As the poverty of conventional energy and the abundance of renewable energy coincide in Tibetan plateau, the on-site renewable energy supply is essential for alleviating energy poverty and decarbonizing buildings. For the on-site supply, a prominent issue is the daily and seasonal mismatch between energy supply and demand. To formulate the mismatch issue and achieve near-zero energy in Tibetan plateau, the on-site energy supply and demand characteristics of an office building are investigated based on modelled photovoltaic (PV) power generation with PVsyst software and electricity consumption data from on-site research, and the impact of energy storage on mismatch alleviation is examined in terms of both short-term and trans-seasonal storage. The results reveal that, without energy storage, the carbon emission reduction rate (α) is limited to 58% due to temporal mismatch, when PV generation equals electricity demand. Energy storage can effectively alleviate the daily mismatch, and α can be increased to 93% by short-term storage. Moreover, the seasonal mismatch is pronounced in the plateau as the enormous heating energy consumption occurs in winter while cooling is not required in summer. It is demonstrated in this study that trans-seasonal hydrogen storage could eliminate the seasonal mismatch and further achieve near-zero energy buildings.