To compare the effects of using different energies in a Smart City, we use the concept of primary energy to quantify and compare the amounts of energy in their form available in nature, whether fossil or renewable.
Primary energy is opposed to final energy, ie the energy in the form in which it is consumed and billed, for instance electricity. The most frequent primary energy sources are oil, gas, uranium, wood before processing as well as wind, solar photovoltaic, hydro or geothermal energy.
The difference between primary energy and final energy represents all losses caused by the transformation of energy in the raw state into consumable energy, these losses occurring during the production or the transportation stage of this final energy.
Consumers compare different systems, which consume energy, through their equivalent primary energy consumption to penalize rightly the inefficient energy transformation systems.
The conversion of the final energy in primary energy is made through factors, mostly fixed by regulation.
In many countries, the conversion factor of primary energies used in thermal applications is 1: the final energy equals the primary energy. For electricity, the production process in a country is more or less effective depending on the national energy mix. The conversion factor of 2.6 in Germany, 2.58 in France, 2.6 in Spain, 2.92 in the UK.
This conversion factor is a regulated factor that depends on the country’s energy mix but also on political inputs. For example, the real French conversion factor of 1 kWh electricity in 1 kWh of primary energy is, in reality, more than 3.2: the regulated factor of 2.58 tends to penalize less the use of electricity as a source of final energy .
Taking decisions based on the primary energy consumption energy gives a more limited role to electricity, especially in thermal applications, unless the energy mix is highly dominated by renewable sources. This reasoning is today no longer enough: for heat production, the direct use of fossil fuels, emitting greenhouse gases and the use of renewable energy are not differentiated; in both cases, the primary energy consumed is the same.
The conversion of primary energy consumption must absolutely be accompanied by a monitoring of the development of the energy mix or primary energy corresponding to renewable energy should gradually converge to 0, to mark a difference with fossil fuels.
In a landscape where some cities will get ahead by deploying energy systems emitting less greenhouse gas, it will be important to allow the application of local conversion factors, allowing for a different local reality. Otherwise, the application of national factors in such a city will slow down the harvest of the benefits of local politics.
As for national factors when it comes to defending a historic national industry, a political input will be welcome to support through these local factors virtuous initiatives on energy transition.