In our research on the status of renewable energy in Central America, we’ve run into an issue of semantics that has potentially wide-reaching consequences for the region. The hang-up comes with the term ‘renewable’ and which energy sources, exactly, it includes. On the surface, the definition seems obvious: renewable energy is inexhaustible energy derived from consistently shining or blowing or flowing sources—very unlike non-renewable energy, of which we have finite stocks that we are quickly moving from their subterranean homes to the atmosphere.

However, when it comes to hydropower, definitions get a bit more complicated. In theory, hydro is renewable energy in that water used to generate electricity is not ‘used up’ in the way that gas or coal is. But the actual history of hydro energy development has been one of restraining some of the world’s mightiest rivers—North America’s Colorado, China’s Yangtze, and South America’s Paraná—behind dams. According to the World Commission on Dams, 60 percent of the world’s rivers have been dammed or diverted; a process that has cost on the order of $2 trillion, displaced between 40 and 80 million people, and reduced many rivers to a trickle before they could reach the sea. In this sense, most dams actually do deplete water stocks flowing to downstream users and ecosystems—bringing into question the idea of hydropower as ‘renewable’ energy.

Source: Probe International | At 7.3 MW, the Chalillo Dam on the Macal River in Belize would be considered “small” hydro. But you don’t need much more than this photo to understand that even “small” hydro’s role in renewable energy strategies should be questioned.

So we’ve had to build a new, more nuanced vocabulary. Small hydro is often used to delineate sustainable hydro, but even the definition of small is elusive. India considers installations under 25 MW to be small, and the United States draws the line at 30 MW (as noted in REN21’s Global Status Report). In their Climatescope 2012 report, Bloomberg New Energy Finance considers small hydro to be anything less than 50 MW. The United Nation’s Clean Development Mechanism classifies ‘small hydro’ as less than 15 MW and micro hydro as under 5 MW. Another category, pico hydro, typically refers to installations of 5 kW or less.

In terms of sustainability, are these definitions meaningful? Yes and no. Many projects that would be considered “small” by most definitions are actually quite devastating to ecosystems and the people who depend on them. The 7.3 MW Chalillo Dam in Belize, built in 2005, cuts through the Mesoamerican Wildlife Corridor that provides migration routes and breeding grounds for species like the tapir, jaguar, and scarlet macaw. The dam also threatens human populations: sediment discharges from Chalillo are causing downstream turbidity levels hundreds of times World Health Organization standards and people who swim in the Macal have reported skin rashes. Resorts in the area have installed swimming pools for their guests to avoid the toxic water—an option that villagers don’t have.

If anything, the attempt at differentiating between small and large hydro is an acknowledgement that size and scope of hydro projects matter to sustainability and that some line should be drawn in the sand, no matter how crude. Few Central American governments have done this, and many continue to lump all hydro into their renewable energy strategies. Costa Rica, which currently generates 76.4 percent of its electricity from hydropower, plans to continue increasing its hydro capacity: a couple of huge hydro projects— Diquís at 627 MW and Revantazón at 292 MW —are planned for 2016 and 2019, respectively.

Rather than MW capacity, the definition of sustainable hydro could be based on a combination of factors such as dam height, location in the river basin, type of reservoir, and dam operations. Upstream-downstream connectivity is especially important: animals need to have a way of moving upstream and organic matter and sediments need to have a route down. And it’s of course best not to dam a river at all. Run-of-river hydro projects can operate on a pico scale in-stream or on a slightly larger scale by building a channel that diverts water to a turbine house and then pipes it back to the river (this type of system may include a partial dam that stores water in a reservoir for low-flow periods).

Source: Practical Action | Run-of-river hydro systems temporarily divert water from a river through a channel, use it to run a turbine, and then return it to the river.

Run-of-river hydro is an excellent option for distributed rural energy, and many projects are already operating in Central America. El Roblar, a 17 kilowatt project in Nicaragua developed by Asociación Fénix, uses a Pelton turbine to generate electricity for 32 households, a church, and a school.

Calling all hydro power “renewable” may look good in national energy plans, but ecosystems (and downstream people) aren’t fooled by semantics.  Dam development in the United States throughout the twentieth century, which resulted in a total of approximately 2,540 hydropower dams, often left communities flooded and wildlife endangered, with social and environmental costs arguably  outweighing the benefits. We’re now tearing down numerous unnecessary dams across the U.S. to restore riverine ecosystems.