An Efficient Alternative

Polygeneration is the most efficient and widely used way, being recommended by the MEEC Group for simultaneous producing the different kinds of energy and usable products on a basis of one prime mover. Cogeneration systems – or combined heat and power (CHP) plants are practised intensively for producing both the electricity and process steam and/or hot water, whereas Trigeneration systems – or combined cooling, heating and power (CCHP) plants have been recently introduced for producing the electricity, process steam and/or hot and chilled water. Nowadays other outputs, such as mechanical energy instead of electricity, or different chemicals (for example, fertilizers) in addition to power, heat and cold are quite common. Sometimes four or more simultaneous outputs are delivered by such a plant, in which case we talk of Polygeneration system.

By using the principles of Polygeneration, less energy is wasted in energy conversion processes. For example, traditional electricity production creates the significant streams of unusable heat as an unavoidable by-product released into the environment, since even the most modern and largest power plants have an overall efficiency of only 50-58 %, whereas a more commonly efficiency is as low as 30-40 %.

With Polygeneration, the most part of heat, previously dissipated into surroundings, is no longer wasted, but used to provide the demands of nearby located greenhouses, shopping centers, district heating or cooling systems and various industries for heat, cold or process steam. In some cases over 90 %, and often over 80 % of the input energy is converted to a usable output with the polygeneration plants. Polygeneration systems can also be installed close to the end-users, resulting in reduction of power transmission and heat transportation losses with an additional energy savings and an increase in energy supply reliability and flexibility.

As a whole, fossil fuel-fired polygeneration plants are helping to reduce both the consumption of carbon-containing fuel (Coal, Heavy Fuel and Diesel Oil or Natural Gas) and a corresponding level of greenhouse gas (GHG) emissions, resulting from combustion of such fuels. A further and cardinal reduction in CO₂ (and, correspondingly, GHG) emissions can be achieved through construction of the polygeneration systems, using renewable energy sources, like solar, wind, and biomass. The biomass-fired plants seem to be especially attractive, taking into account the CO₂ neutrality of biomass derived fuels, practically universal availability of these fuels, as well as an absence of the interruptions in energy supply, inherent in the solar and wind power plants.

Polygeneration is the logical economical choice for the industrial, commercial and municipal clients, when and if the artificial barriers, such as grid connecting cost, interconnections and voltage stability requirements, local laws and regulations are resolved. Polygeneration may be applied within a wide range of scales, from one kilowatt in the houses to hundreds of megawatts in the district heating and industrial schemes.

For example, for heat-to-power ratio in the range from 0.9 to 1.1, specific installed cost of the gas engine-based cogeneration plant does not exceed 900 – 1100 €/kWe, whereas the hourly O&M costs related to the power produced amount to an average of 80 €/MWe (see graph below). Let us assume that power and heat outputs of such CHP plant are equal to 1 MWe and 1 MWth correspondingly, and an annual number of its operation hours adds up to 5800 hr/yr. A purchase of the electricity from the grid and the heat energy from the adjacent boiler house is another alternative solution of satisfying the demands for energy supply. With regard to the average market prices for electricity and heat in the EU countries, the hourly expenses will in this case comprise: 100 €/MWe for purchase of electricity and 50 €/MWth for purchase of heat.

Comparative analysis of two alternatives described above reveals an evident advantage of cogeneration principle in meeting the existing demands for energy supply, resulting in a very short simple payback period (~2.5 years) of the investments and a further significant saving in expenses achieving 406,000 €/yr. However, it should be realized that duration of the payback period and reducing the costs of energy supply depend on a size of the polygeneration plant, type and fuel efficiency of the prime movers, average retail electricity and heat prices, price of fuel consumed and expected annual number of plant operation hours.

Within the framework of the CDM (Clean Development Mechanism) and JI (Joint Implementation) projects, an additional profit could be obtained by the developers of the more energy-efficient district heating systems, using the CHP plants, and biomass-fuelled power plants from trading the emission reduction certificates in the amount of the emissions saved.

MEEC Group helps the independent power and heat producers to develop and register such the CDM and JI projects with the competent authorities.