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Hello,
it is always surprising to notice
that as far as renewal energy is concerned in the media,
in the TV the radio or the web,
there is still a lot of confusion between the units of energy of power.
Quite often journalists could mix up the power of
a specific unit usually given in mega-watt with the amount
of energy produced within a year which should be given in megawatt hour or gigawatt hour.
In order to have good basis to start with,
I will give or maybe recall in the session some useful definitions on power systems.
The appropriate units and give some order of magnitudes.
The joule is a standard unit of energy in the international system.
It corresponds to the work done when applying
a force of one newton through a distance of one meter.
It roughly corresponds to this.
The energy needed to lift an apple by 1 meter.
To achieve this simple motion lifting an apple by one meter in one second,
I hopefully developed a power of 1 watt which corresponds to one joule per second.
Another day life example how much energy is needed to cook some pasta.
You will need to boil, let's say,
three litres of water and it's roughly correspond to 1 million of joules, one mega joule.
Hence the joule and the watt are very small units which are not really
appropriate when you want to quantify the energy or
the power at individual or global scale.
If you pay your electricity bill,
you've probably checked your electric consumption on an electric meter.
This model is typical for all flats in Paris.
The standard unit used by individual electric meters is generally the kilowatt hour.
It is a unit of energy expressed as a product of power kilowatt times hour.
To give some order of magnitude,
1 kilowatt hour correspond to the heat released by
your standard electric heater during one hour.
One kilowatt hour corresponds to 3.6 million of joules, 3.6 megajoules.
Hence, the kilowatt is a useful unit to quantify the individual energy consumption.
For instance.
The mean annual energy consumption per inhabitant is about 27,000 of
kilowatt hour in France and if we consider only electric consumption,
we get a mean value of 7000 kilowatt per capita.
In the US, the typical electric meter is different,
but the unit to quantify individual energy consumption stays the same, the kilowatt hour.
As expected, the mean annual values per capita are higher, almost doubled.
Nevertheless, we stay in the same order of
magnitude then to 50 thousands of kilowatt power.
If we want to quantify the annual energy consumption at the scale of a city or state,
we will generally use the tonne of oil equivalent.
One TOE correspond to the amount of energy
released by the burning of one ton of crude oil.
As different crude oils have different calorific values,
the exact value is defined by convention 1 TOE equals
approximately 42 gigajoules or 11,600 kilowatt hour.
In order to give you some orders of magnitude,
the annual final energy consumption for Paris is
about 5 million of ton of oil equivalent while for
the whole France we reach 154 millions of tonnes of oil equivalent.
I've quantified here the energy consumption using the term final
energy which differs significantly from the primary energy.
If you're not familiar with these distinctions and
want to know what represents the primary, the final,
and the useful energy I suggest you to follow the session and title Primary,
Final and Useful Energy.
Thank you.
Alexandre StegnerProfesseur Chargé de Cours
Pr. Philippe Drobinski
Riwal PlougovenProfesseur Chargé de Cours
Martial HaeffelinSenior Research Scientist
