廢耕地發展能源作物之效益與情境分析

Abstract

台灣缺乏自主能源且面對國際溫室氣體減量壓力，因而有必要發展綠色能源。生質能源是國內推動的綠色能源之一，但是目前台灣發展能源作物之適宜性及效益，大多依據其他各國發展生質能源的經驗與成果，並未考量台灣在自然環境及氣候與各國之差異，無法適當評估能源作物在台灣發展的效益。再者，發展能源作物雖可以解決部分能源及溫室效應氣體之排放，倘若排擠糧食的正常供給，反而捨本逐末，因此本研究擬建立一套方法，分析台灣利用廢耕地發展能源作物之效益，以供進行相關決策分析時參考。 本研究所發展之能源作物效益與情境分析方法包括分區方法、能源作物評選、優選模式建立、效益分析及情境分析等五大步驟。由於能源作物的選擇，涉及作物生長的自然條件及政府政策之推動，本研究因而以柯本氣候分類法為基礎，配合行政區界之調整建立分區方法。能源作物評選則依據地理及氣候等生長因素，主要考量能源作物的適栽性，包括土壤、降雨量、氣溫及日照等因素，其次考量能源作物的特性，包括產量、收獲數、產油率等因素，以篩選出各區較適種之能源作物。效益分析則針對環境、能源、經濟等三種效益，分析效益宜納入的評估因子及計算方法。優選模式是採二階段模式求取近似最佳解。第一階段先放寬生質柴油及生質酒精總需求量為最小需求量再加5%，求取能滿足總需求量的最小栽種面積;第二階段則以第一階段所求出的面積為限，求取最大效益解。 最後設定八種生質酒精及生質柴油需求情境，分析不同需求下各分區之優選作物、面積及效益。結果顯示情境六全面使用B2生質柴油及E3酒精汽油是較佳的方案，平均每公頃廢耕農地可減量約235萬公噸eCO2。

Developing various green energies is important in Taiwan because Taiwan has very limited domestic energy resources and the reduction of greenhouse gases has become an essential national pressure. The biomass energy is thus currently promoted. However, most local biomass energy studies were primarily based on foreign experiences and overlooked Taiwan’s specific natural environment and climate characteristics. As a result, the benefit for developing biomass energy crops in Taiwan was not properly assessed. Furthermore, energy crop development should not affect regular food supply. Therefore, this study was initiated to establish a method to evaluate the benefits of growing energy crops on long-term uncultivated lands in Taiwan. The proposed method includes five major steps: district division, energy crop selection, benefit analysis, optimization model establishment, and scenario analysis. The entire nation is divided into three major biomass energy districts based on the K□ppen climate classification and administrative boundaries. For selecting suitable energy crops to grow in each district, various geological and meteorological factors are evaluated, including soil, rainfall, temperature and sunlight resources. Expected harvest quantities and biomass energy yield rates are also evaluated for assessing the suitabilities for raising various crops. The benefit analysis is implemented for estimating environmental, energy yield and economic benefits. A two-step near-optimum model is applied. The first step relaxes the minimal demand of biodiesel and gasohol by 5% of the total demand. Then, the growing area determined in the first step is set as the upper limit in the second step to find the solution with the best benefit. Eight possible scenarios for various bioethanol and biodiesel demands were analyzed. In each scenario, the optimal growing area of each energy crop and associated benefits were determined. According to the results, scenario 6, 100% usage of B2 biodiesel and E3 gasohol, shows the best unit benefit, about 2.35 million ton eCO2 decrease per hectare.