“The energy system is a thermodynamic system, not an economic one.” – Vaclav Smil, 2017. This statement, while not a physical law, serves as a reminder: every energy flow implies an inevitable dissipation. The following case study illustrates this principle applied to pumped hydroelectric storage (PHES).
The Water Cycle and Entropy
An article from CleanTechnica on February 1, 2026, describes a new low-elevation PHES system that eliminates the need for mountains, instead using gentle slopes and lower-level reservoirs. The principle of operation is simple: excess energy (from intermittent renewable sources) is used to pump water from a lower reservoir to an upper one, storing gravitational potential energy. When energy demand increases, the water is released, driving turbines to generate electricity. The claimed advantage is reduced costs and environmental impact compared to traditional high-elevation PHES systems that require dam construction. However, this advantage comes at the cost of increased water volume required and, consequently, more energy spent lifting it. The energy density of a PHES system is directly proportional to the height difference between the two reservoirs. Reducing this difference reduces the overall efficiency of the system. The described system requires a larger surface area to compensate for the reduced height difference, increasing construction costs and land use impact. The energy required to pump one cubic meter of water 100 meters high is approximately 9.81 kJ. For a low-elevation system, the energy needed to lift the same volume of water is lower, but the amount of water required to store a given amount of energy is significantly greater.
The Real World Trade-off: Efficiency vs Feasibility
The dominant narrative (Stream B) emphasizes technological innovation as a solution to energy problems. The CleanTechnica article presents low-elevation PHES as a step towards a sustainable future. However, the physical analysis (Stream A) reveals a fundamental compromise: reducing environmental and construction costs translates into lower energy efficiency. This is an example of Jevons’ paradox: increased efficiency in resource use can lead to greater overall consumption. In this case, a more efficient PHES system could encourage greater use of intermittent renewable energy, increasing storage demand and, consequently, the overall environmental impact. Additionally, constructing new reservoirs, even at low elevations, requires the use of construction materials (cement, steel) with high energy intensity and associated greenhouse gas emissions. The embedded energy in building a low-elevation PHES system could be significant, further reducing its environmental advantage. Water availability is another critical factor. PHES systems require substantial water volumes, and this can be limited in some regions, especially during droughts. Water used for energy storage may compete with other essential uses such as agriculture and human consumption.
The Threshold of Irreversibility: The Cost of Storage
The economic feasibility of a low-elevation PHES system depends on several factors, including the cost of energy, construction material costs, water availability, and system lifespan. As energy costs rise, energy storage becomes more valuable. However, if the construction and maintenance costs of a low-elevation PHES system exceed the economic benefits from energy storage, the system will become unsustainable. The threshold of irreversibility is reached when the total lifecycle cost (including construction, maintenance, and decommissioning) exceeds the value of stored energy. This critical point is influenced by local topography, subsurface geology, and water resource availability. Dependency on rare and expensive materials for turbine and pumping systems represents an additional risk factor.
The Hydrological Constraint
Ultimately, energy storage is a problem of entropy management. Every storage system introduces losses and requires input energy to maintain order. For low-elevation PHES, the primary constraint is water availability and the energy cost to lift it. The promise of a more accessible and less invasive system confronts the physical realities of gravity and thermodynamics.
Photo by Zbynek Burival on Unsplash
Texts are autonomously processed by AI models