KEY LARGO -- South-facing small windows and Bahama shutters, light paint and a white roof offer clues to the character of this house within a hammock: It is a ''green'' home that proudly wears a photovoltaic system and thermal water heater on its roof and envelopes a 7,500-gallon cistern within its walls.

And while the south side purposely presents a demure if somewhat pinched facade, the north demeanor is typically Keys-ean with stately porches, wide overhangs and French doors opening to the buttonwoods, beach and Florida Bay.

John Hammerstrom, an airline pilot, and Diane Marshall, a creative writing teacher at Florida International University, built the home in 2002. Former Californians with an eco-consciousness, the couple couldn't find the features they wanted in existing Keys houses, so they bought a lot, did their research and created their green dream.

Alternative energy is coming back into fashion as environmental concerns grow and temperatures climb along with the price of oil, hovering near $80 a barrel. The sun's potential power is greatest in the southwestern desert states, but Florida gets some 75 percent of the maximum daily sunshine, enough to power many appliances.

''We're getting all kinds of inquiries,'' said Paul Landino, owner of eMarine in Fort Lauderdale. ``We have been selling self-contained power systems to the islands and doing a lot of land-based stuff here, too.''

State and federal rebates are making systems more affordable. Interest in photovoltaic systems as emergency power during hurricanes is increasing as well.

During Hurricane Wilma, Hammerstrom and Marshall stayed put. With hurricane shutters, solar power, a cistern and steel-reinforced concrete pillars securing their porches, they felt confident enough to ride out the storm.

''During the few times that the power goes out, we get very conservative,'' Hammerstrom said of their energy use.

Learning how to put together the systems that make their home green turned the couple into local experts. Marshall, who wanted to share what they learned, helped create the Keys GLEE Expo (Green Living and Energy Education), an annual workshop that showcases green materials, building techniques, landscaping and even solar cars. (The next one will be May 9 through 11 in Marathon.)

While it is possible to disconnect from an electric power grid with photovoltaics (PV), the couple opted to stay attached and have the utility-generated power run the air-conditioning system, the microwave and dishwasher. Any time their PV system produces an excess of energy, they can send it back to the Florida Keys Electric Cooperative and receive credit.

LIGHTS AND FANS

Their PV system powers compact fluorescent lights and fans in the three bedrooms and three baths, the living room, plus the Energy Star refrigerator, computers, pumps on the water circulation system and washing machine -- about 30 percent of the electricity used in the home throughout the year.

The 2,450-square-foot home, with an additional 1,400 square feet of porches and decks, cost about $300 a square foot (including the ample amounts of interior woodwork), or 15 to 20 percent more than a conventional home, said Hammerstrom.

Their highest electric bill has been $138; in the spring, when the doors and windows can be opened, that amount drops to $20.

The PV system cost $25,000, but rebates worth $11,000 took a significant bite out of that. In addition to the 24 panels on the roof, the system includes eight 6-volt golf-cart batteries to store the energy and an inverter. The inverter, which Hammerstrom calls the brains of the system, converts the DC power to AC and sends it to the appliances and lights. It also monitors the batteries and keeps them full.

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