  In the context of energy transition, industrial plants that heavily rely on
electricity face more and more price volatility. To continue operating in these
conditions, the directors become continually more willing to increase their
flexibility, i.e. their ability to react to price fluctuations. This work
proposes an intuitive methodology to mathematically model electro-intensive
processes in order to assess their flexibility potential. To this end, we
introduce the notion of reservoir, a storage of either material or energy, that
allows models based on this paradigm to have interpretations close to the
physics of the processes. The design of the reservoir methodology has three
distinct goals: (i) to be easy and quick to build by an energy-sector
consultant; (ii) to be effortlessly converted into mixed-integer linear or
nonlinear programs; (iii) to be straightforward to understand by nontechnical
people, thanks to their graphic nature. We apply this methodology to two
industrial case studies, namely an induction furnace (linear model) and an
industrial cooling installation (nonlinear model), where we can achieve
significant cost savings. In both cases, the models can be quickly written
using our method and solved by appropriate solver technologies.
