Power-to-gas (PtG) is one option to integrate more renewable electricity production to the energy system, by offering flexible load, seasonal energy storage and low-GWP (Global Warming Potential) methane. The first step of the PtG process, hydrogen production by water electrolysis, requires electricity with low specific CO2 emissions. Therefore, the operation of electrolyser is most likely variating according to the intermittency of renewable electricity production. The downstream processes of PtG should be capable to follow the dynamics and utilize the produced hydrogen, avoiding curtailment. This could be done with a very dynamic reactor system, or with aid of buffer storages for feed gases. This paper studies the effect of dynamic properties of methanation reactor, hydrogen buffer storage and electrolyser full load hours on PtG system efficiency. The operation of electrolyser is following intermittent renewable electricity production and electricity markets, leading to varying full load hours (FLH) with different characteristics. Enhancement of single parameters related to thermal dynamics of the reactor could improve the system efficiency more than parameters related to the loading of the reactor. Coupled threshold were found for FLH and H-2 storage size, after which average efficiencies became nearly similar as in steadystate operation. (C) 2020 Elsevier Ltd. All rights reserved.