A public housing project in Spain capped by a 20-story tower was able to conserve enough energy that it sold energy back to the grid, the architect says. Passive architectural methods and on-site generation also contributed to a "considerable reduction" in carbon dioxide emissions.

A cogeneration system produces both electricity and heating on site, according to the architects, ACXT. The proximity of the power generation and the usable heat generated as a by-product offers significant energy savings.

The U-shaped project is capped on one end with a 20-story tower. The remaining three sides rise between four and seven stories.

The apartments each occupy the full depth of the building, allowing the designers to place windows into all of the apartment's key living areas. Bedrooms have been positioned to overlook the central garden, while kitchens face outwards toward surrounding streets.

Because much of the building's roof is visible from the various towers in the vicinity, the architects treated the roof as the building's "fifth facade." The building's plant has been hidden in lower level of the building, maintaining the clean surface of the roof.