Project Details
Overview/Objective
Although hydropower offers significant potential for electricity generation and storage, characterization of dissolved gas emissions from hydropower reservoirs is inconsistent and incomplete, leading to highly variable estimates that have ranged from 0.14% to 6.6% of global gas emissions. This uncertainty can pose an obstacle to widespread adoption of these water power resources.
One way that reservoir emissions are currently estimated is by conducting field measurements, but few of the country’s 1,400 reservoirs that support hydropower generation have been sampled, and even fewer are routinely monitored. Adding to the confusion is the fact that reservoirs often have multiple uses, including drinking water and flood control. So, attributing all dissolved gas emissions from reservoirs to just one use, hydropower, can be inaccurate.
To create a more complete and precise picture of hydropower's contribution to global emissions, researchers at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) are using a combination of modeling and new field sampling measurements to quantify the amount of dissolved gases released from each of the most common emission routes—diffusion, ebullition, and degassing.
- In diffusion, gases produced by microbes living in sediments at the bottom of a reservoir bubble up to the surface and into the atmosphere. Warmer temperatures increase the rate of diffusion.
- In ebullition, or bubbling, methane rises to the surface from the shallow areas of a reservoir, which do not have enough water pressure to keep the gas bubbles from escaping.
- Degassing occurs when methane is released as reservoir water passes through hydropower turbines or flood control spillways. These operations typically pull from deeper waters, which often contain higher concentrations of methane.
The ORNL study marks one of the first times all three emission pathways are being measured simultaneously.
Results
With support from the US Department of Energy’s Water Power Technologies Office, the ORNL project team is returning to six hydropower reservoirs in the southeastern United States that it sampled a decade earlier to collect new measurements of dissolved gases. This time the team is using more advanced measurement tools, including drone technology, to gather data. The team is comparing its new findings to its historical data and current model projections.
In addition to collecting new measurements from the field, ORNL researchers are analyzing the effects of local temperature variability and dynamic reservoir operations using the International Hydropower Association’s web-based G-res Model. The project team is also collaborating with the US Environmental Protection Agency’s national reservoir emission survey, which is measuring emissions at 108 reservoirs.
Impact
These new techniques and the data produced by this study will allow the team to identify gaps in knowledge, refine models used to predict gas emissions and provide insight into what factors drive or restrain them. The results could be used to inform potential mitigation efforts, clearing the way for greater adoption of hydropower, which would ultimately result in a more resilient power grid.