The Partnership no. 11

Geothermal energy is

Geothermal energy is becoming increasingly popular in numerous countries. Also – and in some countries even mostly – in greenhouse horticulture. The Netherlands drills down to depths of several kilometres to generate geothermal energy. That costs a lot of money, but the investment is counterbalanced by major social advantages. Hard measures will have to be taken all over the world to halt global climate change. Emissions of greenhouse gases, especially CO², must be drastically reduced. And the only way of doing this is by cutting back on our global consumption of fossil fuels. That’s not so easy with our strong dependence on non-renewable resources such as oil, natural gas and coal. This is true in particular in intensive greenhouse horticulture. In cold and temperate climate zones a lot of fuel is needed to keep the greenhouses and the crops grown in them at the required temperatures. Sustainable heat generation The past few decades the energy efficiency of high-tech farms has improved tremendously thanks to better insulation, more modern greenhouses, total energy systems, more efficient cultivation systems and smarter climate control. But all this isn’t enough. If we want to continue to improve sustainability we will have to make large-scale use of energy sources with a much lower CO² footprint. Water power, wind and solar energy are the most promising sources of electricity, while geothermal energy is an excellent candidate for sustainable heat generation. It all started in Iceland Using geothermal energy in greenhouses is by no means a novelty. Iceland has been doing it since 1924. That’s not so surprising in a country abounding in hot springs, geysers and active volcanoes. “Here, all farms make use of geothermal energy,” says Aad Groeneweg, Sales Advisor of the energy supplier Grodurvörur. The Dutchman has been living in Iceland since 1968, supplying growers with all kinds of horticultural needs, including vegetable seed. “Some growers use special pumps to pump steam through their heating pipes while others use hot water that is pumped up from depths of a few to several dozen metres. The ample availability of geothermal energy close to the surface has enabled greenhouse horticulture to flourish in Iceland, treating the local population to vegetables, flowers and plants grown in their own country.” Iceland’s greenhouse industry comprises a few dozen small farms, some of which are very modern. Most have greenhouses with a total area of no more than 5,000 m², the odd one around 1 ha. However, a group of investors is now planning to build an ultramodern tomato farm with an area of 5 ha near a source of geothermal energy. The idea is for it to focus on export to Great Britain. In expected and unexpected places A few other countries are now also making efforts to exploit geothermal energy for horticultural purposes, whether or not together with other users. Examples are New Zealand, South Korea (e.g. Nongsan; see page 12), Japan and – as yet on the largest scale of all – the Netherlands. New Zealand Gourmet, for instance, has a farm in Mokai near Lake Taupo in the middle of a geologically active area with hot springs. Here, a lot of geothermal energy is available directly at ground level. "That can be very efficiently exploited as an environmentally friendly source of heat – for greenhouses, but also to meet other local heat needs," says Paul Martin, CEO of New Zealand Gourmet. “The availability of geothermal heat and the cold nights make Mokai ideal for growing tomatoes in greenhouses." The fact that geothermal energy should have become so popular in the Netherlands, of all countries, in the past ten years may seem strange. After all, there are no hot springs in the Netherlands. However, deep down beneath the surface – at depths of around 1,500 metres and deeper – are various fault lines via which hot, liquid rock has found a way upwards from the mantle of the earth. What are known as aquifers – masses of water above or near these fault lines, mostly incorporated in porous strata above a layer of impenetrable rock – are consequently heated to temperatures of on average 65 to 85˚C. Pumps and heat exchangers The first Dutch source of geothermal energy was taken into use in 2006. A second project followed a few years later, and a third shortly after. Supported by government subsidies for geological research and trial drillings, and by investment funds for green energy, geothermal energy is steadily becoming booming business in the Netherlands. The water that is pumped up to generate the energy is not hot enough to produce steam. In all the projects launched so far it is passed through a central heat exchanger that is connected to the heating systems of the participating greenhouses. Having released its heat, the water is pumped back to its original depth at an angle. By ensuring a large enough distance between the production inlet and the injection outlet the cooled water has enough time to rise in temperature again and flow gently back to the production zone. This way a source of geothermal energy can be exploited in a profitable manner for dozens of years, possibly even longer. More than 250 ha in the Netherlands The Dutch geothermal power stations heat greenhouse areas of between 10 and 60 ha, depending on their size. Together, the fourteen projects already account for more than 250 ha. This implies tremendous savings in the natural gas that was hitherto used to heat all the greenhouses. And there’s more to come. Another three projects will be launched in 2017, and it is generally expected that the capacity will more than double in ten years’ time. There are even serious plans to drill to a depth of 4 km, where the water is hotter, promising greater thermal yields. Technology Product Geothermal energy, a new boost The Partnership | 33