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FOGHORN
For land-based utility companies, serving intermittent and 
high-power consumers is a challenge. It has an impact on 
the entire grid capacity as this less predictable and intermit-
tent consumer must be calculated into the overall system. 
Ports and piers are often located at the outskirts of the 
grid, making capacity upgrades even more costly to meet 
peak demand. Despite the challenges, the future of electric 
vessels should be welcomed as a future source of increased 
revenue for local utility companies. 
Shore power is already available at many U.S. ports. The 
main purpose is to enable vessels to shut down engines 
while at dock. For large vessels like container ships and 
cruise ships, this provides benefits for both shipowners 
and ports. Shipowners can carry out necessary operations 
while also performing inspection and maintenance work 
prior to next trip. However, once vessels leave the dock, 
they rely entirely on their combustion engines again. 
Shore power and shore charge share similarities, but they 
serve different purposes. 
THE SHIFT FROM AC 
TO DC ONBOARD A VESSEL 
When discussing all-electric vessels, we typically refer to 
battery-operated ships, such as ferries, passenger boats, 
harbor cruise vessels, or similar crafts operating within cit-
ies or ports. These vessels are built around onboard energy 
storage systems (ESS). A DC link in the range of 700-1000 
VDC is commonly used for power distribution. To charge 
such a vessel, the shore side grid power must be converted 
from AC to DC. This raises a fundamental, but technical 
question: Where should the AC/DC transformation oc-
cur, at shore side or on board the vessels? 
AC AS A CHARGING SOURCE
AC shore power can be used for charging. In that case, the 
PHOTOS: SARAH FERRETTI
FOGHORN FOCUS
The ZPP 700/800 are examples of autonomous towers that connects to a vessel less than one minute after arrival and can be 
used for both AC and DC charging. 
PHOTO: ZINUS POWER LLC

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