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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.

bee_rider 640 days ago

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.

That's exactly the same as zelos's example of "the total amount of rope produced in 2019 was thought to be about 500 meters per second". It's a little bit odd, but it's a perfectly correct way to describe the total amount of rope produced in 02019†. Multiplying by the number of seconds in a year isn't additional research. In the same way, you can validly say "the total temperature rise of the teakettle over a minute was thought to be about 1.5° per second" or "the total GDP of South Africa in the early 02020s was thought to be about US$6400 per person per year".

There's nothing incorrect about any of these; it's mostly just a question of which units are the most convenient or unambiguous in a given context. And, I guess, which units your audience is accustomed to seeing; the SI unit for liters of gasoline per 100 kilometers would be square meters, but if you say your new car's gas mileage is 7.8 × 10⁻⁸ m², a lot of people will think you're using the wrong units, and they will surely have a hard time interpreting it.

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† Well, except that in this case the "500" is almost certainly made up; I don't think zelos was looking up South African rope production statistics!

You are mixing things up. On the one side there's the verbiage. On the other hand there's the units. You are mixing these things up in an extremely verbose way and I don't care for for it. Please just stop trying to actively mislead us all.

But hey, you reached your goal, killing the velocity of my comment way up there.

You planted the seed of "doubt". Congrats.

Because of behavior like this: HN is not a great place for discussing anything to do with energy. Fanaticism generally rules. The loudest person wins. This is sad.

kragen 635 days ago

You seem to have copied and pasted your comment at https://news.ycombinator.com/item?id=41998629, where I responded to it.

Probably someone out there will be convinced by "the loudest person", but hopefully most people will instead be convinced by sound reasoning and evidence. That's my goal: understanding what is really true, rather than believing what you copy-paste the most times.

> Solar electric energy production in South Africa in 02019 did indeed average about 500 megajoules per second throughout the year,

Except that isn't what the article says:

"In South Africa, for example, the total amount of energy produced from solar systems in 2019 was thought to be about 500 megawatts"

500 megawatts is literally defined as 500 megajoules per second.

I'm sorry to say that I think you are muddying the waters. Competently, too. Kudos.

What, by giving the standard SI definitions of units so that people can see that the things you're saying are different are actually the same? You have a funny idea of what's muddy and what's clear.

But hey, you reached your goal, killing the velocity of my comment way up there.

You planted the seed of "doubt".

bmicraft 640 days ago

I still don't get it. Is it 500MW averaged over the _whole_ year including nights, or 500MWp?

kragen 635 days ago

The article explains that that number is "the total amount of energy produced" over the year, so it's averaged over the whole year including nights. The peak power is irrelevant to the total amount of energy produced except as an upper bound.

decatur 640 days ago

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.