Rethinking Small Hydropower Projects

October 31, 2022 by Darshil Patel

Researchers suggest that small hydropower plants can be reliable, cost-effective, and flexible.

Hydropower is a significant global energy source and the largest source of renewable electricity. Hydropower provides nearly eight times more power than solar panels and around 1.5 times more than nuclear power plants. It is widely considered one of the fastest-growing renewable energy sources.


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However, there are limited places to build hydropower plants as they need a consistent water supply and a large amount of land. Moreover, dams for hydropower can also cause social and environmental concerns. They can significantly impact aquatic ecosystems, as fish and other organisms can be injured or killed by turning turbine blades.

Reservoirs also affect the aquatic wildlife in that area as the water there is more stagnant than the river water. Therefore, poorly planned hydropower can cause more problems than it claims to solve.

Turning our attention to greenhouse gas emissions, large-scale hydroelectric plants emit approximately 0.06 pounds of carbon dioxide per kilowatt hour during their lifetime, and small-scale plants produce around 0.01 to 0.03 pounds per kWh. To put these figures into perspective, natural gas-generated electricity generates 0.6 - 2 pounds of carbon dioxide per kWh, and coal-based electricity emits 1 to 4 pounds per kWh.

However, the material of the plant decays over time and releases greenhouse gasses. The variability of emissions is very high. Therefore, current estimates suggest that the lifecycle emissions of hydropower plants can be over 0.5 pounds per kWh.

As a result, there is a growing trend of removing dams to preserve ecology. On the other hand, researchers at the University of Maine propose that small hydropower plants can contribute more to the renewable energy future due to their reliability and cost-effectiveness.

Small hydropower projects generate less than 60 megawatts of electricity. The researchers evaluated different types of small hydropower plants with the cost and performance metrics and compared their results with 13 studies conducted across multiple countries.


Evaluating Small Hydropower Projects

University of Maine researchers created a benefit-cost model of small hydropower projects in New England and found incomplete reviews published on the metrics they sought to calculate. Moreover, they found many inconsistencies in the benefit-cost assessment data for small-hydropower projects.

The researchers focused on four major types of small hydropower designs:

  1. Reservoir-based dams: Block water flow in the reservoir and release it through turbines. These plants are more reliable but affect the aquatic ecosystem.
  2. Run-of-river plants: Involve a dam that channels the water from the stream to the turbines with the downstream flow equal to the upstream flow. These dams are less disturbing to fish passage and aquatic habitats.
  3. Pumped storage dams: Lift the water from a lower reservoir and releases it through turbines when needed. 
  4. In-stream turbines: Turbines are placed directly in the flow of a stream of a river without any diversion.


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The researchers categorized small hydropower plants and various specific cost and performance metrics. They also compared their annual capacity, power capacity, benefit-cost ratio, and levelized energy cost.

They conclude that small hydropower plants can contribute to the renewable energy sector. They also highlight the need for more investigations on cost, performance, and ecological impacts with consistent and comparable metrics.


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1 Comment
  • B
    BobMG November 04, 2022

    Very interesting and thought-provoking. BUT the report leaves you wanting MORE!!  In fact, a lot more.  I guess we will just have to wait a bit. I rather suspect that small (i.e. those that use diversion or ‘in-water-flow’) may be ‘efficient’ but are handly any kind of a solution in the ‘large’ sense. Partly because how the heck are you going to collect the outputs of these ‘small’ systems?  Yet still interesting.

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