Optimatility principles for the sustainability of electrical systems : a thermodynamic approach
Résumé
At first sight, aiming for energy efficiency appears to penalize electricity carriers. A close look at electrical energy flow, from primary to final energy, reveals abysmally low efficiency, resulting from the generation mix, transmission and distribution losses, and obsolete equipment. As a consequence, the share of primary electricity has to be reduced in order to achieve low carbon society scenarios in line with energy saving policies. Since it relies on a partial description of the electrical workflow, this viewpoint reveals certain weaknesses that need to be qualified with a long‐term planning assessment. We propose circumventing this drawback using a thermodynamic analysis based on the Gibbs free energy of the electromagnetic field. In particular, the so‐called Maxwell‐Faraday law of induction is the local result of an optimal path towards reversibility of the entire power system, described as a monotherm engine. This approach supports a multi‐scale analysis that naturally addresses those levels that involve huge losses, namely the functional materials, conversion devices and transmission network. As a result, the role played by magnetic energy is clarified: although it is required locally for conversion purposes, magnetic energy's overall value governs the transmission of electrical power through the grid. In addition to indicating kinetic reserve, an evaluation of the power system's reliability should include an assessment of magnetic energy from the very first moment of fluctuation (typically a few ms).
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