than the runner's distance.
Sometimes energy storage devices are surprisingly reported in terms of power (the installation’s power output ends up being more relevant for whatever reason). For grid stability, being able to meet demand is more important than having days of energy, inaccessible, in reserve. So, surprising units isn’t a 100% bulletproof heuristic.
But in this case yeah, there seems to be a mix-up.
There's no mixup. Solar electric energy production in South Africa in 02019 did indeed average about 500 megajoules per second throughout the year, totaling about 16 petajoules; which is to say, it was about 500 megawatts, or, in cursed units, 4 terawatt-hours per year.
Separately, it's true that peak power is often a very important criterion for energy storage systems.
There is a mix up. It might be that the journalist is correctly summarizing the person they interviewed, but that person is wrong, or it might be that the journalist messed it up. But,
> In South Africa, for example, the total amount of energy produced from solar systems in 2019 was thought to be about 500 megawatts, Nana said
This is a very explicit phrasing “the total amount of energy produced” and the units don’t work out. You can figure out what they meant by doing additional research, but that doesn’t make it a non-error.
Power is king for commercial batteries. On whole sale energy markets you often see high prices in one 1/4 hour, and much lower prices 1 hour later.
You can than nicely make an arbitrage profit if you completely cycle the battery.
Also many such batteries have similar Max energy and power limits, e.g. 1.5MWh energy vs 1MW power.
Edit: noticed that HN user kragen has replaced the comment I replied to with a dot, for some reason. This doesn't seem civil to me.
You think it's clear tell that she knew what she was talking about when she wrote "the total amount of energy produced from solar systems in 2019 was thought to be about 500 megawatts".
Similarly you think it's a clear tell that I don't know what I'm talking about when I say that this is an incorrect statement, and that this is a clear tell.
Yes, because, as I explained above, I checked Wikipedia, and that figure turns out to be correct to within at worst a factor of two. Power units such as megawatts measure the rate at which energy is produced, consumed, or otherwise converted, which is to say, the amount of energy used per unit of time. For example, per year. A watt is about 31.6 megajoules per year.
So there's nothing actually wrong with the reporter's statement, even though it would be more precise to say that the average power generated was thought to be around 500 megawatts.
Power is energy per unit time. The statement is like saying "the total amount of rope produced in SA is 500 meters per second". Being generous, you'd assume that's (total production per year) / (seconds in a year), I guess.
Yes, I think that's a perfectly reasonable way to describe the amount of rope produced in South Africa. It uses the correct units and therefore contains no ambiguity. Saying instead that the total amount of rope produced in South Africa was 16 billion meters, leaving the "per year" implied, would, by contrast, be ambiguous and open to misinterpretation; equally plausible interpretations would be "in all of history" (the literal interpretation) or "per month". Unless, as in this case, the statement was qualified with a particular year-long time period, such as "in 2019", in which case "500 meters per second" or "16 billion meters" would be equally unambiguous ways of describing the situation.
"500 meters per second" is not just (total production per year) / (seconds in a year) but also (total production in a day) / (seconds in a day) and (total production in a month) / (seconds in a month).
Meters per second, like watts, has the advantage of being an SI unit and therefore facilitating calculations with other SI units without requiring a bunch of numerical conversion factors.
So the average power produced by those plants was 500MW.
That phrase is still nonsense. The fact that if you go, do your research, get the real numbers, and interpret them you can discover that what the journalist is trying to say is correct is meaningless. You can still cut the journalist out from the process and lose nothing.
But in this case what was being discussed was the rate at which South Africa converted solar energy into electrical energy, which is a power, and the journalist correctly used units of power. Many journalists are indeed staggeringly incompetent, but in this case you are the one who is mistaken.
Agreed, it would be great if everything could always be technically accurate, but like fetch, it is never going to happen. It is wrong basically everywhere. Which is understandable as common vernacular readily interchanges energy and power.
If you map energy -> power the paragraph actually says something sensible.
It could have been worse: if they'd said something like "500 megawatts per week" it would be completely unclear what they even mean. Should you map it to megawatt-hours / week (around 3 MW), because that's a common (kind of goofy) unit to work in? Or does it mean they use (on average) 500 MW?
And MW wasn't even the unit used in the source, the SAPVIA Solar PV Dashboard[1], which shows Megawatt Peak. MWp is a unit that refers to the theoretical maximum power output of a solar PV system (e.g. under ideal conditions.)
These data accord with the article's thesis, but it doesn't inspire confidence that units were conflated. They're not the same thing as megawatts, they don't measure energy, etc.
i think a more useful correction for people whose day to day lives don't require them to keep track of the difference is
MW is rate of energy use with respect to time, not total energy. The rate of energy in science is called "power"
because they both are measures of energy, and the energy/power distinction in science co-opted preexisting words that didn't have those precise meanings. Total energy is the integral of power over time, so it's not really wrong to say "this higher energy battery contains more power" in everyday speech.
This is annoyingly common with journalists and also a very clear tell that they don't have any idea what they are writing about.
Maybe in a few years the writer will understand that it's tricky to store energy in a cost-efficient way and that energy isn't the same as power.
Or perhaps they won't.
Either way, in late 2024, this low level of understanding is pretty tiring.
The writer "has been the the recipient of a 2017 National Association of Science Writers reporting award for coverage of air pollution in Detroit, and a finalist for the 2019 Livingston Award for a series on water politics at the Texas-Mexico border. At The Atlantic, she covers climate change."
The writer's CV doesn't mention any education at all.