Energy bank with heat pump input circuit and hot water output circuit

An energy bank including a heat exchanger, the energy bank comprising an enclosure, and within the enclosure:

• an input-side circuit of the heat exchanger for connection to, and to receive a first heat transfer liquid from, an energy source;
• an output-side circuit of the heat exchanger for connection to, and to supply a second heat transfer liquid to, an energy sink;
• and
• a phase-change material for storage of energy, the phase-change material being sealed within the enclosure and separated from the heat transfer liquids;
• and
• an electrical heating element configured to be used selectively to put heat into the phase-change material;
• wherein the phase-change material within the enclosure includes a plurality of resilient bodies that are configured to:
• reduce in volume in response to an increase in pressure caused by a phase change of the phase-change material;
• and
• expand again in response to a reduction in pressure caused by a reverse phase change of the phase-change material.