Watt? Whats that?

W and Wh  (Watt and Watt-hour), kW and kWh (kilo-Watt and kilo-Watt-hour)

Watt (W) is the unit of power.  Watt-hour (Wh) is th unit of energy.  Adding the "k" makes it kilo-Watt or kW. One kW is 1000 W!   Just like with meters (m) and kilo-meters (km).


Compare W(power) and Wh(energy) with km/h(speed) and km(distance)

Compare W and Wh with speed (km/h) and distance (km).  When a car drives at a speed of 100 km/h ( more power >> faster car) then it will travel a distance of 100 km after One hour, 200 km after two hours.  Distance = Speed x time.  The same is valid for energy and power. 


What is a kWh?  

Well one kWh is the Energy consumed by an appliance of 1 kW "One kilo Watt" or 1.000 W (one thousand Watt) when is used during 1 hour.  Or an appliance of 500 W used during 2 hours. Yes, it is power multiplied by time you use an appliance.


Saving energy, saving kWh: two things matter!

So, when it comes to save on energy, there are two things to watch: first reduce the power of the appliance, less Watts, results in less Energy (Wh) consumed.

How?  Well in the case of light bulbs for example, you could replace an older incandescent light of e.g. 100 W by a 10 W LED light that will provide you as much light!  You save a ten fold.  This works for lighting but also for your older house hold appliances as TV's, Fridges, etc.

Another important parameter is the time an appliance is used.  Like for lights, make use of timers, presence detectors, ambient light sensors to turn lights ON only when needed, i.e. someone is in the room.  Here you have an impact on the quantity of energy used, the "hours" factor.  In order to manage your energy consumption, you'll need tools.  The tool must be able to show you the power of each of your appliances and at the same time, register per appliance, how much time you use it per day, week, month and per year.  

It will show you the kWh consumed per appliance! Smappee is such a tool and shows you the consumption per appliance with their DNA!




The "time" related parameters are provided as: 

  • the number of times this appliances is used: 6271 x per Year
  • the duration each time the the appliance (heating element) turns ON: 7 minutes and 25 secondes
  • the total time this appliance will be ON and consume:  6271 x 7m25 = 10 days and 16 hours
  • the outer circles on the DNA wheel, indicate when (hours, days, days of the week, months) this appliance is in use.  It helps to understand which appliance it is and if it is not longer ON than it should.

The power is averaged over all events: 2044W

The energy as the power x total time:  524 kWh!






My espresso appliance takes 1140W of power. Based on the measured usage data during the months form May to September, Smappee estimates that the machine will be used 1359 times (36 seconds per espresso) or a total of 15 hours and 13 minutes on a yearly basis.  The energy consumed is 1.140 W x 15 hours and 13 minutes = 17 kWh (rounded) and will cost 4.34 EUR (at my average cost of 0,25 EUR per kWh).



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