19 C. In 2011 CombiVliet set up a production facility in Wieringermeer where it grows only tomatoes. The greenhouses are artificially lit from October to March for a total of 2250 to 2500 hours. The electricity the company needs to light the 240,000 m2 of glass comes from the general energy grid. In the service building alongside the greenhouse an energy company has installed combined heat and power plants to generate electricity which is then fed into the grid. The residual heat – normally an unusable waste product of energy generation – is used to heat the greenhouse. An additional advantage is that the waste gas CO2, released when energy is generated, is absorbed by the plants, thereby improving their growth