This paper proposes a mathematical model to perform optimal operational
planning of large-scale energy systems with high share of renewable
energy. Furthermore, it analyses the influence of different unit
commitment modelling approaches on the operational planning outcomes.
The value of co-optimisation of electricity and heating sector is
emphasized in this paper. The results show the influence of massive
renewable penetration in the energy sector towards 2050, and how this
influences generation from other sources such as thermal and hydro.
Including unit commitment constraints with integer variables leads to
more realistic behaviour of the units, at the cost of increasing
considerably the computational time. Relaxing integer variables reduces
significantly the computational time, without highly compromising the
accuracy of the results. Neglecting the unit commitment constraints
leads to inaccurate results in terms of underestimation of costs,
curtailment, wind's and solar PV's average revenue per energy unit sold,
price volatility, and to overestimation of the flexibility of thermal
units. Hence, depending on the purpose of the analysis, it is
recommended to consider carefully the choice of unit commitment
modelling approach and acknowledge the limitations. When the focus is on
prices and revenues, using unit commitment constraints with integer
variables is preferable.