Journal of the Society of Agricultural Structures, Japan

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Average solar radiation must be considered to evaluate the amounts of photosynthesis and growth of plants in a greenhouse. Nevertheless, finding the average solar radiation in a greenhouse is not easy because the light incidence angle and greenhouse frame shadows strongly affect the internal solar radiation the solar radiation amount varies spatially. For this study, three simple methods were used to ascertain the average irradiance in a greenhouse: pyranometer improvement, computer simulation using greenhouse models, and comparison of direct measurements on clear and cloudy days. Results clarified that when the solar transmittance in the greenhouse was measured during cloudy weather, when the greenhouse had no frame shadows, the solar radiation transmittance remained constant even when the solar radiation varied over time. Comparison between clear and cloudy days revealed no difference in transmittance. These findings suggest a method to measure the average solar radiation in a greenhouse. First, using two upward-facing pyranometers, one must be installed outside the greenhouse. The other must be installed inside the greenhouse. Then measurements are taken on cloudy days to obtain the transmittance. Next, the outside pyranometer output must be multiplied by the solar radiation transmittance to obtain average solar radiation in the greenhouse for any time. If necessary, a downwardfacing pyranometer should be installed in the greenhouse. Then its measured value must be subtracted from the inside upward-facing pyranometer output to calculate the average amount of solar radiation in the greenhouse.

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Improve the growth of livestock (calves) in winter, we developed a hybrid hot water supply system connecting a solar water heater and oil heating, and verified economic effects of hot water supply to calves. Water warming in the solar water heater during the study period was 0.9-37.2 °C (average 21.7 °C). Water which supplied to the livestock drinking water tank from the solar water heater via the heat source for oil heating exceeded 35°C on some days. After that, the water temperature decreased with the passage of time due to heat dissipation. Comparing the market of calves at Kawajiri Farm (Shimonoseki City, Yamaguchi Prefecture), which is a demonstration farm, after the introduction of the hot water supply system, the weight of calves increased compared to before, and the daily gain was over 1.0 kg/head, and the profitability improvement was about 42 000 yen/head (difference in average auction price by each bull). It was suggested that the usefulness of this developed hybrid hot water supply system.

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