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The company Brightfarms planned to start to build hydroponic greenhouses on rooftop of grocery stores, across US, throughout 2011. Hydroponics is a method of growing plants using mineral nutrient solutions, in water, without soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite, gravel, mineral wool, or coconut husk. The Greenhouses harvest rainwater and produce food. Greenhouses typically offer the following sets of vegetables & fruits: lettuce and salad green varieties, leafy greens, herbs, tomatoes, peppers and cucumbers. They can potentially cultivate other vegetables & fruits. Because of the cultivation's proximity vegetables & fruits are very fresh and tasty since they don't get older and damaged during long transportation. 

Before the project (and nowadays since the project is starting this year) most of the fruits and vegetables were cultivated far away the shops. For example 90% of the lattuce in US, is coming from California

The initiator, Paul Lightfoot CEO of BrightFarms, was for nearly ten years, the CEO of an enterprise software company that improved the supply chains of major retailer and their suppliers. Previously he was the founder and CEO of Foodline, a venture-backed software company that provided customers and reservations  information technology to restaurants. The company BrightFarms is located in New York, a city with a tradition about greenhouses on rooftop like in the Earth Pledge Fundation.

BrightFarms finances and supports each mini-farm, including the staff and maintenance crew, contractually binding the grocery store below only to purchase fresh, extremely local products from above. This is a departure from the typical approach to rooftop gardening, which puts all design, construction, and maintenance costs on the building-owner. Since the farms cut transportation or preservation costs, they believe they can offer competitive pricing and make each farm a viable business on its own.

BrightFarms has solidified six undisclosed locations throughout the United States as part of their pilot program, but they plan on expanding as soon as possible. They plan on using Nutrient Film Technique(NFT) and Dutch buckets for most of the hydroponic technology, but they say most of the creativity lies in the climate control of the greenhouses. Each building is in a different microclimate and has different HVAC equipment, making temperature control with waste heat and air conditioning a tricky matter. Over time they plan on streamlining the design and build process.

It would be easy to multiply the same model, as the advantages of having local, fresh vegetable are the same in most parts of the world. For a future implementation, points to be considered are energy efficiency in operations, such as reusing heat and heat exchange from the greenhouses.