Energy sustainable greenhouse crop cultivation using photovoltaic technologies

https://doi.org/10.1016/j.rser.2019.04.026Get rights and content

Highlights

  • Electricity demand in worldwide greenhouses is presented.

  • Solar cells are applicable to greenhouses in various ways.

  • Greenhouse-installed photovoltaics can generate large amounts of electricity.

  • Photovoltaic panel shading affects plants below the panels.

Abstract

The sustainability of energy and food supplies has come to represent a major concern throughout the world today. Greenhouse cultivation, an intensive food-production system, contributes fresh vegetables and fruits to the world food supply. Greenhouse crop yields and quality can be improved by microclimate controls powered by fuels and grid electricity inputs. Therefore, producing abundant and quality crops with improved energy efficiency has been pursued as a challenge to be addressed by researchers and practitioners. Although application of photovoltaics (PV) to greenhouses can reduce fuel and grid electricity consumption, PV inherently conflicts with cultivation because both photosynthesis and PV depend on sunlight availability. Various contrivances have been explored to enhance the compatibility of cultivation and PV power generation. This review describes important aspects of greenhouse cultivation, electricity demand in greenhouses, state-of-the-art of greenhouse PV systems, and PV shading effects on plants. Finally, prospects for energy-sustainable greenhouse PV technologies are presented.

Introduction

Photosynthesis converts sunlight energy into biochemical energy that is then transferred to biological energy flowing along the food chain. Most biological activities therefore depend fundamentally on photosynthesis. Electrical charges in photosystems embedded in thylakoid membranes in plant cell chloroplasts are separated when photons from the sun hit chlorophylls in the photosystems. The separated electrons and protons work to produce adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH), which are then used to produce carbohydrates in the Calvin–Benson cycle. Consequently, photon energy from the sun is converted into chemical energy in the form of carbohydrates in plants [1]. Photon yields of photosynthetic CO2 fixation among several vascular plants of diverse origins are fairly constant, equal to 9.3 photons used per CO2 fixation [2,3]. Best-case solar-to-biomass energy conversion efficiency is estimated as 8–10% [3,4].

The matrix of solar cells of photovoltaic (PV) systems comprises semiconductors, organic molecules, and inorganic molecules [5]. Electrical charges in the solar cells are separated when photons from the sun collide with the materials. Negative charges move to the direction of positive charges through an external circuit. Thereby, electricity is extracted from the solar cells [6]. The best efficiencies of crystalline Si, amorphous Si, perovskite, dye sensitized, and organic cells are reported respectively as 26.7, 10.2, 19.7, 11.9, and 11.2% [7].

Although photosynthesis and PV share a similar process of energy transfer from photons to charges, they play different roles for bio-production and electricity production [8]. Plants have not only served directly or indirectly as food for humans; they have also been exploited as energy resources throughout the history of human activities [9]. Demand for plants for use as an energy resource is increasing today under pressures of underground resource depletion and increasing atmospheric-CO2 concentrations [10]. What about the duality of PV? Of course PV cannot be eaten, but it can support various activities related to food production and subsequent supply chains by providing electricity converted from sunlight [11,12].

Greenhouse plant production is a cultivation practice that controls the interior cultivation environment, optimizing it for crop growth and development [13]. Vegetables, fruits, and flowers are cultivated in greenhouses. Fuel and electricity are applied to control the greenhouse interior environment, aiming to improve or stabilize crop yields and quality, but their increasing prices reduce grower profits [[14], [15], [16], [17], [18]]. Accordingly, growers strive to increase crop production efficiency while minimizing fuel and electricity consumption [15,16,[19], [20], [21], [22], [23], [24], [25], [26]]. If renewable energy resources could be used actively in greenhouses, then they could decrease the consumption of fossil fuels and grid electricity [14,22,[27], [28], [29], [30], [31], [32]]. The consequent diminished dependence on traditional energy resources can further mitigate greenhouse gas emissions from the agricultural sector [33].

Greenhouses are typically built on open fields with good sunshine availability because of the fundamentally important demand of sunlight for crop photosynthesis. Therefore, such locations are invariably suitable for PV electricity production [34]. An ingenious and energy-saving plant production system might be achieved if a greenhouse and PV could be integrated appropriately on the same land unit. Nevertheless, a delicate occupancy balance between the crops and PV must be achieved to use sunlight for electricity production in the greenhouse because the sunlight is necessary for plant photosynthesis [34]. Some PV technologies have been deployed already in greenhouse industries, although balance optimization on crop and electricity production remains the subject of intensive investigation.

This review first presents basic aspects of cultivation and electricity demand in greenhouses. Then, PV technology applications to greenhouses to date are summarized. Also, PV shading effects on greenhouse plants are discussed. Finally, possibilities for the additional utilization of PV technologies in greenhouses are explored.

Section snippets

Greenhouse overview

Vegetables, fruits, and flowers are the major crops produced through greenhouse systems [35,36]. Greenhouse walls and roofs are made of transparent glass or plastic, enabling cultivation even when low temperatures restrict open field crop growth [25,37,38]. This merit is particularly useful in temperate zones [[38], [39], [40]]. In addition, the greenhouse extends the cultivation season and broadens the choices of crop species [35,38]. Actually, greenhouses can shorten the cultivation duration,

Temperature

Sunlight penetrates easily into a greenhouse because of roof and wall transparency. The cover materials block thermal leakage. Consequently, the internal temperature becomes higher than that outside [18,37]. By exploiting this thermal property, various technologies related to nighttime heating have been applied. Mainly, such applications are based on the principle of thermal energy storage in walls, soil, or water tanks during daytime, with energy released into the greenhouse during nighttime [

Electrical energy demand for greenhouse environment management

Crop yields and quality can be improved by controlling the greenhouse internal environment using fuels and electricity [70]. Therefore, reducing fuel and electricity consumption to achieve a better growth environment constitutes a major theme of greenhouse cultivation [19,65,109].

Table 1 presents electrical energy demand in greenhouses recorded in the literature across wide geographical regions. Reported original data have various units of electrical energy. To compare all data based on the

Application of stand-alone PV technologies to the greenhouse environment management

Electricity plays crucially important roles in greenhouse management, whereas growers intending to minimize the use of commercial electricity or greenhouses at remote areas are often inaccessible to power lines. In such situations, PV can facilitate greenhouse management. In actuality, the application of solar PV technologies to meet all or part of the greenhouse electricity demand has been attempted (Table 2).

Stand-alone PV power systems are useful where commercial power grids are not

Grid-connected greenhouse PV systems

In southern Europe, solar radiation is excessive during summer [117]. Shading and active cooling using methods such as fogging are necessary. Alternatively, agricultural activity must be suspended [117]. This situation demands exploration of solutions to exploit solar energy in various ways, such as for cooling system operations or for direct sale to commercial grids [117]. If a large-scale greenhouse PV system is connected to the grid, then a large amount of the generated electricity can be

Mitigation of crop shading using PV array spacing and semi-transparent technologies

The whole greenhouse roof area is often covered with opaque conventional PV panels to maximize energy production. However, this scenario is unsuitable for green plant cultivation [34] (Fig. 1a). In fact, the annual global radiation decreases by 0.8% for each additional 1.0% of PV coverage on the roof, as the average of the most common PV greenhouse types [165]. The greenhouse internal light environment varies greatly according to whether the PV modules are concentrated as a single array (Fig. 1

Possible crop yield and quality improvement using dynamic PV shading controls

Photosynthetic photon flux density (PPFD) exceeds 2000 μmol m−2 s−1 around noon on sunny summer days [187,188], whereas photosynthetic light saturation points of major agricultural C3 plants are 500–1500 μmol m−2 s−1 [93,189] (Table 4). Actually, many crop species do not grow optimally at the maximum solar irradiance available in the habitat [3,[190], [191], [192]]. In leaves under full sunlight, up to 80% of the absorbed solar energy must be dissipated to prevent severe damage to

PV power generation using solar irradiance outside the PAR wavelength range

PV power generation and plant cultivation can coexist if the PV cell uses only solar irradiance outside the wavelength range of PAR. Actually, more than 50% of ground-level solar spectrum is not used for plant photosynthesis [3,8,146,190,193]. Near-infrared (NIR) is therefore an attractive energy resource for electricity production in PV greenhouses.

By coating a greenhouse roof with NIR reflective sheets, the roof reflects the NIR-part of solar irradiance to the sky, but it lets the PAR enter

Prospects for energy-sustainable greenhouse cultivation using PV technologies

In light of all the features of greenhouse crop production and PV electricity generation explained in the preceding sections, prospects for PV application to greenhouse cultivation can be inferred.

Using PV energy to compensate for electricity demand in high-latitude greenhouses is actually difficult because of greater needs for energy consumption for heating in winter, a time with less insolation. Improvements of the energy efficiencies of greenhouse electrical appliances and PV cells are key

Conclusions

This review elucidated greenhouse features, the use of electricity for greenhouse environment management, the applications of various PV systems to greenhouses, and the effects of PV shading on plants. Prospects for energy-sustainable greenhouse PV technologies were addressed in the preceding section.

The starting point of energy circulation for life on Earth is the chemical energy converted from sunlight energy by photosynthesis. The availability of solar energy and the distribution of plants,

Declaration of interests

None.

Acknowledgment

This study was partly supported by JSPS KAKENHI Grant Number JP18K05903, Japan.

References (240)

  • A. Vadiee et al.

    Energy management in horticultural applications through the closed greenhouse concept, state of the art

    Renew Sustain Energy Rev

    (2012)
  • A. Vadiee et al.

    Energy analysis and thermoeconomic assessment of the closed greenhouse – the largest commercial solar building

    Appl Energy

    (2013)
  • A. Vadiee et al.

    Thermal energy storage strategies for effective closed greenhouse design

    Appl Energy

    (2013)
  • A. Yano et al.

    Development of a greenhouse side-ventilation controller driven by photovoltaic energy

    Biosyst Eng

    (2007)
  • G. Russo et al.

    Environmental analysis of geothermal heat pump and LPG greenhouse heating systems

    Biosyst Eng

    (2014)
  • J. Xu et al.

    Performance investigation of a solar heating system with underground seasonal energy storage for greenhouse application

    Energy

    (2014)
  • E. Cuce et al.

    Renewable and sustainable energy saving strategies for greenhouse systems: a comprehensive review

    Renew Sustain Energy Rev

    (2016)
  • R.H.E. Hassanien et al.

    Advanced applications of solar energy in agricultural greenhouses

    Renew Sustain Energy Rev

    (2016)
  • G.K. Ntinas et al.

    Carbon footprint and cumulative energy demand of greenhouse and open-field tomato cultivation systems under Southern and Central European climatic conditions

    J Clean Prod

    (2017)
  • L. Chai et al.

    Performance evaluation of ground source heat pump system for greenhouse heating in northern China

    Biosyst Eng

    (2012)
  • C. Kittas et al.

    Air temperature regime in a forced ventilated greenhouse with rose crop

    Energy Build

    (2005)
  • J. Chang et al.

    Assessment of net ecosystem services of plastic greenhouse vegetable cultivation in China

    Ecol Econ

    (2011)
  • G. Tong et al.

    Passive solar energy utilization: a review of cross-section building parameter selection for Chinese solar greenhouses

    Renew Sustain Energy Rev

    (2013)
  • B. Ozkan et al.

    An input–output energy analysis in greenhouse vegetable production: a case study for Antalya region of Turkey

    Biomass Bioenergy

    (2004)
  • A. Yano et al.

    Electrical energy generated by photovoltaic modules mounted inside the roof of a north–south oriented greenhouse

    Biosyst Eng

    (2009)
  • M. Santamouris et al.

    Passive solar agricultural greenhouses: a worldwide classification and evaluation of technologies and systems used for heating purposes

    Sol Energy

    (1994)
  • V.P. Sethi et al.

    Survey and evaluation of heating technologies for worldwide agricultural greenhouse applications

    Sol Energy

    (2008)
  • H. Ling et al.

    Active heat storage characteristics of active–passive triple wall with phase change material

    Sol Energy

    (2014)
  • H. Ling et al.

    Effect of phase change materials on indoor thermal environment under different weather conditions and over a long time

    Appl Energy

    (2015)
  • L. Zhang et al.

    A low cost seasonal solar soil heat storage system for greenhouse heating: design and pilot study

    Appl Energy

    (2015)
  • T. Wang et al.

    Integration of solar technology to modern greenhouse in China: current status, challenges and prospect

    Renew Sustain Energy Rev

    (2017)
  • L. Mariani et al.

    Space and time variability of heating requirements for greenhouse tomato production in the Euro-Mediterranean area

    Sci Total Environ

    (2016)
  • J.L. Garćia et al.

    Evaluation of the feasibility of alternative energy sources for greenhouse heating

    J Agric Eng Res

    (1998)
  • A. Vadiee et al.

    Solar blind system – solar energy utilization and climate mitigation in glassed buildings

    Energy Procedia

    (2014)
  • A. Wahid et al.

    Heat tolerance in plants: an overview

    Environ Exp Bot

    (2007)
  • A. Baille et al.

    Influence of whitening on greenhouse microclimate and crop energy partitioning

    Agric For Meteorol

    (2001)
  • E. Mashonjowa et al.

    The effects of whitening and dust accumulation on the microclimate and canopy behaviour of rose plants (Rosa hybrida) in a greenhouse in Zimbabwe

    Sol Energy

    (2010)
  • H.A. Ahemd et al.

    Shading greenhouses to improve the microclimate, energy and water saving in hot regions: a review

    Sci Hortic

    (2016)
  • R. Leyva et al.

    Cooling systems in screenhouses: effect on microclimate, productivity and plant response in a tomato crop

    Biosyst Eng

    (2015)
  • A. Arbel et al.

    Performance of a fog system for cooling greenhouses

    J Agric Eng Res

    (1999)
  • A. Arbel et al.

    Combination of forced ventilation and fogging systems for cooling greenhouses

    Biosyst Eng

    (2003)
  • V.P. Sethi et al.

    Survey of cooling technologies for worldwide agricultural greenhouse applications

    Sol Energy

    (2007)
  • A. Perdigones et al.

    Cooling strategies for greenhouses in summer: control of fogging by pulse width modulation

    Biosyst Eng

    (2008)
  • M. Garćia et al.

    Climatic effects of two cooling systems in greenhouses in the Mediterranean area: external mobile shading and fog system

    Biosyst Eng

    (2011)
  • P. Thongbai et al.

    CO2 and air circulation effects on photosynthesis and transpiration of tomato seedlings

    Sci Hortic

    (2010)
  • A. Marucci et al.

    Dynamic photovoltaic greenhouse: energy efficiency in clear sky conditions

    Appl Energy

    (2016)
  • Chr Lamnatou et al.

    Solar radiation manipulations and their role in greenhouse claddings: fluorescent solar concentrators, photoselective and other materials

    Renew Sustain Energy Rev

    (2013)
  • J. Bambara et al.

    Energy and economic analysis for the design of greenhouses with semi-transparent photovoltaic cladding

    Renew Energy

    (2019)
  • N. Mattson et al.

    The impact of photoperiod and irradiance on flowering of several herbaceous ornamentals

    Sci Hortic

    (2005)
  • W. Yamori et al.

    Physiological functions of cyclic electron transport around photosystem I in sustaining photosynthesis and plant growth

    Annu Rev Plant Biol

    (2016)
  • Cited by (0)

    View full text