5 ms·

It seems to be very common to not understand, or misunderstand, the difference between power (watts) and energy (watt-hours). Even amongst technically-minded pe

It seems to be very common to not understand, or misunderstand, the difference between power (watts) and energy (watt-hours). Even amongst technically-minded people who should know better. A respected UK newspaper once printed a dramatic article claiming "20 new nuclear power plants" would be needed to power electric vehicles in the UK. This was nonsense and all based on confusing the estimated energy use of an EV fleet (in GWh) for instantaneous power (in GW). They did publish a tiny sheepish apology several days later[1], and changed the online version of the article, but the damage was done and the claim still gets repeated today. [1] https://twitter.com/dpeilow/status/831717762259099648 https://twitter.com/dpeilow/status/831717762259099648

eru 6y ago
I don't even know why we need Watt-hours? Joule work just fine, don't they?
- Reason077 6y ago
  They're measuring the same thing. Except a joule is one watt-second, which is an inconveniently small unit when talking about large energy storage like an EV battery. It would be like road signs measuring distances between cities in inches. Besides, energy has long been accounted for in hour-based units. Your power bill, for example. It's just easier to use those same units when thinking about storage, rather than rebasing everything around seconds.
  - eru 6y ago
    I know that they are both measuring energy. It's just that Watt is usually defined as Joule / second, so Joule seems more fundamental. > They're measuring the same thing. Except a joule is one watt-second, which is an inconveniently small unit when talking about large energy storage like an EV battery. That's what we have SI-prefixes for. A Watt-Hour is also pretty small. We usually use Megawatt-hours or so. Using Giga-Joule instead wouldn't be too much of a difference. > Besides, energy has long been accounted for in hour-based units. Your power bill, for example. It's just easier to use those same units when thinking about storage, rather than rebasing everything around seconds. Yes, tradition seems to be the real reason.
    - __s 6y ago
      Unfortunately seconds & minutes & hours aren't metric
      - Reason077 6y ago
        Exactly! There wouldn't be a problem here if there were 1000 seconds in an hour.
      - eru 6y ago
        True scientists use natural units anyway. https://en.wikipedia.org/wiki/Natural_units https://en.wikipedia.org/wiki/Natural_units ;)
    - TheOtherHobbes 6y ago
      Electrical goods are labelled with kW ratings, and W is just V * A. (Although not many non-STEM people know that.) kWh makes sense as an intuitive unit because it makes it easy to work out how much your heater costs to run for an hour. You can do the same calc in Joules but it's far less intuitive to convert a rating in J/s into J/hr into $/kJ (or worse $/MJ)
      - eru 6y ago
        Mostly agreed. It's not so much that W : = V * A, it's that V is defined as V := W / A. Or to be more precise and pedantic, V := J / C, Joule per Coulomb. In any case, Volt is the derived unit, and Joule is more fundamental.

eru 6y ago

I don't even know why we need Watt-hours? Joule work just fine, don't they?

Reason077 6y ago
They're measuring the same thing. Except a joule is one watt-second, which is an inconveniently small unit when talking about large energy storage like an EV battery. It would be like road signs measuring distances between cities in inches. Besides, energy has long been accounted for in hour-based units. Your power bill, for example. It's just easier to use those same units when thinking about storage, rather than rebasing everything around seconds.
- eru 6y ago
  I know that they are both measuring energy. It's just that Watt is usually defined as Joule / second, so Joule seems more fundamental. > They're measuring the same thing. Except a joule is one watt-second, which is an inconveniently small unit when talking about large energy storage like an EV battery. That's what we have SI-prefixes for. A Watt-Hour is also pretty small. We usually use Megawatt-hours or so. Using Giga-Joule instead wouldn't be too much of a difference. > Besides, energy has long been accounted for in hour-based units. Your power bill, for example. It's just easier to use those same units when thinking about storage, rather than rebasing everything around seconds. Yes, tradition seems to be the real reason.
  - __s 6y ago
    Unfortunately seconds & minutes & hours aren't metric
    - Reason077 6y ago
      Exactly! There wouldn't be a problem here if there were 1000 seconds in an hour.
    - eru 6y ago
      True scientists use natural units anyway. https://en.wikipedia.org/wiki/Natural_units https://en.wikipedia.org/wiki/Natural_units ;)
  - TheOtherHobbes 6y ago
    Electrical goods are labelled with kW ratings, and W is just V * A. (Although not many non-STEM people know that.) kWh makes sense as an intuitive unit because it makes it easy to work out how much your heater costs to run for an hour. You can do the same calc in Joules but it's far less intuitive to convert a rating in J/s into J/hr into $/kJ (or worse $/MJ)
    - eru 6y ago
      Mostly agreed. It's not so much that W : = V * A, it's that V is defined as V := W / A. Or to be more precise and pedantic, V := J / C, Joule per Coulomb. In any case, Volt is the derived unit, and Joule is more fundamental.