Greenhouse effect

12/15/2014 | Words: Lucie Maluck | Pictures: Robert Hack

CHP, tomato plant

Tomato plants as far as the eye can see. It feels like the middle of summer again even though it is cold and rainy outside. In Heiko Hagdorn’s greenhouse, it is summer all year round. The heat recovered from an MTU Onsite Energy CHP plant keeps the temperature at a constant 22°C – the perfect conditions for growing tomatoes.

Are you one of those people who can hardly wait to pick the first tomatoes of the summer season? The pride of holding the shiny red fruit in your hands is one of the highlights of the amateur gardener’s year. Heiko Hagdorn can enjoy that pleasure as early as March. That is when he picks the first tomatoes in his greenhouse. And not just one or two, but several hundred kilos a day.

Of course, Heiko Hagdorn is no amateur gardener. He owns one of the biggest vegetablegrowing businesses in southern Germany. His vine, cherry and cocktail tomatoes are sold to the Edeka supermarket chain through vegetable wholesaler Gemüsering Stuttgart. And he is always certain of one thing: “They taste delicious.” Why? “Because we leave our tomatoes on the vine until they are ripe, instead of picking them while they are still green and allowing them to ripen in transit,” he explains. That means the tomatoes are always fresh and full of flavour when they are made into a salad, soup or sauce, or served at table just as they come.

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Heiko Hagdorn is a tomato enthusiast and in 2008 came up with the idea of turning his
parents’ former outdoor market garden into a tomato greenhouse.

Almost all work done manually
To achieve all this, he and his team have to work very hard. Almost everything they do in the vast greenhouse, which is easily big enough for a football team to train in, is manual work. “Picking the tomatoes is the least of it,” he recounts. And it is certainly true that the crops – as he refers to them – have to be constantly nurtured. They are planted in January – not in the ground as an amateur gardener might do – but on coconut matting a metre off the floor. They grow about 20 to 25 cm a week. That is substantially more than you would expect in your garden greenhouse at home. But Heiko Hagdorn is able to provide the perfect growing conditions for his tomatoes. His plants are drip-watered. And not with rainwater or round-the-clock, but precisely between the hours of 9am and 4pm with water that has been specially enriched with nutrients. “After that the plants have had enough food,” he says. The temperature in the greenhouse is highly conducive to growth too. During the daytime it is a pleasant 22°C, which is turned down to 15°C at night. Under such perfect conditions, the plants develop their first blossoms after only a few weeks. On the large vine tomatoes, the blossom clusters are then pruned so that each cluster produces five tomatoes. “Unfortunately, the tomatoes do not all ripen at the same rate. The ones closest to the plant stem ripen first. If we allowed all the blossoms to grow into tomatoes, the earliest would be overripe while the last are still green,” the tomato expert explains. As he is talking, a bumble bee buzzes past his face. They are required for pollinating the plants just as in any other kind of garden. Except that the amateur gardener has to wait for the bees to arrive when nature disposes. Heiko Hagdorn orders his bees from a wholesaler and they are delivered to the greenhouse by post in a cardboard box.

Learning from the Dutch masters
Tomatoes are not just Heiko Hagdorn's job, but his passion. “I think there is something splendid about tomatoes,” he says when asked why they have been his specific choice of crop. His grandparents used to farm the land where the greenhouse now stands and kept livestock there. Later on, they began to grow vegetables outdoors. But the business was tough and soon became unprofitable. All the same, Heiko Hagdorn did not want to give up his parents’ business, so he looked around for new possibilities. He went to the Netherlands, the land of the world’s best vegetable growers. There he learned the secrets of tomato cultivation and decided to go into the business himself in 2008. “Only six to seven percent of the tomatoes eaten in Germany are actually grown here, so there is plenty of potential available,” he explained. Now his enthusiasm has infected his family too. His parents, Pia and Helmut, help out in the greenhouse, while his wife, Karin, organizes the workforce. And Heiko Hagdorn’s Dutch mentor comes by once a week to advise the family on how to look after the tomato crops. Heiko Hagdorn is a tomato enthusiast and in 2008 came up with the idea of turning his parents’ former outdoor market garden into a tomato greenhouse.

Combined Heat and Power module produces sustainable energy

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The CHP module from MTU Onsite Energy stands right next to the
greenhouse and generates 1,523 kW of electrical power
and 1,507 kW of heat.

Together, they form an enterprise that is working well and constantly developing. Hence in 2014, the family decided to invest in a Combined Heat and Power (CHP) module so they could  generate their own power for the greenhouse.“Simply because it’s sustainable,” is Heiko Hagdorn’s reasoning for his new acquisition. The 12V Series 4000 L64 unit from MTU Onsite Energy generates 1,523 kW of electrical power and 1,507 kW of heat. Most important for the Hagdorns is the thermal energy for heating the greenhouse. This is not needed every day, but rather in cloudy or colder weather. That is why the Hagdorns have installed a heat storage tank where they store the heat captured from the CHP module. So it is there “on tap” whenever the temperature in the greenhouse drops too far. But what happens to the electricity? “We feed it into the public power grid,” explains Heiko Hagdorn. That does not happen continuously, but only when the energy provider needs electrical power. Following the shutdown of numerous nuclear power plants in Germany and the large increase in renewable energy sources, the country’s power supply became more erratic than in the past. If there is a fresh wind along the coast and sunny weather across the country, the renewable energy sources are running at full tilt and there is a surplus of power available. However, if coastal winds are still and clouds cover the sky, energy providers have to turn to smaller, local power plants such as Heiko Hagdorn’s CHP module. The energy provider starts up the Hagdorn’s CHP module using an interface and then draws the power. “As we can be very flexible, we benefit from more favourable remuneration models. We are working on the assumption that the CHP module will have paid for itself in five to six years, even if it only runs for around 3,000 hours a year,” Heiko Hagdorn outlines. Not only is the power from the module used by the Hagdorns in their greenhouse. Even the CO2 emissions benefit plant growth. These are purified and then used later on to fertilize the crops.

“There are lots of tricks of the trade that you learn along the way,” Heiko Hagdorn relates. Along that way, he has developed from tomato lover to professional grower and is now an energy trader as well. So he is a few steps ahead of the average amateur gardener. But he still has one thing in common with that species – the delight and the sparkle in his eyes when he picks the first juicy red tomatoes of the harvest.

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