A photovoltaic/wind/diesel generating system with a battery (PWD system) is discussed from the viewpoint of total CO 2 gas emissions during system lifetime. The total emissions are the sum of the emissions occurring at manufacturing and operating. First, the manufacturing CO 2 emissions of the photovoltaic generator and the wind turbine generator are calculated by “the process analysis method.” This method considers the material used in each generator, its weight and its CO 2 emission rate. On the other hand, the manufacturing CO 2 emissions of the diesel generator and the battery are calculated using “the interindustry (input‐output) table.” Second, the PWD system is operated on a computer so that the fuel consumption of the diesel generator is a minimum assuming that hourly series data of electric load, insolation intensity, wind speed, and air temperature are known during the year. And CO 2 emissions occurring at system operation are obtained from the annual fuel consumption of the diesel generator. The results show that CO 2 total emissions of the PWD system are lower than those of the conventional diesel generator system. The CO 2 total emissions reach a minimum when the photovoltaic/wind generating ratio is 50/50. The CO 2 emissions of manufacturing decrease with increasing of the wind generating ratio from 100/0 to 0/100. The CO 2 total emissions decrease as the natural energy ratio increases. It is, however, saturated to about 60% when the ratio is more than 60%. And the CO 2 total emissions increase with increasing of the battery capacity. It is concluded that the PWD system plays an important role in decreasing considerably the CO 2 total emissions while the total system cost is high under the present price circumstances.
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Kemmoku et al. (2001) studied this question.