POWER September 2020 - 37

RECIPROCATING ENGINES
Efficiency, Reliability, and Resiliency
In addition to being flexible, reciprocating
engines are also highly efficient.
" Modern simple cycle medium-speed
recip plants have net heat rates in the
8,000-8,400
Btu/kWh
range
(HHV
[higher heating value], measured on the
high side of step-up transformers). This
translates to approximately 10% less
fuel consumption per MWh than the
most-advanced aeroderivative gas turbine, "
Lehtonen said.
Tütken also boasted about the efficiency
of reciprocating engines over a wide
range of load and operating conditions.
" Engine power plants can achieve an efficiency
rate of more than 50% in singlecycle, "
he said. " As part of a cogeneration
power plant, you can even get a system
efficiency of as much as 95%. "
Furthermore, engines are less sensitive
to altitude, ambient temperature,
and humidity variables than other technologies.
For example, studies have
found that gas turbine efficiency deteriorates
by about 1% for every 10-degree
increase in temperature above International
Organization for Standardization,
or ISO, conditions. That can translate
into a power output reduction under
some conditions of 5% to 10% for gas
turbines. Reciprocating engines, meanwhile,
retain their rated efficiency and
power output over a broader range of
ambient conditions.
To compensate for output reductions,
gas turbine OEMs use various techniques
to cool inlet air and boost turbine
output, including evaporative coolers
and mechanical chillers. However, inlet
air cooling requires additional power
consumption, and the effectiveness of
cooling systems is highly dependent on
ambient humidity. No water consumption
is required for reciprocating engines.
Recip plants use closed-loop radiator
cooling, and water injection is never
needed to increase power output.
Benefits of Islanding
Pacific Gas and Electric's (PG&E's)
Humboldt Bay Generating Station in Eureka,
California, a facility commissioned
in 2010 with 10 Wärtsilä 18V50DF engines,
completed a reconfiguration in
June that will allow portions of Humboldt
County to be separated from the
larger grid and energized exclusively
from the plant when transmission
sources that import, export, and stabilize
power to nearby areas are impacted.
PG&E said " islanding " 20 cities
and towns, including Eureka, Arcata,
McKinleyville, and Fortuna, as well as
some tribal communities, is possible
now using the plant.
" This represents a significant milein
Humboldt County
stone, not just
where customers will benefit directly,
but for all of the customers in our service
area who will benefit as we look
for innovative solutions to reduce the
impact of Public Safety Power Shutoffs
[PSPSs], " Andy Vesey, CEO of PG&E's
utility company, said in a statement announcing
the project's completion.
PSPSs are one of the measures
some California utilities have taken to
address wildfire risk during times of
When it comes to reliability, engines
are hard to beat. " Forced outage rates are
less than 1% per unit, which means for
a multi-unit plant the probability of all engines
being down at once for an outage
is infinitesimally small (compared to a single-shaft
plant). Also, maintenance can be
staged to assure maximum online capacity
at any point in time, " said Lehtonen.
Williams also noted the benefit provided
by a multi-engine plant. " When a
single, high-capacity turbine goes offline
for maintenance or service, we lose all
of the power generation capability at that
plant. Alternatively, by operating a fleet
of multiple gas generator sets, we have
additional units available to pick up the
slack if one goes offline, " he said.
The black-start capability that engines
offer is another benefit that cannot be
overstated. Many plant owners have
selected reciprocating engines because
of the resiliency this advantage delivers
during severe weather or other natural
disasters (see sidebar).
2. NorthWestern Energy is constructing a 58MW
power plant near Huron, South Dakota,
that will include six Cat G20CM34 gas generator
sets. The engines will replace combustion
turbines currently operating at the Huron Generating
Station. Courtesy: Caterpillar Inc.
September 2020 | POWER
A Solid Choice for Power Generators
Recip plants often have a standardized,
modular design that minimizes construction
time, making them much faster to
build than a combined cycle gas turbine
or steam/boiler plant. Typical execuwww.powermag.com
high
temperatures, extreme dryness,
and high winds. In certain situations,
companies will cut power to areas to
reduce the risk of an equipment failure
sparking a wildfire. Victims of wildfires
filed billions of dollars in claims against
PG&E, forcing the company to file for
bankruptcy on Jan. 29, 2019. The company
emerged from Chapter 11 on July
1, 2020, and has taken a variety of
steps to avoid future trouble.
" Our residents and businesses endured
hardships during safety shutoffs
even when there wasn't a wildfire
threat in Humboldt County, " Humboldt
County's First District Supervisor Rex
Bohn said in a statement. " PG&E leadership
answered our calls to make sure
they did everything they can to reduce
impacts next time. "
Depending on the situation, as many
as 67,000 customers, who might have
lost power when areas outside of Humboldt
County faced extreme weather
conditions, can now remain energized
by islanding with the recip plant. PG&E
said the size of the energized area is
scalable to the scope of the potential
PSPS event and other conditions that
could be impacting the grid at the time.
tion timelines range from a year to 18
months for turnkey projects. Commissioning
usually takes from one to two
months depending on the plant size.
" As with every new generation plant
that we plan to build, we performed an
exhaustive assessment of the current
and anticipated power need for the area
serviced by the Huron Generating Station.
We also conducted a survey to evaluate
all available technologies and select the
mix that best meets our needs, " Williams
told POWER, noting that reciprocating
engines were the lowest-cost means of
meeting NorthWestern Energy's portfolio
resource adequacy requirements.
" In this particular instance, reciprocating
engine technology will provide
the best solution. It gives us the quick
ramp-up, reliability, and right-size energy
blocks that we need to cost-effectively
cover periodic deficits for our customers.
It also provides us with a measure of insurance
to address peak load electrical
demand in today's dynamic power market.
If we see a spike in power prices,
we can rapidly start the precise number
of reciprocating-engine generator sets
that we need to minimize costs for our
customers, " he concluded. ■
-Aaron Larson is POWER's
executive editor.
37
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POWER September 2020

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