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Sometimes energy storage devices are surprisingly reported in terms of power (the installation’s power output ends up being more relevant for whatever reason)

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.

kragen 2y ago
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.
- lysace 2y ago
  > 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"
  - kragen 2y ago
    500 megawatts is literally defined as 500 megajoules per second.
    - lysace 2y ago
      I'm sorry to say that I think you are muddying the waters. Competently, too. Kudos.
      - kragen 2y ago
        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.
        lysace 2y ago
        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".
        kragen 2y ago
        I was explaining why the misconception you were repeating was wrong. (It turned out to be a popular one.) I suppose that since you still haven't figured out that it was wrong, that looks like "misleading" to you, but actually you are the one doing the misleading. It's good to doubt your beliefs; that way you can abandon the false ones. Try it. I think it is pretty common for reasoning to require a fairly long explanation to become clear. Hopefully I've achieved that for most readers, even if you are still struggling. But if you object to this thread being "extremely verbose", why are you copying and pasting the same comment into it here and in https://news.ycombinator.com/item?id=41998632 https://news.ycombinator.com/item?id=41998632?
- bee_rider 2y 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.
  - kragen 2y ago
    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. ______ † 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!
    - lysace 2y ago
      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.
- bmicraft 2y ago
  I still don't get it. Is it 500MW averaged over the _whole_ year including nights, or 500MWp?
  - kragen 2y 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 2y 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.

kragen 2y ago

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.

lysace 2y ago
> 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"
- kragen 2y ago
  500 megawatts is literally defined as 500 megajoules per second.
  - lysace 2y ago
    I'm sorry to say that I think you are muddying the waters. Competently, too. Kudos.
    - kragen 2y ago
      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.
      - lysace 2y ago
        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".
        kragen 2y ago
        I was explaining why the misconception you were repeating was wrong. (It turned out to be a popular one.) I suppose that since you still haven't figured out that it was wrong, that looks like "misleading" to you, but actually you are the one doing the misleading. It's good to doubt your beliefs; that way you can abandon the false ones. Try it. I think it is pretty common for reasoning to require a fairly long explanation to become clear. Hopefully I've achieved that for most readers, even if you are still struggling. But if you object to this thread being "extremely verbose", why are you copying and pasting the same comment into it here and in https://news.ycombinator.com/item?id=41998632 https://news.ycombinator.com/item?id=41998632?
bee_rider 2y 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.
- kragen 2y ago
  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. ______ † 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!
  - lysace 2y ago
    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.
bmicraft 2y ago
I still don't get it. Is it 500MW averaged over the _whole_ year including nights, or 500MWp?
- kragen 2y 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 2y 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.