Hydropower

Hydroelectric power harnesses the kinetic energy of falling water in a river for electricity production. In this section we focus specifically on dammed rivers.

Economics and Future Potential

The cost of hydroelectric power is highly variable and site specific.

The threshold between small and large hydro varies by source and is typically between 10 and 50 megawatts of capacity. Source: International Renewable Energy Agency (¹ and ²), Logan et al. ³, OpenEI, ⁴, Salvatore et al. ⁵, Energy Information Administration ⁶.

Hydropower is highly capital intensive, with operations and maintenance comprising only 2-2.5% of the total cost ¹. Generally, projects in remote areas or that otherwise have logistical challenges are more expensive, as are smaller projects. Cost estimates are complicated by the fact that dams often have additional economic functions, such as irrigation and flood control, which can be worth 4-100% of the electricity the dam produces ⁷.

As a mature technology, there are no clear pathways for significant cost reduction in hydropower other than general improvements in civil engineering ¹. Despite their maturity, the American and world hydro industries still have potential to grow.

Current, economic, and technical potential for hydropower in the United States and in the world. Technical potential is the maximum amount of hydropower that can be extracted with current technology; economic potential the maximum feasible production that is economically viable under current conditions. Sources: Deng et al. ⁸, International Energy Agency ⁹, World Energy Council ¹⁰.

A more recent estimate is that there are 3,600 TWh of annual hydropower capacity in the world can produced at a levelized cost of less than 10 cents/kWh ¹¹.

In the United States and globally, pumped hydro comprises 13-20% of all hydro installation.

Hydropower can be used for pumping water as energy storage or as energy production. Sources: Department of Energy ¹² for the United States, International Hydropower Association ¹³ for the world.

Environmental and Social Impact

Like the economic impact, the environmental and social impacts of hydroelectricity are highly site specific, and it is difficult to generalize to all projects. Major impacts include the following:

• loss of biodiversity ¹⁴,
• damage to local ecology, particularly by impeding the flow of a river,
• climate impacts of the construction and operation of a dam,
• displacement of communities and agriculture through flooding,
• loss of archeological heritage ¹⁵,
• risk of a catastrophic failure.

The following internal and external costs of hydropower are estimated.

Sources: Sheridan ¹⁶, Tajziehchi et al. ¹⁷, Bruckner et al. ¹⁸, Kumar et al. ¹⁹, Mattmann et al. ²⁰.

Small hydro generally has higher environmental costs per-kWh than large hydro ²¹, ²², ²³, ²⁴. Run-of-river hydropower, which operates with little or no energy storage in the form of a reservoir, tends to have lower environmental impacts but still disrupts riverine ecosystems ²⁵.

The biodiversity impact of hydropower varies widely. The most impactful economic sites that are not yet developed have over 1.4 million times the impact as the least impactful sites ²⁶. Of the remaining potential, 0.3% accounts for 25% of the terrestrial ecosystem impact, and 3.9% of the potential accounts for 51% of the ecosystem impact.

Dam Removal

As of 2011, less than 1% of dams in the United States were under consideration for removal ²⁷. The economic value of a dam decreases over time as the reservoir becomes silted, and sometimes removal is deemed to be a more sensible option than further maintenance, especially when the biodiversity costs of dams are considered ²⁷.

Fish ladders, which allow fish to travel past a dam, are a partial solution.

Source: ²⁸.

For some species, fish ladders do not work very well; less than 3% of American shad successfully pass from the first dam to spawning grounds on three large rivers on the Atlantic coast ²⁹.