The present invention belongs to the field of control systems, in particular controllers of different processes. The invention relates to a modular controller for energy management, which can be adapted with regards to the manager's needs. The invention additionally relates to a method of modular assembly for different input signals as well as a method of energy management using the said controller. The essence of the invention is in that the controller has a housing inside which nine empty slots are provided; said slots may be equipped with arbitrary components with regards to the system to be controlled with the controller. Said empty slots may be provided with one or more of the following components such as relay, digital output, digital input, analogue output, analogue input, optically separated input, reading current signal, reading temperature sensor, etc. The controller may control usage or manufacture of gases, electricity and/or heat.