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The use of Direct Current in greenhouse horticulture appears to be a very promising alternative. A pilot in the greenhouse horticulture sector demonstrated a positive business case for the use of Direct Current (DC) for greater durability of components, as well as cost and material savings. DC also supports the idea of climate-neutral greenhouse horticulture, as demonstrated in the Direct Current Roadmap.

The DC Roadmap, presented last Friday, is a report compiled by Berenschot at the order of RVO.nl for the Energy Top Sector and TKI Urban Energy. This DC Roadmap focuses on ‘DC microgrids’ and seven specific areas of application. A microgrid is defined as follows: ‘a system of interconnected sources and users that can operate, either independently or linked, on a higher-level grid and can exchange energy’.

Greenhouse horticulture comprises a DC microgrid

The various DC microgrids are, with respect to the innovation phase, at the beginning of the S curve: there is a great deal of uncertainty and there are numerous, divergent opinions and ideas about the value (social or otherwise) of DC microgrids. The report, however, revealed that DC is highly promising in greenhouse horticulture; only second to the market for public lighting. The reporters visited greenhouses whose entire indoor electrical system is set to DC. In this, a single, centralised AC to DC transformer is used, to which a lighting system with DC light fixtures (SON-T or LED) and in some cases a CHP unit is connected.

Advantages of DC in comparison to AC

The use of DC in greenhouses extends the life of the light fixtures. Using thin film condensers instead of electrolytic condensers allows greenhouse growers to opt for components with a longer useful life. In addition to this, material savings can be achieved because a DC system uses cables that are smaller in diameter, which therefore require less copper. Researchers also reported that DC makes the integration and control of systems easier. It enables light fixtures to be dimmed individually because the DC cabling simultaneously allows for the control of lighting (powerline communication). Lastly, the centralised conversion of AC to DC will ensure that less energy is lost in comparison to local conversion per lamp (2 - 3%) at the start of operations.

Rounding off the pilot phase

The Roadmap predicts that the pilot phase for using DC in greenhouse horticulture will be rounded off soon. Sustained growth is possible due to the increasing demand for sensors and PV systems. The first successful pilot was completed in the Netherlands and demonstrated a positive business case. This pilot is being conducted at the Jaap Vreeken bouvardia nursery. The pilot is currently being continued at a larger scale.

Conducive to LED systems

Newly built or renovated greenhouses can now also be fitted with DC electrical systems. This applies primarily to nurseries with DC-fed SON-T or LED (in the near future) light fixtures. It is anticipated that using DC will also decrease the costs of LED systems. In the future, priority will be attached to the use of PV panels and the integration of smart innovations (such as controllable light fixtures and smart sensors) in greenhouse horticulture. The integration of these technologies can strengthen the benefits of a DC microgrid.

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With the second crop in the Winterlight greenhouse at the Energy Innovation and Demo Centre (IDC) in Bleiswijk (NL) coming to an end, it’s time to draw some initial conclusions. The predominant feature of the greenhouse is its extremely high light transmittance.

Growers don’t only stand to gain from this in the winter but in the dark autumn months too: the 10%-plus light gain the designers were aiming for has turned out to be a reality. This not only means that all the partners involved in the project did a fantastic job, but also that the models used in the design process, such as RAYPRO, have proved their worth.

Results

On the crop side, the two high-power crops we grew also yielded good results, despite the thrips problems we had in the first crop. With a few growing weeks to go, the tally is currently 268 cucumbers with an average fruit weight of 407 grams, bringing the total yield to more than 109 kg/m2. We are pleased with the outcome on the energy front, too. In this greenhouse, which is single glazed and has two high-transparency screens and a dehumidifier with heat recovery, we used less than 20 m3/m2 gas between the end of December and mid-November. But this did mean that we had to buy in around 13 kg of CO2.

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Hortinergy is an online software package for designing energy-efficient greenhouses by simulating energy consumption and comparing technical solutions.

Energy is a major expense in greenhouse horticulture. There are currently several solutions on the market that can help reduce your energy bill. The dilemma is how to choose the best configuration adapted to the climate outside and inside the greenhouse and the crops grown in it. This is the first online software solution to simulate the energy consumption of an existing or planned greenhouse anywhere in the world.

User-friendly

Suitable for a wide range of users, from growers to consultants and greenhouse equipment manufacturers, it is user-friendly and it takes less than 15 minutes to enter your parameters. To simplify the user experience, equipment manufacturers can spotlight their branded products for selected pre-set parameters. Hortinergy is a decision-making tool for sizing equipment and optimising investments: users can compare energy efficiency and technical scenarios with a simple online interface.
www.hortinergy.com
Stand number: 12.132

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Nuon, Heineken Netherlands, the municipalities of Rotterdam and Leiden, Warmtebedrijf Rotterdam (Rotterdam Heat Supply) and the province of Zuid-Holland have taken an important intermediary step towards the completion of the ‘Leiden Region Heat Supply’ project. The six parties signed a Declaration of Intent on 4 April 2016.

This will bring the construction of the 43-kilometre underground pipeline one step closer. The pipeline will transport residual heat derived from industrial applications from the port of Rotterdam to Leiden via an eastern route. After completion of this heat pipeline, the residual heat will be used to heat the city of Leiden and the surrounding areas. This system will provide the Heineken brewery in Zoeterwoude with steam for its brewing processes, among others, in lieu of the natural gas the company currently uses to generate heat. The pipeline will be part of an even larger district heating network that is still to be completed in the province of Zuid-Holland. The new pipeline will enable allow an estimated 50 million m3 of natural gas to be saved on an annual basis.

Open heat net

In the future, other municipalities and business enterprises along the pipeline - such as greenhouse horticulture firms - will be able to benefit from this heat supply, too. In addition to this, the system also offers opportunities for other sources of heat, such as geothermal heat or biomass. Provincial Executive member Han Weber: ‘This is an important step towards the realisation of an open heat network in Zuid-Holland, the heat hub. The Provincial Authorities are primarily identifying opportunities for expansion. We are engaged in involving more suppliers of sustainable heat sources, such as geothermal heart and biomass, and more customers, such as the Oostland greenhouse horticulture region. This will result in a heat infrastructure that serves a broad interest.’

Due to the availability of residual heat from industrial sources, which would otherwise be lost, less natural gas will be used in the Leiden region in the future. That will result in a considerable reduction in CO2, estimated at 90,000 tons a year. A reduction in CO2 emissions like this is consistent with the sustainability objectives of all parties involved.

Heat pump

With the signing of the Declaration of Intent, the six parties laid a solid foundation for close collaboration. From here onwards, the parties will actually proceed with the construction of the pipeline and the supply of heat. A new type of heat pump will be developed in order to make it suitable for use at the Heineken brewery. Additionally, investigations are being conducted into the best possible solutions for the construction of the pipeline and the best integration of the underground pipeline in the area.

Watch the video about this unique project here (Dutch spoken).

Source/photo: Programmabureau Warmte Koude Zuid-Holland.

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'We should not depreciate the closed greenhouse', 'Greenhouse growers should rely less on feelings and more on knowledge' and 'In the greenhouse sector of 2050 gas is no longer relevant'. These were some of the remarkable statements that were made at the well-attended EnergiekEvent 2016 in Bleiswijk, where the 10th anniversary of Kas als Energiebron was also celebrated.

Looking back, Kas als Energiebron (Greenhouse as a Source of Energy), the innovation and action programme for energy efficiency and sustainability in the greenhouse horticulture sector, was found to be successful. The energy efficiency of the Dutch greenhouse growers has increased significantly, while the energy sources are becoming more sustainable. Especially thanks to geothermal and residual heat, wind energy, (semi-)closed greenhouses, diffuse glass, LED lighting and - the manual is in need of a reprint - Next Generation Cultivation.

Micro-controller

The best news of the EnergiekEvent was that the increased energy efficiency does not affect the quality or production. But it does require more data, knowledge and insight of the growers. "Before, there used to be one measuring unit on each hectare. In the future we want to change this to smaller units. Maybe even to micro-controllers for every plant, not only for the production, but also for the quality. For example, think of LED lighting to enhance certain plant components," says Sjaak Bakker, manager of Wageningen UR Greenhouse Horticulture.

Bakker outlined a future in which electricity will play a leading role. "We are rapidly moving towards an all-electric situation. Just look at electric cars, batteries and what's happening in LED lighting. They are already thinking about lighting through foils or glass cells."

Our CO2 supply should also be different in 2030 or 2050, Bakker said. "If we no longer burn gas in the future, where would we get our CO2 from? An example might be extracting CO2 from the air."

Closed greenhouses

Next Generation Cultivation is being succesfully applied in various crops, including tomato and gerbera. An estimated 15 to 20% of the Dutch growers is using this method. A lot of knowledge has been gained in closed greenhouses and during previous research, Bakker said. "In Next Generation Cultivation many things that were already developed have been put together: think of temperature integration, research on screens, air movement, etc."

The closed greenhouse is disappearing, it seems. But Wilco Wisse, chairman of Kas als Energiebron and staffmember of Lans Tomaten, thinks that closed greenhouses should not be depreciated. "We ourselves also have an Optima greenhouse of 1.5 hectares and we know better than anyone how difficult it is to make profits with it. It is actually a huge solar collector though, it stores excess heat of the summer and supplies it in the winter. Therefore, we should not depreciate the closed greenhouse.”

Sustainable future

Leo Oprel, currently working as a policy advisor at the Ministry of Economic Affairs - who is considered as the founder of Next Generation Cultivation at Wageningen UR - outlined a sustainable vision of Dutch horticulture, in which:

  • new greenhouses will look very similar to existing greenhouses
  • gas has been replaced by sustainable electricity and heat
  • virtually no chemical pesticides are used
  • the use of CO2 for growth is limited
  • knowledge is crucial
  • climate control will include energy and ventilation management
  • heat exchangers will become commonplace to transfer energy from the moist greenhouse air to the incoming drier air
  • cultivation is done with more humidity, with a very homogenuous greenhouse climate
  • light is the key for temperature control
  • the diffuse greenhouse roof transmits more light and there are more screens hanging above each other
  • super translucent greenhouses will determine the production - and the existence - in the winter
  • light will be flexibly captured above a certain level in the summer and will be available for energy storage
  • excess radiation is immediately absorbed without the greenhouse air heating up too much
  • assimilation lighting is used on the basis of the requirements of the plant
  • the artificial light is also dimmable because it works with direct current
  • the heat requirement is reduced to 10 cubic meters of gas per m2
  • geothermal energy and heat pumps with heat/cold storage supply the residual heat
  • the backup will consist of batteries
  • offices and industrial buildings supply additional electricity with roof-integrated solar panels
  • windmills are a regular appearance in horticultural areas
  • proud entrepreneurs have created a sustainable future!

Kas als Energiebron, the innovation and action plan for energy efficiency and sustainability in greenhouse horticulture of LTO Glaskracht Nederland and the Ministry of Economic Affairs, will continue until the end of next year. Both the greenhouse horticulture industry and the government want to continue with the program. The ministry of Economic Affairs wants to maintain the 50/50 cost sharing – but is still negotiating with LTO.

At the end, the participants visited the workshops and greenhouses at Wageningen UR/Delphy Improvement Centre, where they were informed of the latest research.

Text/photos: Mario Bentvelsen.