ISHS Acta Horticulturae 801: International Symposium on High Technology for Greenhouse System Management: Greensys2007
PLANT SOLARIMETER FOR ENERGY BALANCE |
| Author: | T. Takakura |
| Keywords: | solarimeter, energy balance, cosine law, energy balance, greenhouse environment control |
| Abstract:
The objective of this research was to develop a solarimeter which can accurately measure the amount of solar energy entering a plant canopy in a greenhouse with limited space. Normal hemispherical solarimeters which have black sensors of a flat plate type have been widely used for energy analysis of such greenhouses. However, a large error was found in energy analysis with ordinary solarimeters when the sun’s altitude becomes low. It was found that the cosine law for a flat sensor causes an error since the surface of a plant canopy which receives the sun’s energy is not flat. It was proved that if measured solar energy by an ordinary solarimeter is modified by the cosine law to obtain solar radiation received by a normal plane along with the change in the sun’s altitude, the error was minimized. In order to develop an economical solarimeter to measure solar radiation received by the surface normal to the direct solar radiation, a photodiode was placed at the bottom of an opaque white ping-pong ball which had a hole for the photodiode at the bottom. The ping-pong ball acted as a constant area which receives solar radiation and as an integration sphere once the radiation was trapped inside. The data measured by the developed solarimeter showed relatively similar values of solar radiation received by the normal plane to the direct radiation as measured with a hemispherical solarimeter. It was concluded that this solarimeter can be used to form better control strategies for greenhouse environment control. A patent has been applied on this solarimeter. | |
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