The Difference between Energy and Power: Do Not Confuse

"Work" Preface: A joule is used as either a unit of energy or a unit of work. Technically, energy is the ability to do work (effort or input for potential work) while work is the measured effect of applied energy (accomplishment or result or output); directional mechanical work = force * distance and the motively similar thermodynamic work = energy transferred. Your electric bill measures what reached your meter (the work/accomplishment from the power company's view), not how much benefit you wrung out of it.

• energy = work (technically, the ability to do work)
  
• power = work rate (energy per time)

• joule (J) = energy (work)
• watt (W) = power (rate of work, energy per time)
• watt-hour (Wh) = energy (work)

• energy = J
• power = J/s

The trick is that the word "watt" includes a built-in time component:

• 1 watt = 1 joule per second (Jps or J/s)

So, a watt is a transmitting speed, or rate per time, like miles per hour (mph) or bytes per second (bps). You do not see the "ph" or "ps" at the end of "watt" because "watt" replaces "Jps" or "J/s."

• 1,000 watts = 1,000 joules per second

You can think of watts like a speed but it is never "watts per second," it's either "watts" or "joules per second." Solar panels and generators usually are rated at their maximum "speed" of watts or kilowatts (not kilowatt-hours, not kWh).

• 12,000 joules PER SECOND = 12,000 watts = 12 kilowatts

You can drive a car 60mph but whether you did 60mph for 1 second or for 12 hours determines how far you traveled. That's where watt-hours or kilowatt-hours (kWh) enter the picture. A watt-hour (Wh) is a sum of all joules used over time, a cumulative energy total like miles driven on an odometer.

• 1 watt-hour (Wh) = 1 joule per second for an hour (3,600 seconds) = 3,600 joules (energy)

• 1kW=1,000W (power)
• 1kWh=1,000Wh (energy)

If you did a "speed" of 0.5kW for 24 hours, then you totaled 12kWh.
If you did a "speed" of 1kW for 12 hours, then you totaled 12kWh.
If you did a "speed" of 2kW for 6 hours, then you totaled 12kWh.

A final definition will allow you to make sense of many consumer electronic labels:

• watts (W) = volts (V) * amperes (A)

High-school algebra works perfectly on all these letters:

• W * h = Wh
• 2W * 3h = 6Wh

Algebraic division works perfectly on "joules per second" and other time rates.

• J/s = 1 joule divided by 1 second

Now you can use algebra to transform units when comparing information that appeared apples-oranges at first.

Good luck.