POWER November 2010 - 55

DISTRIBUTED GENERATION
ing cost of generation must be compared with
utility purchased power. The strength of the
microturbine option lies with combined heat
and power (CHP) or combined cooling, heat,
and power (CCHP), where the clean exhaust
heat can be recovered and productively used.
The primary value of any microturbine for
most business customers is its ability to reduce
the cost of energy. In addition to using
standard financial analysis methods to evaluate
a project, microturbines are often eligible
for federal incentives when operating on a
renewable fuel and a federal 10% investment
tax credit that may be taken as an upfront
grant. Many states also have rebate and incentive
programs to stimulate the purchase of
clean, efficient generation solutions.
Although an attractive payback on investment
is usually necessary to generate serious
customer interest, several market drivers help
determine how rapidly microturbine technology
is adopted, as explained below.
Microturbines Meet Low Emissions
Limits. An increasing number of regulators
around the world are adopting ultra-lowemissions
levels similar to those of the California
Air Resources Board (CARB). This
means that other generation alternatives,
such as reciprocating engine generators, often
must add selective catalytic reduction
3. Efficiency contest. The electrical efficiency of the competitive offerings in the microturbine
size range. Source: Capstone Turbine Corp.
40
38
36
34
32
30
28
26
24
22
20
18
16
14
Solar Turbines Mercury 50
Capstone C200
Elliott TA 100R
Ingersol Rand MT 250
Opra Turbines OP16-3B
(DLE)
Solar Turbines Saturn 20
Kawasaki GPB15D
systems. Several microturbine manufacturers
meet the CARB requirements without active
exhaust after-treatment, providing significant
cost advantages to owners.
One of the benefits of microturbine technology
is its capacity to achieve extremely
low exhaust emissions levels. Continuous
lean premix combustion provides low levels
of oxides of nitrogen (NOx), carbon monoxide,
and unburned hydrocarbons (often measured
as volatile organic compounds).
As a useful point of comparison, natural
Capstone C1000
General Electric GE5-1 (DLN)
Siemens SGT-100
Solar Turbines Centaur 50
Solar Turbines Centaur 40
Rolls Royce 501-KB5S
Kawasaki GPB30D
Rolls Royce 501-KB7S
Kawasaki GPB60D
gas-fired reciprocating engines produce NOx
at a rate about half of the average utility-scale
power generation system. The 65-kW Capstone
C65 (whose heat rate is about 11,800 Btu/kWh
LHV) produces NOx at a rate of approximately
9 ppmvd, a fraction of rate of a large natural
gas-fired reciprocating generator set.
In sum, microturbines offer superior performance
without the need for costly active
exhaust cleanup. Emissions are a key reason
why a major oil and gas company exploring
large shale reserves recently ordered 18 lowemission
C65 microturbines in August to
provide prime power for its central processing
facilities and metering sites in the Eagle
Ford shale gas development in south Texas.
Microturbines Meet Tough Utility InDresser-Rand
KG2-3E
Dresser-Rand KG2-3C
1
2
3
Power output (MW)
4. Practical part-load efficiency. This figure illustrates the part-load efficiency of a series
of five 200-kW microturbine modules functioning in tandem compared with using a single,
larger turbine. The area of the curve between the two part-load lines represents fuel savings.
Source: Capstone Turbine Corp.
Max efficiency mode
35
30
25
20
15
10
5
54
200
400
Power (kW)
www.powermag.com
600
800
1000
Load share
4
5
6
terconnection Requirements. Some areas
of the world limit grid connection of traditional
synchronous generators due to their fault
current contribution to an already stressed
distribution system. Most microturbines use
power electronics with digital processor controls.
This approach allows integrating the
unit's protective relaying functions into the
microturbine itself, including current limiting
in the presence of a utility fault condition.
Most microturbines use power electronics
to convert the high-frequency output from
the generator to 50 or 60 Hertz 400V to 480V
three-phase AC, which is useable by customers.
The high-frequency AC from the turbogenerator
first passes through an inverter and
is converted to DC. From this internal DC bus,
a second inverter stage creates suitable 50 or
60 Hertz AC. This output is filtered to meet the
low harmonics requirements of IEEE 519.
An advantage of this type of microturbine
technology is that the output inverter includes
integrated protective relay functions, so little or
no addition equipment is required to meet many
local utility interconnection requirements.
Microturbines Make Integrated Systems
Possible. Multiple units can be linked
into a microgrid that offers many advantages
for owners. (See " Microgrids Promise
Improved Power Quality and Reliability, "
June 2008 in the online archives at www
.powermag.com.) A single power system controller
can manage multiple engine packages
to synchronize their voltage outputs, adjust
POWER| November 2010
Efficiency (%)
Electrical efficiency (%)

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POWER November 2010

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