‘Direct current has no disadvantages’
It takes a certain amount of courage to be the first grower in the world to switch to direct current. It has lots of advantages, but the world is simply already geared to alternating current. Jaap Vreeken: ‘We’re making substantial savings, and we can tell a good sustainability story. There aren’t any disadvantages, and that’s what we’re going to tell everyone in our demo facility.’
Vreeken Bouvardia grows Bouvardia in 12 acres of greenhouses in Rijsenhout, The Netherlands. The Bouvardia, grown for cut flower production, is very sensitive to damage from salt, and its cultivation can result in high losses. This is actually a perfect crop for a very experienced grower. After all, an easy plant – one that anyone can grow – quickly becomes a mass-produced crop.
The company is more than a hundred years old but has had various locations. ‘We’ve always been involved in innovation’, says the grower. ‘My father was a pioneer in the cultivation of Lisianthus and Trachelium. Bouvardia was similar: a niche product about which little cultivation knowledge was available. So when we were asked if we wanted to conduct a test using direct current at our company, it didn’t take us long to agree. We like trying out new things.’
AC: a legacy from the past
Assimilation luminaires as well as many other electronic devices use direct current (DC), and solar cells produce direct current. But the power grid is based on alternating current (AC). As a result, every assimilation luminaire needs a converter to convert AC into DC. Alternating current is actually a legacy from the early years of the power grid when it was technologically easier to develop a reliable grid based on AC. Since then, the grid has grown exponentially. Now, however, its limits are becoming clear. Many electronic devices operate internally on direct current so that conversion losses occur everywhere. A change, however, would be difficult because everything is designed for AC.
This is why the project at Vreeken Bouvardia is really revolutionary. ‘Here, alternating current is not being converted into direct current at each luminaire or every device. Instead, this is being done by a single converter outside of the greenhouse’, says Vreeken. ‘This means that luminaires can be produced in much smaller versions.’ The lighting equipment allows more sunlight into the greenhouse and generates less heat, which substantially improves its life expectancy and reliability.
Lamps can be regulated individually
Bouvardia is a short-day plant that initiates flowers as soon as the day-length drops below a certain number of hours. The entire 12 acres receive lighting; the sections where the plants are being kept from flowering receive a day-length of 18 hours. As soon as they are deemed ready to initiate flowers, this is decreased to 12 hours. After harvest, the plants are pruned of all leaves.
‘During this stage, using full lighting would be inadvisable. The big advantage of DC luminaires is that every lamp can be regulated individually. After pruning, I can go back to reduced lighting just to keep a bud from forming. I can also reduce the light level at the end of cultivation. With the DC grid, I can dim the lights or turn them off or on whenever I want, depending on the crop stage. This saves me 25% on energy as compared with an AC grid’, he says.
The cooling system, ventilation system and a cogeneration plant operating on DC are also connected to the DC grid. ‘You can reduce a normal cogeneration plant to 75% capacity. For one operating on DC, this is 40-50%. This opens up new possibilities, too. During off-peak periods when electricity is cheaper, you can reduce the capacity of the cogeneration plant and have the lamps at full capacity. During peak periods when electricity is more expensive, the reverse is true.’
If the entire horticulture sector would switch to DC, this would result in huge savings – not only on direct energy costs but also on investment costs. ‘For every acre, you could eliminate 1800 pounds of copper cabling. You would have to invest less, and you would earn it back sooner,’ he indicates.
Behind his greenhouse is a field with a growing number of solar panels. Solar panels generate direct current that can be sent directly to the horticulture holding and to other buyers without any conversion losses. Vreeken is considering street lighting, for example. Every conversion into AC that can be avoided saves energy.
In addition to the direct savings resulting from avoiding conversion losses and from making more efficient use of the greenhouse systems, the grower sees yet another significant advantage. ‘We can promote ourselves among our customers with a good sustainability story. Florists are looking for the story behind cut flowers. We can honestly tell them that we are growing “sun bouvardias”; after all, our electricity comes from solar energy and is being utilized as efficiently as possible. This is truly unique.’
But it isn’t meant to remain unique. In the company’s demo facility, other growers are gradually being updated about the advantages. When asked whether there were any disadvantages, he has to think long and hard. ‘I really can’t think of a single one’, he says.
Gavita advocating DC
He is very enthusiastic about Gavita’s role in the project. Gavita sees major advantages in DC and is investing a great deal of effort in both the awareness of its advantages and the realization of such a charismatic project. As Vreeken sees it, ‘They’re working really hard on this. GreenTech is sending shuttle buses our way, and they’re generating publicity everywhere. Growers, however, still have to be really convinced, and this is where positive PR plays an important role. We’re introducing something really unique that’s going to benefit the Dutch economy. Dutch horticulture needs constant innovations to hold on to its international position. I’m glad I can contribute something by what I’m doing.’
The transition to direct current at Vreeken Bouvardia was made possible by a consortium by the name of Doe DC, an abbreviation for Demonstratie Ontwikkeling Energie-Instrastructuur DC (demonstration of the development of DC energy infrastructure).Partners in this project are: Vreeken Bouvardia, Gavita, Direct Current, Stichting Gelijkspanning, Stallingsbedrijf Glastuinbouw Nederland, Solar Green Point, and Siemens Nederland.
Sponsors are: The Dutch Ministry of Economic Affairs (its Sustainable Local Energy Initiatives scheme), the Municipality of Haarlemmermeer, LTO Noord Fondsen, LTO Glaskracht Nederland (Greenhouse as Energy Source), Meermaker, and Greenport Aalsmeer. The Alliander power company provides the grid connection.