Photovoltaic (PV) energy systems and power-generation systems using biomass are designed and evaluated in terms of energy, economics and CO2 emissions. The calculated values of CO2 emissions for dispersed and centralized PV systems are 5 and 15 g-C/kWh, respectively. Biomass gasification combined cycles (GCC) give lower CO2 emissions of 3 g-C/kWh. These values are one or two orders smaller than those of existing thermal power plants. The evaluated electricity costs are $0.16/kWh for dispersed PV systems, $0.29/kWh for centralized PV systems, and $0.03-0.07/kWh for GCC systems. Biomass can supply the most economical electricity, however, it requires 100 times more land than PV systems.