Abstract
AbstractHydropower is considered green energy and promoted to reduce greenhouse warming. However, hydropower is typically generated using reservoirs and reservoirs are known to emit substantial amounts of the greenhouse gas methane (CH4) to the atmosphere. In many reservoirs ebullition is the dominant pathway of CH4 emission. We show that continuous diurnal pumped‐storage operation, which combines water pumping into the reservoir typically during the night and water drawdown during high demand of electricity, is beneficial for reducing CH4 ebullition associated with hydropower generation. This conclusion is based on ebullition fluxes and water levels measured over 3 months in Schwarzenbach reservoir located in Germany. The reservoir was managed using three modes of operation: (1) diurnal pumping and turbination, (2) no pumping and no turbination, and (3) diurnal turbination. Cross‐correlation analysis indicates that ebullition fluxes predominantly occur during diurnal water level decrease associated with turbination. Consistently, average ebullition fluxes of CH4 were negligible during Mode (2) and substantial during Modes (1) and (3). During Mode (3) the average CH4 ebullition flux was ~197 mg m−2day−1, ~12 times larger than during Mode (1) (16 mg m−2day−1). Our data indicate that overall CH4 ebullition is about 3 times larger during 51 days of operation consisting of 38 days of no turbination followed by 13 days of diurnal turbination than during 51 days of continuous diurnal pumped‐storage operation. This suggests that continuous diurnal pumped‐storage operation leads to reduced CH4 ebullition from reservoirs and is therefore advantageous compared to modes of operations involving long‐term, large‐amplitude turbination cycles.
Highlights
Reservoirs are anthropogenic systems constructed to collect, store, and manage water by blocking the natural water flow of streams and rivers with artificial dams and/or by complex pumped‐storage operation in artificial water systems
We show that continuous diurnal pumped‐storage operation, which combines water pumping into the reservoir typically during the night and water drawdown during high demand of electricity, is beneficial for reducing CH4 ebullition associated with hydropower generation
Our data indicate that overall CH4 ebullition is about 3 times larger during 51 days of operation consisting of 38 days of no turbination followed by 13 days of diurnal turbination than during 51 days of continuous diurnal pumped‐storage operation
Summary
Reservoirs are anthropogenic systems constructed to collect, store, and manage water by blocking the natural water flow of streams and rivers with artificial dams and/or by complex pumped‐storage operation in artificial water systems. Pumped‐storage hydropower plants are considered to be the most efficient systems to store electric energy (Kobler et al, 2019) and may play an important role in the management of renewable energy. The number and size of hydroelectric power reservoirs, and especially of pumped‐storage systems, have increased substantially during the last years (Barbour et al, 2016; Deane et al, 2010; Rehman et al, 2015; REN21, 2017) to satisfy the increasing demand of energy and energy storage and the requirement to reduce greenhouse gas (GHG) emissions linked to energy production (Barbour et al, 2016; Commission, 2011; Ibrahim et al, 2008; Kobler et al, 2019). Hydroelectric energy has traditionally been considered green energy because its production seems free of GHG emissions to the atmosphere (Hoffert et al, 1998; Victor, 1998), and hydropower is promoted as a climate neutral alternative energy source to fossil energy
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