The aim of this work is to assess the effectiveness of biomass gasification power plants in Russia (Irkutsk region) and compare them with other types of electricity and heat cogeneration systems. Biomass, which is waste from logging and wood processing, is considered as fuel for gasification plants. As a criterion, the cost of energy is used. Analytical relations are obtained for the cost of electric energy at a given cost of thermal energy and vice versa, thermal energy at a given cost of electric energy. These relationships are applied to assess the economic efficiency and compare small-power plants (up to 200–500 kW) such as mini-combined heat and power (CHP) on fuel chips and fuel pellets, coal-fired CHP and gas and liquid fuel power plants (gas-piston and diesel power plants). The latter are equipped with heat recovery boilers and supply consumers with heat and the electric power simultaneously. The calculation results show that the cost of electricity when using wood fuel is significantly less than the cost of electricity from a diesel power plant due to the use of cheaper fuel. In this regard, for autonomous energy systems of small power, especially near logging points, energy supply from biomass gasification power plants is a preferable solution than the use of diesel power plants. Wood fired energy cogeneration systems (mini-CHP) can also successfully compete with coal and gas power plants if they have cheap wood fuel at their location. With the introduction of carbon dioxide emissions charges, the use of not only wood chips, but also pellets becomes competitive in comparison with coal and gas.