  Grid-connected hybrid renewable power systems with energy storage can reduce
the intermittency of renewable power supply. However, emerging energy storage
technologies need improvement to compete with lithium-ion batteries and reduce
the cost of energy. Identifying and optimizing the the most valuable
improvement path of these technologies is challenging due to the non-linearity
of the energy system model when considering parameters as independent
variables. To overcome this, a novel investment-based optimization method is
proposed. The method involves linear optimization of the hybrid renewable
energy system and subsequent investment optimization, accounting for
diminishing improvements per investment. Applied to thermal energy, pumped
thermal energy, molten salt, and adiabatic compressed air energy storage
technologies, the results show that enhancing discharge efficiency is most
valuable for all technologies. Reducing discharge capacity costs and energy
storage capacity cost can also become important. Charge capacity cost and
charge efficiency are found to be of lesser significance. The study provides
detailed improvement pathways for each technology under various operational
conditions, assisting developers in resource allocation. Overall, the
investment-based optimization method and findings contribute to enhancing the
competitiveness of emerging energy storage technologies and reducing reliance
on batteries in renewable energy systems.
