Over Yonder Cay – the Carribean's renewable energy island

4 February 2015 • Written by Marilyn Mower
Over Yonder Cay is a Bahamian island that is completely powered by renewable energy sources.

Most sailing yacht owners harbour a sly smugness that their pastime and their mode of seagoing transportation approaches carbon-neutral. But once tied to the dock, many good intentions fade in the power-hungry reality of luxury living ashore. Enter Dr. Ed Bosarge and Marie, his wife, owners of the sailing yachts Tenacious and Marie, and now an entire Bahamian island that runs on its own grid of renewable energy.

To date, the system has offset more than 600 tons of CO2 and should avoid the production of more than 950 tons annually, double the annual emissions from the Bosarge’s two yachts. Over Yonder Cay, which was completed in March 2012, is approximately 70 acres and encompasses four villas, a boathouse and seaplane base, a deep-water marina, pools, and numerous support buildings entirely powered by wind and sun. Located in the Exuma chain near Sampson Cay and Bell Island, the island sits on the edge of North Cut.

When the Bosarge Family Office purchased the island, the idea was to develop it to be independent of diesel fuel.

‘My first thought was to set up the island to run on ammonia gas,’ says Bosarge. Converting large diesel generators, vehicle engines and outboards to burn liquid ammonia, however, proved a bit more difficult than powering the island with wind, sun and storage batteries. More than 1,200 Evergreen cells are arrayed in the solar field, putting out 260 kilowatts per hour of DC power at peak output, which is sent to the inverter room for conversion to 480V AC power. The three permanent magnet wind turbines each pump out a maximum of 100 kilowatts of AC power. The island is set up on a 13,200V grid with all utilities buried well underground.

A computer-controlled system either pulls the AC power directly or triggers stored DC power from the batteries to flow through an inverter for use. All unused power is fed to the storage batteries, and Bosarge says the entire island could run for several days on the battery power alone. By comparison, a neighbouring resort island burns through $1.8 million in diesel annually to power the island. Bosarge says he will recoup his alternative energy investment at Over Yonder in about four years.

The system has offset more than 600 tons of CO2 and should avoid the production of more than 950 tons annually, double the annual emissions from the Bosarge’s two yachts


Unless the island is in full party mode, the wind and solar farms are putting out more power than can be used or stored, and one of the wind generators is taken offline once the batteries are full.
‘It drives me crazy to waste power,’ says Bosarge. ‘We are planning to load bank our extra energy by creating a 550,000-gallon cistern and bring an additional 20,000-gallon watermaker online. Watermakers are the most power-hungry devices on the island. If we make water with the extra power we have during the windy spring months, we can store it for the summer when the winds are light.’

Over Yonder’s inverter house – a concrete bunker – contains 540 2V flooded lead-acid 2,500ah storage batteries, each weighing 330 pounds.

‘We looked at lithium-ion and glass mat batteries, but both of those need to be cooled, and when we were getting started, we didn’t know if that was feasible,’ says Mike McGuire of Hurricane Hill Development Corp., the engineer behind the design and installation. ‘This system is infinitely scalable and when we replace the batteries in the normal course of events, we may switch to glass mat batteries, which will allow us to stack the batteries and thus double or triple our capacity.’

While Over Yonder Cay is the first such alternative power hybrid island in The Bahamas or Caribbean, when planned water turbines are placed on the edge of the North Cut, it will be the first in the world to draw and balance power generation from three renewable sources.

‘Water turbines are more reliable than wind; two to three knots of current courtesy of the moon gets us the output of twenty knots of wind,’ says McGuire.

Originally published: January 2011.

Marilyn Mower

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