Electrical Energy Producing Greenhouse Shading System with a Semi-Transparent Photovoltaic Blind Based on Micro-Spherical Solar Cells

Abstract

An increasing population and limited arable land area endanger sufficient and variegated food supplies worldwide. Greenhouse cultivation enables highly intensive plant production and thereby enables the production of abundant fresh vegetables and fruits. The salient benefits of greenhouse cultivation are supported by ingenious management of crop environments, assisted by fossil fuel and grid electricity supplies. To reduce dependence on traditional energy resources, various studies have investigated exploitation of renewable energies for greenhouse environment management. Among them, solar photovoltaic (PV) technologies are anticipated to feed electrical energy to greenhouse appliances for microclimate control. This study proposes a venetian-blind-type shading system consisting of semi-transparent PV modules as blind blades based on micro-spherical solar cell technology to achieve greenhouse shading and electricity production concurrently. In response to the solar irradiance level, the PV blind inclination was altered automatically using a direct current (DC) motor driven by electrical energy generated by the PV blind itself. The PV blind was operated continuously during a five-month test period without outage. Moreover, the PV blind generated surplus electrical energy of 2125 kJ for blind system operations during the test period. The annual surplus energy calculated under the present experimental condition was 7.8 kWh m −2 year −1 , suggesting that application of the PV blind to a greenhouse roof enables sunlight level control and electrical appliance operations in the greenhouse with a diminished fuel and grid electricity supply, particularly in high-insolation regions.Energies 2018, 11, 1681 2 of 23 produces carbon dioxide emissions, the amounts of which should be reduced in the agricultural sector [2]. Under these circumstances, various studies have been conducted to use renewable energy for managing greenhouse crop environments [3,4]. Among them, solar photovoltaics (PVs) are expected to feed electricity to appliances that are used for greenhouse environment management [5].Deploying PV arrays on the sunny ground beside a greenhouse is the simplest and most effective mode of electrical energy generation. For instance, fan and pad cooling systems in Saudi Arabia [6] and in Arizona [7], a fog cooling system in Malaysia [8], and heat pump systems in Italy [9,10] were operated with power from ground-mounted PV arrays. Nevertheless, installing PV arrays partially on a greenhouse roof might be preferred if the PV panels are intended as shading materials. Shading is a fundamentally important practice for greenhouse cultivation in high-insolation regions, such as Spain [11] or Saudi Arabia [12]. Previous studies conducted in Japan [13] and in the Mediterranean region [14,15] demonstrated that an adequate level of shading mitigates excessive temperature rises in greenhouses in summer, improving crop growth and quality [16,17]. Conventionally, nets [14,15,18] and reflective coatings [18,19] have been used as practical ...

An optimal switching approach toward cost‐effective control of a stand‐alone photovoltaic panel system under stochastic environment

“…We assume that switching the panel angle from θ i → θ 1 − i ( i = 0,1) is impulsive and consumes a fixed electric cost, which is here set as a constant c . The assumption of impulsive switching can be justified since the system we are assuming can switch the panel angle in usually less than 10 seconds. This duration is much shorter than the timescale of the problem, which can be at least several days or weeks.…”

“…The numerical computation here puts emphasis on optimal control of the panel angle equipped with a greenhouse located at Shimane University, Matsue, Japan. Figure is a conceptual image of our experimental system focused on in this section.…”

“…As in the works of Li et al, the panel considered is facing east and has the angle of inclination of 26.5° from the horizontal plane. In the context of the present mathematical model, the system has been operated with the following empirically determined policy: …”

“…Doubling the spatial resolution results in the relative difference of, at most, 0.3% between the computed value functions. Here, we examine θ 0 = 26.5° and θ 1 = 116.5° as in the experimental system . The irradiance I t is computed using the procedure in Appendix B.…”

“…Our objective is to present a new mathematical framework for modeling, analysis, and control of a stand‐alone PV system with emphasis on an existing system. The PV system considered in this paper is a conceptualization of those installed in an experimental greenhouse . A characteristic of this experimental PV system is that its panel angle can be switched in a discrete manner by consuming stored energy, potentially serving as a simplified and more efficient alternative to continuous tracking systems .…”