Earl Bakken, the 91-year-old inventor of the pacemaker and a longtime Big Island resident, already has his 9-acre Kona Coast estate off the grid but now wants to power it without any fossil fuels.

Bakken is the founder of Medtronic Inc., a Minneapolis-based medical device maker with 49,000 employees and $17 billion in annual revenue. He retired to Hawaii in 1990 and finished building his estate, which he calls Bakken Hale, in 1999.

The Kiholo Bay property consists of a main residence of approximately 18,000 square feet, a guest residence and personal office of 3,000 square feet, a garage, a greenhouse and an orchard. Bakken produces all of his fresh water through a reverse osmosis system. All communications and telecommunications systems for the property are wireless.

Now Bakken has started building one of the largest private residential photovoltaic systems in Hawaii not connected to a utility electrical grid.

Until now Bakken has relied on three propane-fueled generators for his electrical power. He will stop using propane once his solar system is in place.

To help power his home at night or on cloudy days, Bakken is buying a battery system built by Pittsburgh-based Aquion Energy. The system includes 46 washing-machine-size batteries each weighing 3,300 pounds.

"They wanted to be able to run with three days of autonomy," Ted Wiley, vice president of product and corporate strategy at Aquion Energy, said Tuesday. "If it was cloudy for three days, they will be totally fine."

If it stays cloudy for a fourth day, a rarity on the Kona Coast, Bakken would use biodiesel backup generators.

Bakken’s solar system will comprise 512 solar panels installed on land next to his tennis court. Renewable Energy Services in Hono­kaa is putting in the 176-kilowatt solar array. The estate can run on about 30 kilowatts of power, and the rest will be used to recharge batteries.

"We’re about a third of the way through the project right now," said Peter Shackelford, president of Renewable Energy Systems.

"This is a uniquely large system for off of the grid. If this battery turns out to be what we all think it is, it is a game changer."

The batteries will be put in place in March and will be the largest storage system Aquion has installed, Wiley said.

"It’s going to be the biggest one that we’ve done," he said. "A typical household system would be something like 6 to 8 kilowatts."

Bakken began construction of the PV system in October and hopes to be done with the installation in June, said Adam Atwood, lead coordinator at Bakken Hale.

"It’s considerably bigger than any other system on the Big Island," Atwood said. "There are larger commercial system, but for a private system, it is very large for a family residence."

Bakken said he wants his estate, located within Kiholo Bay Wilderness Park, to be used to teach the community about alternative energy.

"I want to educate young people and get them interested in electronics," he said. "Other people around here who want to put in solar systems can come and ask how it is done."

When operational, Bakken Hale will have a tour for students, Atwood said.

"We are going to turn it into more of an educational center where we’ll bring in classrooms and students and take them through the whole facility," Atwood said.

Because Bakken hopes to use his home as a catalyst to promote green energy, the materials of the Aquion battery are one reason he chose the company, Atwood said.

"Aquion battery has no dangerous or toxic components," Atwood said. "We have a reef system right outside the house; we are very interested in maintaining the reef system."

The batteries are made from sustainable material including activated carbon, cotton and salt water, Wiley said.

"They are completely sustainable, totally safe. You can touch it with your hands," Wiley said.

The system is far outside the norm for off-grid installations, said Marco Man­gels­dorf, president of Hilo-based ProVision Solar.

"This is, by order of magnitude, much, much larger than any other residential system," Man­gels­dorf said.