Professional BoatBuilder - December-January 2018

40 PROFESSIONAL BOATBUILDER

SYSTEMS: Battery Technology

capacity of 1.2 kWh with a cost one-

tenth to one-  h that of the same

capacity lithium-ion.

Happily for lithium-ion, this cost

comparison is grossly misleading. At

best, the lead-acid battery will deliver

only half its capacity each time it is

discharged and recharged (cycled),

whereas lithium-ion will easily deliver

80% of its capacity.  e lead-acid battery

can be cycled only hundreds of times

before it fails, whereas lithium-ion,

depending on its chemistry and con-

struction, can be cycled thousands of

times. A true measure of the cost of a

battery is how much energy can be

cycled through it during its lifetime

(what I call the lifetime kWh through-

put), divided by the battery’s purchase

price.  is will yield a cost per kWh of

throughput. In many applications, if

the capabilities and cycle life of lithium-

ion can be fully exploited (in practice,

this is o en not the case), even at

today’s prices lithium-ion will have a

lower cost per kWh of throughput

than any lead-acid battery.

 e deeper we delve, the better it gets

for lithium-ion. Let’s say I am running

my main engine or generator to charge

the battery at anchor. We have to

include the engine run time, fuel, and

maintenance in the cost of the energy

being produced, along with the battery

cost per kWh of throughput. If I have

an 8-kW charging device and I have

lithium-ion batteries that can absorb

the full 8 kW to a high state of charge—

whereas lead-acid batteries will, on

average, absorb only half this—then I

can cut the engine run time for battery

charging in half. If I run the numbers, I

will  nd this dramatically reduces my

cost of energy, more or less regardless

of the cost of the lithium-ion batteries.

(For more on calculating onboard

energy costs, see “Running the Num-

bers,” PBB No. 120, and “Taking

Charge,” PBB No. 148, page 60.)

Electrical System Advances

Both LFP and NMC have the prop-

erties we need for the massively power-

ful 8-kW+ alternator-type device we

are currently testing. A relatively small

strong proponent of LFP,

has seen the writing on

the wall and is developing an NMC

o ering. But at the same time, the

Yanmar Technical Bulletin allows only

LFP to be used with Yanmar’s factory-

installed alternators.

Cost Comparisons

Once the safety issues are resolved,

cost becomes the major drawback of

lithium-ion batteries.  e individual

cells may not be that expensive, but

they have to be packaged into a bat-

tery, and an e ective BMS added.  is

BMS needs to be custom-developed

for the relatively low-volume marine

marketplace.  e net result is that it’s

hard to  nd a marine lithium-ion bat-

tery that retails for less than $1,000 per

kilowatt-hour (kWh) of capacity, and

some run as high as $2,000. By com-

parison, a 100-amp-hour (Ah), 12V

lead-acid battery has a nominal

the result that 60% of new car sales

have been diesels, there is now talk of

banning diesels altogether from city

centers. Automotive manufacturers

are scrambling to adjust to this new

reality, with a massive reorientation

toward electric cars.  is will require

lithium-ion batteries in large numbers

at low costs. To achieve this, the indus-

try will have to settle on a speci c

chemistry and format, and tool up the

factories for volume production. Once

this happens it will, to some extent,

lock in a technology that will domi-

nate the marketplace.

As of now, it looks like NMC will be

the chemistry of choice. Already at

least two marine lithium-ion battery

players—Torqeedo and Volta—have

partnered with automotive suppliers

to repackage NMC cells for the marine

marketplace. Lithionics, formerly a

This 174' (53m) trimaran

(above) was recently equipped

with electric propulsion sup-

plied by lithium-ion batteries

from Lithionics (right). While

Lithionics initially favored

lithium-ion iron phosphate

(LFP), it’s now developing

nickel manganese cobalt

(NMC) as well, recognizing that

chemistry’s growing preference

in the automotive world.

Left—While the price per

unit for marine lithium-ion

batteries, such as this

Volta with built-in BMS,

and their related systems

can be prohibitive, lithium-

ion batteries can reduce

energy costs over their

lifetime.

COURTESY VOLTA

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