eli5: How is the use of watt-hours useful?

Question

I’m confused why the term watt-hours (Wh) is used. Watts is joules per second. So watt-hours is joules per second per hour. There are 2 time measurements within the same term.

Why not just use joules for total amount of energy used and watts for consistent/average output over a specific time? I assume watt-hours is how many watts are consistently produced over an hour period but it is used often in unhelpful scenarios. When talking about say solar generation, someone could say “my solar array produces 12kWh every day”. So 12kWh for 24 hours means your solar array produces 0.5kW of power for the entire day. How was watt-hours helpful in anyway to describe the solar array’s power output?

Or when talking about a cities power output, the reports are measured in Gigawatt-hours over the entire year. Why is quantifying a cities yearly output over an hour long period helpful?

Now if we compare the 2 given examples, it becomes even more confusing. If I had a solar array that produces 12kWh every day, how many solar arrays would I need to power a city the needs 5000 GWh every year? 5000 GWh every year is around 570.78 MW, so if I just used the standard watts over watt-hours I would have a simple convertion between scenarios while still having the option to say “0.5kWs each day” or “570.78MWs for a year”.

Sorry if this is sounding like a rant post but I’m really annoyed at this term.

In: 2

Answer 1

So that you can know the hourly rate as opposed to the per second.

If you have a battery that outputs 36KW in total and you need to calculate how long it will power a 200W device. Well if you just do 36000 / .2 you now know how many *seconds* it will power your device but we usually don’t think in seconds itd be a lot more convient to know the number of hours. So lets divide it by 3600 for the number of seconds per hour.

Well if we are going to do that, then instead of going through the extra step to calculate the hourly consumption rate, why not just simply, divide the total power by 3600 seconds to directly give you the hourly rate. Now you just have to do 10/.2 a much simpler and more straightforward calculation to tell you the hourly consumption.