Dash-IQ said:
I'm confused, gerbi are there generators that consume an energy source(hydro,coal,gas,etc...) that have an efficiency over 80% Power plants based have much more less percentages.
Check this
link.
When you calculate the thermal efficiency of any complex power cycle, you have to look at the efficiencies of the individual machines which make up the plant.
For example, in a conventional coal-fired generating plant, you have a boiler, which burns coal to make steam for a steam turbine, and an alternator driven by the steam turbine which makes the electric power coming out of the plant.
Now, the individual efficiency of each major machine in this process can be relatively high. For example, modern boilers can be designed to be about 88% efficient, that is, 88% of the total heating value of the coal consumed by the boiler is transmitted to the steam coming out of the boiler. Steam turbines are wonderfully simple machines, and it is hard to design one with less than 85% efficiency. Similarly, a properly designed alternator can be up to say 98% efficient.
When you combine these individual efficiencies to estimate an overall thermal efficiency for converting a pile of coal into a bunch of megawatts coming out of the plant, you have to multiply all these efficiencies together, which brings the final value down a bit. Thus:
Boiler: 88%
Turbine: 85%
Alternator: 98%
Combined efficiency: 0.88 * 0.85 * 0.98 = 0.73 = 73%
From this 73% efficiency is still to be deducted the losses for the various auxiliary machinery which is required to run the plant, like pumps and blowers, before you get to the largest amount of heat loss in the plant, the condenser, which turns the exhaust steam from the turbine back into liquid water, which is then pumped back into the boiler and turned into steam again.
If, instead of a steam plant, you have a gas turbine or large diesel engine turning the alternator, you can eliminate the need to heat water to turn it into steam and condense it back to liquid again, plus all of the associated machinery and its losses. This helps to raise the theoretical efficiency of the generating plant, but you are no longer able to use relatively cheap coal as a fuel. You must use a liquid fuel or natural gas, which are a bit more expensive.
