this gets to be a very complex subject, one that we have been debating over at microcogen with some vigor
for quite some time.
"can cogen compete with the power company"
answer, no, maybe, yes ... depending on your criteria that will be considered
1. yes it can compete favorably when it comes to emission, generally the emissions are much lower per kw/hr
or btu/hr, or however you want to quantify the product of the cogen
2. no you cannot compete with the power company based on kw/hrs/gallon of diesel fuel, they buy their fuel
for much less to start with, and their generators are much more efficient that our smaller ones.
3. yes you can compete if you burn an alternate fuel that has a lower cost, such as nat gas in some area's of the country
being dramatically lower than diesel fuels ,btu/dollar basis.
in order to do so you must do the following
1. recover all of the available excess waste heat from the cooling system, that is if the thermostat maintains the engine temp
at 195 degrees F, any excess heat that would otherwise be dumped via a radiator must be recovered and put to use either heating water, providing for space heating, or charging a thermal mass (all easily done), and/or possibly driving an absorption cooler/chiller (more complex), and
2. you must recover ~ 75% of the waste heat that would normally be dumped out the exhaust, and put it to the same uses as outlined above, this is somewhat more complex but doable for the diy'er.
3. you must determine the sweet spot for the prime mover, that is where it runs the most efficient and cleanest, generally this is
somewhere around 90% of its full load rating. you must then maintain that loading when the unit is in operation.
4. the cogen must be sized appropriately for the loads it will service, so that when it is running all of its available Btu's and electrical output is put to use and not simply dumped. generally speaking for most cogen this is best done in the colder months of the year which coincidentally works out it is the darkest time of the year, and the time of the year where folks are generally couped up inside
and place the largest draw on a system. (more heat requirements, more lighting, more tv/stereo, more refrigeration, cooking, washer and drier etc)
if the area of the country you live in for instance has perhaps 4 months of dark, rain, windy, snow weather, and you have a family
with a couple kids, it is easy to determine and size a cogen so that it can be most effective and compete very well with the utility company "if" you can get decent fuel rates. the rates don't have to be stupendously low, just reasonable
based on rates for natural gas in central kansas for december 2010, i can produce electrical power for a bit less than half of what the power company charges for electricity, "only" if when the cogen is operating in cogen mode, and all of the heat is used properly. the cost of production includes the price of the fuel, first cost of the prime mover, depreciation, repairs/maintenance and depreciation of a battery/inverter system to cover lighting loads when the cogen is shut down.
cogen is site specific,fuel and fuel cost specific, and application specific, must like wind power... it isn't the answer for everyone certainly, however it might be the answer for a lot of folks, and if all one is considering is the environmental impact when it comes to cogen vs engine driven genset, cogen is the clear winner running away.
bob g
