No abstract

Energy demand of greenhouses is an important factor for their economics and photovoltaics can be considered an alternative solution to cover their electrical and heating needs. On the other hand, plants cultivated under different solar radiation intensities usually appear different physiological adaptations. The objective of this research was to investigate the effect of photovoltaic panels' induced partial shading on growth and physiological characteristics of lettuce (Lactuca sativa L.) and rocket (Eruca sativa Mill.) plants. Our results indicate that lettuce productivity and the corresponding photosynthetic rate were not affected under the photovoltaic cultivation in comparison with the reference one. On the other hand, the rocket cultivation was less productive and showed lower photosynthetic rate under photovoltaic panels than in the reference greenhouse. The different physiological response between lettuce and rocket seems to be associated with the effect of environmental factors such as solar radiation intensity, temperature and humidity apart from the possible inherent characteristics of each plant species.

No abstract

No abstract

No abstract

Great advancements in technologies such as big data analytics, robots, remote sensing, the Internet of Things, decision support systems and artificial intelligence have transformed the agricultural sector. In the greenhouse sector, these technologies help farmers increase their profits and crop yields while minimizing the production costs, produce in a more environmentally friendly way and mitigate the risks caused by climate change. In greenhouse farming, especially in the Mediterranean region, a lack of knowledge and qualified personnel able to uptake new knowledge, the small size of farms, etc., make it difficult to implement new technologies. Although it is necessary to demonstrate the advantages of innovations related to sustainable agriculture, there is a little opportunity for specific training on greenhouse production in cutting-edge technologies. To gain insight into this problem, questionnaires for greenhouse farmers and intermediaries were developed in multiple choice format and filled in by the stakeholders. A statistical analysis was performed, and the results are presented in graphical form. In most cases, the findings confirmed that producers who run small farms, in most cases, have a lack of knowledge, especially on how to manage climate control systems or fertigation systems. The majority of farmers were elderly with a low level of education, which makes it difficult to be aware of the training issues, due to distrust and a lack of innovation culture. Therefore, their strategy was usually survival with cost control. However, young graduates have been recently returning to agriculture, and they are open to training activities and innovation. The most desirable training offer should be related to sustainable agriculture and precision agriculture technologies.

Covering only a small proportion (ca. 20%) of the greenhouse roof with photovoltaic panels contributes considerably to its energy demands without affecting plant growth and quality. © 2018 Society of Chemical Industry.

In this paper we present irradiation aspects for the use of glass type fresnel lenses instead of typical glass or plastic covering materials of greenhouses. They can be mounted stationary on the greenhouse roof, combined with linear absorbers to receive and convert the concentrated solar radiation into heat, electricity or both. The absorbers are of small width, depending on the selected concentration ratio and are properly moved to truck the concentrated beam solar radiation, with the diffuse solar radiation not received by the absorber. The advantage of the linear fresnel lenses to separate the direct from the diffuse solar radiation makes them suitable for lighting and temperature control of the greenhouse interior space, providing light of suitable intensity level and without sharp contrasts. The incident beam solar radiation is concentrated on the absorber and can be taken away from the glazed space, achieving lower illumination level and avoiding the overheating of it. In low intensity solar radiation, the absorber can be out of focus leaving the light to come in the interior space and keep the irradiation at an acceptable level for the cultivated plants. The distribution of solar radiation on the focal plane of linear fresnel lenses and the collected solar radiation regarding absorber width and incidence angle of solar radiation are given. The study includes also design concepts for thermal and photovoltaic absorbers, emphasised to hybrid photovoltaic/thermal type linear absorbers, which convert solar radiation simultaneously into electricity and heat.