The idea of going offshore to satisfy our renewable energy needs isn't new, but the grand vision of Japan’s Shimizu Corporation goes way beyond harnessing green energy at sea for use in cities on Terra firma – it takes the whole city along for the ride. The company, along with the Super Collaborative Graduate School and Nomura Securities, is researching the technical issues involved in constructing its Green Float concept – a self-sufficient, carbon-negative floating city that would reside in the Equatorial Pacific Ocean.

The concept would comprise individual floating cells or districts resembling water lilies with a radius of 1km (0.62 miles) that would form a compact village that could house 10,000 to 50,000 people. Joining these districts together would form a city or module that would be home to 100,000 people, while a group of modules would form a country (though we assume there is some red tape involved before you get a seat at the U.N.).

Floating cities in the sky

The majority of the inhabitants would live in 1km high “City in the Sky” towers located at the center of the circular cells, while additional “Waterside” residential zones comprising low-rise townhouses would be located on the outer edge of the structure’s outer circumference. To take advantage of the cooler temperatures, the tower residences and services would be located at the top of the tower at an elevation of 700 m (2,296 ft), providing year-round temperatures of 26-28 °C (79-82 °F). As the population of the cities grow, additional cells could be added, spreading out like the water lilies they resemble.

The central tower would be surrounded by grassland and forests, while the outer circumference would adjoin marine forests, lagoons and beach resorts. The cells are designed to be completely self-sufficient in terms of food with the 1 km high towers containing a plant factory, while livestock and other farming would take place in “plains” also surrounding the tower. Seafood lovers would obviously also be well catered for through fishing the surrounding ocean and the marine forests.

Carbon negative

The cities would use a number of technologies to make a carbon negative system. The designers say the compact form of the city alone would allow a 40 percent reduction of CO2 through more efficient transport and distribution, while energy conservation through increased thermal insulation, facility efficiency and next-generation technologies would provide a further 30 percent reduction. The use of solar power provided by space satellites, ocean thermal energy conversion and wind and wave technologies would provide an additional 30 percent reduction. The ocean would also be used for carbon sequestration.

The Green Float concept would also produce zero waste by recycling resources and converting waste into energy. It would even help clean up the oceans by collecting any passing “garbage islands” for use as an energy resource.

Location, location, location

The islands would be located at the equator as it isn’t prone to typhoons and the climate is stable. However, in the event of large waves, strong elastic membranes would be attached to the lagoons around the outer circumference of the cells, with the shallows above the membranes standing 10m (32.8 ft) above sea level. The water pressure difference between the lagoons and the ocean would limit the movement of the membranes and buffer the force of the open sea waves. Additionally, 20-30m (66-98 ft) high seawalls would be constructed to handle a worst-case scenario.

The Green Float concept was on display at the recent Innovation Japan University Exhibition 2010 where DigInfo TV was told that the Green Float cities wouldn’t be fixed in place but would literally float slowly on the ocean currents. Given much of the technology included in the concept doesn’t exist yet, Shimizu, as part of a three-way agreement with the Super Collaborative Graduate School, and Nomura Securities, will initially concentrate on nurturing R&D projects on the technologies required for such a project. However, the company’s hopes of turning it into a reality by 2025 may be a little ambitious.

But ambition isn’t something that seems to be lacking at Shimizu. The company also proposes encircling the moon in a belt of solar collectors that would collect solar energy and transmit it to Earth using microwave and laser transmission technologies. You definitely couldn't accuse this organization of thinking small.