A combined experimental and modeling study was performed to evaluate the relation between sorbent characteristics and process performance for solid sorption postcombustion CO2 capture. A pulverized coal (PC) and a natural gas combined cycle (NGCC) power plant were considered, addressing CO2 and H2O sorption. The measured isotherms for PEI/silica sorbent were implemented in an equilibrium-based flow sheeting model. The PC regeneration heat demand is 3.9 GJ/ton CO2 captured. This is lower than that of the NGCC and, though a direct comparison is not valid, similar to a literature MEA case. Solid sorption systems hold the promise to be energetically superior to MEA: a 2-fold increase in CO2 adsorption capacity (to 4.4 mmol/g) yields a regeneration heat demand of 3.3 GJ/ton, even when accompanied by a similar increase in H2O adsorption capacity.