  An energy storage technology is valuable if it makes energy systems cheaper.
Traditional ways to improve storage technologies are to reduce their costs;
however, the cheapest energy storage is not always the most valuable in energy
systems. This paper reviews techno-economic storage valuation methods and
expands them by the new "market potential method" which derives a system-value
by examining the capacities obtained from a long-term investment planning
optimisation. We apply and compare this method to other cost metrics in a
renewables-based European power system model, covering diverse energy storage
technologies. We find that characteristics of high-cost hydrogen storage can be
equally or even more valuable than low-cost hydrogen storage. Additionally, we
show that modifying the freedom of storage sizing and component interactions
can make the energy system 10% cheaper and impact the value of technologies.
The results suggest to look beyond the pure cost reduction paradigm and focus
on developing technologies with value approaches that can lead to cheaper
electricity systems in future. One practical and useful value method to guide
energy storage innovation could be the market potential method.
