1 Global energy consumption

In recent decades, there has been a significant increase in global energy consumption in virtually all sectors, led by some countries like China and India, for example. Non-renewable sources of energy, which are still predominant, increase pollution, nuisances and greenhouse gas levels. Faced with the consequences on the population, fauna, flora and climate, it is necessary to turn to renewable energies.

One of the factors to be addressed before defining the potential of power-to-gas technology is the overall energy consumption, its evolution and the associated technical challenges (production, distribution and storage).

1.1 Strong growth in energy demand

The overall increase in prosperity leads to an increase in energy requirements, whether for transport, industry, tertiary or residential sector. The evolution of the gross national product is an indicator of the energy consumption, although a factor of uncertainty remains on the relation between these two parameters. Thus, projections for the next decades evaluate several scenarios.

1.1.1 Evolution of total energy consumption

Data for recent decades show a steady increase in consumption (Figure 1.1), even if it is weighted by climatic variations or economic crises. In 2020, the COVID pandemic and the associated lockdowns resulted in decrease of energy consumption of 4.5% for all sectors. However, 2021 saw a rebound with a growth of 5%, remaining slightly higher than 2019.

Figure 1.1: Global gross energy consumption in exajoules (BP Statistical Review of World Energy 2021).

This energy comes from different sources: non-renewable sources such as oil, coal, gas and uranium and renewable sources such as wind, solar and hydropower. The contribution of each of these sources also varies from country to country (Figure 1.2).

Figure 1.2: Contribution of different energy sources in Germany, China and the USA in 2021 (data: Our World in Data).

A comparison of consumption trends shows that for many countries there is a tendency towards a decline or stabilisation of primary energy consumption (Figure 1.3) in recent decades. However, this does not mean that consumption by energy type or sector has also declined or remained stable for all countries, as shown in Chapter 2.

Figure 1.3: Comparative changes in primary energy consumption.

1.1.2 Energy storage

While solid or liquid fuels can be stored in large volumes, electricity storage is very limited in relation to production and consumption for technical (mainly relatively low capacity of available systems) and financial (high costs per kilowatt for some solutions such as batteries) reasons. The main electricity storage technology is Pumped Hydro Storage which represents over 90% of worldwide storage capacity (160 GW of power and 9,000 GWh of capacity in 2020). Electricity storage therefore remains very limited in relation to consumption (Table 1.1) or generation capacity.

The actual storage capacity of electricity is out of proportion in relation to production capacity or consumption when compared to that of natural gas or stored petroleum products. In the USA and China, the capacity of electricity storage accounts for about 1.5–2% of production capacity, with Japan being an exception, which is close to 6%. One could certainly include some of the hydropower plants as “latent” electricity, but they cannot be really considered as storage.

Unlike the storage of electricity, gas, liquefied natural gas and oil or petroleum products stocks allow an autonomy of up to several months. The actual volumes in reserve vary according to management strategies, market prices (e.g. ideally purchases when prices are low) and level of consumption in relation to production or import. The maximum capacities of these reserves as well as the quantities stored are also constantly changing over the year, in view to ensure energy independence from potential risks (conflicts, very high prices) or respond to a high demand.

1.1.2.1 Electricity peak load

The management of peak loads (Figure 1.4) is critical for electricity suppliers. It depends mainly on the use of this electricity. Electrical heating is still widespread in some countries, and at very cold temperatures, demand is rapidly increasing. The same may happen in summer with the development of air conditioning. Electricity providers must be able to respond to them without delay. They have to balance real-time production and consumption to respond to these peaks.

Figure 1.4: Example of peak consumption.

In case of demand greater than production, the low capacity of the electricity storage units requires either the use of imports if possible or run gas-fired power plants with a very rapid start-up time.

1.1.3 Energy consumption

Among the different countries, changes in primary energy consumption in recent years have experienced different trajectories. While in the long-standing industrialised countries (USA, Japan, UK, Germany etc.) the consumption has stabilised or decreased. China for example does not yet show such a trend: it is still increasing (Figure 1.5). With a few exceptions, fossil fuels are still dominating.

Figure 1.5: Evolution of energy consumption (Our World in Data).

1.1.4 Projection of the evolution of world energy consumption

In order to meet this growing demand, the strategies of each country are differentiated...