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Summary form only given. Japan Aerospace Exploration Agency (JAXA) has been conducting studies on space solar power systems (SSPS) using microwave and laser beams for years since FY1998 organizing a special committee and working groups. In case of microwave based SSPS, the solar energy must be converted to electricity and then converted to a microwave beam. The on-ground rectifying antenna would collect the microwave beam and convert it to electricity to connect to commercial power grids. In the laser based SSPS, a solar condenser equipped with lenses or mirrors and laser-generator would be put into orbit. A laser beam would be sent to an Earth-based hydrogen generating device. JAXA is proposing a roadmap that consists of a stepwise approach to achieve commercial SSPS in 20-30 years. The first step is tens of kW class technology demonstration satellite to demonstrate microwave or laser power transmission. The second step is to demonstrate robotic assembly of 10 MW class large scale flexible structure in space on ISS co-orbit. The third step is to build a prototype SSPS in GEO. The final step is to build commercial GW class SSPS in GEO. This paper presents the results of these study effort of JAXA and from those results, identifies the most promising SSPS concepts, including their key technologies.