“Flower and tomato cultivation on gas is coming to an end” was the headline of an article published by the Dutch national newspaper Financieele Dagblad (FD) on March 23. The headline was even more poignant: “High Gasoline Prices Force Four in Ten Greenhouse Farmers to Close Permanently or Temporarily.” What about energy consumption in greenhouse horticulture and when can we grow climate-neutral?
In addition to labor costs, energy is a major cost element affecting the price of our greenhouse products. For plants in greenhouses to grow optimally, a sophisticated mix of heat, light and CO2 is necessary.
For much of the time this can be done naturally in our Dutch climate. Good soil, water, CO2 and enough sunlight that provides the right temperature and light for growth.
However, at certain times of the year or even during the day there is too much or too little light and the temperatures are too low. As early as the 17th century, work was already underway to regulate the temperature. The winegrowers worked with “flat glass”, windows placed on low stone walls to let in the heat during the day. The windows were then “opened” and then closed at night and on colder days to keep the heat inside.
The first systems that stored heat a little longer and could also be used in a greenhouse were the wall greenhouses. A thick brick wall was built against which the windows were placed at an angle. The wall absorbed heat from the greenhouse during the day and slowly released it at night.
A few hundred years later. The Netherlands is still at the forefront of greenhouse horticulture. Our horticulturists now use high-tech greenhouses for growing vegetables, flowers and potted plants all year round. In order to do this as efficiently as possible, we no longer only use the light and heat of the sun, but we use other sources in addition when it is too cold, too hot, too dark or too bright.
We use lights in times when there is not enough light. This lighting has since become more and more LED lighting in recent years instead of the old fixtures which mainly gave off a lot of heat. We have fabric screens to prevent excess heat during the day and the same screens help us keep the heat inside at night. We use cooling systems and can provide additional CO2 in greenhouses.
To do this, we use a (gas) boiler or a combined heat and power (CHP) system. The boiler produces heat and we extract CO2 flue gases for use in the greenhouse. We not only produce heat and CO2 with cogeneration but also electricity for lighting.
Another good thing to know is that greenhouse horticulture feeds a lot of its electricity back into the grid. They use the heat themselves and the “leftover” energy can be used by others. Compared to the production of electricity in a power plant, where it is not always possible to use the heat released, this is a significant step forward in terms of efficiency.
Systems used by horticulturists are also on standby to handle the spikes. Since a cogeneration can be increased or reduced much more easily, it is an important link in what is called congestion management.
In recent years, all sorts of new solutions have been devised for storing energy over more or less long periods of time. The heat produced during power generation can be temporarily stored in a buffer tank when the heat is not needed in the greenhouse. This means that peaks and troughs can be compensated for during the day.
It is a good solution to serve as a ‘daily buffer’ but it will not solve the difference in ‘free’ heat between the summer and winter periods! The greenhouse effect means that heat from the sun can easily seep into the greenhouse, but not leave it. During the summer the windows must be open to dissipate this heat, but of course a much better solution is to store the excess heat so that it can be used during the winter.
This is done in an increasing number of farms using heat and cold storage. Heat is pumped into the ground in the summer and extracted in the winter. From 2006, Grower Maurice van der Hoorn in Ter Aar built the first “gasless greenhouse” to use this system.
The use of geothermal energy has also been extended with wells dug in deeper layers of the earth, for example at a depth of 2.3 kilometers under the Trias project. The hot water from these springs is used to heat the greenhouses. This is done via a heating network to which around fifty companies will be connected.
An excellent solution, but the use of geothermal heat requires significant investments and the fact remains that electricity (for lighting, pumps and cooling) and CO2 will still be needed. The latter can also be supplied, for example, via the so-called PCAP pipeline that can supply the CO2a waste from Shell, for example, to horticulturists via a long pipeline.
Electricity rates are a major concern for horticultural business owners. Due to government regulations, it has become fiscally very unattractive to buy green electricity. This means that these entrepreneurs always choose to produce their own electricity with cogeneration. This therefore means that they need gas again, even if they could do without it otherwise.
Thus, a lot is already happening in the horticultural sector in terms of energy efficiency, but the sector is not yet climate neutral. The overall objective is for the entire sector to be able to do without natural gas by 2040.
Yet there are also companies that think it takes too long. the Koppert Watercress for example, plans to be energy neutral by 2025. A greenhouse has been built which costs one million euros more per hectare than a “normal” greenhouse. It’s a colossal investment, but one that will save a substantial amount of energy.
Several innovations are currently being tested in this company as well. One of the other companies involved in this project is the Delft-based company Physee, which has been working for several years on the development of windows that transform light into electricity. They are developing a coating for greenhouses that converts UV light, which normally cannot be used by the plant for growth, into photosynthetic active radiation (BY). This means that more light (for growth) can enter the greenhouse. It is a “free” light, which means that no lamps need to be switched on.
Another innovation being tested at Koppert Cress is the thermal battery from Thermeleon. The technology they are developing is similar to that of the walls used in the very first greenhouses to store heat. The system stores heat when it is too hot in the greenhouse and releases it when the temperature drops.
Overall, particular attention is already being paid to innovations in the field of energy in greenhouse horticulture. There are a number of developments, but they are often too expensive or too risky for a grower to undertake on their own. This is, as is often the case, where cooperation is important! There are probably also innovations outside the sector that would be very well suited to horticulture. I am very keen to know which companies are developing innovative products that we as a horticultural sector could use. Not only to produce as quickly as possible in a climate-neutral way, but also to ensure that our horticulturists will still be able to produce enough healthy and safe food for our region in 10 years.
About this column:
In a weekly column, alternatively written by Eveline van Zeeland, Eugene Franken, Katleen Gabriels, PG Kroeger, Carina Weijma, Bernd Maier-Leppla, Willemijn Brouwer, Maarten van Andel and Colinda de Beer, Innovation Origins is trying to figure out what the future will look like. These columnists, sometimes joined by guest bloggers, all work in their own way to find solutions to the problems of our time. So tomorrow will be good. Here are all previous articles.