Storing Thermal Energy in Steel and High-Capacity Materials

Storing energy as heat is a well-established concept in energy engineering. In thermal energy storage (TES) systems, surplus energy (often from electricity or direct heat sources) is converted into heat and retained in a material with high thermal capacity. The basic physics relies on raising the material’s temperature (sensible heat storage) or inducing a phase change (latent heat storage) to “charge” the storage, and later extracting the heat to “discharge” energy when needed. Materials like steel, concrete, rock, molten salts, and phase-change alloys can serve as thermal reservoirs, each with different advantages:

  • Sensible Heat Storage: Heating a solid or liquid without phase change. For example, solid steel or iron blocks, packed rock beds, or tanks of molten salt store heat by increasing temperature. The energy stored equals the mass × specific heat × temperature rise. Steel has a moderate specific heat (~0.5 kJ/kg·K) but can be heated to very high temperatures (600–800 °C or more), allowing substantial energy density . Other solids like concrete or ceramic bricks similarly store sensible heat; e.g. “thermal battery” systems use inexpensive materials (dirt, sand, etc.) heated resistively .
  • Latent Heat Storage: Using phase change materials (PCMs) that absorb/release heat at a constant temperature. Examples include molten salts (solid↔liquid transition) or metals like aluminum (solid↔liquid). PCMs can store large amounts of energy per mass via the heat of fusion. However, metals like steel have very high melting points (~1500 °C) making them impractical to fully melt in typical systems; instead, steel is usually used below its phase change, as a sensible heat medium.
  • Thermochemical Storage: (Beyond the scope of steel) involves endothermic/exothermic reversible reactions to store energy. While very energy-dense, this is more complex (examples: metal hydrides, salt hydration cycles) and not directly related to using bulk steel, so it’s usually mentioned for completeness.

Why steel? Steel and similar high-thermal-capacity alloys can store heat at high temperature without degrading. Steel’s thermal stability and conductivity make it suitable for solid-state heat banks. Importantly, steel is structural: it can function as both storage medium and container. High temperatures (600+ °C) improve energy density and also enable the option of reconverting heat to electricity with better thermodynamic efficiency. Other common media like water are limited to 100–150 °C unless pressurized, and molten salts decompose above ~565 °C . By contrast, steel (or iron) can tolerate much higher temperatures, unlocking greater energy storage per unit mass and the ability to drive turbines. Early proposals for grid storage envisioned a variety of media – “from salt to rock to steel” – to hold thermal energy that can later be turned into power .

Engineering Approaches and Current Technologies

A range of technologies today utilize these principles of thermal storage:

  • Molten Salt Tanks (CSP Plants): Concentrated solar power (CSP) facilities have long used molten nitrate salts to store heat from sunlight. For example, the Gemasolar tower in Spain and others use huge insulated tanks of salt heated to ~565 °C; this stored thermal energy can drive steam turbines at night. Molten salt TES is commercial in several solar plants, though challenges include salt freezing (typically melts at ~240 °C) and corrosion at high temperatures . Still, it has proven effective for multi-hour storage on grid scale. (Gemasolar achieved 24-hour solar power using 15 hours of salt storage.)
  • Solid Media Thermal Batteries: These include rocks, concrete, or metal blocks as heat media. A notable example is Siemens Gamesa’s Electric Thermal Energy Storage (ETES) pilot in Hamburg, which uses 1000 tonnes of volcanic rock heated with resistance coils. The rock bed (kept at ~750 °C) can store ~130 MWh_th of energy for about a week . When needed, the hot rocks produce steam to run a turbine. The pilot, completed in 2019, demonstrated feasibility and the company planned to scale to gigawatt-hour levels . The appeal of rocks or sand is their low cost and availability, albeit with lower thermal conductivity than metals.
  • High-Temperature Sand or Particle Storage: Similar to rocks, plain sand can be used. In 2022, a Finnish company (Polar Night Energy) opened a “sand battery” at the Vatajankoski power plant. It consists of a 4 m diameter, 7 m tall steel silo filled with ~100 tons of sand heated to 500–600 °C by excess renewable electricity . The sand battery stores ~8 MWh of heat and can output ~100 kW of thermal power for the district heating network (about 80 hours of supply) . Impressively, the insulated sand can hold heat for months, enabling seasonal storage (charging with summer solar or cheap wind to use in winter) . Sand is extremely cheap and abundant, and the system reportedly operates at ~99% thermal efficiency for heat usage (meaning very little heat loss over time) . This real-world project highlights how simple materials can serve as an energy bank for a town’s heat, analogous to a thermal “savings account” for winter .
  • Steel Heat Storage Systems (Lumenion and others): Steel is emerging as a promising solid medium for high-temperature storage. Berlin-based startup Lumenion has demonstrated a 2.4 MWh storage unit using steel plates, charged by resistive heating up to 650 °C . In operation, it can later release the heat for district heating or drive a steam turbine for power. Lumenion’s pilot, integrated with Vattenfall’s Berlin energy network, stores excess solar/wind power as heat and can discharge to a cogeneration plant . While the small pilot did not include electric power generation (due to regulatory economics at that scale), larger planned installations (50 MWh and up) will incorporate turbines . The company’s concept is a “steel battery”: a large 4-ton steel block acts as the thermal core, heated when electricity is cheap and delivering heat on demand .
    Engineering and performance: The steel core is housed in heavy insulation to minimize losses. Electric heating elements (cheap and simple) convert electricity to heat at nearly 100% efficiency. According to Lumenion, round-trip efficiency back to electricity is only ~25% (Carnot-limited), but if the low-grade leftover heat (e.g. ~100 °C steam) is utilized for heating, the overall energy efficiency can reach ~95% . In other words, as a combined heat-and-power storage system, very little energy is truly “wasted” – any heat not converted to electricity still serves heating needs. This dual use is key to making thermal storage competitive.
    Real-world usage: The Lumenion prototype (2.4 MWh, 340 kW charge rate) went online in 2019, and a larger 40 MWh system was planned next . Such a system can buffer daily renewable cycles – for example, storing midday solar energy to supply heat at night. Notably, the steel block can handle rapid charging (high power input) without the costly power electronics that batteries need . This makes it well-suited to absorb sudden surges of renewable power. Lumenion’s technology was recognized as a “Megawatt Winner” in energy storage innovation .
  • Phase-Change and Novel Materials: Some startups and researchers explore metals and exotic PCMs. One example is Azelio (Sweden), using molten aluminum alloy (melting ~600 °C) in a 13 kWh TES coupled to a Stirling engine for off-grid electricity at night. Others like Antora Energy use carbon blocks heated to ~2000 °C and then convert heat to electricity via thermophotovoltaic panels . These systems aim for ultra-long lifetimes and low cost at scale. The variety of approaches underscores that thermal storage can be achieved with many materials – often inexpensive, abundant ones – as long as they have high heat capacity or latent heat and can be cycled without degradation .

Economic Feasibility for Grid-Scale and Off-Grid Storage

From an economic perspective, thermal energy storage in materials like steel offers some compelling advantages, especially for large-scale and long-duration storage:

  • Low Cost per Energy Unit: Many thermal storage media are cheap (or even essentially free, like dirt or waste materials). The expensive parts of a TES plant are usually the insulation and heat exchangers, not the storage material itself. A solid media system is often far less costly than electrochemical batteries when scaled up. For instance, Lumenion estimates their steel-based storage can operate at an amortized cost of about €0.02 per kWh of thermal energy, given a 40-year life and ~150 cycles/year . By contrast, a lithium battery providing the same energy would deliver at ≥€0.08 per kWh (and likely with a shorter lifespan) . The key is that steel tanks or concrete silos are relatively inexpensive to build large, whereas battery costs scale roughly linearly with MWh capacity. This makes TES economically attractive for grid-scale, long-duration storage (10+ hours up to seasonal) – a niche where lithium-ion struggles due to high capital cost for large energy reserves . Studies by NREL and others have found that properly engineered thermal storage could be significantly cheaper than alternatives like compressed air or pumped hydro for long durations, while being more geographically flexible .
  • Long Lifespan and Low Degradation: Thermal storage systems can often operate for decades with minimal capacity fade. Solid materials like steel or rock do not “wear out” from thermal cycling the way batteries lose charge capacity after many cycles. For example, a well-designed steel storage tank might last >30–40 years, limited mostly by corrosion or insulation aging. PCMs can undergo many melt/freeze cycles before degradation. This longevity spreads the capital cost over a longer period, improving lifecycle economics. It’s noted that “thermal batteries tend to have very long lifespans—measured in decades rather than years”, especially compared to chemical batteries .
  • Efficiency and Operating Cost: Converting electricity to heat is essentially 100% efficient (all the electrical energy becomes thermal energy via resistive heating). If the goal is to use the heat directly (for industrial processes, space heating, etc.), the round-trip electric→heat→use efficiency can be extremely high (often >90%). Losses only come from heat leakage over time, which can be kept quite low with good insulation (a well-built thermal store might lose just a few percent per day or less). One source notes that simply storing heat for later use can be ~95% efficient in practice . This means little “waste” of the energy during storage, unlike battery self-discharge or conversion losses in other storage types. However, if one intends to produce electricity from the stored heat, efficiency drops due to thermodynamic limits (Carnot efficiency). A high-temperature store (e.g. 600 °C steel) feeding a turbine might convert ~30–40% back to electricity. The remainder isn’t truly wasted if it can be utilized as low-grade heat (cogeneration). In economic terms, using the heat in any form extracts value. For grid applications, often the primary use of thermal storage is to supply heat when needed (displacing fuel), and any power generation is a bonus.
  • Grid-Scale Arbitrage and Renewables Integration: Thermal storage can monetize the spread between off-peak and on-peak energy prices. In grids with high wind/solar, electricity sometimes becomes very cheap or even negative-priced during oversupply. Thermal storage units can “charge” during those periods (effectively getting paid to take energy or buying very low-cost power) and then deliver energy back (as heat or power) when prices rise. For example, in Europe increasing renewable penetration has led to hundreds of hours of negative electricity prices per year; a thermal storage can exploit this by absorbing excess power and later selling heat at three or four times the rate of the process need . In Finland’s case, a study found that using TES to soak up all negative-price periods could extend them from ~700 hours to nearly a quarter of the year, greatly improving renewable utilization . This arbitrage earns economic value from what would otherwise be waste energy. Grid-scale TES thus functions like a financial storage: buying energy low, storing it, and “withdrawing” high – analogous to a trader or bank, but with energy units.
  • Off-Grid and Remote Applications: In off-grid scenarios, thermal storage can improve economics of microgrids or remote facilities. For any location that relies on diesel generators or expensive fuel for power and heat, adding solar panels plus a thermal storage can cut fuel use dramatically. For instance, an off-grid farm could use midday solar electricity to heat a large water tank or concrete slab, then use that heat at night for warmth or even drive a small engine. Some communities use seasonal thermal storage (e.g. heating water or underground boreholes in summer) to supply winter heating, avoiding the purchase of fuel – effectively storing economic value across seasons. A real example is Drake Landing Solar Community in Canada, which stores summer solar heat in ground boreholes to achieve nearly 100% solar heating in winter – saving residents money on natural gas. While steel isn’t used in that case, the principle is the same: invest energy when it’s abundant to avoid high expenditures later. In developing regions, simple “heat batteries” (like insulated oil or salt in a cooker) allow cooking at night with heat stored from daytime sun, displacing costly or unhealthy fuels. All these off-grid uses highlight that thermal storage can substitute for fuel or electricity that would otherwise cost money, thus acting as an economic reservoir for the community.

Of course, economic feasibility depends on context. Thermal storage makes most sense when there is a significant price or availability differential between charging times and discharging times – for example, lots of free/cheap renewable energy vs. expensive energy later, or plentiful summer heat vs. needed winter heat. If cheap energy is not available, then charging a TES at high cost only to get a portion back may not pay off. Additionally, converting stored heat back to electricity involves expensive equipment (turbines, generators) and has lower round-trip efficiency, so TES is often best used for applications that can use the heat directly (space heating, industrial processes, etc.). In those niches, it can be extremely cost-effective. For instance, industrial heat accounts for a huge share of energy demand, and thermal batteries can supply high-temperature heat at lower cost than electric batteries or fuel boilers in many cases . Startups like Rondo Energy (ceramic brick batteries) and Antora (carbon block batteries) claim they can deliver process heat at a fraction of the cost of using electricity or gas, by charging when power is cheap . These claims are being tested in pilot installations.

In summary, thermal storage in steel or similar media shows strong economic potential for large-scale, long-life, heat-centric energy storage. Its capital costs per kWh are low and mostly upfront; its operation is simple (just resistive heating and heat transfer); and its asset life can be very long. These systems are less suited to rapid, frequent cycling or high round-trip electricity storage (where batteries still dominate), but they excel in the role of “energy value banks” that shift large amounts of energy across time to smooth out supply and demand.

Heat as a Currency or Store of Economic Value

The idea of using stored heat as a form of “currency” or store of value is an intriguing analogy. In economic terms, a store of value is any asset that can retain worth over time for future use. Usually we think of money, gold, or Bitcoin as stores of value – but could heat be treated similarly? A few perspectives help illuminate this question:

  • Historical and Theoretical Analogies: The notion of an energy-backed currency has been proposed in the past. Notably, automaker Henry Ford in 1921 suggested replacing the gold standard with an “energy currency” based on units of electricity . He envisioned huge power plants where one unit of currency would equate to a certain amount of energy (perhaps 1 kilowatt-hour), and this would be more stable and democratic than gold. Ford argued this could “break the grip of banking elites” and even prevent wars, since wealth would be tied to usable energy available to all . While his plan never materialized, it foreshadowed later ideas: essentially money directly linked to energy reserves. In a similar vein, economists and futurists have sometimes mused about energy as the ultimate currency since it underpins all economic activity. A modern commentary on this concept notes that unlike fiat money which can be printed, “energy cannot be fabricated – it must be produced, stored, or converted, making an energy-denominated economy self-limiting and grounded in physical reality.” . Proponents highlight that a kilowatt-hour is a universal, objective unit – “1 kWh means the same everywhere” – and energy as currency would have intrinsic value since it can perform work . In theory, a heat battery or any energy storage could act as a “bank” and issue energy credits backed by actual joules stored .
  • Real-World Examples of Heat-for-Value Exchange: While we don’t literally pay for groceries with a cup of hot water, there are cases where thermal energy is treated as a commodity that holds value over time:
    • District Heating Credits: In some heating networks, utilities buy excess heat from industrial processes or waste incinerators and give credit that can be sold or used later. The heat essentially becomes a tradable asset. For instance, a factory’s waste heat might earn it “heat credits” that it can use in winter or sell to others on the network – analogous to currency in a limited context.
    • “Heat Banks”: The term is sometimes used for facilities that store heat for later use (like seasonal storage in aquifers or big water tanks). One could deposit heat (in summer) and withdraw in winter. A community that invests in such a heat bank has effectively stored economic value: they spent money to collect and save heat when cheap (or free from the sun) to avoid buying expensive fuel later. This isn’t a currency you carry around, but functionally it’s a value storage instrument – much like a battery stores value by preventing future expenditures.
    • Energy Trading and Tokens: There have been pilot projects where neighbors trade electricity via blockchain tokens (e.g. one home sells solar power to another). Similar could be imagined for heat in microgrids – e.g. a building with surplus solar-heated water “sells” it to a neighboring building through a shared loop, receiving some credit. Those credits, if denominated in heat units, start to look like a local currency. However, this is niche and requires infrastructure for heat transfer.
    • Industrial Metal as Energy Storage: A tangential example is aluminum smelting: producing aluminum consumes a large amount of electricity, essentially storing that energy in the metal’s chemical bonds. In energy crises, aluminum production is sometimes curtailed and even the metal can be seen as embodied energy. One could imagine metal stocks as an energy store (smelt when power is cheap, later remelt or oxidize to release energy), though this is not done as a currency system per se. Similarly, proposals exist to use iron fuel cycles (iron powder produced with excess electricity and later burned for heat). These concepts treat materials as energy value carriers that can be transported or traded – a step closer to energy as currency.
  • Heat and “Intrinsic Value”: Unlike paper money or even Bitcoin, stored heat has direct usefulness. If you possess a reservoir of heat, you can warm homes, drive turbines, dry grain, etc. In that sense, it’s a commodity with intrinsic utility, more akin to owning a barrel of oil or a pile of coal (which historically have been stores of value too). People have long stored firewood or coal for winter – effectively saving value in a physical energy form. What’s new is the idea of doing it with renewable heat and high-tech storage. One could argue that a battery or heat store filled with energy is a better store of value than a cryptocurrency, because if all else fails you can survive with it (keep lights on or stay warm) – it has tangible worth. This is somewhat philosophical, but it speaks to the appeal of energy as a basis of value: “Energy underlies all economic activity… energy is the most fundamental denominator of value” .

Despite these analogies, using thermal energy storage as a literal currency faces practical hurdles:

  • Portability & Transfer: A good currency is easy to transfer. Heat is not – you can’t easily move a quantity of high-temperature heat over long distances without losses (unlike moving gold or sending Bitcoin digitally). Thermal energy is inherently local unless converted to electricity or contained in a portable medium. This limits heat’s use as a general currency, except in very localized energy networks.
  • Storage Losses: Money doesn’t “leak” out of your wallet over time, but heat will gradually leak away despite insulation. A store of heat isn’t perfectly stable – over months some percentage will be lost. (Some systems like underground seasonal stores have losses but still retain majority of energy over half a year; for example, Finland’s sand battery can keep stored heat for months with minimal loss .) Still, the need to maintain the store (and the inevitability of some loss) means heat value depreciates if not used, unlike a stable store of value which ideally holds its worth.
  • Fungibility and Standardization: Currencies are fungible (one unit is identical to another). Heat storage units might differ in temperature, medium, and availability. 1 kWh of heat at 600 °C is more valuable (can do more work) than 1 kWh at 60 °C. To use heat as currency, one would need standard units and quality grades (much like different karats of gold or purities). This adds complexity – an “energy currency” system might require defining a standard unit (say 1 kWh of electricity or high-grade heat) and conversion factors for other forms .
  • Not a Passive Store – More like a Battery: Storing heat is closer to investing in a battery or fuel reserve, which typically depreciates or requires upkeep, rather than holding a passive asset that just sits. While a tank of oil can sit for years as a store of value, a tank of hot molten salt will need constant insulation and eventually cool if not recharged. So thermal storage is an active store of value – useful but not as effortless as holding gold bars.

In practice, it may be more useful to think of heat storage as a form of energy banking or insurance rather than a day-to-day currency. It lets you bank cheap energy (like depositing money in savings) and withdraw when needed, with some “interest” in the form of reduced costs or revenues from energy arbitrage. Some researchers use the term “heat batteries” for these systems precisely because they behave like rechargeable economic assets .

One interesting aspect is value retention of the storage material itself. A bar of gold retains value intrinsically; a thermal storage made of steel might also hold residual value – the steel can be recycled or sold later. Lumenion pointed out that their steel units retain much of their value after 40 years because the steel can be scrapped or repurposed, offering a payoff at end-of-life . In a sense, the material is a collateral that holds value like a commodity (steel prices fluctuate but steel isn’t worthless). This is a contrast to a degraded lithium battery which might have little value at end of life. So in that regard, a big hot steel block has some parallels to gold: it’s tangible, recyclable, and (to a lesser degree) value-dense.

Thermal Storage vs Traditional Stores of Value (Gold, Bitcoin, etc.)

To directly compare thermal energy storage with classic stores of value:

  • Durability: Gold is chemically stable and can sit for centuries; Bitcoin exists on a blockchain and doesn’t “age”. Thermal energy, by contrast, decays (heat dissipates). A perfectly insulated storage is impossible, though good designs can hold heat for a long time. If one’s wealth were in the form of stored heat, it would literally warm the environment over time and shrink. Thus, as a long-term store of value, thermal energy is less durable – you’d have to constantly maintain or top-up the “account” to preserve value. The materials (steel, salt) might last decades (so the container of value is durable), but the energy content leaks away like a melting ice cube. In economic terms, this is like a currency with a negative interest rate or storage cost.
  • Liquidity and Transferability: Gold and Bitcoin can be readily traded or liquidated globally. Thermal energy is not easily transferable unless converted. For example, if you “own” 100 MWh of heat in a plant, you can’t directly use it to buy something unless there’s a marketplace and infrastructure to deliver that heat to someone else. You’d likely have to convert it to electricity or steam and sell that – incurring losses and effort. This lack of easy liquidity means heat storage is not a convenient medium of exchange or global store of value. It’s valuable to its owner but not universally exchangeable in the way gold coins or bitcoins are.
  • Value Stability: Gold’s value is relatively stable long-term (inflation hedge, etc.), and Bitcoin’s value – while volatile – is purely market-driven. The “value” of stored heat depends on energy markets and needs. If you have a tank of heat, its worth is tied to the price of the energy it can replace. Energy prices can fluctuate due to supply/demand, fuel prices, weather, and so on. In a scenario of steadily rising energy costs, stored heat becomes more valuable (you saved expensive fuel); but if energy becomes cheap or policies change, stored heat could lose value. It’s somewhat analogous to commodities markets. There’s also a time value: heat is usually most valuable in the near-to-medium term. Unlike gold, which might hold value over centuries, heat is meant to be used sooner – it’s a short-term store (hours, days, months, maybe a season). It doesn’t appreciate with time; if anything you hope it doesn’t depreciate before use.
  • Intrinsic vs Perceived Value: Gold and Bitcoin derive value largely from perception (scarcity, trust, collective agreement). Thermal energy storage’s value is intrinsic – it is literally useful energy. This means in a functioning market, it will always have at least the value of the equivalent fuel or electricity it can displace (minus any losses). In a crisis situation, having energy could be more immediately useful than holding gold or crypto. For example, if there were a sudden fuel shortage in winter, a town with a large heat storage has a life-saving asset, whereas gold bars wouldn’t keep anyone warm. In niche scenarios, one could imagine thermal energy being highly valued and even traded like emergency currency (e.g. “I’ll give you X liters of oil or a battery charge in exchange for access to your heat storage for an hour”). However, these are extreme cases. In stable times, we convert energy to money and vice versa through markets, rather than using energy directly as money.
  • Niche or Speculative Systems: There have been speculative ideas like “Bitcoin mining as an energy currency mechanism” – effectively turning electricity into a digital asset that can be reconverted by selling the Bitcoin. Some have called Bitcoin a “battery” for monetary energy (store electricity by mining coins, since coins can be traded for electricity elsewhere). But this is indirect and comes with huge inefficiencies . A more direct speculative system could be something like energy-backed cryptocurrencies (tokens redeemable for so many kWh from a storage facility). In principle, one could issue certificates for heat storage (like warehouse receipts). For example, a company might sell “heat coins” each guaranteeing 1 MWh of heat from their storage on demand. If people trusted it, it could circulate. There are modern analogues: some startups talk about “energy tokens” or using blockchain to trade energy, essentially creating localized energy currencies . These are early-stage and not mainstream, but they show a potential for heat or energy to function like a backing for currency, at least in microcosms.
  • Opportunity Cost: If one uses capital to build a thermal storage (or buy gold, or buy Bitcoin), there is an implicit comparison. Gold just sits but is low-risk. Bitcoin sits but is high-volatility risk. A thermal storage can actually produce useful services (heat, electricity), potentially generating revenue or savings. It’s more akin to investing in an asset that yields utility. In economic comparison, storing energy could have a payoff if it avoids fuel costs or earns via arbitrage – it’s an active asset. Traditional stores of value don’t inherently produce anything (though they can be collateralized or lent). So one might ask: is a thermal storage a better store of value because it can also generate heat/power (value creation), or worse because it requires effort and has losses? The answer depends on circumstances – but it’s clear a thermal storage is closer to capital equipment, whereas gold/Bitcoin are passive assets.

Bottom line: Thermal energy storage can function similarly to a store of value in certain niche contexts, especially where energy is critical. It enables one to time-shift purchasing power in the energy domain – much like storing value for future use. However, it lacks the universal liquidity and stability of traditional money or gold. It is best viewed as an energy reserve that has economic value, rather than a general-purpose currency. Just as we wouldn’t use barrels of oil at the checkout counter, we likely won’t use “heat coins” at scale until we have seamless energy trading infrastructures. That said, as the world moves toward renewables, energy storage does become an important form of wealth (nations with big energy storage can better handle fluctuations, companies with energy reserves can arbitrage markets). We might see more financial instruments tied to stored energy (futures, guarantees, etc.), effectively turning heat reserves into financial assets.

Conclusion

Using heat stored in steel or other high-capacity materials as a way to store both energy and economic value is more than just a fanciful concept – it’s happening in practice, albeit in a controlled manner. Technologies like steel heat batteries, molten salt tanks, and sand silos serve as “thermal piggy banks” for excess energy, allowing us to deposit energy when it’s abundant and withdraw it when needed. The physics of these systems are well-understood, and engineering trials have shown they can be efficient, long-lasting, and cost-effective. In energy markets, such storage introduces an element of time-value of energy, analogous to interest: the heat saved during low demand can fetch a higher price later, generating economic value.

However, the notion of heat as money is mostly useful as an analogy or in tightly defined ecosystems (microgrids, district networks). Thermal energy isn’t about to replace dollars; instead, it underpins value by ensuring energy availability. It’s helpful to remember that all money is ultimately a claim on resources and work, and energy is the capacity to do work. In that sense, a robust thermal storage is a store of real value – it guarantees a certain amount of work (heat, power) can be delivered in the future. This is fundamentally similar to why gold or Bitcoin is valued (a guarantee of future purchasing power under certain assumptions), though realized in a very different form.

In comparing thermal storage to gold or Bitcoin, we find that each excels on different fronts:

  • Gold and Bitcoin are fungible, inert stores of wealth suited for trading and saving, but have no direct utility (you can’t heat your house with a Bitcoin).
  • Thermal storage is useful and productive, saving money on energy bills or making money via grid services, but it is bound by physical constraints and locale, making it less handy as a tradeable asset.

There may be niche “speculative” systems where energy storage units are traded like commodities or backed by blockchain tokens, effectively creating an energy currency. These are early and experimental. The broader impact of thinking of heat as value is that it encourages investment in storage: businesses and communities might treat stored renewable heat as a financial asset in project evaluations. In fact, some industrial thermal storage makers highlight residual asset value (recyclable steel, etc.) to sweeten the economic case .

In conclusion, heat storage in materials like steel can indeed store economic value – by preserving energy that would otherwise be wasted and by providing energy security that has monetary worth. It is not a convenient medium of exchange like currency, but it is a strategic store of value in the energy economy. As the world transitions to renewable energy, such thermal “value vaults” will likely become more common, not as literal money, but as critical assets that ensure energy availability and price stability. In the energy-financial ecosystem, they play the role of the battery or bank that keeps the system running smoothly – quietly accumulating value when conditions are right and releasing it when it’s most needed, much like a prudent savings account for our energy needs.

Sources:

  • Advantages of thermal energy storage (cheap abundant materials, long life, high efficiency for heat use) 
  • Lumenion steel heat storage at 650 °C (Berlin pilot, 2.4 MWh, plans for 40 MWh, 50% electricity possible but mainly heat) . Techno-economic details: 4-ton steel block, ~25% electricity conversion, €0.02/kWh cost vs batteries €0.08, 40-year life, ~95% total efficiency with cogeneration . Steel storage retains value after decades (recyclable) .
  • Siemens Gamesa volcanic rock storage (130 MWh_th pilot, 750 °C, steam turbine for power) . Plans to expand to GWh scale .
  • Polar Night Energy “sand battery” (Finland 2022) – 100 kW/8 MWh, hundreds of tons of sand at 500–600 °C in a steel silo, holds heat for months, 80+ hours duration, used for district heating . Demonstrates seasonal heat storage and arbitrage of cheap wind power .
  • Henry Ford’s 1921 proposal of an “energy currency” backed by units of electricity (replace gold standard) ; modern discussion of energy as a currency (1 kWh as universal unit, cannot be printed, energy-backed economy) .
  • Market and use-case context: Negative electricity price opportunity for thermal storage to save excess renewable energy and reduce costs ; thermal storage vs Li-ion for long duration (NREL: particle/sand storage can beat batteries in cost for 10–100h range) .