Page 27: of Marine News Magazine (March 2017)

Pushboats, Tugs & Assist Vessels

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the relatively large amount of fuel required, we assumed the hydrogen would be stored as a liquid at a temperature of 20 degrees Kelvin, using a single cryogenic tank and a regasi? ca- tion system similar to Liquid Natural Gas (LNG).

We made one major change to the design ground rules for the fuel cell option. The baseline vessel has suf? cient fuel for 35 days of operation. This is due to the client’s need for re- serves in the event of a major earthquake. The vessel actually refuels every two weeks but it carries the full weight of fuel.

EBDG’s modeling adjusts the size and weight of the fuel for the different scenarios based on fuel consumption and the 35-day capacity. The fuel cell version cannot carry large quan- tities of liquid hydrogen (LH2) since LH2 has much less en- ergy density than diesel fuel. We sized the LH2 storage tank to suit a resupply every four days with a 20% margin from a standard tank truck with a capacity of 3,200 kg of LH2.

Bottom Line / Looking Ahead

It can therefore be concluded that hybrid propulsion needs to be evaluated on a case-by-case basis. Some take- away thoughts are as follows: • Battery costs are coming down. Our model assumed $1,000 per kW-H of capacity while some vendors are now looking at prices closer to $800 per kW-H.

• Recharging during the day helps reduce the size and cost of batteries substantially.

• Electrical rates vary widely across the U.S. Our study assumed $0.0768 per kW-H. Many areas have price ad- justments for transportation projects or environmental ini- tiatives. Learn more about your local electrical utility!

• Battery life should be carefully evaluated. Given the rapid changes in battery technology, is a long battery life really the wisest decision?

• Fuel cell technology is real but the fuel is very expensive given the current sources of supply. As the hydrogen supply in- frastructure develops, fuel cells will become increasingly attrac- tive as an option, despite the complexities of cryogenic storage.

• Using solid data as input to the evaluation is essential to have con

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