A fully integrated, area-efficient and ultra-low power management system for micro-power solar energy harvesting applications is proposed. This system harvests energy from miniaturised solar cells connected in series to charge a rechargeable microbattery. This circuit occupies less area compared to conventional inductive and switched-capacitor DC-DC converters, while achieving better efficiency during battery charging. Owing to very low power consumption of the circuit, efficiency remains high even under reduced light intensity. The proposed circuit was fabricated in a 0.18 mm CMOS process and occupies a core area of only 0.15 mm(2) to charge a NiMH microbattery. The average power consumption of the whole power management system is less than 300 nW.