A system for cooling electronics includes at least two modular thermal energy storage cards stacked in one of a horizontal or a vertical stack, where the stack provides cooling to a portion to electronics. The cards include: a thermally conductive enclosure bounding an interior cavity, a cell wall structure that includes cells disposed within the interior cavity and in thermal communication with the thermally conductive enclosure, a phase change material having a melting point where the phase change material disposed within the cells and in thermal communication with cell walls of the cells, and a thermally conductive interface disposed between the thermally conductive enclosure and a portion of the electronics that includes a heat generating surface. The thermally conductive interface extends from the interior cavity a distance beyond the interior cavity of the enclosure and is in contact with the heat generating surface.