The Battery Park City Authority in New York City is holding a competition asking developers to submit plans for the nation’s first eco-friendly residential high-rise. The building must incorporate such features as solar panels, fuel cells, non-toxic and recycled building materials, roof-top gardens, and gray-water systems, which reuse water collected from sinks, showers, and laundry facilities to flush toilets and water plants. It also must be 30 percent more energy-efficient than required by the state, bring in 30 percent more natural light than required by the city, and have plumbing that uses 10 percent less water than required by the feds. The impetus for the undertaking came from New York Gov. George Pataki (R), who has promised a tax break to builders to go green. Not interested in high-rise living? A model environmental home, a totally refurbished 1920s arts-and-crafts-style house, will be open for public viewing in a few weeks in Cambridge, Mass.