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The road map for a sustainable and economic viable greenhouse horticulture depends on the local conditions and climate.
Netherlands and Northern Europe
For the Netherlands the most promising directions to reach a fossil free greenhouse horticulture is to make use of fossil free heat sources like waste heat from industry or geothermal heat and/or to use green electricity as the major energy source. Technically both options have proven to work, as can be seen in the scenarios shown in the Greenhouse Energy Guide. It will depend on the local availability and price for fossil free heat sources and/or green electricity to determine which is the most suitable pathway to go.
For illuminated greenhouses the electric power connection to the grid is in general already that large that the additional electricity demand for not only lighting but also heating of the greenhouse is likely to be possible. However, if a group of growers in a conglomerate of greenhouses increase their electric power consumption this might be problematic. This holds in particular if next to the increment of the demand, the local production of electricity is reduced or unstable. With the phasing out of Combined Heat and Power, such a decline of local electricity production is very likely. The pathway based on heat pumps to accommodate the heat demand of greenhouses will therefore be very much dependent on the expansion of the electricity grid.
The phasing out of CHP is a result of European agreements on reductions on CO2-emissions. In order to comply to these agreements, changes in taxes and charging for CO2-emission in the context of the European Emission Trading System (ETS) result in a gradual increase of the costs for burning gas ETS. Especially for small growers the costs for gas are increasing fast, so there the consequences are the largest.
The decline of installed CHP will be somewhat tempered because next to the increased costs of base-load CHP-operation, the benefits from peak-demand electricity production are likely to increase as well. These peak electricity prices are expected to become high, but the yearly number of hours that CHP-engines will run are expected to decline. Other, fossil free heat sources are therefore likely to become the main heat source.
In North European countries other than the Netherlands, CHP plays a less prominent role in the energy supply for greenhouses, but other aspects related to the transition towards fossil free greenhouses are quite similar. This means that it is not so much a technical issue that determines the most viable option, but predominantly the local availability of the alternative energy sources (fossil free heat or green electricity).
In future hydrogen might be an option as energy carrier. Hydrogen can be produced from electricity surpluses during summer and, after storage be used in winter. Hydrogen-driven CHP could than serve a similar function as the natural gas driven CHP nowadays. However, taking the 'merit order' of the added value of hydrogen, the chemical industry and the mobility sector will be the logical first consumer.
Mediterranean
The rapid growth of the greenhouse industry in southern Europe followed the introduction of plastic-houses. The industry's remarkable success, coupled with limited economic alternatives for the local population, has highlighted the importance of preserving intensive horticulture for the future. Simultaneously, there's been a growing recognition of the ecological diversity at regions which are most suitable for greenhouses, namely the coastal regions .
Mediterranean plastic greenhouses are generally used in areas with high radiation and favorable temperatures, allowing almost year-round production of tomato, sweet pepper or cucumber. The demand of fossil energy for heating is small. However there is a tendency towards increased application of heating in Mediterranean greenhouses. When combined with active dehumidification techniques this even can add to sustainability, since it can reduce the production loss due to fungal diseases. Currently the heated greenhouses are usually high tech greenhouses heated with natural gas, but there are clear commitments to limit the use of fossil energy and serious search for alternative sources, such as biofuel or new applications of solar energy.
Middle east
In the middle east and the gulf region, the biggest concern on the sustainability of the greenhouse sector is it’s water use. Although greenhouses are more water efficient than open field horticulture, the growth of greenhouse cultivation on land that was not used for agriculture before increases the water demand.
Increasing the accuracy of the irrigation control and applying proper nutrient management to prevent salinization helps to lower the water use, but the most water saving techniques are based on using a closed greenhouse.
The water consumption of greenhouses in the warm regions is partly coming form the need for irrigation, which is generally larger than in northern latitudes. But in the arid regions, next to the irrigation water, large amounts of water are used for cooling of the greenhouses by pad&fan systems. In a pad&fan system, water is evaporated in order to cool down the hot desert air. This cooling technique is very effective in case the humidity of the air around the greenhouse is low (say, less than 40% RH). Pad&fan cooling can be even twice the amount needed for irrigation.
The Greenhouse Energy Guide shows that the large water consumption can be solved by using a closed greenhouse, cooled with AC-cooling. These coolers create a cold surface that cools the greenhouse are and on this cold surface water vapor condenses. Water that just before was transpired by the crop. In this way not only the water used for evaporative cooling on pad&fan systems can be avoided, but also a large fraction of the irrigation water can be recovered. Moreover, as the greenhouse is closed, the inside CO2-concentration can be increased with only a limited amount of CO2-dosing. This increases crop production.
Both factors together give a large saving on water needed per unit of fresh product.
However, the water saving is reached at the expense of a large amount of electricity. The electricity of a closed greenhouse in the gulf region is more than the electricity consumption of the average illuminated greenhouse in Northern latitudes.
It will depend on the CO2-emission associated to the large electricity consumption of closed greenhouses in the Middle East if such closed greenhouse can be called a sustainable development.
East Asia
In the context of greenhouse gases and sustainability there have seen various shifts and developments in recent years. Many East Asian countries, including China, Japan, and South Korea, have been increasingly investing in renewable energy sources like solar, wind, and hydroelectric power. Despite the push for renewables, coal remains a significant energy source in East Asia, particularly in countries like China and India. However, there's a growing emphasis on reducing reliance on coal due to its significant contribution to greenhouse gas emissions and air pollution. Many countries are investing in cleaner coal technologies or gradually shifting towards cleaner energy sources.
In general, the total greenhouse area is increasing, also high tech greenhouses, driven by the demand for year-round production of fruits, vegetables, and flowers, especially in regions with extreme climates or limited arable land. The Asian greenhouse sector has increasingly incorporated advanced technologies such as climate control systems, hydroponics, and automation. This integration aims to optimize growing conditions, improve yields, and reduce resource usage and in general the focus has shifted towards growing high-value crops, such as tomatoes, cucumbers, peppers, and various leafy greens. Efforts are being made to enhance sustainability, including the adoption of energy-efficient technologies, recycling water and nutrients, and implementing eco-friendly pest and disease management practices. This is partially driven by government support through subsidies and, technology incentives. Current challenges are excessive water usage, pesticide residue and energy consumption.
However, there is discussion on whether it is profitable to operate high-end glass greenhouses and whether more high-tech greenhouses are needed. High energy consumption because of heating in cold regions and cooling in warm regions leads to high energy cost and limits the sustainability of greenhouse production.
In recent years, photovoltaics have gradually become a reality from a long-term perspective and has been put into operation in more and more regions of China. This can contribute to the electrification which is to be expected.