An electric modular system for connection to a hybrid power plant. An enclosure (CNT), e.g. a standard size container houses: 1) a first electric converter system (CV1) connected to an electric output of a wind turbine and generates a first DC output, 2) a second electric converter system (CV2) arranged connected to an output of a photovoltaic source (PV) or a battery (BT) and generates a second DC output, 3) an output electric converter system (CV0) receiving the first and second DC outputs and generates an electric output e.g. for connection to an electric grid. A cooling system (CLS) with a flow duct to receives air from outside and provides a controllable amount of cooling to the electric converter systems accordingly, e.g. via controllable flow resistive elements. A cooling controller (CC) senses output loads (L1, L2, L0) of the electric converter systems (CV1, CV2, CV0) and controls the cooling system (CLS) to direct an amount of cooling to the electric converter systems (CV1, CV2, CV0) as a function of their electric output loads (L1, L2, L0). Especially, back-to-back mounted sets of cabinets with modules of the electric converter system, and each with a dedicated cooling unit allows effective use of cooling capacity according to the actual electric load situation.