An energy system includes an solar hydrogen producing unit (101) that produces hydrogen through decomposition of water by a photocatalytic effect, a fuel cell (103) that generates electricity by a reaction between the hydrogen produced by the solar hydrogen producing unit (101) and an oxidizing gas and discharges water as a reaction product, and a water distribution mechanism (104) that returns the water serving as the reaction product discharged from the fuel cell (103) to the solar hydrogen producing unit (101). With the configuration, an energy system that suppresses an amount of external water supply to a low level to achieve good water balance can be provided.