Our goal is to provide vegetable factories enabling cultivation in all conditions, whether in a desert, frigid clime or the middle of the city," said Tokitaro Hoshijima, project director, Project PV at Mitsubishi Chemical Corp of Japan. The company plans to launch its vegetable factory business, including a combination of solar cells and light-emitting diodes (LED), at around the end of 2009.
The firm's vegetable factory will shut out the outside world and totally control the interior environment, including temperature, humidity, CO2 concentration, nutrients and illumination. Running costs will be minimized through a combination of solar cells and LEDs. Mitsubishi Chemical has entered the vegetable cultivation field through a tie-up with Fairy Angel Inc of Japan, already experienced in commercial vegetable factories, to cooperatively develop a new type of vegetable factory integrating solar cells and LEDs. An experimental plant will be constructed in part of Fairy Angel's newest plant, scheduled to come online in August 2008, and used from this fall to optimize vegetable growth parameters for the solar cell/LED design.
Zero Electricity Costs
Vegetable factories are hot these days: consumer interest in food safety is surging, and vegetables cultivated in cleanroom factories are becoming increasingly popular. For producers, foodstuff-related firms and other parties in the field, vegetable factories mean planned production, unaffected by changes in the season, weather, or other factors.
These vegetable factories face a major problem, though, in the high cost of electricity for lighting, air conditioning and other uses, which accounts for about 30% of total running cost. Mitsubishi Chemical hopes to cut electricity cost for vegetable plants to zero.
According to a source at Mitsubishi Chemical, switching from florescent lights to LEDs will cut power consumption far enough to make it possible to use solar cells to supply the load. Engineers use red and blue LEDs, which cover the absorption peaks of chlorophyll, to achieve more efficient illumination than that available from red-deficient florescent tubes. The intermittent illumination that LEDs excel at is ample for photosynthesis, and the end result is a major reduction in power consumption. Engineers believe that illumination on a 200us cycle is sufficient for cultivation.
Using solar cells also means a higher initial cost, though. Mitsubishi Chemical hopes to resolve this problem by using organic solar cells, costing a fraction of what Si-based solar cells cost. The firm plans to resolve fundamental obstacles to volume production by 2015, stating that organic solar cells would cut cumulative costs (power source and lighting-related expense) to the same level as florescent lamps running off the commercial grid in about seven years, and end up about 30% lower in a decade (Fig 1). Si-based solar cells will be used to construct a factory with zero CO2 emissions in operation, and once organic solar cells enter volume production they will be used to construct a vegetable factory.
by Satoshi Okubo