Effective planning and management of hybrid renewable energy systems through graph theory

Hybrid renewable energy systems (HRES), mixing conventional and renewable power sources and, occasionally storage units, have become the norm as regard to electricity generation. Robust long-term planning of such systems requires stakeholders to test different layouts and system configurations, while their operational management relies on forecasting surpluses and deficits to achieve optimal decision-making. However, both tasks, which in fact constitute a flow allocation problem across power networks, are subject to multiple peculiarities, arising from the nonlinear dynamics of the underlying processes, subject to numerous technical and operational constraints. Interestingly, a mutual problem emerges in water resource systems, also comprising network-type storage, abstraction and conveyance components. In this vein, triggered from well-established simulation approaches from the water domain, we introduce a generic, i.e. topology-free and time-agnostic framework, key methodological elements of which are: (a) the graph-based representation of the power fluxes; (b) the effective handling of energy uses and constraints through virtual nodes and edges; (c) the implementation of priorities via proper assignment of virtual costs across all graph components; and (d) the configuration of the overall problem as a network linear programming context, which allows the use of exceptionally fast solvers. Specific adjustments are required to address highly complex issues within HRES, particularly the representation of conventional thermal and pumped-storage hydropower units, as well as the power losses across transmission lines. The modelling approach is stress-tested by means of configuring a hypothetical HRES in a non-interconnected Aegean island, i.e. Sifnos, Greece.