台灣發展太陽能加熱系統之環境與經濟效益評估

Abstract

為了改善能源結構及降低溫室氣體人均排放量，推展太陽能加熱系統(SWHS)為當前重要能源政策之一。唯由於各區域特性不同，適宜性及效益亦因而不同。本研究因而建立一套方法分析在台灣發展SWHS之適宜性及環境與經濟效益。 由於各地的輻射量不同，加上行政區域劃分方式影響政策的推動，本研究因而以自然條件為主、行政區為輔的方式分區，以作為後續分析之依據。以往的分析方法是依據全年太陽潛能累積值計算效益，但由於各區每日日照資源無法延至數日後使用，節能效益估算亦因而失真。故本研究依據各分區之水溫資料及太陽潛能估算系統之熱輸出，並依據熱輸出量多寡決定該日是否為有效日照天，再以各分區之有效日照天數比例計算效益值，進而考量單雙桶之影響。接著探討SWHS在各分區使用適宜性之差異，並以成本效益及政府的能源政策建立程序分析之。然後依據發展狀況、旗艦計畫執行率、補助費用、傳熱率、初置成本、維修費用及折現率等建立七種不同情境，並推估各情境下的安裝量，及評估與比較各情境下的環境與經濟效益，以作為相關決策或規劃之參考依據。 各情境分析後結果顯示環境效益在現況下及所替代能源為電力、柴油及天然氣時，估計約分別可減少eCO2 37,175噸、18,721噸及14,157噸。而當旗艦計畫執行率達100%時，環境效益約為現況1.5倍。豐日照與外島區在無補助下之回收年限約在18.9至21.2年間，其他地區則長達24年以上，誘因因而較小。當初設成本降低10%-30%及含補助時，回收年限則可縮短為12.8至7.9年。傳熱率技術提昇可增加有效日照天數，增加7%-20%時各區最多約可增加9-20日。當折現率值由1.86%增為3%-5%時，各區約可縮短收年限9.1%-17.5%。依結果可看出現今以豐日照區的推廣效益較佳，而中日照區的回收年限長，誘因較為不足。上述情境分析結果可作為台灣在不同區域發展SWHS與相關決策之參考依據。

In order to improve the energy structure and reduce the GHG emission per capita, promoting renewable energy applications such as the solar water heating system (SWHS) has become an essential national policy. However, regional characteristics can greatly affect the applicability and potential benefits of using SWHS. This study thus proposed a method for assessing the regional applicability and environmental and economic benefits of SWHS in Taiwan. To facilitate various regional analyses, the entire country is divided into four SWHS development regions based on the level of radiation in each region and administrative boundaries. Previous studies generally implemented their analyses based on the annual solar radiation that may overestimate the energy benefit because, for a SWHS application, the solar radiation energy captured today generally can not be preserved until the next day, even the radiation is excessively high. Therefore, this study determines effective days based on whether the potential heat output, estimated from the water temperature and solar radiation in each region, of each day is enough to run a SWHS or not. The energy benefit of a SWHS is then estimated based on the number of effective days, instead of on annual radiation. The potential benefit for installing two storage tanks is also analyzed. A procedure is established for analyzing the applicability of a SWHS in each region based on its potential cost benefit. Seven scenarios are established according to the development status, the ratio for achieving the national policy target, subsidy, heat transfer rate, fixed and maintenance cost, and discount rate. The environmental and economic benefits among scenarios are also estimated and compared. Under current situation, the environmental benefit, in term of eCO2 reduction, for substituting electricity, diesel and natural gas are 37,175, 18,721 and 14,157 tons, respectively. If the target of the national SWHS development policy is achieved, the environmental benefit is expected to increase about 50%. The payback period without subsidy in the high radiation and island areas is between 18.9 and 21.2 years, while for other areas it is more than 24 years. If the initial fixed cost is decreased by 10%-30% and providing subsidies, the payback period can be shortened to 12.8-7.9 years. If the heat transfer rate increases 7%-20%, it can increase 9-20 effective days. When the discount rate is increased from 1.86% to 3% -5%, the payback period can be shorten about 9.1%-17.5%. The results show that promoting SWHS in high radiation areas is effective, but for other areas with less radiation the payback period is still too long. These scenario results are expected to facilitate related decision analyses for developing SWHS in different regions.