By Jeff Opperman
How much hydropower generation does the world need to maintain a stable climate?
That’s a crucial question given that we are facing not just a climate crisis but a nature crisis too. And (1) even with the dramatic recent growth of wind and solar PV, hydropower remains the world’s largest source of renewable and low-carbon generation; and (2) hydropower projects often have far greater negative impacts on communities and nature than other renewable generation technologies.
The International Renewable Energy Agency (IRENA) released a report last week with an answer to that question: to maintain a stable climate, it claimed that global hydropower capacity would have to double by 2050. To do this, annual investments in hydropower would need to increase by a factor of five from today’s level.
The problem is, when it comes to hydropower and climate, there are many other questions that should be asked – and answered. (Spoiler alert: for those looking for a short summary – a doubling of hydropower would have massive negative impacts on people and nature, but is no longer necessary as the world now has many options for low carbon and low cost electricity systems that could avoid most of these impacts).
What are the implications for people and nature of doubling global hydropower capacity?
The IRENA report acknowledges that hydropower projects can have some negative impacts on communities and ecosystems but simply references various best practices for dealing with those impacts. It does not grapple with the fact that a doubling of global hydropower would necessarily require some major tradeoffs.
A doubling of hydropower means about 1200 gigawatts (GW) of new hydropower capacity globally. For reference, the largest hydropower dam in the world, Three Gorges, is 22.5 GW, so IRENA’s call for expansion is more than 50 times that scale.
Recent research led by WWF examined the impacts on the world’s rivers from building all the hydropower dams in the best available global database of planned dams. These dams represent about 600 GW of new capacity—so just halfway to the IRENA recommendation—and, if built, they would fragment 260,000 km of free-flowing rivers globally.
That number may sound abstract, so here’s something perhaps more tangible: if all currently planned hydropower dams were built, they would fragment more than half (52%) of the remaining free-flowing big rivers in the tropics, including 61% of those in South America, 41% of those in Africa, and the only two free-flowing big tropical rivers in Asia (the Irrawaddy and Salween rivers).
These free-flowing big tropical rivers currently support the most productive freshwater fisheries, and their sediment maintains river deltas that support tens of millions of people, globally crucial agriculture and industrial supply chains.
Hydropower dams have been the leading cause for the damming of big rivers around the world and the results of this damming have been displacement of millions of people, dramatic declines in migratory fish (76% decline globally since 1970), and the sinking and shrinking of major deltas, such as the Nile and Mekong.
Even getting halfway to the recommended increase in global hydropower would be doubling down on these negative impacts. Clearly, there are no best practices available to deal with an actual doubling of global hydropower. There would simply be massive tradeoffs borne by rivers and the people that depend on them across the world.
Given these massive tradeoffs, the generation from proposed hydropower expansion must be a big part of the climate solution, right?
Not really. The recent WWF study found that dams with a total of just over 200 GW of hydropower capacity are proposed for free-flowing rivers, with 75 GW of that on the biggest rivers. This level of development on big rivers would generate less than 1% of the renewable electricity needed by 2050 to meet the 1.5° C climate target – even as it would fragment more than half of the world’s remaining large tropical rivers.
In brief, for an amount of electricity that is basically a rounding error in 2050 generation needs, the world would have to accept a dramatic loss of a globally important ecosystem type, one that hundreds of millions of people currently depend upon. It would also erode efforts to reverse the catastrophic loss in freshwater biodiversity – and undermine the goals of the new Global Biodiversity Framework agreed to by all nations at the Convention on Biological Diversity conference in December.
Could the world reach climate targets with a lower amount of hydropower expansion?
Yes. The IRENA recommendation is just one answer to the question of how much hydropower is needed to achieve climate targets. While the International Energy Agency offers a similar answer, other global studies of energy and climate have concluded that a far lower increment of new hydropower could be consistent with climate targets.
A study led by the University of Technology Sydney projected a global energy system that would be consistent with the 1.5° C target and this included about 300 GW of new hydropower by 2050, approximately 1/4 of the IRENA recommendation. Similarly, a recent study from the Joint Global Change Research Institute, part of the U.S. Department of Energy’s Pacific Northwest National Laboratory, modeled multiple pathways for global energy systems to achieve climate targets. While some pathways featured a doubling of hydropower, a pathway that assumed the continued rapid decline in cost of wind and solar PV projected global hydropower increasing by only about 1/3 from its level in 2015 – similar to the UTS study, this is about 1/4 of the expansion called for in in the IRENA report.
Sure, models are just that, models, and they reflect their data sources and assumptions. But looking at a range of models can offer insights; looking more broadly across a range of models suggests that it is quite plausible that the world can achieve climate targets with far lower levels of hydropower
How does hydropower compare to other renewables in terms of costs and speed of development?
Models that assume a continued rapid decline in the cost of wind and solar suggest that the world can build low carbon grids with lower levels of hydropower. Assuming a rapid decline in the cost for wind and solar has been a good bet for a long time now. In 2010, costs of solar PV had been steadily falling, so the IEA predicted that costs would fall by another 40% by the end of the decade. Instead, they dropped by over 90%, with a 2020 cost that was 1/4 of what the IEA had predicted. For decades now, analysts have consistently, and dramatically, underestimated future cost declines and future capacity additions of solar. Solar PV and wind have already become the cheapest form of electricity on the planet and impressive cost declines will likely continue.
Beyond cost, solar and wind projects tend to be far simpler compared to hydropower projects. A study by EY found that, among types of large infrastructure projects, hydropower was first or second in terms of the frequencies of delays and cost overruns, and the size of those delays and overruns.
When time is of the essence— as it is for delivering power to people that lack it or for the stability of the planet’s climate — solar and wind offer both low costs and rapid deployment. Further, much of the world’s hydropower — both current and planned — are in areas likely to experience increased water scarcity, jeopardizing the reliability of hydropower generation. And this is not just a modeling result: hydropower projects around the world have been experiencing declines in generation due to drought and water scarcity, even on huge rivers such as the Zambezi, resulting in major economic disruption for
Zambia and Zimbabwe.
But isn’t hydropower important for balancing the variable generation from wind and solar?
Yes, hydropower is one of the technologies that can balance the variable nature of wind and solar generation to help keep a grid stable and reliable. But this service can be provided in a number of ways, including batteries and other forms of storage that are also experiencing rapidly declining costs. Even within the hydropower sector, there are a variety of ways to expand this grid service, including reoperating existing hydropower dams and cascades, modernizing and/or expanding existing hydropower projects and adding turbines to currently non-powered dams. Further, a form of hydropower called pumped storage hydropower (PSH) can function like a battery and thus balance grid variability. Pumped storage can be built and operated in ways that have far lower impacts on rivers; off-channel PSH can essentially avoid any impacts on rivers, with a very small total development footprint. The IRENA report calls for increased investment in all of these approaches.
So, what is the best set of energy technologies to meet climate targets?
There is no single answer to this question – it will depend on a range of factors for any given country, region or grid, including the existing set of generation assets, the transmission system, and the cost and potential for various renewable generation technologies, along with options for storage and grid management and interconnections.
But there is a guiding principle. Grids should strive to be LowCx3: low carbon, low cost, and as low conflict as possible, avoiding or minimizing conflicts with communities, rivers and other ecosystems.
That is, plans for providing energy to countries should examine a range of options and select those that meet climate targets with a set of investments that are cost-competitive (and thus equitable and politically viable) and that strive to avoid or minimize negative impacts on people and nature as much as possible, recognizing that nearly all options for generation will have some impacts.
In the report Connected and Flowing we examined this approach, integrating river models with grid capacity expansion models to show that LowCx3 grids are possible – and that if countries around the world pursued LowCx3 grids, impacts on rivers could be reduced by 90%.
Hydropower will play a role in these LowCx3 grids, including upgraded existing projects, pumped storage, and carefully planned new dams.
“How much hydropower is needed to meet climate targets?” is just one question – and if we don’t ask other questions, we’re likely to get answers that are wrong for our dual global crises of climate and nature. Start asking a range of other questions, and answers will emerge that point toward a future with both a stable climate and healthy rivers, and one that avoids a set of unquestioned tradeoffs.
[This piece was written by Jeff Opperman, WWF Global Lead Freshwater Scientist]