Corvus Energy of Richmond, B.C. has achieved impressive fuel savings aboard the world’s biggest hybrid electric ferry through its high power lithium polymer battery solutions. “The direct fuel savings for this ferry are currently between 15 and 20 per cent,” says Brent Perry, the company’s CEO. “In a year, that amounts to enough fuel to run 600 cars and saves the equivalent amount of carbon emissions.”

The Danish ferry company Scandlines commissioned the refit of the Prinsesse Benedikte this past summer from diesel electric power to hybrid electric power. Its successful conversion and resultant fuel savings have led to it being nicknamed the Prius of the Sea. “With total system-installation costs of approximately $4.5 million, the conversion will pay for itself within 2.7 years through direct fuel savings alone,” says Mr. Perry. “And it will continue to generate substantial operational savings based on the 10-year battery life.”

The Prinsesse Benedikte typically carries two trains, 200 trucks, 300 automobiles and up to 1,300 passengers. “The first big challenge was coming up with a battery solution that could generate all the required power,” says Mr. Perry. A 2.7 megawatt-per hour module was installed to generate enough power for a small town. Before the retrofit, the ferry had to continually operate four diesel generators at approximately 30-per cent efficiency to ensure it always had enough power to drive its electric motors. This inefficient use consumed 320 to 330 grams of fuel per generated watt-hour. Now, relying on Corvus’ lithium polymer nickel manganese cobalt battery power system, the ferry only needs to continuously run one generator at 92-per-cent efficiency to charge the battery system, while a second generator is operated for only about 20 minutes every two hours when the system senses that additional power is necessary. The generators operated at such high-efficiency rates use only about 200 g of fuel per watt-hour – more than 100 g less than inefficiently-run generators.

Corvus’ proprietary batteries make the biggest difference in how they can instantly multiply the power they obtain from the generator. The battery module can discharge 10 times its regular power capacity for up to 27 MW/h of power within seven milliseconds. “It works so fast that when the generators went off line at one point, none of the people aboard even noticed, and the ferry’s engineers were so astounded that you could have knocked them over with a feather,” Mr. Perry says. “We ran the boat for nearly 22 minutes before the generators were restarted.” The batteries recharge from empty to full within 30 minutes. “The battery’s capacity to quickly recharge and deliver peak power within seven milliseconds has the ferry depending on the fuel generators for just one-quarter to one third of the time,” says Mr. Perry.

In fact, the speed of the power delivery was actually one of the challenges when retrofitting the Prinsesse Benedikte. “Generators normally have a two-minute start-up cycle,” Mr. Perry explains. “So we had to work with Siemens in Kongsberg to develop computer algorithms and control mechanisms to enable the Prinsesse Benedikte to adapt to power being transferred so quickly.”

Corvus and Scandlines have so far identified 23 ways to optimize battery use for a payback on investment within 2.7 years instead of the originally estimated 4.3 years. And efforts will continue to identify additional energy-saving opportunities over the next 18 months. “We’re now looking at shutting off the fuel-driven engines when the ferry arrives in harbour so that the vessel electrically powers alongside the dock and stays in that fully electric mode while loading and unloading,” Mr. Perry explains. “We’re only planning to switch the engines back on when the ferry is out in the water, which again will mean less fuel use, less air pollution, as well as less noise.”

Mr. Perry says the work that Corvus is doing is not so much a revolution as an evolution in optimizing existing battery technology. “We deter mine a vessel’s power requirements and then figure out how we can supply a substantial portion of that energy with rechargeable batteries so that an installation or retrofit quickly pays off both economically and environmentally,” Perry says.

In addition to fuel savings, reduced reliance on diesel power will result in reduced maintenance expenses, and significantly longer engine life.

Further savings may be feasible when shore power is used to charge the batteries while loading and unloading.