A high efficiency, low profile and high step-up dc-dc converter is proposed for low dc voltage renewable energy system. Generally, the power source such as photovoltaic array and the fuel cell stack have low voltage output because of that a high voltage step-up converter is required to boost the voltage much higher than the voltage level for front-end application. The efficiency and voltage gain of conventional dc-dc converter are limit due to the parasitic components. In order to solve the above mentioned problem, the proposed converter is based on active-clamp technique and the converter is the combination of a forward converter and a flyback converter. Multiple secondary windings can be employed for low profile design and help to reduce high transformer copper loss and high output rectifiers conduction losses. The proposed converter is confirmed with experiments on 250-W prototype and the maximum efficiency of ±94% was measured at full load.