The Exergy of Electrification: Heat Pumps, Hydrogen and the Rational Use of Electricity

The Premium Carrier: Electricity as Convertible Currency

Electricity is the only energy carrier that modern civilization produces at essentially 100 percent exergy. This status as pure work potential without residue allows it to be converted into almost any other form of energy or service with minimal loss. It can be transformed into shaft work at approximately 95 percent efficiency, or applied to computation, light, chemistry, and separation. Most significantly, when used to drive a heat pump, a single unit of electricity can deliver several units of heat by conscripting ambient energy. This universal optionality makes electricity the "convertible currency" of the energy system, a premium asset that provides unmatched flexibility in how it is deployed.

However, this premium is manufactured at a significant thermodynamic and economic cost. In the current energy mix, thermal generation typically requires two to three units of fuel exergy to produce just one unit of electricity—a "Carnot tax" paid by the fossil fuel fleet. Even in a fully decarbonized system, the cost of the premium carrier remains high, accounted for in capital, materials, land, and grid infrastructure. Furthermore, the value of clean electricity is fundamentally "hour-shaped." While it may be abundant and nearly free during spring afternoons, it becomes the most expensive commodity in the economy during the still evening peaks of winter. Because electricity is pure exergy produced at a real cost, it is never "too cheap to allocate" indiscriminately.

Treating electricity, gas, and heat as fungible units in energy statistics and building codes is a root error described as carrier-neutral accounting. This approach ignores the vast difference in quality between a unit of premium electricity and a unit of low-grade heat. Such innumerate accounting allows highly inefficient practices—such as using resistance heating for low-temperature duties—to appear viable because they are labeled "100 percent efficient" in first-law terms, despite annihilating the carrier's exergy. A rational transition requires moving away from politically negotiated primary-energy factors toward physics-derived accounting that recognizes electricity for the high-quality exergy it is. Failing to do so risks a transition that is priced in unnecessary power plants, as every wasted kilowatt-hour represents a turbine that must be built and a grid connection that must be queued for.

Would you like a summary of the next section, which details the allocation principle and the electricity merit order?

The Electricity Merit Order: A Demand-Side Dispatch Stack

For a century, power systems have functioned by dispatching generators according to a merit order, ensuring the cheapest resources meet demand first. As the transition to clean energy accelerates, the central instrument for managing this shift is a demand-side mirror: an electricity merit order that ranks every claim on a clean kilowatt-hour by its exergy leverage. This metric measures the service exergy delivered at the duty per kilowatt-hour of electricity consumed, providing a thermodynamic audit of how effectively a premium carrier’s quality is utilized or multiplied.

Electricity is the convertible currency of the energy system, produced at essentially one hundred percent exergy. Because it can be converted to shaft work, computation, or chemistry with minimal loss, or leveraged through a compressor to deliver multiple units of heat, the proposed uses of this currency differ in delivered service by a factor of nearly a hundred. The merit order sorts these uses into three distinct regimes based on their leverage:

• Preservers (0.8–0.95 leverage): These include motors, drivetrains, electronics, and electrochemistry. In this regime, electricity performs duties that only electricity can, passing its quality through nearly intact.
• Multipliers (COP 3–5): Heat pumps and vapor recompression represent the only uses that deliver more energy than they consume. By spending one premium kilowatt-hour to conscript three to five units of ambient or waste heat, these machines achieve an exergy dividend that retires whole fuel streams at a fraction of the electrical demand.
• Destroyers (0.05–0.3 leverage): This regime includes the resistance heating of low-grade duties and complex molecule chains. Here, the premium carrier is annihilated to serve low-quality needs, such as warming a room to 21 °C, which carries a second-law efficiency of roughly 6 percent.

The resulting merit order provides a rigorous build sequence for energy ministries and utilities. It ranks irreplaceables first, followed by preservers and multipliers. Fourth place is held by honest electrothermal processes, where high-temperature duties (800–1,700 °C) justify the use of resistance, induction, or arc heating because the task itself requires high-grade energy. Molecule chains and destroyers are ranked last; these are considered rational only in specific edge cases, such as when utilizing curtailed midday power or serving duties where no direct electrical route exists.

Electricity is the convertible currency of the energy system: spend it first where nothing else is legal tender, spend it through machines that multiply it wherever heat is the duty.

This ranking is not a rationing scheme but an allocation principle. Every wasted clean kilowatt-hour represents a turbine that must be built, a grid connection that must be queued for, and a scarce winter hour that another user must go without. By prioritizing high-leverage uses, the merit order ensures that the most expensive and highest-quality commodity in the economy is not squandered on low-grade duties that ambient energy or building envelopes could serve.

Audit of Motion and the Heat Divide

The transition to a decarbonized economy requires a rigorous audit of how high-quality energy is utilized, moving beyond the simplistic goal of "electrifying everything" to a strategy of "electrifying intelligently." This audit is performed by evaluating the exergy leverage—the service delivered at the duty per kilowatt-hour (kWh) of electricity consumed. When comparing mechanical work and thermal duties, the delivered service efficiency reveals a vast disparity in how effectively different technologies preserve or multiply the value of the premium carrier.

Motion: The Clean Sweep

Mechanical work represents electricity’s home ground, where the carrier’s quality is preserved almost perfectly. In the audit of transport, battery-electric vehicles (BEVs) emerge as the most efficient route by a significant margin. A BEV delivers approximately 0.73 kWh at the wheel for every kWh consumed from the grid, accounting for losses in charging, battery round-trips, and the drivetrain. In contrast, alternative pathways for motion suffer from severe thermodynamic tolls. Hydrogen fuel cell vehicles deliver only ~0.29 kWh at the wheel, while e-fuels—synthetic fuels burned in internal combustion engines—deliver a mere ~0.13 kWh. The battery route thus provides three to five times the service per unit of electricity compared to its competitors, a result determined by simple division rather than policy preference.

Heat: The Great Divide

Thermal duties represent the greatest divide in electrification, splitting between "multipliers" and "destroyers." The audit identifies a massive mismatch in building heat, where the highest-quality energy (electricity) is often used to serve the economy's lowest-quality demand (maintaining a room at 21 °C). Resistance heating, despite being labeled "100 percent efficient" under first-law energy accounting, represents a catastrophic loss of quality, achieving only ~6 percent second-law efficiency. It essentially annihilates the premium carrier to produce low-grade warmth.

Conversely, the heat pump acts as a multiplier. By using one unit of premium work to conscript ambient energy, it delivers three to five times more heat than the electricity it consumes. At a systemic level, heat pumps can retire a boiler's full fuel stream at only one-third of the electrical demand required by resistance heating. This leads to the fundamental "compressor rule" for rational electrification: for any heat duty below 100 °C, electricity should only arrive via a heat pump. This rule ensures that society does not build three power plants to satisfy a demand that a compressor could meet with one.

Summary of Service Efficiency

*Note: Heat pumps deliver more energy than they consume by leveraging ambient sources.

Industrial Spectrum and Molecule Assignments

Industry represents a complex thermodynamic spectrum where the suitability of electrification is determined by the grade of the duty. Unlike residential comfort, which sits at the bottom of the exergy scale, industrial processes span from low-temperature washing to the extreme thermal requirements of metallurgy. Within this spectrum, the merit order dictates a shift in technology based on temperature: for any industrial heat duty below 200 °C, the procurement rule is clear: electricity should only arrive through a compressor. In this band, high-temperature heat pumps and Mechanical Vapour Recompression (MVR) function as multipliers, conscripting ambient or waste heat to deliver three to six units of useful service per unit of electricity consumed. Using resistance heating for these low-grade duties constitutes a failure of allocation, as it misses the enormous exergy dividend available through multiplication.

The Inversion: Honest Electrothermal Duty

As temperatures rise, the thermodynamic justification for different electrification routes undergoes an honest inversion. At the summit of the spectrum (800–1,700 °C), the duty’s own Carnot grade matches the high quality of the electrical carrier. In these regimes, technologies such as resistance, induction, and electric arc heating earn their status as "preservers." Because a duty at 800 °C carries a Carnot factor near 70 percent, converting electricity directly to heat at these temperatures achieves 80–95 percent efficiency with a precision that combustion cannot match. In these instances, the heating element is innocent; it is the high grade of the task that justifies the direct use of the premium carrier.

The Hydrogen Admission Ticket

Molecules, specifically hydrogen produced via electrolysis, hold a valid but strictly ticketed assignment in the industrial merit order. Because electrolysis involves a conversion toll—delivering only one-fifth to one-eighth of the service a heat pump provides per clean kilowatt-hour—it is ranked as a fifth-tier allocation. Hydrogen’s "admission ticket" is the absolute absence of a direct electric route. This ticket is valid for chemical feedstocks such as ammonia and methanol, and for processes like direct-reduced steel where hydrogen performs a necessary chemical role rather than a thermal one. However, the ticket is denied for general heating; using hydrogen for warmth is innumerate, as it requires five to eight times the generation capacity of a compressor-based system to deliver the same service.

Ultimately, the role of hydrogen in industry is not as a general-purpose fuel but as a specific chemical instrument. While indispensable for aviation, shipping, and seasonal reserves where energy density is the binding constraint, hydrogen-for-heating remains the destroyer regime’s most expensive habit. By adhering to the merit order, industry ensures that premium exergy is spent where it is "legal tender" rather than being annihilated for low-grade warmth.

Buildings: The Canonical Exergy Mismatch

Residential and commercial buildings represent the most significant thermodynamic discrepancy in the modern energy economy. While these structures account for approximately one-third of final energy consumption, their primary requirements are for the lowest-quality energy available: comfort heating at roughly 21 °C and domestic hot water at approximately 55 °C. When analyzed through the second law of thermodynamics, these duties carry Carnot factors of only 7 percent and 12 percent, respectively. This reveals a "building inversion" where the energy demand is massive but low-grade, while the true exergy demand—reserved for lighting, electronics, and appliances—is relatively small and highly specific. The electrification era threatens to exacerbate this mismatch by serving these low-quality needs with electricity, the highest-quality carrier civilization produces, unless guided by rigorous design principles.

The LowEx Design Stack

To resolve this mismatch, the LowEx design school dictates a specific hierarchy for building retrofits and construction. This methodology ensures that every unit of premium exergy is leveraged to its maximum potential by reducing the grade of energy required at each stage of the building's operation. The design stack is organized as follows:

• Envelope first: The primary objective is to minimize the total demand through insulation and airtightness. This stage has essentially infinite leverage, as exergy that is not demanded does not need to be generated or distributed.
• Low-temperature emitters second: By utilizing radiant floors or oversized radiators, a building can maintain comfort using supply temperatures of 30–40 °C instead of the traditional 70 °C. This reduction in the "lift" required by heating machinery significantly enhances system performance.
• Heat pump third: Only after the load is minimized and the emission temperature is lowered should a multiplier technology be introduced. Sizing a heat pump to a LowEx-optimized building allows for a smaller, more efficient machine.
• Storage and networks fourth: Thermal mass and district connections allow the building to shift its remaining demand to hours of electrical abundance, integrating the structure into the wider grid as a flexible asset.

Avoiding the Inverse Retrofit

A critical failure in contemporary national retrofit programs is the tendency to read this stack "upside down." Starting a retrofit at the boiler room by simply replacing a fossil-fuel burner with a resistance heater or a hydrogen boiler represents a catastrophic misallocation of resources. Serving a 21 °C room with a resistance element annihilates electricity’s quality at a mere 6 percent second-law efficiency. Similarly, using hydrogen for space heating delivers only a fraction of the service that a heat pump would provide per kilowatt-hour spent. Implementing the stack in the correct order ensures that the transition relies on multiplication rather than the brute force of overbuilding generation and grid capacity to satisfy low-grade warmth.

Would you like a summary and analysis of the next segment, which covers the role of time, batteries, and scarcity in the exergy merit order?

Time and Policy: Scheduling Scarcity

Integrating time-based scarcity into the allocation strategy requires recognizing that clean electricity's quality is constant while its availability is not. Renewable systems produce two distinct commodities under the same name: abundant-hour electricity during periods of high solar and wind output, and scarce-hour electricity during the stillness of a winter evening. Because every wasted clean kilowatt-hour represents a turbine that must be built or a grid connection someone else must wait for, the allocation strategy must be both a ladder of leverage and a clock of availability. High-leverage uses earn the right to consume scarce winter-evening hours, while low-leverage "destroyer" regimes and molecule chains must justify their consumption against curtailed abundance only. When a resistance element runs on otherwise wasted midday power to charge a storage heater, it acts as a defensible system participant; however, the same element operating at 6:00 p.m. in January represents three power plants of demand wearing a single plug.

Converting Demand into a Grid Asset

Thermal storage and smart EV charging are critical tools for converting demand into a grid asset, effectively reducing peak generation needs. Thermal storage, such as building mass or industrial gravel banks, represents the cheapest flexibility available, allowing multipliers like heat pumps to bank cheap hours as heat at grade. Similarly, the EV fleet's demand is movable by software, turning transport into a reserve that can drink abundant hours. These schedulable claims—including electrolysers that are interruption-tolerant by design—allow the system to shave peak demand and size storage capacity more conservatively. By moving demand first, the expensive insurance of firm capacity is minimized, resulting in the smallest possible clean infrastructure that still delivers all required services.

The Five Policy Instruments

To implement this merit order without relying on a central authority to assign electrons, policy must adopt five specific instruments to ensure markets and codes stop lying about energy quality:

• Honest Accounting: Deriving primary-energy and carrier factors from physics and exergy rather than political negotiation, removing the "100 percent efficient" alibi for resistance heating.
• Hourly Prices: Ensuring scarcity and abundance signals reach the meter, allowing thermostats and chargers to respond to real-time grid conditions.
• Leverage-Ranked Support: Directing public money and grid-connection priority toward multiplication (heat pumps) before annihilation (resistive power-to-heat).
• Updated Building Codes: Requiring low-temperature readiness and emitters at the moment of system replacement to lock in decades of low-lift performance.
• Leverage Disclosure: Requiring every electrification plan to publish its portfolio's average exergy leverage, ensuring "gigawatts electrified" is no longer a proxy for "services delivered."

The National Stakes: A Worked Example

The stakes of scheduling and leverage are quantified in a national example comparing routes for heating one million homes. A strategy based on resistance heating demands approximately 12 TWh during the system's scarcest hours. Utilizing hydrogen boilers is even more demanding, requiring 21 TWh due to the repeated annihilation of quality throughout the electrolysis and combustion chain. In contrast, the merit-order route—combining building envelopes, low-temperature emitters, heat pumps, and thermal storage—requires only 2.7 TWh with just one-sixth of the peak demand. The resulting savings in infrastructure and generation capacity are sufficient to fund the national retrofit program several times over, proving that intelligent electrification is a matter of arithmetic rather than opinion.

Key findings

• Exergy Leverage Disparity — Proposed uses for one kilowatt-hour of electricity differ in delivered service by a factor of nearly a hundred.
• The Heat Pump Dividend — Heat pumps are the only uses that deliver more energy than they consume by conscripting 3-5 ambient units per premium unit.
• Hydrogen Heating Inefficiency — The hydrogen-for-heating chain is five to eight times less efficient than heat pumps per unit of clean electricity.
• Industrial Grade Justification — Resistance heating is only thermodynamically rational when the task grade (e.g., 1,000 °C) justifies the carrier's quality.

Method and assumptions

The paper employs thermodynamic analysis based on the second law of energy, specifically using 'exergy leverage' as the primary metric. Leverage is defined as the service exergy delivered at the duty per kilowatt-hour of electricity consumed. The work audits various energy chains (transport, heating, industrial) by calculating chain-honest indicative efficiencies and Carnot factors. It draws upon the 'LowEx' design school and IEA international building-exergy annexes. The analysis assumes electricity is a 100 percent exergy carrier and models national-scale impacts using a 'Worked Example' comparing three technological routes for heating one million homes, incorporating seasonal COP and peak-coincidence factors.

Where it applies

• National Energy Planning — Using the electricity merit order as a build sequence to prioritise grid connections and generation buildout.
• Building Code Reform — Mandating low-temperature emission readiness and heat-pump-only electrification for duties under 100 °C.
• Industrial Strategy — Differentiating between low-grade heat duties suitable for MVR and high-grade duties requiring arc or induction.

Terms used

• Exergy Leverage — The ratio of service exergy delivered at the point of use to the kilowatt-hour of electricity consumed.
• Carnot Grade — The thermodynamic quality of heat determined by its temperature relative to the ambient environment.
• MVR — Mechanical Vapour Recompression; an industrial process that uses electricity to upgrade the grade of waste steam.
• Destroyer Regime — Demands where the premium quality of electricity is annihilated, such as low-grade resistance heating.
• LowEx — A design philosophy focused on serving building comfort using the lowest possible energy grades available.

Questions and answers

Is resistance heating always a poor choice?

Not necessarily. It is rational for high-temperature industrial processes (above 800 °C) where the duty matches the grade, or as a last resort for small intermittent loads and backup elements when run during hours of curtailed abundance.

Why shouldn't we use hydrogen for home heating?

Hydrogen-for-heating requires five to eight times more clean electricity than a heat pump to deliver the same room warmth, creating an immense and unnecessary burden on power generation and grid infrastructure.

How does the merit order handle renewable energy surpluses?

The merit order is schedule-aware; abundant hours (like midday solar) permit lower-leverage uses like thermal storage or electrolysers, while scarce winter hours must be reserved for high-leverage preservers and multipliers.

What is the 'building inversion'?

It is the observation that while space heating dominates a building's energy volume, it represents only a sliver of its exergy requirement, whereas electronics and light represent small volumes but high quality requirements.

How to cite

Bakker, W. A. (2026). The Exergy of Electrification: Heat Pumps, Hydrogen and the Rational Use of Electricity. Exerginity White Paper Series, No. 8. August 2026. exerginity.com