The connection of distributed energy sources to the distribution network, among other influences, results in a redistribution of power flows in the network, and thus a change in the amount of working energy losses. At a certain moment, depending on the consumption in the network and the power injected into the network by the power plant, the loss of manpower may be greater or less compared to the situation without the connected power plant. However, the current value of labor losses is not important, but primarily the total losses of labor energy on an annual basis. For this reason, the methodology for calculating the annual losses of working energy in the distribution network under the conditions of a connected distributed source is elaborated in the paper, starting from the known chronological curves of load and production. Appropriate calculations were made on the example of a real distribution network and a wind power plant that is planned to be connected to it.