France just changed the way to compare electricity of nuclear origin to other forms of energy (direct combustion of oil, for example). Thus, as electricity of nuclear origin represented a little over 32% of the global energy consumption in France in 2000, this percentage went down to 16% in 2001. How is it possible to explain such a change?
The explanation lies in the fact that there are several (actually maintly two) ways to compare energies. Mother nature does not endow us with all the energies we use on a daily basis: no natural process allows electricity to “come out of the wall” by itself ; there is no natural spring of gasoline or butane ; only plants know how to use directly solar energy to get something else than heat out of it. The energies that we use, and that are labelled “final energies”, are obtained from the sources available in nature, that are labelled “primary”.
The latter include raw hydrocarbons (coals, oil, natural gas), fissile or fertile atoms (primarily uranium 235 and 238, and thorium 232), fusible atoms (those woth which it is possible to achieve nuclear fusion) or those able to produce some (deuterium and lithium), the kinetic energy of natural elements (wind, water, etc), the electromagnetic rays of the sun, and the natural radioactivity of the Earth (geothermal energy).
From these sources of primary energy we will get final energies (gasoline or diesel oil, purified coal, purified natural gas, electricity, mechanical energy, etc), through various transformations (such as refining for oil). Electricity, just as hydrogen, are final energies, non existant in nature, and obtained from primary energies by industrial processes of various kinds. The final energy is thus the energy that is “used for something” by the end user. It is the gallon of gasoline one puts in a car tank, or the electric kWh that puts the washing mashine in action.
It is then easy to understand that it is either possible to compare the primary energy consumptions, of the final energy consumptions. When going from primary energy to final energy, we must take into account the efficiency of the conversion device (typically a power plant in the case of electricity), and, as the case may be, of transportation. Generally speaking, a country always has a higher primary energy consumption than final energy consumption, the difference between the two representing the losses in the energy system. For example, in a power plant the first stage consists in producing heat, either by burning a fuel, or by splitting uranium atoms in two, ,and this thermal energy will be partially converted into electricity in a generator, the remaining fraction (of heat) being evacuated in the environment., or sometimes (in the case of cogeneration) used to produce steam. It is because France just changed the way to compare nuclear energy to the other ones, as explained below, that the percentages decreased.
How much does France consume of this or that?
The final energy consumption is generally known from weights of fuels burnt, or from kWh consumed if it is electricity.
Each fuel has its own energy content, which means that when burning one tonne of this fuel, we get a certain amount of energy, under the form of heat, that can be measured in joules (which is the legal unit), or more exactely in billion of joules, called gigajoules (Gj). Comparing two fuels doesn’t raise any particular problem: we just have to take a tonne (or a kg) of each of the fuels, burn it, and measure the amount of heat freed in each case. This measure will allow to establish a value for each fuel.
Then, in order not to manipulate billions all the time, energy people are accustomed to using an unit more comfortable than the gigajoule, which is the tonne oil equivalent (or toe), that is worth, by definition, 42 billion joules (actually 41,6 exactely). By definition, a tonne of oil frees, on average, 1 toe of heat when burnt, and the other fuels can be measured in toe just as follows:
|Type of fuel||Energy released by the combustion of one tonne (GJ)||1 tonne of this fuel is worth (toe)|
|Crude oil, diesel oil||42||1,000|
It is then possible to use a single unit to expose the consumption of fuels in France, which is what follows:
|Type of fuel||Final consumption in France (Mtoe)|
|Solid fuels (coal, lignite, etc)||7,31|
|Liquid fossil fuels (oil and derivates)||76,90|
|Gaseous fossil fuels (natural gas)||32,27|
|Thermal renewables (mostly wood)||11,26|
Final consumption in France in 2000.
And what about electricity ? It doesn’t burn ! Most certainly, but electricity carries energy, and this energy can also be measured in joules. So, a kWh (kilowatt.hour) represents, by definition, 1,000 Watts consumed for one hour (that is 3600 seconds, I recall to the absent minded !), so that 1 kW.h = 3.600.000 joules. If we use another multiple, the megawatt.hour (symbol MWh, worth 1,000 kWh), we get:
1 electric MWh = 3,6 billion joules = 3,6 GJ = 0,086 toe
It is this convention that is used by default internationally, and that means: we break down the Gj consumed by the end-users (that is the population and the office or industrial activities) by nature of source, and it is the proportion of electricity in this total that is significant. We will then say that we consider the proportion of electricity in the final energy consumptiom.
As the french electricity consumption amounted to 400.000.000 MWh (or 400 TWh ; 1 TWh = 1.000.000.000 kWh) in 2000, if we convert this electricity on the final energy basis we get an equivalence of 400.000.000 x 0,086 = 34 million toe. The breakdown by source then is what follows:
|Type of energy||Final consumption in France (Mtoe)||Share in the total|
|Solid fuels (coal, lignite, etc)||7,31||4,5%|
|Liquid fossil fuels (oil and derivates)||76,90||47,5%|
|Gaseous fossil fuels (natural gas)||32,27||19,9%|
|Thermal renewables (mostly wood)||11,26||6,9%|
Share or the different types of energy, in the final consumption in France in 2000.
So here is how, just by changing the rule (same energy in the power plant, or same energy at the end-user’s place), the share of electricity changes by a factor two ! Let’s note that a simple rule increases or diminishes the global energy consumption in France by more than 50 million tonnes oil equivalent…
Isn’t there a “perfect” system?
If we think hard, we should be able to figure out a good compromise between the two approaches. How can we do ? There is a way: separate the two different “kinds” of electricity.
Part of the electricity we use as a final energy cannot be replaced by something another source (at least with present technologies). It’s the electricity that we use to light our homes, run the lifts, operate the washing machines or our computers, or, in the industry, run the electric engines or perform electrolysis. The word “specific” is used to designate this electricity. For this kind of “specific” electricity, the good equivalence is the energy used in the power plant: we cannot substitute this electricity by another energy source at home or in a factory, so this electricity has to be produced no matter what.
On the other hand, another part of electricity is used to heat, cook, or produce hot water, and for these usages it is possible to use natural gas or oil products. However, a central heating using natural gas or fuel oil has an efficiciency of 60% to 80% (the rest is lost through exhaust fumes and in the pipes in the basement), when an electric radiator or a water heater has an efficiency of 100% or almost.
Let’s now have a look at the amounts devoted to each usage (in France).
|Usage||(TWh)||Share in the total|
|Thermal usages (heating etc)||100||25%|
|Specific usages (engines, lamps, etc)||300||75%|
Let’s now suppose that we use the “final energy equivalence” when electricity can easily be replaced by something else (heating, hot water), and the “in the power plant equivalence) when it is specific electricity. We then get to the following table:
|Usage||(TWh)||Conversion factor (toe/MWh)||Total (toe)|
|Thermal usages (heating etc)||100||0,086*||8,6|
|Specific usages (engines, lamps, etc)||300||0,222||66,6|
(*) assuming boilers have a 100% efficiency.
(**) this value is calculated, of course.
So, eventually, we get the following share of electricity in the total energy consumption of France:
|Type of energy||Total consumption in France in million toe (year 2000)||Share in the total|
|Solid fuels (coal, lignite, etc)||7,31||3,4%|
|Liquid fossil fuels (oil and derivates)||76,90||35,5%|
|Gaseous fossil fuels (natural gas)||32,27||14,9%|
|Thermal renewables (mostly wood)||11,26||5,2%|
If we use a comparison basis that aims to “stick at best” to reality, we get something which is close to the result obtained with the “French rule”, and anyway it is this way to compare that has a “physical” meaning. In other terms, if we decide to pull out from nuclear energy, it is neither 88 Mtoe, nor 34 that we will have to replace by oil and gas (or renewables for a small fraction), but something around 75 Mtoe, everything remaining the same otherwise.
There is one exception to this reasoning: hydroelectricity and wind power, since there is not the intermediate stage of heat production when using these primary energies. The “final energy” equivalence is then the good one.