Abstract
Nowadays, the traditional energy sources used for greenhouse heating are fossil fuels such as LPG, diesel and natural gas. The global energy demand will continue to grow and alternative technologies need to be developed in order to improve the sustainability of crop production in protected environments. Innovative solutions are represented by renewable energy plants such as photovoltaic, wind and geothermal integrated systems, however, these technologies need to be connected to the power grid in order to store the energy produced. On agricultural land, power grids are not widespread and stand-alone renewable energy systems should be investigated especially for greenhouse applications. The aim of this research is to analyze, by means of a mathematical model, the energy efficiency of a photovoltaic (8.2 kW), hydrogen (2.5 kW) and ground source gas heat pump (2.2 kW) integrated in a stand-alone system used for heating an experimental greenhouse tunnel (48 m2) during the winter season. A yearlong energy performance analysis was conducted for three different types of greenhouse cover materials, a single layer polyethylene film, an air inflated-double layer polyethylene film, and a double acrylic or polycarbonate. The results of one year showed that the integrated system had a total energy efficiency of 14.6%. Starting from the electric energy supplied by the photovoltaic array, the total efficiency of the hydrogen and ground source gas heat pump system was 112% if the coefficient of the performance of the heat pump is equal to 5. The heating system increased the greenhouse air temperatures by 3–9 °C with respect to the external air temperatures, depending on the greenhouse cover material used.
Highlights
Greenhouses are one of the most modern expressions of recent agriculture and it is expected that they will increase in number in the future, especially in those areas with hostile climatic conditions [1]
Starting with the heating required by an experimental greenhouse to operate during the winter season, the research includes an evaluation of the technical aspects of the ground source gas heat pump, the hydrogen production and its storage, the photovoltaic system, and analyzes the connections and the effects among these components
The experimental setup consists of a solar photovoltaic–hydrogen system powering a low enthalpy geothermal gas heat pump used for heating a greenhouse by way of hot air flow coming out of a fan-coil unit
Summary
Greenhouses are one of the most modern expressions of recent agriculture and it is expected that they will increase in number in the future, especially in those areas with hostile climatic conditions [1]. Starting with the heating required by an experimental greenhouse to operate during the winter season, the research includes an evaluation of the technical aspects of the ground source gas heat pump, the hydrogen production and its storage, the photovoltaic system, and analyzes the connections and the effects among these components. In this plant, the electrolyzer was a critical component with which water was divided into hydrogen and oxygen and the technical challenge was to make it work consistently despite the interrupted power from solar energy sources. An efficiencies analysis was conducted in order to define the total performance, as well as the power production and consumption of the integrated renewable energy system
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