Integrated gasification combined cycle (IGCC) plants have significant potential for efficient power generation with carbon capture and storage (CCS). The IGCC process with CCS, however, has multiple temperature and flow constraints which severely limit its flexibility to meet the dynamic demands of the current grid. A novel energy and CO2 storage system based on the reversible reaction of CaO with CO2 has therefore recently been proposed, to enable a temporary increase in the IGCC peak power output. This is achieved by (1) providing additional high quality heat for electricity production and (2) providing temporary CO2 storage, thus reducing the parasitic load of the CCS system by reducing the energy requirements for acid gas removal (AGR) and CO2 compression. In contrast to existing concepts, the carbonation-calcination loop herein is operated in a cyclic mode; the CaCO3 produced during carbonation is not regenerated immediately, but stored until off-peak periods during which the CaCO3 is regenerated resulting in a concentrated CO2 stream ready for sequestration. The present article assesses the operating limits and thermodynamic performance of the integrated system. The latter includes a quantification of the cycle and round-trip efficiency, the energy loss factors, and a comparison with other load-shifting solutions proposed in the literature for a given load cycle. The CaO based energy storage system can be effectively used to modulate the IGCC net power output by about +/- 20-25% with respect to its nominal output, this while capturing 90% of the CO2 emissions. The load cycle considered results in 0.75%-pt (percentage point) efficiency penalty compared to continuous nominal operation, and this is within the literature range reported for other coal plants with CCS. The storage round-trip efficiency is about 60%. The makeup flow required to maintain the particle reactivity was found to be the key factor limiting the round-trip efficiency.