Introduction
Cogeneration, also known as combined heat and power (CHP), is the simultaneous production of heat and power, utilizing one fuel source. Power plants and heat engines in general, waste up to more than half its available energy. With a CHP system, excess heat that would normally be wasted can be captured and converted in to electricity. By converting this excess energy into useful power, we are able to achieve efficiencies as high as 89% (1). This in turn means there is less fuel needed, making it so there is less pollution produced. While cogeneration has been used in power plants for awhile now, we will discuss the use of it on a smaller scale such as homes, cars, offices, etc.
History of Cogeneration
At the beginning of the twentieth century, steam was the main source of mechanical power. However, as electricity became more controllable, many small "power houses" that produced steam realized they could also produce and use electricity, and they adapted their systems to cogenerate both steam and electricity. Then from 1940 to 1970, the concept developed of a centralized electric utility that delivered power to the surrounding area. Large utility companies quickly became reliable, relatively inexpensive sources of electricity, so the small power houses stopped cogenerating and bought their electricity from the utilities.
During the late 1960s and early 1970s, interest in cogeneration began to revive, and by the late 1970s the need to conserve energy resources became clear. In the United States, legislation was passed to encourage the development of cogeneration facilities. Specifically, the Public Utilities Regulatory Policies Act (PURPA) of 1978 encouraged this technology by allowing cogenerators to connect with the utility network to purchase and sell electricity. PURPA allowed cogenerators to buy electricity from utility companies at fair prices, in times of shortfall, while also allowing them to sell their electricity based on the cost the utility would have paid to produce that power, the so-called "avoided cost." These conditions have encouraged a rapid increase in cogeneration capacity in the United States (2).
Micro-CHP
Micro-CHP systems differ from large scale CHP systems used in power plants. Industrial CHP systems generally generate electricity, and the heat is a useful by-product. Whereas home and smaller commercial micro-CHP systems are driven by heat demand, and deliver electricity as a by-product. Micro-CHP systems will generally produce enough electricity than what is instantly being demanded, which makes them a desirable system to have. 
Micro-CHP Systems
Automotive Applications
Cogeneration has been used in automobiles for a long time. The heater and air conditioner in a car is operated using waste heat from the engine. BMW has come up with a cogeneration system that they call a Turbosteamer. Combining the innovative assistance drive with a 1.8 litre BMW four-cylinder engine on the test rig reduced consumption by up to 15 percent and generated 10 kilowatts more power and 20 Nm more torque (3). This increased power and efficiency comes for, well, … nothing. The energy is extracted exclusively from the heat in the exhaust gases and cooling water so it is essentially a quantum leap in efficiency.
The Turbosteamer is based on the same principle of the steam engine: liquid is heated to form steam in two circuits and this is used to power the engine. The primary energy supplier is the high-temperature circuit which uses exhaust heat from the internal combustion engine as an energy source via heat exchangers. More than 80 percent of the heat energy contained in the exhaust gases is recycled using this technology. The steam is then conducted directly into an expansion unit linked to the crankshaft of the internal combustion engine. Most of the remaining residual heat is absorbed by the cooling circuit of the engine, which acts as the second energy supply for the Turbosteamer.
Residential
Micro-CHP systems in homes are especially useful in that the extra electricity produced and not needed by the house, can be resold to the electrical utility (4). This electricity is useful in the way that it is instantly disturbed and used over the electrical grid. If enough electricity is produced by multiple micro-CHP systems, there would be a smaller demand for electricity produced by the electrical utility. This would directly affect the amount of fuel needed to produce the demand for over all electricity. Another positive to this system is it being fairly easy to configure. An electrical meter would now not only measure the power entering the home, but also the power being redistributed by the micro-CHP system. In the United States, many federal and state laws require utility operators to compensate anyone adding power back to the electrical grid. Micro-CHP systems can be used in other ways in houses other then re-selling electricity back to utility companies. The micro-CHP systems can produce heat and electricity simultaneously. While the electricity can be used to run household appliances such as lights, TV, computers, kitchen appliances, etc. Whereas the heat produced can be used to provide hot water, and heating in some cases to the house. The engines used in these systems to produce electricity can be either internal combustion or Stirling engines. Most of these systems run on either propane, natural gas, or in the case of the Stirling engine concentrated solar energy and biomass. The by-product of the electricity generated is heat. One 6-kW unit provides 10 gpm of hot water at 140 to 150°F (5). This heat can be used for heating the home, or even used for a spa. The efficiency of one of these systems can be as high as 90%, compared to 30% when receiving electricity from a central power station.
The ultra-quiet MCHP unit produces 3.26 kilowatts of heat and 1.2 kilowatts of electric power.
Advantages and Disadvantages
Advantages
Financial:
Tax efficient investment with claimable Enhanced Capital Allowances
Lower fuel costs that come with using less fuel
Excess electricity generation can be sold to the utility company
Operational:
unit can be used as a standby generator when the electricity grid fails
Unit can be used as a standby boiler if the boiler goes out of service
Unit can produce Heat, Electricity and Cooling simultaneously
Reduces site fuel costs
Very quiet
Environmental:
More work with less fuel means lower pollution output
Improves energy efficiency
Reduces greenhouse gas emissions (in particular CO2
Lower SOX emissions with the use of natural gas as a fuel
Best use of natural gas resources
Disadvantages
The main disadvantage for using cogeneration is that the demand for steam and electricity must occur simultaneously. This is not a crippling disadvantage in that it can be remedied. Electricity, produced by a cogeneration system in a home, that isn’t being used, can be sold to the electric company. Also when heat is not required, as in the summer months, the heat produced by the cogeneration system can be used to run a steam-powered air conditioning system. These systems are initially more expensive than the normal electric units, however, in the long run the system makes up for the cost difference. One other disadvantage is that a decent amount of cogeneration systems still use fossil fuels as their main fuel source. While a CHP system will cut back on the amount of fuel needed, there is still a concern for air pollution any time fossil fuels are being burned. Finally, some CHP systems do not capture as much waste heat as others. This means some systems are not as efficient as others. One such example would be diesel engines, due to the fact they do not have as high of an efficiency in some CHP systems as others.
References
- http://en.wikipedia.org/wiki/Cogeneration Cogeneration-Wikipedia, the Free Encyclopedia
- http://science.jrank.org/pages/1572/Cogeneration-History-cogeneration.html Cogeneration - History Of Cogeneration
- http://www.gizmag.com/go/4936/ BMW unveils the turbosteamer concept
- http://en.wikipedia.org/wiki/MicroCHP Micro Combined Heat and Power-Wikipedia, the Free Encyclopedia
- http://www.toolbase.org/Technology-Inventory/Electrical-Electronics/combined-heat-power Combined Heat and Power Systems for Residential Use
Group Members
Justin Smoker
Jacob Pessia
