Striving to prevent climate changes, global community has established favourable national feed-in support schemes for the renewable electricity. Renewable energy is promoted through these schemes in the whole world and, particularly, in European Union (EU). Frequently, the support is provided by a guaranteed purchase price, which is significantly higher than the market price of electricity. In EU, an Electricity Market Law prescribes that an electricity producer, which operates renewable energy sources, may acquire the right to sell all the produced electricity at a guaranteed purchase price. As a result all the energy, which is produced from renewable energy sources, is sold to the public trader (PT) at a guaranteed purchase price, but the PT sells and buys energy at the market prices. All electricity consumers pay the difference. The main drawback of this support scheme is related to the absence of the coordination of power plant (PP) operation with the electricity market price or indirectly, electricity demand. This paper demonstrate that cooperation of the PT and PP operator in the market conditions could minimize additional cost of the support for the consumers and/or provide an additional income to PT and the PP owner. For this purpose, the coalition between PT and PP will be formed. Then, using scenario approach, planning problem of the day-ahead PP operation will be formulated as maximization of the expected total profit over the day taking into account profits of both PT and PP. Co-operative game theory and the Shapley value can be applied for the fair additional profit allocation. We demonstrate the advantages of the collaboration by the case study of a small hydro PP and the PT. The modification of the schedule of the PP to adjust to the electricity market prices and, thus, the electricity demand creates an additional income for the PT. It is concluded that the support principles of PP have to be reviewed. Proposed stochastic approach, formulation of the objective function and Shapley allocation can increase the effectiveness of the operation of any kind of PP, provided that the daily power production is controllable, but water or fuel resources are constrained.