Energy in Greenhouses

It’s February, and Wageningen University’s Greenhouse Challenge has officially started. For the next few months, teams all over the world will be designing an urban farming system for the Bijlmerbajes, a former prison complex near Amsterdam (what is it with prisons and urban farming?). I am participating, helping out with the technical side of our group, Green Spark.

To give the teams some background and inspiration, the organisers of the challenge have provided a series of webinars covering many aspects. This week we had two technical webinars – one on circularity, and one on energy.

Today’s article is on the the latter: energy in plant production systems, given by Professor Geert Verbong, chair of System Innovations and Sustainability Transitions at Eindhoven University of Technology.

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The webinar. I swear, every screenshot I have is with his eyes closed.

Greenhouses as a source of energy?

The webinar was about the transition to a more energetically-sustainable greenhouse. People have been working on this for a while in the Netherlands. The Dutch horticultural industry constantly innovates, achieving impressive yields with high efficiency. Kas als Energiebron (the greenhouse as a source of energy) is an initiative by LTO (an organisation for farmers and greenhouse growers in the Netherlands) and the Dutch government.

In 2006, Kas als Energiebron built an experimental greenhouse, at a company called Hydro Huisman, to see whether a greenhouse could produce energy. Here are some of the innovative technologies they used:

  • Fine-wire heat-exchange systems (FiWiHEx).
  • Aquifer thermal energy storage (ATES), storing excess heat in a layer of wet sand underground.
  • Heat pumps, to supply and store heat when needed.

All of this was to collect, store, and reuse energy. The results obtained by Wageningen University and Research were promising. They expected that this greenhouse could produce more energy in a year than it used. The problem was that this isn’t economically feasible for growers.

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Picture from AP Holland.

Next-generation growing

In 2016, new goals and innovations were introduced:

  • Climate-neutral greenhouses by 2050
  • Geothermal energy
  • Solar photovoltaics
  • Semi-closed greenhouses, using ATES.
  • Better insulation.
  • More efficient systems in general.

This would be gradually implemented. Professor Verbong suggested that these goals weren’t really ambitious enough, especially since a lot of the solutions are already out there.

One approach that interested me was Het Nieuwe Telen (next-generation growing), another initiative by Kas als Energiebron. Het Nieuwe Telen includes a course for greenhouse growers. It aims to save energy and maximise yield through helping growers apply the knowledge of physics and plant biology.

Over 300 growers have done this, and the savings have been staggering. Simply by changing the way they control their climate, growers have been able to use 25% less energy – without a single change to their greenhouse’s infrastructure. A lot of it has to do with controlling humidity. By fitting new equipment, savings could be increased to 35%.

Professor Verbong’s projections

Greenhouses need to be seen as an energy utility. Many of them already are, using natural gas to generate electricity whilst supplying heat and CO2 to the greenhouse. Growers sell their energy to the grid, to the point where it’s become a significant source of income for many. That said, installing these cables is quite a task and the cables often outlast the greenhouses themselves. There are also vested interests, though the industry has managed to gain support.

Things could also be changed on a system level. Supply-driven smart grids, or an energy internet as Jeremy Rifkin calls it, would help improve efficiency. Through the EU, there is less protectionism within Europe, leading to lower energy prices overall. Renewable energy is becoming more competitive, though so have fossil fuels recently. Grid pricing is becoming based on marginal cost* – and nothing beats renewables for that.

Professor Verbong also raised political choices to be made. Will there be a top-down EU supergrid, or will our energy supply be based on local initiatives, or cooperatives? These don’t seem mutually exclusive, but I’ll stop now, because I don’t know much about the European energy market.

Back to the scale of a city. Professor Verbong said that an entire city can’t become zero-energy within its own boundaries. I suppose this is because within its own area, there isn’t enough solar or wind energy to power a city.

Greenhouse horticulture – and vertical farming, for that matter – will remain energy-intensive operations. The Dutch horticultural sector needs to adapt to a future without natural gas. The question is how this energy will be supplied. Electricity? Heat? Biomass?

There isn’t enough biomass to completely cover the industry, but it could play a complementary role. Heat is still a good option, as long as it’s high-quality heat, so at higher temperatures. A general trend seems to be electrification. The changes are likely to be incremental.

*As more and more energy starts coming from renewable sources, this might not be such a good idea, according to this article.

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