How secure is our energy supply?

The energy transition poses challenges for countries, cities, and regions. The use of sustainable sources of energy is key to halting climate change. At the same time, the costs of the energy system must not spiral out of control, and supply security must be ensured. These three aspects – sustainability, costs, and supply security – form what is known as the energy trilemma.

The energy trilemma was developed by the World Energy Council to support policymakers in designing the energy systems of tomorrow. By modeling the three criteria on a sound scientific basis, different energy scenarios can be compared quantitatively, ideally revealing the path that offers the optimal balance between the three target variables.

The sustainability and costs of different energy systems can already be reliably quantified using a number of models. Until now, however, this has not been the case for supply security. “Many of the existing models were vague, not user-friendly, and not designed for today’s modeling capabilities,” says Matthias Sulzer, Head of Empa’s Engineering Sciences department. Together with researchers from Empa, ETH Zurich, and the Lawrence Berkeley National Laboratory in the US, Sulzer has developed a better way for quantifying energy supply security. The work was recently published in the journal iScience.

The model takes the form of a pyramid with five levels. The researchers have provided quantitative indices for each level. The bottom level, self-production, is a simple energy balance calculation: How much energy can a country produce from its own resources annually, and how much does it consume? The second level describes autonomy; i.e., how much energy needs to be imported over the course of the year, and how secure are the import routes. Starting on the third level of the pyramid, system adequacy, dynamic effects come into play. “Here, we examine hourly – or at an even higher resolution – whether the energy demand can be met at any given time from any source,” explains co-author Georgios Mavromatidis, head of Empa's Urban Energy Systems Laboratory. The fourth level deals with self-sufficiency: Can the country manage without imports at certain times? At the top level, the researchers talk about complete autarky, where the country can live off its own energy production at any time throughout the year (or even longer).

Although the levels build on each other, Mavromatidis stresses that they should all be considered simultaneously. “Modern energy systems are very complex. The pyramid is intended to help assess the various indices correctly and clarify the terminology,” says the researcher. Its key strength over existing models is that its higher levels take dynamic effects into account. “Renewable energy systems in particular are operated very dynamically, because wind and sun are not always available to the same extent,” says Mavromatidis. “An average annual balance is thus not a good indicator of supply security in such a system.”