In this study, the optimum scale of a power-generation plant was discussed for the model area using statistical data on a direct combustion power plant and a small-scale gasification power plant. With regard to the direct combustion power generation, the optimum scale of a power-generation plant was a generation capacity of more than 3 MW and an energy-conversion efficiency of more than 18%. Its fuel cost of electricity was 10.5 yen/kWh. On the other hand, the optimum scale of a small-scale gasification power plant was a generation capacity of 1 MW and an energy-conversion efficiency of 27%. Its fuel cost was 4.3 yen/kWh. In the distributed system, the optimum scale of six small-scale gasification power plants was a generation capacity of 0.1 MW and an energy-conversion efficiency of 20%. In order to limit fuel costs of direct combustion power generation up to 10.17 yen/kWh calculated by the average electricity price in Japan, 18.17 yen/kWh, minus the assumed fixed costs of the power-generation, 8 yen/kWh, it is necessary to improve energy-conversion efficiency or to construct forest roads. Forest road construction reduces fuel costs of electricity due to the reduction of skidding/yarding distances, as well as total cost including the cost of forest road construction. Therefore, it is important to reduce fuel costs remarkably by developing forest road networks. It is important to use small-scale gasification power-generation for energy utilization of forest biomass resources because of its higher energy-conversion efficiency.

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The costs of harvesting forest biomass resources, including cutting, chipping, yarding and transport, in the Chichibu area of Saitama Prefecture were calculated. The amount of biomass harvest from each subcompartment was calculated for the following three types of harvesting: thinning of artificial forests, final cutting of artificial forests, and thinning of natural forests. The harvesting type was determined from forest registers. Terrain and yarding distance were used to determine the system for harvesting biomass. Two scenarios for generating electrical power from biomass were considered. In the first scenario (Scenario A), a medium-scale power plant would be set up in the middle of the target area. In the second scenario (Scenario B), nine small power generating facilities would be set up in each of the 9 municipalities of the target area. Compared with Scenario A, the cost per cubic meter of biomass would lower in Scenario B; however, the cost per kilowatt of power would be higher in Scenario B because of greatly varying differences in power generation efficiency. In Scenario A, 19GWh/year of electrical power could be produced, but in Scenario B, the power production would be too low and would not be cost effective. If the yarding distance was shortened by 100m, the amount of energy that could be produced in Scenario A would increase slightly. If the maximum yarding distance of all subcompartments were shortened to 100m, enough biomass to produce 92.4GWh/year of electrical power would become available in Scenario A. In Scenario B, the power plants would become cost effective and would have the potential to generate 2.8GWh/year of electrical power.

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We analyzed the variation in production of logging residues based on logging systems, by examining data on logging by forestry enterprises in Yamanashi prefecture for the past five years. At present, 1/2 of the cut volume, including stems and shoots is transported to timber markets, and only 1/6 of that occurred as logging residue in wood yards, where it was easier to collect residues than in forests from an economic standpoint, due to the different logging systems and low-quality timber. The whole cut volume including stems and shoots had a positive proportional relation with that for timber production, regardless of the logging systems, and also had a relation with that for logging residue in wood yards if limited to whole tree harvesting. It is would be desirable to sift to operational systems that can use logging residue as woody biomass energy. Whole tree harvesting by forestry machinery would be recommended, and up to 2/5 of the whole cut volume would be expected to end up as logging residue in wood yards.

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