Not all loads are turned on at all times, and many come one after another, each for a short duration of time in a set sequence.
Therefore, the required generator capacity in kW is always less than sum total of kW ratings of all connected loads.
This time diversity in their power demand is taken into account by assigning a load factor to each load equipment based on the heritage data on a similar ship built and operated earlier.
What is ship load factor?
The load factor (LF) – also known by other names such as demand factor,
diversity factor, utility factor, or duty factor
Is defined as the average power over a period of time as a fraction of the peak (or rated) power of the equipment.
Thus, the load factor indicates to what extent a specific load contributes to the total load on the generator, which aggregately powers all the connected loads. If the timevarying load power p(t) is expressed in kW over any specific operating period T (e.g., at sea, in-port loading, etc.), then the load factor during that operating period is:
For example, a 10 kW motor used at full load for 4 h and at one-half load for 2 h during a 12-h period on loading days at the port has a load factor of
(10 × 4 + 5 × 2) ÷ (10 × 12) = 0.42
during the daytime loading period. During other periods, it may
have a different load factor, such as zero at night.
The ship power plant capacity factor may be calculated on a seasonal or annual basis. It measures the fraction of the ship power plant’s peak rated capacity in kW that is used over the period.
A higher capacity factor of the ship power plant means the equipment is utilized for more hours, resulting in a lower capital cost per kWh delivered to the users.