IEEE Electrification Magazine - September 2017 - 14

cost reductions in the supply chain.
Within the maritime battery segment, system designs focusing on
improved battery safety are another
clear trend.

Why Choose Battery Power?

The term cold
ironing refers to
the use of shore
power to operate a
marine ship when
it is in a harbor.

There are several different ways
to integrate a battery scheme into
a ship's electric power system,
and the method used will determine which potential benefits can
be realized. The traditional cargo ship configuration,
where the propulsion power is provided by a main
combustion engine directly connected to the ship's
propeller through a shaft, will have more limited possibilities than for diesel-electric configurations.
Recently, diesel-electric dc grid designs allowing for
easy integration of battery systems have received
much attention, with promises of improved overall
efficiency due to generator sets running on variable
speeds and fewer energy conversions. The most common benefits of a maritime battery hybrid power system are presented in the following sections.

(Figure 6). For ships with the facility
to store energy, this shore-based
power may also be utilized during
the operation of the ship, e.g., for
sailing into and out of harbors in
densely populated areas.

Running Fewer Engines
(Power Redundancy)

Several ship types have requirements for power redundancy for
certain types of operations. This is
particularly relevant for ships with dynamic positioning (DP) systems. The requirements for DP do not allow
for the start of generators, and the redundancy requirements must therefore be ensured by the machinery in
operation at any time (the spinning reserve). Running
engines at low loads generally leads to higher specific
fuel oil consumption, higher specific emissions, and
increased maintenance costs. The current DNV GL DP
rules allow for Li-ion batteries to fulfill the requirement for redundant power. This enables fewer running engines, leading to reduced fuel consumption,
emissions, engine running hours, and maintenance
costs (Figure 7).

Cold Ironing
The term cold ironing refers to the use of shore power to
operate a marine ship when it is in a harbor. Cold ironing
first came into use when all ships had coal-fired engines.
When a ship was tied up in port, there was no need to
continue feeding the fire, and the iron engines would
cool down, eventually going completely cold-hence, the
term cold ironing. Recently, cold ironing has been considered as a means to mitigate local air pollution by significantly reducing and, in some cases, completely
eliminating, harmful emissions from diesel engines

Running Engines at Optimal Loads
The specific fuel oil consumption and the emissions
from an internal combustion engine are dependent on
the engine load. Typically, engines are calibrated for
optimal performance at 60-85% of the engine load. For
ship types that experience large load variations during
operation, the introduction of batteries may allow the
engines to operate at an optimized point with respect
to fuel oil consumption and/or emissions. This can
be achieved by selecting the size of the engines such

Figure 6. The DNV GL concept ship Revolt connected to shore power. (Photo courtesy of DNV GL.)

I E E E E l e c t r i f i c ati o n M agaz ine / SEPTEMBER 2017

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2017