This study examined and compared two energy storage technologies, i.e. batteries and pumped hydro
storage (PHS), for the renewable energy powered microgrid power supply system on a remote island
in Hong Kong. The problems of energy storage for off-grid renewable energy were analyzed. The sizing
methods and economic models were developed, and finally applied in the real project (case study).
The results provide the most suitable energy storage scheme for local decision-makers. The two storage
schemes were further divided into 4 options. Accordingly, the life-cycle costs (LCC), levelized costs for the
renewable energy storage system (LCRES) and the LCC ratios between all options were calculated and
compared. It was found that the employment of conventional battery (Option 2) had a higher LCC value
than the advanced deep cycle battery (Option 1), indicating that using deep cycle batteries is more suitable
for a standalone renewable power supply system. The pumped storage combined with battery bank
option (Option 3) had only 55% LCC of that of Option 1, making this combined option more cost-competitive
than the sole battery option. The economic benefit of pumped storage is even more significant in the
case of purely pumped storage with a hydraulic controller (Option 4), with the lowest LCC among all
options at 29–48% of Option 1. Sensitivity analysis demonstrates that PHS is even more cost competitive
by controlling some adjustments such as increasing energy storage capacity and days of autonomy.
Therefore, the renewable energy system coupled with pumped storage presents technically feasible
opportunities and practical potential for continuous power supply in remote areas.