This experimental study shows the results of an analysis of the performance of a stand-alone renewable energy system for greenhouse heating on a winter day. The systems consist of photovoltaic panels connected to an electrolyzer which during daylight hours produce hydrogen by electrolysis and then store it in a pressure tank. During the night, thanks to a fuel cell, the hydrogen is converted into electricity in order to feed a ground source geothermal heat pump to heat a tunnel greenhouse. The procedure for estimating hourly solar radiation, hydrogen production and consumption for short-term energy storage on a partly cloudy day is also given. The solar energy usability concept, the capacity of energy storage systems and the thermal energy load govern the effective energy management of the system. This performance analysis is necessary to determine the actual total efficiency of integrated photovoltaic, geothermal and hydrogen renewable energy systems and their contribution to the load. The overall system efficiency obtained, starting from the amount of solar energy available during daylight hours until it is used as thermal energy at night, was 11%
Abstract:A greenhouse containing an integrated system of photovoltaic panels, a water electrolyzer, fuel cells and a geothermal heat pump was set up to investigate suitable solutions for a power system based on solar energy and hydrogen, feeding a self-sufficient, geothermal-heated greenhouse. The electricity produced by the photovoltaic source supplies the electrolyzer; the manufactured hydrogen gas is held in a pressure tank. In these systems, the electrolyzer is a crucial component; the technical challenge is to make it work regularly despite the irregularity of the solar source. The focus of this paper is to study the performance and the real energy efficiency of the electrolyzer, analyzing its operational data collected under different operating conditions affected by the changeable solar radiant energy characterizing the site where the experimental plant was located. The analysis of the measured values allowed evaluation of its suitability for the agricultural requirements such as greenhouse heating. On the strength of the obtained result, a new layout of the battery bank has been designed and exemplified to improve the performance of the electrolyzer. The evaluations resulting from this case study may have a genuine value, therefore assisting in further studies to better understand these devices and their associated technologies.
Technological peculiarities of cultivation and harvesting of some agricultural crops make it necessary to use asymmetric machine-and-tractor aggregates. However, for the time being there is no sufficiently complete, analytical study of the steady movement of such machine-and-tractor aggregates. This necessitates the development of a theory of stable movement of the aggregates which would allow choosing their optimal kinematic and design parameters. On the basis of the results of mathematical simulation, a system of linear differential equations of the second order is obtained describing transverse displacement of the center of masses of the aggregating wheeled tractor and turning of its longitudinal axis of symmetry by some angle around the indicated center of mass, as well as the deviation angle of the rear-trailed harvester from the longitudinal axis of the tractor at any arbitrary moment of time. This system of differential equations can be applied for numerical calculations on the PC, which will make it possible to evaluate the stability of the movement of the asymmetric machine-and-tractor aggregate when it performs the technological process.
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