Should we redefine our energy indicators?

The energy transition will require clarification and enrichment of the way we measure energy production and consumption. In addition to traditional indicators such as energy intensity, new and more relevant indicators such as “energy efficiency”, “grey energy” or “total cost of ownership” should be used.

Traditionally, one of the main energy indicators has been energy intensity, which measures the amount of final energy consumed per unit of GDP produced [→ Q9]. Its relevance is questionable. At first glance, Switzerland has improved its energy intensity in recent years, but this is oblivious to the fact that its economic fabric is gradually de-industrialising. As a result, Switzerland is increasingly importing semi-finished products or consumer goods that it no longer produces itself, but which require energy in their manufacture and transport. It is much more appropriate to use an indicator that takes account of this indirect energy (grey energy).

The situation is even more confusing with regard to the concept of energy efficiency. A direct electric heater, for example, has an apparent energy efficiency of 100%, suggesting that this technology is perfectly efficient. In reality, this only reflects the fact that all the electricity consumed by the radiator is converted into heat without losses. However, with the same amount of electricity, it is possible to provide four times as much heat by operating a heat pump, which is 400% efficient [→ Q26].

Energy efficiency is defined as the ratio of useful energy (e.g. heat supplied) to energy consumed (purchased). This indicator is relevant only when comparing similar technologies offering the same service: comparison between condensing and non-condensing boilers, or between different photovoltaic solar panel technologies. But it does not allow an objective comparison of very different technologies or uses; a thermal solar collector offers an efficiency 4 times higher than a photovoltaic panel (60% against 15%). However, the former provides heat and the latter electricity, which are not at all comparable, because a kWh of electricity is much more valuable than a kWh of heat [→ Q50].

The indicator that allows a real and consistent comparison between different technologies is “exergy efficiency”. Exergy measures the quality of the energy under consideration, i.e. its potential to provide a given energy service. Exergy efficiency is the ratio of energy supplied to energy received (or purchased). The concept of exergy efficiency really makes it possible to characterise the quality of a technical system and its potential for improvement. For example, since the exergy of electricity is much higher than that of heat, the exergy efficiency of a solar thermal collector will often be of the same order or lower than that of a photovoltaic panel, although its energy efficiency (in the traditional sense) is 4 times higher, as mentioned above. Similarly, boilers (gas, fuel oil, wood, etc.), whose manufacturers boast high energy efficiencies (80-110%), actually have a poor exergy efficiency (less than 10%) and are therefore not future-proof solutions [→ Q24].

The question of the relevance of the indicators also arises for the measurement of greenhouse gas emissions, expressed in quantities of CO₂-equivalent [→ Q65]. Often, only direct emissions related to the use of equipment are counted. As a result, renewables, electric cars and nuclear power plants appear to be “climate neutral” by virtue of the fact that they do not directly emit greenhouse gases. However, this approach is insufficient, as it does not consider indirect emissions during production, transport, decommissioning at the end of life, etc. Measuring only direct emissions therefore does not allow an objective differentiation between good and bad technologies from a climate point of view [→ Q65]. The “CO₂-equivalent” indicator is relevant as long as it is applied to the entire supply chain of the goods and services under consideration.

A similar reasoning concerns the notion of “cost”, which is usually the only indication of economic performance provided to the consumer. If only the cost of purchase is taken into account, the consumer is likely to be put off by greener alternatives. For example, an energy-saving light bulb is more expensive to purchase than a halogen bulb. Similarly, the price of an electric car is higher than that of a petrol-driven car of a comparable class. But the reality is that the low-energy light bulb, like the electric car, can be very economically advantageous over its lifetime, given its lower running costs [→ Q44]. So another indicator, “total cost of ownership”, should guide purchases and should be the focus of a communication effort.