  Islanded microgrids powered by renewable energy require costly energy storage
systems due to the uncontrollable generators. Energy storage needs are
amplified when load and generation are misaligned on hourly, monthly, or
seasonal timescales. Diversification of both loads and generation can smooth
out such mismatches. The ideal type of battery to smooth out remaining
generation deficits will depend on the duration(s) that energy is stored. This
study presents a controls co-design approach to design an islanded microgrid,
showing the benefit of hybridizing tidal and solar generation and hybridizing
lithium-ion and flow battery energy storage. The optimization of the
microgrid's levelized cost of energy is initially studied in grid-search slices
to understand convexity and smoothness, then a particle swarm optimization is
proposed and used to study the sensitivity of the hybrid system configuration
to variations in component costs. The study highlights the benefits of controls
co-design, the need to model premature battery failure, and the importance of
using battery cost models that are applicable across orders of magnitude
variations in energy storage durations. The results indicate that such a hybrid
microgrid would currently produce energy at five times the cost of diesel
generation, but flow battery innovations could bring this closer to only twice
the cost while using 100% renewable energy.
