Solar radiation distribution inside a monospan greenhouse with the roof entirely covered by photovoltaic panels

In the present work the variation over space and time of the amount of the photosynthetic photons flux density, inside a greenhouse entirely covered with photovoltaic panels was investigated experimentally and numerically. The greenhouse had 10.00 m spam width, 50.00 m length, 3.00 m height of the gutter, 6.60 m height of the edge. Data were acquired in the period 18^th April-8^th June 2014 by one sensor outside and one inside the experimental greenhouse built in Southern Italy. Numeric simulations were performed by means of commercial software Autodesk^® Ecotect^®. For the investigated greenhouse model, the exposed percentage - the ratio of the calculated insolation at a particular point within an enclosure to the simultaneous unobstructed outdoor insolation under the same sky conditions - was calculated over a three dimensional grid formed by 50x10x15 cells each with 1.00x1.00x0.20 m size. The long-term analysis demonstrated a good capability of the numerical model to predict the shading effect inside a photovoltaic greenhouse combining the daily calculated exposed percentage with measurements of solar radiation. The model was able also to predict the qualitative behaviour of the variation of photons flux during the day even if the measured values showed a higher fluctuation of values.