This paper discusses optimal energy management in a grid-connected hybrid generation system which consists of wind turbine, solar array, fuel cell and electrolyzer. There is also a hydrogen storage tank and a combinational heating system in the aforementioned system. This hybrid structure supplies the electrical and thermal demand of a building. Since the system has the capability to trade power with the grid, hourly tariffs of exchanging power have also been considered so that a wide range of operational modes are covered. Thermal demand of the building is supplied using recovered heat of the fuel cell and also electric heating system. Choosing the suitable model for each subsystem, the paper formulates energy management in this hybrid system in the form of a non-linear and constrained optimization problem and evaluates various well-known heuristic techniques to solve it. By comparative assessment of these techniques, Interior Search Algorithm (ISA) is suggested as the elite technique and the results of ISA-based stimulations are presented in detail. Moreover, the influence of initial state of charge of the hydrogen tank on operating cost as well as charge remained is discussed, proving that not only it has a determining effect on the two aforementioned terms but also it possesses an optimal point which is dependent upon operational parameters of the hybrid structure. To achieve this goal, a novel criterion is introduced in order to determine the optimal value of initial state of charge of the hydrogen tank. Finally, the price fluctuations of tank-stored hydrogen are discussed and it is shown that the final price is lower than the initial one. (C) 2016 Elsevier Ltd. All rights reserved.