Measurement and prediction of solar radiation distribution in full-scale greenhouse tunnels

Radiative heterogeneity in greenhouses significantly influences crop activity, particularly transpiration and photosynthesis. This is especially true for plastic tunnels, which are the most commonly used greenhouse type in the Mediterranean basin. A computer model was generated for this study based on sun movement, greenhouse geometry, transmittance of the cover and weather conditions. Experiments to test model accuracy were performed in a standard 8 m wide east-west orientated lettuce tunnel located near Avignon (southern France). Solar radiation distribution was studied using 32 solar cells placed on the soil surface along 4 sections situated either in the tunnel centre or near the west gable end. Measured and simulated data of transmittance were close together for both cloudy and clear sky weather conditions. The tested model was then used to simulate solar radiation intensity distribution at the soil level in various tunnel types for different periods of the year. Simulated results revealed high radiative heterogeneity in tunnels, mainly due to effects of gable ends, vent openings and frames. Statistical analysis indicated that solar radiation inside the greenhouse at ground level was higher in the N-S orientated tunnel than in the E-W orientated tunnel in March and June, but radiative heterogeneity was higher in the N-S orientated tunnel, especially in June. Transversal heterogeneity in the E-W orientated tunnel was much higher than longitudinal heterogeneity. Global heterogeneity increased from March to June for both tunnel positions although its relative value remained approximately unchanged. Greenhouse tunnel / radiative heterogeneity / computer model / simulation Résumé – Mesure et simulation de la distribution du rayonnement solaire dans les serres tunnels. L'hétérogénéité radiative sous serre influence fortement l'activité du couvert et plus particulièrement la photosynthèse et la transpiration. En ce qui concerne le tunnel, le type de serre le plus répandu dans la région méditerranéenne, l'absence de données expérimentales ainsi que la complexité des échanges radiatifs expliquent pourquoi la répartition fine du climat radiatif demeure mal connue et pourquoi elle est rarement prise en compte dans les modèles de simulation numérique. Dans cette étude, un modèle informatique de transfert radiatif sous tunnel a été développé. Il tient compte de la position du soleil dans le ciel, de la géométrie du couvert et de la présence d'ouvertures, de la présence de structures et de petits bois Agronomie 20 (2000) 41–50 41 © INRA, EDP Sciences Communicated by Gérard Guyot (Avignon, France) * Correspondence and reprints [email protected] S. Wang, T. Boulard 42