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Introduction
As the global push to decarbonise the electricity grid intensifies, hydroelectric power is increasingly touted as a cornerstone of the renewable-energy transition. But while the concept sounds straightforward and green, the reality is far more nuanced. From huge pumped-storage schemes to smaller river-flow installations, hydro holds both promise and challenge. In this feature we examine the pros and cons of hydroelectric power, spotlighting the ambitious Coire Glas pumped-storage project in the Scottish Highlands as a case study of the opportunities — and trade-offs — involved.
What is hydropower?
Hydroelectric power — often simply called hydropower — is electricity generated from the potential or kinetic energy of flowing water. According to the Encyclopaedia Britannica, “water is collected or stored at a higher elevation and led downward through large pipes or tunnels … the difference in these two elevations is known as the head.” (Britannica)
A special sub-category is pumped-storage hydropower, where water is pumped uphill during times of surplus electricity (e.g., when wind or solar output is high) and then released to generate power when demand is high. (Britannica)
In practice, hydropower can deliver large-scale generation, flexible dispatch, and (in many cases) low carbon emissions. But it also comes with substantial upfront costs, ecological impacts, and geographic constraints.
Spotlight on Coire Glas: Britain’s “natural battery”
Located on the shores of Loch Lochy in the Scottish Highlands, between Fort William and Inverness, the Coire Glas pumped-storage scheme is one of the most ambitious hydro projects currently in the United Kingdom. (sserenewables)
According to project documentation, Coire Glas would have a potential generating capacity of up to 1,300 MW, with energy storage of around 30 GWh — enough to supply over three million homes for more than 24 hours at full output. (Wikipedia)
SSE Renewables describes it as “… the first large-scale pumped storage project to be developed in the UK for more than 40 years.” (Coire Glas)
A key milestone: In 2024, exploratory tunnelling works were completed, marking a major step in the development. Energy Voice
As such, Coire Glas offers a concrete example of how hydro (especially pumped storage) can be positioned as a vital part of the low-carbon energy future — while also underscoring the complexities that come with scale.
The Case For Hydroelectric Power
In favour of hydropower, several compelling arguments emerge:
1. Low operational carbon emissions
Hydro plants generate electricity without burning fossil fuels. Lifecycle analyses show very low greenhouse-gas emissions compared to coal or gas-burning plants. (Wikipedia)
Given the urgency of meeting net-zero targets, this is a major plus.
2. Flexibility & Grid Stability
Unlike some renewables, hydro (and especially pumped storage) can respond quickly to changes in demand or generation. According to technical sources: “Hydropower is a flexible source of electricity … stations can be ramped up and down very quickly.” (Wikipedia)
The Coire Glas project explicitly cites its ability “to ramp to its full generating capacity in under 60 seconds … start generating in under 10 seconds.” (SSE)
In an energy system with high shares of variable renewables (wind and solar), this flexibility is increasingly valuable.
3. Long lifespan & low fuel cost
Once built, hydro plants often operate for decades with minimal fuel costs (the “fuel” being water). Many older schemes continue to function well beyond 30-50 years. (SolarReviews)
Over time, this can translate into lower cost of electricity (though this must be considered alongside upfront investment).
4. Energy storage / “natural battery” capability
Pumped storage transforms hydro into a form of energy storage — water pumped during low-demand/low-cost periods, then released during peaks. This helps smooth out the variability of wind and solar, avoiding wasted renewable energy and reducing the need for fossil fuel backup. (Britannica)
Coire Glas is explicitly described as Britain’s largest “natural battery”. (Water Power Magazine)
The increasing importance of this role is signalled in recent reports: “Flexible storage is essential for net-zero carbon operation of Britain’s electricity system.” (The Guardian)
5. Domestic energy security
Hydro can provide domestic, often scalable power generation, reducing dependence on imported fuels. Especially for countries with suitable geography (mountains, tall heads, flowing water), it can enhance energy sovereignty.
6. Multi-purpose benefits
In many instances, hydro reservoirs also support flood control, water supply, recreation and tourism. While these benefits vary by site, they show how hydro can integrate into broader resource management strategies.
“Flexible storage is essential for net-zero carbon operation of Britain’s electricity system.”
— Industry commentary on the value of long-duration storage The Guardian
The Case Against Hydroelectric Power
Despite the benefits, hydroelectric power also brings significant challenges and trade-offs. Key criticisms include:
1. High upfront capital cost & long development timeframe
Large hydro projects require major civil works (dams, tunnels, reservoirs, pipelines). The cost and time to build are substantial. Some academic research suggests that many large hydro dams suffer cost overruns and long delays, reducing their risk-adjusted return. arXiv
In other words: great benefits, but big risks.
2. Site/geography dependency and limited scalability
Successful hydro projects depend on the right geography: sufficient head (height difference), reliable water flow, and often remote terrain. As one blog puts it, “While hydroelectric energy is completely renewable, there are limited places in the world that are suitable for plant construction.” greengeeks.com
In the UK context, hydro accounts for only ~2.2% of renewable energy sources, partly because of these constraints. The Eco Experts
Thus, hydro is not a universal solution — it works best where nature allows.
3. Environmental and ecological impacts
Despite being clean during operation, hydro projects can have substantial environmental footprints. Large dams may flood ecosystems, disrupt river flows, affect fish migration, alter sediment transport, and change water temperatures downstream. (Wikipedia)
Even pumped-storage schemes, while less invasive than mega dams in some cases, still involve tunnelling, reservoirs and potential habitat impact. An assessment of Coire Glas noted that “some gaps exist in how the project considers the combined impacts of pumped-storage hydropower development in the Scottish Highlands.” (Hydropower Sustainability Alliance)
For local communities and conservation interests, these impacts matter — and may provoke opposition.
4. Dependence on water availability & climate vulnerability
Hydro generation depends on water: rainfall, snowmelt, river flows. Droughts or changing precipitation patterns (related to climate change) can reduce output. This is a real risk for future operation. (Green Geeks)
In extreme events, dam failures or infrastructure damage (though rare) can carry catastrophic consequences.
5. Social displacement and land use
Very large hydro projects have sometimes required relocation of communities, flooding of extensive land, and disruption of local ways of life. While far less common in developed countries like the UK, this legacy remains a moral and political challenge. (SolarTech)
Even smaller schemes may raise concerns about changing landscapes, recreation access and cultural heritage.
6. Marginal additional benefit in some markets
Because many of the best hydro sites have already been developed (especially in places like the UK), the marginal gains from new hydro may be smaller, more logistically difficult or more contentious. In short: easy wins are largely done.
“Some gaps exist in how the project considers the combined impacts of pumped-storage hydropower development in the Scottish Highlands.”
— Sustainability assessment of Coire Glas Hydropower Sustainability Alliance
Balancing the equation: When does hydro make sense?
Given the above, the question is not simply “Is hydro good or bad?” but rather under what circumstances and at what scale it makes sense. A few guiding principles emerge:
- Match scale to geography: In mountainous, high-rainfall regions with appropriate topography (such as parts of Scotland), large pumped-storage schemes like Coire Glas make sense. In flatter low-flow regions, small-scale run-of-river may be more appropriate.
- Assess full lifecycle and social-environmental impacts: The benefits of low carbon and flexible power must be weighed against ecosystem, land-use and social impacts.
- Align with grid needs: As the grid fills with intermittent renewables, the value of dispatchable storage grows — making pumped-storage hydro more attractive.
- Obtain stable policy and investment regime: The upfront cost and long pay-back period mean that hydro projects require stable regulatory, reward and financing frameworks.
- Ensure adaptive resilience: Given climate risks (e.g., drought, altered rainfall patterns), hydro schemes should include robust water-management and climate‐resilience planning.
- Seek local community engagement: For hydro projects to succeed, they must engage with local stakeholders, address recreation, cultural and ecological concerns, and deliver tangible local benefits.
Why the UK needs more storage — and how hydro fits in
In the UK (and globally) the electricity transition is accelerating. But while wind and solar generation are growing rapidly, the challenge lies in matching supply with demand and balancing the system when the wind stops or the sun sets.
Recent coverage noted that pumped-storage hydropower is increasingly being seen as a key component of this balancing act:
“Flexible storage is essential for net-zero carbon operation of Britain’s electricity system. It helps balance the system by ensuring there’s always a large volume of ‘back-up’ power on standby, that can be delivered in very fast timescales if required.” The Guardian
And in Scotland’s Highlands, the Coire Glas scheme is positioned as a national asset: a “natural battery” to support grid stability and deliver clean power at scale.
Yet a major hurdle remains: policy and investment mechanisms. Without appropriate financial incentives or regulatory frameworks, large storage projects struggle to secure the funding required. For Coire Glas and others, the question is whether the investment climate will align. The Times
Coire Glas: Benefits, risks and what it tells us
Let’s examine Coire Glas in more depth, exploring what it offers and where the risks lie.
Benefits
- Scale & storage: Up to 1.3 GW capacity and 30 GWh storage, enough to power ~3 million homes for ~24 hours. (Coire Glas)
- Rapid response: Capable of moving from standby to full output in under a minute, offering valuable grid-balancing capability. (SSE)
- Doubling UK storage capacity: The scheme would more than double current British long-duration electricity storage capacity. (Coire Glas)
- Long-term sustainability certification: The project achieved a benchmark hydropower sustainability standard, described as “a testament … to the diligence and dedication of the Coire Glas project team.” (Stantec)
- Community and economic benefits: The developer reports local employment (≈30 % local workforce), and educational/community funds linked to the project. (SSE)
“Coire Glas … the first large-scale pumped storage project to be developed in the UK for more than 40 years.”
— SSE Renewables project description Coire Glas
Risks and criticisms
- Geological and environmental complexity: The Great Glen fault zone and mountainous rock terrain present challenging ground conditions for tunnelling and construction. (The Geological Society of London)
- Ecological and cumulative impact gaps: A sustainability assessment noted that “some gaps exist in how the project considers the combined impacts of pumped-storage hydropower development in the Scottish Highlands.” (Hydropower Sustainability Alliance)
- High capital cost and financing uncertainty: Early estimates suggest total investment could be up to £1.5 billion. And the scheme is dependent on regulatory support (e.g., cap-and-floor mechanisms) to unlock investment. (Energy Voice)
- Water-resource and climate risk: While Scotland is relatively wet and mountainous, climate change may still affect rainfall and reservoir inflows — something large-scale hydro must guard against.
- Time to deliver: Given the scale, Coire Glas may not come online until the early 2030s, meaning it won’t immediately solve current storage constraints.
Beyond large dams: small-scale and run-of-river hydro
While pumped-storage schemes like Coire Glas grab headlines, another dimension of hydro is smaller-scale installations — often run-of-river projects, micro-hydro systems on estates or farms, and refurbishments of older hydro infrastructure.
These variants carry their own calculus:
- Advantages: Lower cost, fewer large-scale disruption, quicker permitting, suitability for remote or rural areas.
- Challenges: Limited energy storage capacity, dependency on flow, lower head, less dispatchability. For run-of‐river, for example: “A plant without pondage … generates much more power when seasonal river flows are high … and much less during drier … months.” (Wikipedia)
- Suitability in UK: Small-scale hydro is already part of the mix, but its overall share remains modest. One review noted hydro comprises only about 2 % of UK renewables. (The Eco Experts)
The takeaway: small hydro won’t replace large grid-scale storage, but it can play a complementary role — especially in distributed generation, rural resilience and local electricity schemes.
“Hydropower is a flexible source of electricity … stations can be ramped up and down very quickly.”
— Encyclopaedia Britannica on the nature of hydroelectric power Wikipedia
The bottom line: Is hydropower good?
If we distil the evidence:
- Yes, hydroelectric power is good insofar as it provides low-carbon electricity, dispatchable generation, long life and supports grid flexibility.
- But, it is not a panacea. It faces high upfront cost, site-specific limitations, environmental and social impacts, and supply-side constraints (water, geography).
- The balance depends critically on context: geographic suitability, grid architecture, financing, policy frameworks, ecological stewardship and local community buy-in.
For countries (or regions) with appropriate terrain, rainfall and infrastructure, large-scale pumped hydro (like Coire Glas) offers one of the most effective ways to store large blocks of clean energy and support a high-renewable grid. For many other places, smaller hydro or run-of-river may be the appropriate scale — but with less grid-balancing effect.
In short: hydropower is one important arrow in the quiver of clean energy solutions, but only if thoughtfully implemented, well-regulated and matched to context.
What the future holds
Looking ahead:
- As more wind and solar capacity is deployed, the need for long-duration energy storage grows. Hydroelectric pumped storage is well positioned to meet this need.
- Policy and financing mechanisms will be critical: frameworks that reward storage value (not just generation) will unlock more hydro projects.
- Environmental and community standards are tightening. Future hydro must meet rigorous sustainability criteria — as evidenced by Coire Glas achieving a hydropower sustainability standard. (Stantec)
- Climate change adds both impetus and risk: more renewables mean more need for storage, yet shifting hydrology may challenge traditional hydro assumptions.
- In the UK, we may see a wave of new pumped-storage projects (and repurposing of older hydro assets) — though geographic constraints mean hydro will not dominate alone.
Conclusion
As nations grapple with the twin imperatives of decarbonisation and energy-system reliability, hydroelectric power remains a vital option — albeit one that demands careful implementation. The scale and ambition of the Coire Glas project illustrate both the potential and the complexity of modern hydro-storage.
Ultimately, hydro will never be the only renewable technology, but in the right place and with the right conditions it can deliver clean, flexible power for decades. In that sense, yes — hydro is a good thing. But like all major infrastructure, it comes with responsibilities: to society, to nature and to future generations.
