Storage solves timing, not poor thermodynamics
A buffer can absorb heat when the source is available and release it during a later process cycle. It can also extend compressor runs, reduce cycling and shift electricity consumption. It cannot make an excessive temperature lift efficient.
Choose the stored temperature
Water storage is simple for moderate temperatures. Pressurised water, steam accumulators or phase-change media may suit higher duties but add cost and safety requirements. Storing at the lowest temperature that serves the process usually limits loss.
Model useful capacity
Tank volume alone is not energy capacity. Usable temperature range, stratification, heat exchanger approach, insulation loss, charge rate and discharge rate determine how much process duty the store can cover.
Sources
General technical explanation. No specific external source claims are made on this page.