Later this year, a double-rigged crane will hoist a giant power turbine part way up One Penn Plaza, a black monolithic skyscraper next to Madison Square Garden. When the natural gas-powered generator on the 12th floor starts, it will not only produce some 6.2 megawatts of electricity — enough to power up to half the 57-floor building on a busy day — but it will also siphon off excess steam and use it to help heat and cool the 37-year-old skyscraper.