• Lithium-ion batteries dominate headlines, but most global energy storage relies on simpler methods.
• These methods include pumped hydro, compressed air, gravity, and thermal storage using sand or rock.
• These low-tech systems offer cheap, long-duration storage with minimal degradation, using abundant materials and basic physics rather than complex chemistry.

When we talk about energy storage today, lithium-ion batteries tend to dominate the conversation. They are sleek, compact, and have become the default image of the clean energy revolution. Yet behind the headlines, a quieter cast of characters has been doing the heavy lifting. Some of the most effective ways to store energy are not based on exotic chemistry at all, but on gravity, heat, air, and even sand. They are often strange, wonderfully simple, and surprisingly effective.

If the world’s energy transition were a movie, lithium-ion batteries would be the star, but these humble technologies would be the supporting actors who keep the story running when the hero needs a break.

Pumped hydro, the veteran that never retired

The simplest of all energy storage systems is also the oldest. Pumped hydro works by moving water uphill when there is surplus power and letting it flow back down through turbines when demand peaks. It sounds trivial, but this two-reservoir arrangement still represents over 90 percent of all the world’s stored energy capacity. It uses nothing more sophisticated than gravity and geography, yet delivers vast amounts of long-duration storage at a cost that most modern batteries can only envy.

Its only limitation is location. You need hills, valleys, and reservoirs, which means not every region can build one. But wherever the terrain allows, pumped hydro is the workhorse of renewable integration. It does its job quietly, often with decades of reliability, while newer technologies are still proving their worth.

Compressed air, pressure in a cave

Another remarkably straightforward idea is compressed air energy storage. Imagine an underground cavern or an old salt mine where air is pumped in under high pressure when electricity is cheap. When demand rises, the compressed air is released through turbines to generate power. The system uses physics rather than chemistry, relying on pressure instead of potential difference.

A creative variation on this concept involves abandoned mineshafts where sand or heavy blocks are raised when energy is abundant and lowered when it is scarce, generating electricity through regenerative braking systems. It is literally lifting and dropping weight, a child’s game of gravity turned into grid infrastructure. There is something beautifully simple about storing energy by hoisting sand up a mine shaft and letting it fall back down when needed.

Molten sand and hot rock, heat that waits

If water and air can store energy, why not sand. In Northern Europe, several projects are experimenting with storing renewable electricity as heat inside large insulated silos filled with sand or rock. During periods of high renewable generation, electric heaters warm the sand to several hundred degrees Celsius. The stored heat can then be released hours or even days later to provide district heating or industrial process energy.

This approach is gaining attention because of its economics. Sand is cheap, abundant, and stable, while the systems require little maintenance and can last for decades. A sand battery may not sound glamorous, but it delivers energy storage at a cost far below any chemical battery. The drawback is that it stores heat, not electricity, so it works best when paired with heating systems or industries that can use the heat directly. Still, given that most of the world’s energy demand is for heat rather than electricity, the potential is enormous.

Carnot batteries, turning heat back into power

Closely related are so-called Carnot batteries, systems that store electricity as heat and then convert it back into electricity when needed. These systems might not match lithium-ion batteries in round-trip efficiency, but they win on cost, durability, and material availability. They often use molten salts, ceramics, or concrete blocks to retain heat and can operate at high temperatures for very long durations.

Their advantage lies in flexibility. They can deliver heat for industrial uses, provide electricity back to the grid, or do both. They blur the line between thermal and electrical energy systems, offering a bridge between renewable generation and industrial decarbonization.

Gravity storage, the return of the rock

Gravity-based storage is another oddly intuitive idea making a comeback. Instead of using water, these systems rely on heavy weights, often concrete blocks, that are lifted by electric motors when there is excess power and lowered to drive generators when electricity is needed. Some designs use tall towers, others use deep mine shafts, but all operate on the same principle that powered water mills centuries ago.

What makes gravity storage appealing is its simplicity and longevity. There are no chemical reactions, no degradation over cycles, and no dependence on rare materials. It is energy storage at its most literal, potential energy stored in height and mass.

The value of simplicity

What unites these unconventional systems is not glamour but practicality. They are simple to understand, made of common materials, and often piggyback on existing infrastructure such as mines, quarries, or district heating systems. They do not require lithium, cobalt, or nickel. They do not overheat or degrade with time. And they can deliver storage on the scale of hours, days, or even weeks at a fraction of the cost of grid batteries.

They also store energy in forms that align better with demand. While electricity grabs the headlines, much of the world’s energy use is thermal. Industrial heat, space heating, and hot water consume far more energy globally than lighting or electronics. By storing energy as heat, these technologies address a part of the system that lithium batteries cannot easily reach.

A reality check

Of course, no technology is perfect. Geography limits pumped hydro, geology constrains compressed air systems, and heat storage only works where there is a demand for heat. Efficiency can be lower than that of chemical batteries, and converting between heat and electricity always comes with losses. But when measured by cost per unit of stored energy, simplicity often wins.

As with heat pumps or carbon capture, success depends not only on technology but on the surrounding ecosystem of policy, infrastructure, and market design. These systems thrive when there is cheap renewable power to absorb and a predictable market for their stored output. Without those conditions, even the cleverest engineering will sit idle.

The humor of serious simplicity

There is something faintly comic about humanity’s tendency to overlook the obvious. We send satellites into orbit to forecast renewable generation, but sometimes forget that a lake and a hill can do the same job as a billion-dollar battery. The energy transition is filled with elegant complexity, yet some of its best solutions are the ones that would make a Victorian engineer nod in approval.

The future of energy storage may indeed feature cutting-edge chemistries, quantum materials, and solid-state breakthroughs. But it will also depend on gravity, sand, heat, air, and water, quietly doing the work they have always done. The brilliance lies not in their novelty, but in our rediscovery of their value.

Sometimes the smartest move in a high-tech world is to remember that simplicity still works.

By Leon Stille for Oilprice.com

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Leon Stille

Leon Stille has a background in energy sciences (MSc and BSc) and is pursuing a PhD in energy policy. He currently runs his own company,…

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