New and emerging CHP
One new development is the use of fuel cells for cogeneration. Fuel cells convert the chemical energy of hydrogen and oxygen directly into electricity without combustion and mechanical work, such as in turbines or engines.
A fuel cell consists of two electrodes separated by a membrane. Hydrogen passes over one electrode and oxygen over the other. The electrode surface has a catalyst that splits the hydrogen gas into protons and electrons. Only the protons can pass through the membrane and react with the oxygen and electrons on the other side to make water. The electrons cannot pass through the membrane and, in the process of bypassing the membrane, produce electricity for use in the home.
Fuel cells are much less polluting and about twice as efficient as typical steam-turbine electricity production. Once the hydrogen has been obtained, the fuel cells' only by-products are heat and water. The hydrogen is usually produced from natural gas by a process known as reforming.
The total efficiencies of cogeneration systems reach 85 to 90%, while the heat to power ratio is in the range 5:4. Fuel cells with a capacity of 1 kWe provide heat and power for single family houses, whereas bigger applications of around 300 kWe can be used in hospitals, for example. It needs to be said, however, that fuel cells are not yet commercially available. Fuel cells are an emerging technology and their high cost precludes their use in most on-site generation applications: fuel cells are finding a small niche market in smaller applications with high power costs, severe environmental constraints, and high power quality requirements.
With total system efficiencies 30% to 50% greater than "cogeneration," trigeneration is the simultaneous production of power/electricity, hot water and/or steam, and chilled water from one fuel. Basically, a trigeneration power plant is a cogeneration power plant that has added absorption chillers for producing chilled water from the heat that would have been wasted in a cogeneration power plant.
Trigeneration plants can reach system efficiencies that exceed 90%. In addition to the economic benefits and advantages, trigeneration plants reduce our dependence on foreign energy supplies and help our environment by dramatically reducing greenhouse gas emissions such as carbon dioxide - when compared to typical power plants.