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Distributed generation is used to provide onsite electricity and
heat generation for commercial and industrial purposes. Sometimes these
power systems only operate as a back-up power source, while more
advanced ones are designed to operate at all times. Because of the high
efficiency of these advanced units, this strategy can provide lower
cost energy to the customer, and be used as a component of a more
expansive energy management strategy. The onsite generation of
electricity avoids the loss of electricity from transmission and
distribution losses, which can account from 9% of all power generated.
Many industry observers liken the migration of energy production from
centralized to distributed to the migration of computer technology from
mainframe to desktop. Microturbines
Micro-turbines are small gas turbines used to generate electricity
on-site. Air is drawn in and compressed by spinning blades and mixed
with a gaseous fuel, many times natural gas. This mixture is combusted
in the middle combustion chamber, with the hot gases streaming out the
back through another set of turbines. The rear turbine blades are
connected to the front turbine blades, which draw in the air and enable
the continuation of operation.
Roughly the size of a refrigerator, these units typically have power
outputs in the range of 25-kW to 300-kW. In comparison, gas turbines in
large power stations have much higher power outputs of around 100-MW to
300-MW. The small size of micro turbines is a major advantage that
allows them to be situated right at the source of electricity demand.
Diesel Engines
The
diesel engine is an internal combustion engine like a gasoline engine,
but unlike a gasoline engine, the fuel is not ignited by a spark
instead, it is compressed and heated until its auto-ignition
temperature is reached. Both engines use fuels derived from oil, but
with slightly different physical and chemical properties. Petroleum
fractions used for diesel fuel are chosen for their good auto-ignition
properties and they are very similar to fuel oil used for residential
heating.
Diesel engines are used for low-maintenance stand-by power systems, and
in the transportation market. Diesel engines power large trucks in the
U.S. primarily, but Europeans have long used the engine to power
automobiles as well. In 2004, diesel cars represented 44 percent of all
cars sold in Germany, which is the biggest European market. Diesel cars
commanded a similar market share in France, Spain and across the rest
of Europe. If the current trend continues, in a year or two
diesel-powered cars may exceed 50% of all new cars sold in some of the
biggest European markets.
Fuel Cells
A fuel cell is a device that converts chemical energy directly into
electricity via a modified oxidation process. The process also produces
heat, water and possibly carbon dioxide depending on the fuel used. The
different varieties of fuel cells are distinguished by the electrolyte
used, though the construction of the electrodes is also different in
each case. However, in all types, there are separate reactions at the
anode and the cathode, and charged ions move through the electrolyte,
while electrons move round an external circuit. There are five types of
fuel cells. They differ by the chemistry temperature they operate on,
catalysts used and raw fuel input.
CHP—Cogeneration
Combined Heat and Power (CHP) is sometimes also referred to as
cogeneration—the production of both power and steam for commercial or
industrial uses. Any on-site power generation technology can be used
for this strategy, although microturbines and fuel cells are generally
chosen.
The production of onsite heat is a very energy intensive process, so
coupling its production with electricity allows for greater
efficiency—with some processes over 70% efficient, as compared to
35%-40% for many large-scale coal-fired central stations which are the
mainstay of the U.S. power generation fleet.
Clean Coal Technologies
Coal is the remnants of organic material that has undergone tremendous
pressures and temperatures as it was buried within the earth for
millions of years due to its origin, there are many parts to coal that
cause significant pollution as it is burned to generate electric power.
Since the burning of coal produces over half of all electric power in
the U.S., finding ways to minimize its impact is important.Clean coal
technologies refer to any technology that allows coal to be burned
cleaner—either with the release of far less pollutants, or in a more
efficient manner that reduces the amount of pollution produced while
the total energy produced increases. Technologies that control
pollutants such as mercury, SOx, NOx, and particulates are being joined
by some that can capture and store underground (sequestrate) CO2. Other
technologies control these pollutants and increase the efficiency by
turning the coal into a gas and burning it in a gas turbine (IGCC –
Integrated Gasification Combined Cycle).
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