As the Northern Hemisphere slowly cools and darkens and snow levels reach new heights in many parts of Russia, Canada, Korea [1], US and other parts of the world… the question of reliable electricity supply creeps up in people’s minds.
The now famous German “Dunkelflaute” both during November and December 2024 made people realize that wind and solar may not be the best idea for getting us through the winter… but is “clean” hydro power and pumped storage the solution?
Hydro power, which is motion or electrical power derived from natural flowing river water, has been used for centuries, is one of the oldest and largest forms of “renewable” power. Hydro is natural, doesn’t pollute the air and doesn’t leave any worrisome waste.
However, a peer-reviewed study [2] on hydro power put it as follows “Hydropower is currently the largest renewable source of electricity, but its contribution to climate change mitigation is not yet fully understood.”
“Renewable” power from water does not appear as “green” as we are told, why?
Let us explore the origins and current uses of hydro power, its importance to our global electrical system and the environmental impact.
As always, things are not as simple and “clean” as they seem. Disclaimer… unlike wind and solar, I fully support the development and use of hydro power, despite the challenges faced.
Let me summarize for those who want to get to the point:
- Hydro is important, making up almost 15% of global power generation, but its future expansion is limited, as suitable river flows are largely used up and water scarcity remains a challenge
- Hydro is weather dependent and therefore NOT reliable, as water levels and availability changes depending on weather conditions. But hydro’s reliability is much higher and its output more predictable than for wind or solar… I would not call hydro “intermittent”
- Hydro has a serious impact on the environment, it is NOT “net-zero” nor “green”, it impacts land-use, flora, fauna, and thus biodiversity. It requires large amounts of raw materials and energy to be built.
- Regarding the “climate” hydro appears about “half as bad” as coal or gas when considering the 20y global warming potential
- Hydro Power: History and Today
Humans have utilized water in many forms for millennia. Over 2,000 years ago, the Greeks employed water wheels to grind wheat into flour, while Egyptians used Archimedes water screws for irrigation in the third century B.C. Innovations in harnessing waterpower also emerged in China during the Han Dynasty between 202 B.C. and 9 A.D [3].
The evolution of modern hydropower turbines began in the mid-1700s with French hydraulic and military engineer Bernard Forest de Bélidor, who authored the pioneering Architecture Hydraulique. In 1849, British-American engineer James Francis developed the first modern water turbine, known as the Francis turbine, which remains the most widely-used water turbine in the world today. The world’s first hydroelectric project was used to power a single lamp in the Cragside country house in Northumberland, England, in 1878 [3].
There is an estimated 60.000 to 70.000 hydro power plants HPPs globally, those are only plants over 75 MW [4]. About 21.000 HPPs are in operation in Europe alone with an additional 8.500 planned, many of which are small scale.
Figure 1: Francis Turbine (based on free images from Shutterstock)
Hydro today is the biggest source of “renewable” electricity, with solar close on its heels. 1,4 TW of global installed hydro capacity in 2023 generated about 4.400 TWh or 16% of global power last year. For comparison 2 TW of coal capacity generated about 36% of global electricity. Please remember that electricity is only a fraction of the total energy we consume making up 40% of primary energy, here we only speak of power = electricity.
Figure 2 puts the generation capacity of hydro into perspective in comparison to the planned wind and solar generation capacity. Pumped hydro makes up about 1/7th (13%) of the total installed hydro capacity, the majority is conventional hydropower like a dam or river turbines.
New capacity installations are limited by available river flows and environmental concerns, so the world does not expect much more new hydropower to come online, but pumped storage everyone speaks about.
Some countries are richer in hydro power than others, Norway (85+% of power), Iceland (~75%), Brazil (~65%), and Canada (~60%) are some of the most famous ones enriched by natural water flows to harness, serving relatively small populations and industries compared to their landmass.
Figure 2: Global Electricity capacity from solar, wind, hydro and bioenergy in IEA’s “net-zero” pathway; Source IEA [5]
Figure 3: Switzerland’s hydrodam the Grande Dixence
2. Electric generation from hydro, reliability, and the “Energy Transition”
Hydropower varies widely and surprising to many Europeans, it is not reliable. To illustrate the variability and weather dependability of hydro generation, BloombergNEF recently confirmed that in 2022 hydro generated 135 TWh more than the year before, and in 2023 the same hydro generated over 50 TWh less. These numbers appear small compared to hydro’s global generation of 4.400 TWh, but don’t underestimate the impact made (Figure 3). These changes are driven by varying river flows, rainfall, and temperatures.
- FYI on changing rainfall and its causes… the IPCC AR6 Chapter 12 relies on the IPCC’s conventional approach to detection and attribution of weather events to “human caused climate change”, and appears to dismiss event attribution studies in one sentence:
- “The usefulness or applicability of available extreme event attribution methods for assessing climate-related risks remains subject to debate.” [5]
Another example, in the first five months of 2024, hydropower generation in Vietnam was more than 20% lower year-on-year. Such variability is known all over the world as you can see in the Figure below and clearly means you can never compare the reliability of hydro with that of a thermal or nuclear power station. The natural capacity factor of most hydro is lower than 80%, while that of thermal power plants is close to 100%. The utilization of hydro may be very high, but utilization does not equal natural capacity factor. For more details on this subject please see my blog post addressing the natural capacity factor.
Hydropower is considered “renewable” because the “fuel” is naturally occurring water. When it comes to the “climate” discussion, hydro is considered “net-zero” in all major “decarbonization studies”, just the same as wind, solar, and even biomass. This is clearly a mistake as explained in the next section.
On hydro and pumped storage as backup: Pumped storage means using electricity to pump water “up” into a reservoir and later “release” it when required to generate electricity. Of course, pumped storage requires access to mountainous regions, which are far from large cities such as New York, Washington, Chicago, Beijing, Moscow, London, Paris, Warsaw, or Berlin
Norway’s hydroelectric system is widely discussed as a backup for the German and European “renewable” energy systems. Norway’s “hydro facility” is one of the world’s best with energy storage capacity at almost 90 TWh, compared with a total annual electricity output of almost 140 TWh, which is almost all of Norway’s consumed electricity (NVE Report 2021). These numbers show that precipitation must replenish around 50 TWh annually. The hydroelectric reserve itself varies by 60 TWh from year to year, so the net export capability of Norway can easily fall to zero.
Neither Germany nor Europe could possibly rely on Norway as its backup, even if the entire hydroelectric system was dedicated to German or European backup and nothing were to go to Norway itself. When will German politicians and energy planners understand this?
On top, would Norway or any hydro rich country freely give away its valuable power to neighboring countries? The Financial Times [7] already had the answer and wrote early this month about Norway’s Minister for Energy, Terje Aasland “Norway campaigns to cut energy links to Europe as power prices soar…country’s energy minister describes ‘shit situation’ as domestic prices hit highest level since 2009”.
Last year Mr Aasland already clarified preemptively “We are looking at how to limit exports in situations where reservoir filling becomes critically low. Then we must secure enough power for our national consumption” and “Norway Will Curb Power Exports If Home Supplies Are at Risk” [7]
Figure 4: Source: IEA Electricity Report, Jul 2024, based on National Bureau of Statistics of China [8]
3. Climate?… Raw materials, land-use, Biodiversity, and more
Let’s come to the meat of the story, how good or bad is hydro power really for the environment? Well, I personally would say it is an amazing source of power with limited impact on the environment, if and only if it is employed reasonably and only where truly suitable. It appears obvious that any “blind push” for as much hydro as possible to “save the climate” will cause more harm than good.
As a positive example for hydropower. We are exploring the possibility of employing small scale hydro turbines in unused completely deserted areas of Southern Africa with river flows that can secure off the grid electricity for computing (AI, or even bitcoin mining). Here no one is harmed, its off the grid, that means we are not taking away someone else’s ‘green power” and it is simple, economically efficient and safe without altering natural habitat (if you are interested, reply to me).
To give a flavor of the “undisputed” issues surrounding hydro power let us briefly look at raw materials, the “climate”, ecosystems, fish mortality, and energy accidents.
Raw Materials: It may not come as a surprise to you that the amount of cement required to build large dams is enormous … but how does it compare to other sources of reliable and less reliable electricity? The Department of Energy studied this and came up with the below comparison that may surprise many.
Figure 5: Raw material use for Hydro and other means of electricity production. Source: Department of Energy, details at www.unpopular-truth.com/graphs
“Climate”: Interestingly, the real “climate impact” of a reservoir is the difference between GHG emissions before and after flooding [9].
The emissions from hydroelectric reservoirs arise from the decomposition of organic matter that was either flooded during reservoir construction, transferred to the reservoir by river runoff, grown in the reservoir such as by algae production, stems from dead trees protruding from the water, or was grown in newly created marshes in the drawdown area.
Besides reservoirs, there are other ecosystems that influences the greenhouse gas (GHG) fluxes. While rivers and lakes emit GHGs, forests, peatlands and wetlands rather bind them [10]
The IPCC (Figure below) estimates hydro’s lifecycle emissions at the high about double that of coal!
Figure 6: The IPCC gives a very large lifecycle emission range for hydro… at the upper end for than double that of coal [10]
Logically, hydropower storage projects tend to release more “emissions” than run-of-river plants. There does not exist any “net-zero” impact pumped hydro storage to backup intermittent wind and solar
Another study went further “Calculations are made for 18 dams that are planned or under construction in Brazilian Amazonia and show that emissions from storage hydroelectric dams would exceed those from electricity generation based on fossil fuels.”
Ecosystems: Large scale hydropower actually has devastating impacts on freshwater ecosystems and alters the ecosystem services provided by natural rivers. In Europe, it affects one of the most degraded ecosystems, as only 40% of surface water bodies are in a healthy ecological status. Over 80 “green” environmental organizations wrote to the EU “Counting on new hydropower to accelerate Renewable Energy deployment in Europe is irresponsible.” [11]
Fish mortality: One of the few comprehensive studies on fish mortality was conducted by Radinger et al 2021. They found that on average over 20% of passing fish die from hydroelectric turbines. For the scientifically minded reader the measured average was 22.3% with a 95% confidence interval between 17.5–26.7%.
The authors conclude in the study “We argue that within such conflicting interests, agreeing on tolerable [fish] mortality rates is difficult and that stakeholders must consider aspects of animal welfare, population ecology, and biodiversity conservation, but also the economics of hydropower, environmental policy, and societal acceptance.”
Energy accidents: Kim et al 2021 [12] studied global energy accidents and found that when normalized by electricity generated, wind and hydroelectricity clearly cause the most fatalities per unit of energy produced.
Figure 7: Fatalities normalized by electricity generation (MTOE) – Source: Kim et al 2021, [12]
The green image of hydro power as a benign alternative to fossil fuels is false, says Éric Duchemin, a consultant for the Intergovernmental Panel on Climate Change (IPCC). “Everyone thinks hydro is very clean, but this is not the case” [9]
Figure 8: Selected fish mortality from hydro turbines (Radinger et al 2021) [13]
4. Summary
Hydro is beneficial, when developed responsibly, but both river flow hydro and hydro dams, have many economic and environmental issues. Hydro is NOT reliable and large parts of the world experience significant variation in river flows, making hydro power seasonal and year on year unpredictable. However, the unpredictability is only a fraction as concerning as the intra and day-to-day variation that wind and solar offer us. For that reason, in my opinion, hydro is economically desirable.
Hydro has a large raw material footprint, a significant “greenhouse gas” impact, and most importantly negatively effects biodiversity and fish. Even direct human mortality normalized by electricity generated appears to be very high.
I am still of the opinion that hydro power is environmentally “acceptable”, as long as it is developed and operated consciously and not “blindly”.
Yet, claiming hydro to be “net-zero” is not just unrealistic but just outright wrong. Most large studies mistakenly assume “zero greenhouse gas” impact for hydro (as they also wrongly do for wind and solar). Shouldn’t we be honest with ourselves?
MIT’s climate portal [14] correctly wrote “Large dams carry a number of social and environmental concerns” and the continue “There’s still room for hydro to grow, but most countries will not build out as much hydropower as they theoretically could—and that may be for the best.”
Links and Resources
[1] Kältereport (“cold report”) No 46, Dec 2024, with all sources, link
[2] Scherer Pfister 2016: Hydropower’s Biogenic Carbon Footprint, PloS One, link
[3] Energy.gov and hydropower.org, link and link
[4] Hydropower Tracker, link
[5] IEA on hydro power capacity, Dec 2024, link [6] IPCC AR6 Chapter 12, summarized by Prof. Pielke Oct 2024, link
[6] Financial Times, Dec 2024, link
[7] Montel 2022 and Bloomberg 2023 on Norways Power exports, link and link
[8] IEA Electricity Mid-Year Update, Jul 2024, link
[9] Hydroelectric Power’s Dirty Secret Revealed, resilience, Feb 2005, link
[10] IPCC: WG3 AR5 Annex 3 – Technology-Specific Cost and Performance Parameters, 2018, link
[11] Open Letter to EU: Counting on New Hydropower to Accelerate Renewable Energy Deployment in Europe Is Irresponsible, Feb 2023, link
[12] Kim et al 2021, Critically Assessing and Projecting the Frequency, Severity, and Cost of Major Energy Accidents, Jul 2021, link
[13] Radinger et al 2021: Evident but Context-Dependent Mortality of Fish Passing Hydroelectric Turbines.” Conservation Biology, link
[14] MIT Climate Portal, Why Aren’t We Looking at More Hydropower?, Mar 2021, link