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13/9/21

Carbon emissions from hydropower reservoirs: facts and myths

经过多年的不确定, the science around hydropower’s carbon footprint is now clearer than ever, 写阿兰Kilajian, esball国际平台客户端(IHA)高级可持续esball国际app专家Sara Mercier-Blais, 魁北克大学教科文组织全球环境变化讲座研究员, 蒙特利尔(UQAM).  

阿兰和莎拉是G-res工具团队的成员, 一个多方利益相关者的研究项目,关注世界各地水电水库的碳排放. 在这篇博客, 他们利用最新的科学来解决esball国际app水电排放的常见问题和误解, 尤其是由水坝形成的水库.  


We need hydropower to address climate change and reduce global carbon emissions. 真或假?

真正的. Global action against climate change is centred around a need to reduce carbon emissions. 对于能源部门, 这意味着一个快速的转变, 和增加的, renewable and low-carbon sources of electricity such as solar, 风力和水力发电.  

通过取代煤和天然气热电厂, 这些低碳替代品提供了抵消大量排放到大气中的能力. 今天, hydropower’s flexibility and storage capacity are integral to tackle climate change, as they can help stabilise energy production when coupled to variable renewables, such as when solar and wind power are unavailable due to a lack of sunshine or wind.  

IHAesball国际app水电碳足迹的简报 为了了解使用可再生水电代替化石燃料在全球可避免多少排放.  

水电的平均排放强度与风能和太阳能等其他可再生能源相当. 真或假?

真正的. 任何一种能源的排放强度都是指每单位能源产生的温室气体排放量(多以gCO2-eq/kWh表示). 一项使用G-res工具对全球近500个水电水库的研究发现,水电的中值为23 gco2当量/千瓦时, which aligns with the Intergovernmental Panel on 气候 Change (IPCC) estimate of 24 gCO2-eq /千瓦时.

When we compare this value with other energy sources, 只有核能和风能的平均生命周期温室气体排放强度低于水电, 都是12 gco2当量/千瓦时. 对于太阳能,其值为48 gCO2-eq/kWh. 天然气和煤炭的价值是 490和820 gco2 eq/kWh 分别.

当然,这只是一个中值. 在少数罕见和极端的情况下, hydropower reservoirs have been 记录 to produce significantly higher emissions, while others have close to zero emissions or can act as 碳汇.

Hydropower reservoirs do not release greenhouse gas (GHG) emissions. 真或假?

假. It was long believed that inland waters (in other words, 河流, 湖泊和人工水库)并不释放温室气体排放,相反,它就像一个管道,在陆地和海洋之间运输碳.

我们现在知道内河实际上是 温室气体产生的来源. Lakes and 河流 collectively emit as much CO2 than oceans take up. 由平方米, 湖泊比海洋活跃80倍,比陆地景观活跃30倍. As reservoirs are human-made lakes, they are also a source for GHG transformation.  

更多最新的知识表明在现实中, 尽管有共同的信念, 水电水库确实会排放温室气体. 的 emissions primarily come from microbial processes that decompose organic matter into GHG. It should also be noted that the carbon processing in reservoirs can work two ways, 同时排放和吸收排放. This explains why, in a limited number of cases, reservoirs can act as 碳汇.

Hydropower storage projects tend to release more emissions than run-of-river plants. 真或假?

真正的. 的 main difference between storage and run-of-river projects is the creation of a reservoir. 一个储存项目需要一个水库来储存水,以便在需要电力时使用,而一个河流发电厂, which generates energy using the natural flow of a river, 没有或最少的水积累.

创建存储库时, a terrestrial environment is flooded and transformed into an aquatic environment. This flooding has multiple effects on the GHG emissions of the system.

第一个, 当新的土地被洪水淹没, 更多的碳, 大部分来自洪水泛滥的土壤, 是否可以转化为温室气体排放. 第二个, as the water slows down and begins to accumulate in the reservoir, aquatic bacteria have more time to transform the available carbon into GHG emissions. 更多的碳和更多的时间等于更多的排放.

Finally, the longer the water stays in the reservoir (i.e. 它的停留时间),就越倾向于在表面变暖,而在接近底部时却保持寒冷. This temperature gradient can create something we call a 斜温层 that acts as a physical barrier for small molecules like CO2 and CH4. 斜温层以上, 你会得到含氧良好的水,大气中的碳与氧混合产生二氧化碳. 温跃层以下, 在缺氧环境中,碳会转化为CH4,因此CH4起到了屏障的作用, the CH4 produced in the deeper parts of the reservoir stays there. So, if a project’s water intake is located under the 斜温层, CH4  will be released downstream through the turbine – a process we call 脱气.  

Degassing is one of four emissions pathways associated to reservoirs. 的 other three include CH4 bubbling, CO2 diffusion and CH4 diffusion. 而径流植物可能仍然有不同的排放与不同的途径有关, 由于径流电厂的水停留时间较短,且占用的土地较少,这些项目的蓄水成本往往低于蓄水项目.

所有热带储层的排放量都很高. 真或假?

假. 它是众所周知的和 记录 由于年平均温度较高,热带地区水库的温室气体排放量往往更高. This created the myth that all tropical reservoirs have high emissions.  

Temperature is only one of the many elements influencing the carbon footprint of reservoirs. 水在蓄水池中花的时间, 水淹土壤碳含量和水库浅层碳含量对水库温室气体排放剖面均有贡献.  

例如, 在热带地区,一个大而深的储层可以产生大量的能源,其每单位能源产生的碳足迹很可能很低.  

Clearing vegetation in the impoundment area significantly reduces reservoir emissions. 真或假?

假. 而大多数人认为被淹的树木和植被是蓄水区碳的主要来源, 事实并非如此. Most of the carbon actually comes from the soil and more specifically the top 10cm of soil.  

主要原因是,细菌很难分解地上生物量中的碳而不是土壤中的碳. 一个明显的例子是法属圭亚那的Petit Saut水库,那里的树木在蓄水30年后仍在被采伐. 有时,淹水森林甚至可以为水库中的鱼类提供重要的栖息地.

Clearing vegetation has been 记录 to improve water quality in the reservoir. But for the clearing to be effective, all the material would need to be disposed. 这带来了自身的挑战, 最常被考虑的选项, has very significant impacts and exporting the biomass is not practically feasible, 特别是大型水库.  

Field sampling is the only way to estimate emissions from hydropower. 真或假?

假. 与进步 科学认识 and data availability related to GHG emissions from reservoirs, we now have the knowledge to predict emissions without going directly on site.  

一个例子是温室气体储存(G-res)工具. 的 G-res工具 使用由该领域专家创建的概念框架,在在线界面中集成最新的科学,以估计水库的温室气体排放. 这些工具帮助水电公司和研究人员估计和报告水库的净温室气体排放,而不需要进行昂贵的实地取样活动. 在预可行性阶段,它们作为避免高排放项目的筛选工具尤其有价值.  

It is impossible to reduce reservoir emissions after a 水电专业ject is constructed. 真或假?

假. Although it’s easier to implement carbon reduction measures in the design phase of a project, 有一些创新的方法,水电业主可以减少水库排放,即使在他们的项目建成后.  

下面是一些例子:

  • 改变操作水平. 浅海岸区面积是影响储层温室气体排放的多种因素之一. More littoral equals more CH4 production which equals more GHG emissions. 在某些情况下, 改变操作水平可以减少浅海区域的数量,从而减少水库的温室气体排放量.
  • 安装曝气设备. 可以安装曝气装置,增加水中的溶解氧,减少下游CH4的释放量.
  • 在温跃层上增加二次进水口. Hydropower operators will often need to refurbish their asset over time. 任何大型翻新项目都有机会在温跃层上增加二级进水口(或多级进水口),以使含氧水通过涡轮机循环,减少脱气量.
  • 将甲烷排放转化为能源. A 研究 是否探索了从储层中回收生物甲烷并将其转化为潜在能源的可能性. 的y suggest that the recovered methane could be pumped directly to large consuming centers, 在当地储存并由燃气轮机燃烧用于发电或净化用于运输. 的 approach both reduces emissions and provides a additional source of energy generation.  

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