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Micro combined heat and power or micro-CHP is an extension of the idea of cogeneration to the single/multi family home or small office building in the range 0,3 - 50 kW. Local generation has a higher efficiency as it lacks the 8-10 % energy losses when transporting electricity over long distances and the 10-15 % energy losses on long distance heat transfer due to the difference between the hot energy carrier (water) and the colder external environment. The most common systems use some form of methane as their energy source and emit carbon dioxide. == Overview == Micro combined heat and power(CHP) systems in homes or small commercial buildings are often fueled by natural gas to produce electricity and heat. A micro-CHP system is a small fuel cell or a heat engine driving a generator which provide electric power and heat for an individual building's heating, ventilation, and air conditioning. A micro-CHP may primarily follow heat demand, delivering electricity as the by-product, or may follow electrical demand to generate electricity and heat is the by-product. When used primarily for heat in circumstances of fluctuating electrical demand, micro-CHP systems may generate more electricity than is instantly being demanded. The heat engine version is a small scale example of cogeneration schemes which have been used with large electric power plants. The purpose is to utilize more of the energy in the fuel. The reason for using such systems is that heat engines, such as steam power plants which generate the electric power needed for modern life by burning fuel, are not very efficient. Due to Carnot's theorem, a heat engine cannot be 100% efficient; it cannot convert anywhere near all the heat in the fuel it burns into useful forms such as electricity. So heat engines always produce a surplus of low-temperature waste heat, called "secondary heat" or "low-grade heat". Modern plants are limited to efficiencies of about 33 - 60% at most, so 40 - 67% of the energy is exhausted as waste heat. In the past this energy was usually wasted to the environment. Cogeneration systems, built in recent years in cold-climate countries, utilize the waste heat produced by large power plants for heating, piping hot water from the plant into buildings in the surrounding community. However, it is not practical to transport heat long distances, due to heat loss from the pipes. Since electricity can be transported practically, it is more efficient to generate the electricity near where the waste heat can be used. So in a "micro-combined heat and power system" (micro-CHP), small power plants are instead located where the secondary heat can be used, in individual buildings. Micro-CHP are defined by the EC as being of less than 50 kW electrical power output. In a central power plant, the supply of "waste heat" may exceed the local heat demand. In such cases, if it is not desirable to reduce the power production, the excess waste heat must be disposed in e.g. cooling towers or sea cooling without being used. A way to avoid excess waste heat is to reduce the fuel input to the CHP plant, reducing both the heat and power output to balance the heat demand. In doing this, the power production is limited by the heat demand. In a traditional power plant delivering electricity to consumers, about 30% of the heat content of the primary heat energy source, such as biomass, coal, solar thermal, natural gas, petroleum or uranium, reaches the consumer, although the efficiency can be 20% for very old plants and 45% for newer gas plants. In contrast, a CHP system converts 15%–42% of the primary heat to electricity, and most of the remaining heat is captured for hot water or space heating. In total, as much as 90% of the heat from the primary energy source goes to useful purposes when heat production does not exceed the demand. CHP systems are able to increase the total energy utilization of primary energy sources, such as fuel and concentrated solar thermal energy. Thus CHP has been steadily gaining popularity in all sectors of the energy economy, due to the increased costs of electricity and fuel, particularly fossil fuels, and due to environmental concerns, particularly climate change. CHP systems have benefited the industrial sector since the beginning of the industrial revolution. For three decades, these larger CHP systems were more economically justifiable than micro-CHP, due to the economy of scale. After the year 2000, micro-CHP has become cost effective in many markets around the world, due to rising energy costs. The development of micro-CHP systems has also been facilitated by recent technological developments of small heat engines. This includes improved performance and cost-effectiveness of fuel cells, Stirling engines, steam engines, gas turbines, diesel engines and Otto engines. PEMFC fuel cell mCHP operates at low temperature (50 to 100 °C) and needs high purity hydrogen, its prone to contamination, changes are made to operate at higher temperatures and improvements on the fuel reformer. SOFC fuel cell mCHP operates at a high temperature (500 to 1,000 °CP) and can handle different energy sources well but the high temperature requires expensive materials to handle the temperature, changes are made to operate at a lower temperature. Because of the higher temperature SOFC in general has a longer start-up time and need continuous heat output even in times when there is no thermal demand. CHP systems linked to absorption chillers can use waste heat for refrigeration.〔(Tri-Generation success story )〕 A 2013 UK report from Ecuity Consulting stated that MCHP is the most cost-effective method of utilising gas to generate energy at the domestic level.〔(The role of micro CHP in a smart energy world )〕〔(Micro CHP report powers heated discussion about UK energy future )〕 Delta-ee consultants stated in 2013 that with 64% of global sales the fuel cell micro-combined heat and power passed the conventional engine-based micro-CHP systems in sales in 2012.〔(The fuel cell industry review 2013 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「micro combined heat and power」の詳細全文を読む スポンサード リンク
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