(示意圖/圖片來源:Pixabay)

生質能為全球再生能源最大來源,除提供穩定電力,同時又能夠減少碳排放與空氣汙染,美國身為最大的溫室氣體排放國之一,又是如何利用生質能?政府研究報告成果與再生能源配額制度(Renewable Portfolio Standards,簡稱RPS),加上豐富林業資源,皆對促進生質能發展產生決定性影響。

政府研究

美國有不同贊助或資助生質能之相關研究,其研究從國家實驗室到大學甚至是政府補助計畫,計畫數量相當多。美國能源部主導此項研究,並發表了有關生質能概況與未來預測之報告,其中,在Billion Ton報告中便指出,美國擁有豐富的生物質料源,同時也是再生能源最大來源,其數量高達3.9 quadrillion BTUs,包括農業、林業與都市廢棄物,甚至是藻類之生質能,其中23%能源來自木質、21%來自(液態)生質燃料,而有5%來自廢棄物(2016 Billion-Ton Report)。這些來自政府報告及額外技術支援,可提升發展生質能之誘因與降低知識障礙,而在學術界制定的發展框架下,什麼樣的因素能夠提高應用程度?

 

 

 

 

 

(圖片來源:EIA (2016), “Southern states lead growth in biomass electricity generation” )
圖1 2005與2015年美國生質能發電

再生能源配額制度

首先,由使用生質能最多的州來看,南部各州對再生能源選擇,受限於地理條件限制、太陽能與風力發電效率較差、卻擁有豐富生物質料源等影響,因此傾向使用生質能。在這樣的情況下,不同的州會利用不同誘因措施。維吉尼亞州計畫將燃煤電廠改為生質能電廠,並鼓勵燃煤與生質能混燒,而位於維吉尼亞州Dominion Power有三座運作中的51MW電廠,每座電廠須在2025年將再生能源發電比例提升至15%,以作為自願減排一部分。再生能源配額制度(RPS)要求電力供應者須使用一定比例再生能源,此舉有助於提升生質能使用,一般來說,燃煤電廠轉換成生質能電廠或混燒生質能較為便宜,而且配置時程上比其他替代能源更快。

佛羅里達州設有美國最大生質能電廠之一的「恩斯維爾再生能源中心」,裝置容量高達102.5MW,該電廠於2013年12月正式商轉。當時生質能同時具備溫室氣體減量與減少化石燃料使用之誘因,美國西部在2010年至2015年間生質能發電同樣有顯著成長,在此期間生質能發電成長15%,其中西部成長動力主要來自加州少數大型電廠,這些電廠也幫助加州達成再生能源發電目標。

表1 美國各州生質能消費
(資料來源:美國EIA)

從美國上述各州可以發現有類似情況,這11個州在生質能的消費量及其占整體能源比率都是最高的,例如:緬因州、奧勒岡州及華盛頓州對再生能源有強力的承諾,但是因缺乏陽光而大量利用現有水力發電、同時卻擁有充足的林業資源。不過,南部的各州未對再生能源發展作出相同承諾,他們缺乏水力發電資源,但似乎接受部分再生能源供應商對再生能源的15%自願承諾。對美國各州而言,生質能代表快速、便宜與簡便之方式去達成再生能源目標。

對亞洲的啟示

我們如何將美國生質能政之策經驗應用於亞洲,特別是臺灣?首先,值得注意的是生質能技術與運作模式已相當成熟,美國擁有廣大的森林與農業區域,因此創造了豐富的(生質能)料源,但是臺灣或其他較小的亞洲國家並沒有具備這些條件,然而我們也從經驗中發現,對能源供應商發展再生能源之要求同樣具有效果,而美國使用最多生質能的州通常在發展其他再生能源方面之機會較少,可歸因於產業間比較利益不同使然。

(責任翻譯:吳周燕)

 


Biomass Use in the United States: Policy and Geographic Impacts

Globally biomass remains the largest single source of renewable energy and can reduce both carbon emissions and air pollution while providing stable power. How then has one of the largest greenhouse gas emitters, the United States, utilized biomass?  A combination of indirect research and renewable portfolio standards combined with abundant forestry resources has encouraged widespread biomass development.

Government Research

There were a variety of programs in the US that sponsored or enabled research into the combustion of dry biomass for energy. From national labs to universities to government grants, listing them all here would be extensive. Principally the Department of Energy led this research and published significant reports about the state and predicted future of biomass. One such report, the Billion Ton report clarified the widespread US of biomass in the US as the largest source of renewable energy at 3.9 quadrillion BTUs including the use of biomass from agriculture, forestry, municipal waste, and even algae. Within that number 23% of the energy comes from wood, biofuels cover 21% and waste 5% (2016 Billion-Ton Report). These reports from government, and additional technical support create soft incentives and lower the knowledge barriers for biomass adoption. While academia laid out the framework for development, what factors have led to this high level of usage?

 

 

 

 

 

(Source: EIA (2016), “Southern states lead growth in biomass electricity generation” )
Figure 1  Biomass Electricity Generation in the United States in 2005 and 2015

Renewable Portfolio Standards

First, look at the states with the highest biomass use. Southern states tend to use biomass for renewable energy because the geological conditions at the time made solar and wind less efficient while providing an over-abundance of plant materials. Within that context, different states utilized different incentives. Virginia has a statewide program to convert coal plants to biomass and encourage co-firing of both coal and biomass material. Dominion Power in Virginia operates three plants at 51 megawatts (MW) each as part of their voluntary reduction to generate 15% of its electricity from renewable sources by 2025. Renewable portfolio standards, which require electricity providers to use certain percentages of renewable energy have benefited biomass adoption. Often, converting a coal plant into a co-firing or strictly biomass plant can be cheaper and faster than setting up other types of alternative energy.

Florida opened one of the largest new biomass plants in the United States, the 102.5 MW Gainesville Renewable Energy Center. The plant began generating power commercially in December 2013. Biomass at the time seemed alluring for both cutting GHGs and reducing fossil fuel use. The western part of the United States also had notable growth in biomass between 2010 and 2015, increasing electricity generation from biomass by 15% over that period. Most of the growth in the West comes from a few large plants in California that are helping the state meet its renewable electricity target.

Table 1  Biomass Consumption in the United State
(Source: U.S. Energy Information Administration)

Looking across the United States you can see that the above states share common themes. These 11 states have the highest total use and proportion of biomass for energy. States such as Maine, Oregon, and Washington have strong commitments to renewables, lack sunlight, have largely exploited existing hydropower, and ample forestry resources. Whereas the southern states do not have the same commitment to renewable development they also lack the same hydropower resources, but do seem to embrace the 15% voluntary commitment by some energy providers for renewables.  For all states, biomass represents a fast, cheap, and easy way to meet renewable targets.

Lessons for Asia

How can we apply this biomass policy experience to Asia, specifically Taiwan? First, it’s worth noting that the technology and operational models for biomass have been well established. However, the context differs greatly. The US has large forests and great swathes of agricultural areas, this creates abundant source material, this will unlikely be the case for Taiwan or other smaller Asian countries. However, we can see from experience that requirements for energy providers to develop renewable energy works. The states that use the most biomass tend to have fewer opportunities for other renewable energies.


【延伸閱讀】

從農場到電廠:美國生質能作物援助計畫檢討
Lowering the Cost of Biomass: The US Experience 

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