鈴木 誠一

<p>海洋温度差発電（OTEC）は，再生可能エネルギーの中でも資源量が多く，気象の影響を受けず24 時間発電可能なことから，実用化が広く期待されている。しかしOTEC の発電コストは高く，中でも取水コストが大きな割合を占める。本稿では，既に報告されている久米島でのOTEC 実証計画書を基に，取水を含めた設定条件を最適化した場合の発電コストを試算，評価した。久米島実証計画の1,250 kW規模での発電コスト120.5円/kWh（取水施設を内部化，助成なし）に対して，取水施設の最適化により，50.5円/kWh，さらにリスク対応として設置されている取水管２条を統合することで43.4円/kWhとなる。新たな技術開発を仮定しなくとも，諸設定の最適化で，離島の小規模ディーゼル発電と十分価格競争が可能である。OTECの本格的普及には，発電コストの更なる低減を要するが，表層水水温の制約の下，現状の取水技術，発電装置技術では限界があり，スケールメリットや高温側熱源補助装置の形態，効果について検討する必要がある。</p>

Sustainable carbon fixation system with large scale afforestation in arid land has been proposed for the mitigation of global warming. To avoid the problem of rainfall shortage and the large evaporation loss, our afforestation system has adopted a water-harvesting system. We have set a research site near Leonora (mean annual rainfall and evaporation are about 200 mm and 2,500 mm, respectively), Western Australia. We have so far developed an original runoff simulation model for understanding of water behavior involving penetration, evaporation and runoff. In previous studies, the best values of corrective coefficient of penetration (PR), and equivalent roughness coefficient (N) were determined by fitting numerical results to the water level data of the collecting pond of a watershed within 6 km × 4.8 km. In the present paper we extend this model to the larger area of 43 km × 52 km to evaluate the change in water penetration before and after the afforestation of bare ground, assuming that penetration rate of the bare ground changes to that of woodland by the afforestation. Then we evaluate effect of afforestation on penetration water amount by comparing the calculated results before and after afforestation in the large area. Finally we show the strategy to select appropriate afforestation sites and the way to evaluate the effects of afforestation on the vegetation of the peripheral areas.

The biodiesel derived from animal fats has the problem of high Cold Filter Plugging Point (CFPP, an index of the low temperature property). Therefore, the pyrolysis method has been paid attention to. In this method, the ester bond of triglyceride, the principal ingredient of oils and fats, is cracked by the decarboxylation reaction. As a result, the biodiesel consist of hydrocarbons is produced and its CFPP is lower than that of conventional biodiese. Authors have so far clarified the following two facts. The decarboxylation occurs to triglyceride after it is converted to fatty acid. The Pd-loaded active carbon is effective for the promotion of the decarboxylation of the fatty acid. However, Pd is expensive. Therefore, cheap Ni catalysts were tested in this report. As a result, it was clarified that the Ni-loaded brown coal is effective for the promotion of the decarboxylation of fatty acid.

The geographic location of new emissions is shifting from the industrialised countries to the newly emerging economies, expanding at a pace of over 5% per annum despite global economic slowdown. India, the 6th largest consumer of energy would spend US$ 19.4 billion (@ US$ 100/barrel) on importing gasoline by 2020, if viable renewable sources of energy are not developed. Biofuels are credible supplement for liquid fossil fuels even at present. They are easy to transport and fall in zero emission category. Biodiesels derived from Jatropha can be locally produced in rural areas for agricultural purposes. Jatropha is being promoted as biofuel crop in India through large scale plantations and nurseries and by women's self-help groups who use a system of microcredit to ease poverty among semiliterate Indian women. The Life Cycle Analysis was done for a typical arid area, Panna, M.P. (India) for Jatropha cultivation on wasteland, poor agricultural land, scantily planted forest land. The LCA investigation scope includes four landuse change scenarios with four input change scenario in cultivation stage. The economic return to farmers at different selling price of Jatropha seeds have also been studies with carbon mitigation option in diesel replacement in transportation.