Beyond Monoculture V.2 Greenhouse Technology Dutch greenhouse technology is widely recognized as the most advanced in the world. The Netherlands continues to be a global leader in this sector with ambitious goals for improvement. In 2006, the Energy-Producing Greenhouse Transition Programme was launched, with the objective of ensuring that greenhouses built from 2020 onwards be entirely energetically self-sustaining. Because the physical design of greenhouses is such an active area of research, it is not something we focused on in the development of the Polydome concept. However, any Polydome system will necessarily rely on a combination of existing and emerging energy technologies in order to satisfy the goals of energy self-sufficiency and CO2 neutrality. Here we present a quick overview of some of the technologies at the forefront of the discussion. Closed Greenhouses Most greenhouses are vented during the warmer months of the year to get rid of excess heat and humidity. Closed greenhouses are not vented, which means they accumulate rather than dissipate heat. Cold ground water is pumped through heat exchangers in the greenhouse, cooling the air by absorbing the heat. The now-warm water is pumped back into the ground, where it retains its elevated temperature for many months, acting as a heat battery. In winter, this warm water can be pumped back up to heat the cold greenhouse air. This approach can provide a total energy savings of around 30% relative to annual demand (the rest consists of electricity needs). A closed greenhouse collects more heat than it needs for its annual heating, which means that it can also export energy to heat neighboring residential areas. Not venting also leads to higher internal CO2 concentrations, which can boost yields by over 20% (as shown in a demonstration site operated by company Themato). Reduced exposure to pests also results in lower agrichemical use, while lower rates of evaporation lead to less water consumption. FiWiHex Fine Wire Heat Exchangers, or FiWiHexes, are one of the technologies that allow closed greenhouses to work. Using a heat exchanger with a multitude of fine wires increases the surface area available for heat transfer, ensuring a fast and efficient exchange of heat. Geothermal Heating Depending on the specific location of a greenhouse, deep well geothermal energy can also be an option for greenhouse heating. One company claims to provide 80% of its total energy in this way. Integrated Solar Technologies A variety of solar technologies for greenhouses are in conceptual development or pilot testing stages. Thermal solar technologies focus on collecting heat (in ways similar to the closed greenhouse approach). Integrated solar photovoltaics are used to generate electricity. The pilot project Elkas was the first greenhouse in the world to produce electricity relying fully on solar technology. The Daylight System, developed by Technokas, is a unique approach that uses fresnel lenses to convert direct sunlight into electricity while allowing indirect light to be used for plant growth. The lenses focus direct light onto a strip of photovoltaics, and the entire system is water cooled further generating a source of heat capture. Biogas CHP Currently, Dutch greenhouses have the capacity for around 3000 MW of Combined Heat and Power (CHP) systems to efficiently generate heat, electricity, and CO2. The use of CHPs has reduced original greenhouse energy demand by 20 - 30%. However, conventional CHP plants are still dependent on fossil fuel combustion. With access to sources of biomass (livestock manure, tree coppicing, green waste from cities, etc.), greenhouses can also generate sufficient biogas to power bio-CHP plants on their terrain. Several companies are exploring this route. Sensor Technologies & LED lighting A number of innovations in greenhouse operation will eventually lead to greater efficiency and energy savings. Advanced sensor technologies can provide more accurate feedback for when environmental controls are needed. High power LED lighting could offer greater control over the fraction of light spectrum used, while cutting energy demand. Polydome: High Performance Polyculture Systems 17 Pagina 16

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