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Preparing an Existing Diesel Power Plant for a Wind Hybrid Retrofit:
Lessons Learned in the Wales, Alaska, Wind-Diesel Hybrid Power Project
Stephen Drouilhet, P.E.
National Renewable Energy Laboratory
1617 Cole Blvd.
Golden, CO, 80401 USA
1 Introduction
In countries around the world, there are many communities not served by national or regional
electric grids. In many of these communities, power is generated by small diesel power plants
that range in size from about 100 kW to several MW. There are thousands, perhaps tens of
thousands, of isolated diesel-powered villages worldwide. In the state of Alaska alone, there
are approximately 200 diesel-powered communities. In addition to village power systems, there
are hundreds or thousands of diesel plants providing power to a variety of remote commercial
and industrial facilities, including mining operations, military bases, resorts, and fish farming and
processing operations.
There are many reasons why diesel power systems are so widespread. Diesel generators are
by far the lowest capital cost electric generation technology in the sub-MW size range. They are
a well-established and well-understood technology and there is a worldwide support
infrastructure in place. When properly operated and maintained they are also very robust and
reliable. However, diesels also have major disadvantages. They are noisy and emit significant
air pollution. Though relatively cheap on the world market, transportation costs can make diesel
fuel very expensive in remote locations. In arctic communities, where fuel may only be delivered
once per year, fuel storage costs also are very high, and the risks of major fuel spills greater.
Finally, because diesels require frequent oil changes and other service at regular intervals, they
have a relatively high maintenance cost per kWh delivered.
Wind-diesel hybrid power systems preserve the advantages of diesel generators while
mitigating their disadvantages. Wind turbines have a higher cost per installed kW capacity, but
zero emissions, zero fuel cost, and lower routine maintenance requirements than diesels. Rural
utilities and national energy agencies worldwide are beginning to see the opportunity that wind-
diesel hybrids offer to reduce the life-cycle cost and environmental impact of rural electric
service. Because an existing diesel plant frequently represents a substantial investment, it often
appears more cost-effective to retrofit wind turbines, system controls, and any other required
ancillary components to the existing power system rather than build a completely new wind-
diesel hybrid system from the ground up. This was true in the case of the Wales, Alaska, High-
Penetration Wind-Diesel Project, a technology demonstration project in which the National
Renewable Energy Laboratory (NREL) collaborated with the Kotzebue Electric Association
(KEA), the Alaska Village Electric Cooperative (AVEC), and the Alaska Energy Authority (AEA).
Most of the engineering effort on the Wales project focused on the design and development of
the new system components, primarily the main system controller and the energy storage
subsystem. Comparatively little attention was paid to the diesel plant itself and to the
modifications necessary to successfully integrate it into a fully automated wind-diesel hybrid
system. Consequently, many diesel plant shortcomings were overlooked until they manifested
themselves in the field during the start-up and commissioning of the wind-diesel hybrid system.
The resulting problems revealed that in such a system, the diesel plant must perform to a higher 2
standard of performance than is often expected of the typical village power plant, which is
usually designed to be completely manually operated. These higher performance requirements
necessitate more rigorously designed diesel plants. Design shortcomings were found in all of
the major diesel plant subsystems (engine cooling and fuel systems, generators, controls,
switchgear, and distribution system). These shortcomings primarily affected the following areas:
ease of retrofit system installation, frequency and voltage stability, time for diesel start-up and
synchronization, generator paralleling, load-sharing stability, and plant and engine temperature
control. This paper discusses each of the relevant plant design considerations in detail, in
hopes that by sharing this experience, system integrators and project planners will give proper
attention to diesel plant preparation (or replacement), and future wind-diesel systems will be
installed and commissioned more quickly and cost-effectively.
2
Overview of the Wales, Alaska, High-Penetration Wind-Diesel Project
The configuration of the Wales wind-diesel system is shown in Figure 1. The system is
composed of the existing diesel power plant, two 65-kW wind turbines, an AC/DC rotary power
converter, a battery bank, two electric boilers serving as secondary loads, and a Programmable
Logic Controller (PLC)-based main system controller.
Wind penetration is a term referring to the ratio of the wind power output to the village electric
demand. According to the classification scheme used at NRELs National Wind Technology
Center, a high-penetration wind-diesel system is one in which the annual wind energy output of
the wind turbines is at least 50% of the annual primary electric demand and in which the system
has the capability to provide electric power with no diesels running during periods of sufficient
wind power availability. The Wales wind-diesel system is thus a high-penetration system,
because the Wales wind turbines are projected to generate approximately the same amount of
energy annually as is consumed by the primary village load, and because the power system can
operate diesel-off as long as the short-term average wind power exceeds the average load by a
small margin.
The individual components of the wind-diesel system and their role in its operation are
discussed in detail below.
2.1 Diesel Power Plant
The pre-existing diesel plant in Wales consists of two Cummins LTA10 and one Allis-Chalmers
3500 diesel gensets, rated as shown in Figure 1. Prior to the implementation of the wind-diesel
system, the plant was entirely manually controlled, with the operator deciding when to run the
various generators and manually starting, stopping, and synchronizing them to the grid. The
gensets are of different ages and origins and, prior to this project, were equipped with various
assorted voltage regulators, governors, and actuators.
Manual diesel operation is incompatible with the effective implementation of a high-penetration
wind-diesel system. Maximum fuel savings demands that only the most efficient diesel(s)
adequate to meet the net load (village load minus available wind power) are run at all times.
Furthermore, to capture the additional fuel and maintenance savings made possible by a
reduction in diesel run time, the diesels must be shut down completely when there is more than
enough wind power to meet the load. Under such an operating regime, the starting and
stopping of any particular genset will be more frequent and unpredictable than is feasible with a
manually controlled system. For this reason, the first step in system installation was to retrofit 3
all diesels with controls making them capable of automatic starting, stopping, sync