Thermal energy storage apparatus

A thermal energy storage apparatus, including:

• a block of a heat-absorbing material, the block being a single mass of compressed material in the form of machinable sintered graphite and having a plurality of holes machined therein;
• and
• a plurality of heat storage elements, the heat storage elements including a phase change material stored in a containment vessel;
• wherein each heat storage element is in thermal contact with the block of heat-absorbing material, each storage element being received in a respective hole machined in the block, and wherein the holes are evenly spaced with predetermined intervals therebetween wherein the containment vessel storing the phase change material includes a substantially cylindrical sidewall, a first end and a second end, wherein the sidewall has a thickness which increases along the length of the sidewall from the first end to the second end, such that, on undergoing a phase change, the phase change material preferentially expands in the direction of the first end.