Recent developments of III-nitride materials and devices for energy applications such as photovoltaic, thermoelectric, and hydrogen generation are discussed. Although there are only few reports on InGaN based solar cells, some superior properties of this material including radiation tolerance and tunable band gap overlapping with solar spectrum considered it as a suitable candidate for space based and multijuction solar cell. Design and characterization, of InGaN based efficient p-MQW-n solar cells are presented. For the thermopower generation, we discuss the potential of InGaN alloys as thermoelectric material. Good thermoelectric materials possess low thermal conductivity and high Seebeck coefficient with high electrical conductivity. The thermal conductivity about two orders less than that of GaN and thermoelectric figure of merit as good as that of SiGe alloys are measured in In0.36Ga0.64N alloy. Our results indicate that InGaN alloys can be used to convert heat energy directly into electrical energy. Generation of hydrogen by splitting of water using InGaN alloy electrodes and solar energy via photoeletrochemical effect is also discussed.