PTES systems typically use a high-efficiency heat pump to charge hot and cold thermal reservoirs, and later run the temperature difference through a heat engine to recover electricity. They promise flexible siting, long life, and reliance on abundant materials, but round-trip efficiencies and project economics are highly configuration-dependent.
- Modern PTES concepts target round-trip efficiencies of 40–65% (AC–AC), depending on temperature levels, working fluids, and integration with industrial heat.
- Typical durations are 6–20 hours, with storage media ranging from packed-bed solids to molten salts and phase-change materials.
- Indicative CAPEX ranges for early PTES plants are in the order of 100–250 USD/kWh, with potential to fall below 100 USD/kWh if standardized designs scale.
- PTES competes best where it can share assets with industrial heat systems or recycle low-temperature waste heat, improving overall economics.
1. Technology benchmarks: architectures and key parameters
PTES architectures vary widely, but most combine a heat pump, thermal reservoirs, and a heat engine cycle. Some schemes use the same turbomachinery operating in reversed modes; others use dedicated heat pumps and turbines.
| Architecture | Storage media | Typical temperature levels | Target RTE (AC–AC) |
|---|---|---|---|
| High-temperature PTES | Molten salts / packed solids | 300–600 °C hot, ~ambient cold | 50–65% |
| Mid-temperature PTES | Concrete / ceramics | 150–350 °C hot, ~ambient cold | 45–60% |
| Low-temperature PTES | Water/ice, phase-change | 0–120 °C | 40–55% |
Unlike purely electrical storage, PTES sits at the intersection of power and thermal engineering. Facilities often resemble industrial plants rather than containerized batteries, with implications for permitting, siting, and operations.
2. Economics: where PTES LCOS can land
PTES capital costs are currently driven by turbomachinery, heat exchangers, and thermal storage tanks. The table below summarizes indicative ranges for early and scaled deployments.
| Metric | Early PTES projects | Scaled PTES (target) | Li-ion 8h reference |
|---|---|---|---|
| CAPEX (USD/kWh) | 160–280 | 80–160 | 150–250 |
| CAPEX (USD/kW) | 800–1,400 | 500–900 | 500–900 |
| LCOS, 10–12h (USD/MWh discharged) | 150–230 | 100–170 | 130–190 |
PTES becomes more attractive when it can share or substitute for other thermal assets—such as boilers, chillers, or process heaters—rather than serving purely as a standalone power asset.
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3. Use cases: when PTES is a good fit
PTES is particularly interesting where both electricity and heat are valuable:
- Power plants with district heating: PTES can act as a flexible boiler/heat pump plus storage asset, improving CHP operation.
- Industrial sites with large low- to mid-temperature heat loads and on-site renewables.
- Grid-scale LDES where siting constraints limit pumped hydro and where thermal integration is possible.
Integration tip: PTES projects that treat electricity and heat as co-products often deliver stronger economics than power-only concepts.
4. Technical constraints and risks
Despite promising pilots, PTES still faces several challenges:
- Complexity: PTES plants combine turbomachinery, heat exchangers, and thermal storage, resembling small power plants rather than modular batteries.
- Efficiency sensitivity: deviations from design temperatures or part-load operation can materially reduce RTE.
- Materials and working fluids: high-temperature components and fluids need long lifetimes and clear environmental profiles.
Bankability note: lenders will scrutinize turbomachinery guarantees, thermal storage performance, and O&M assumptions more closely than for containerized storage.
5. Global perspective: where PTES pilots are emerging
PTES development is concentrated in regions with strong decarbonization targets, high renewable penetration, and sophisticated grid operators:
- Europe: multiple demonstration projects tied to district heating and industrial clusters.
- United Kingdom: interest in PTES for grid balancing and integration with thermal networks.
- North America: early pilots exploring PTES as part of LDES portfolios in high-renewables states.
6. Outlook to 2035: PTES in the LDES mix
By 2035, PTES may become a standard option in planning studies for grids and industrial clusters, especially where combined heat and power are valuable. Its eventual role will depend on:
- Demonstrating reliable RTE at commercial scale.
- Achieving CAPEX reductions through modularization and learning-by-doing.
- Clear regulatory treatment of hybrid power-heat assets.
7. Implementation guide: evaluating a PTES project
For utilities and industrials, PTES evaluations should integrate both power and heat system perspectives:
7.1 Screening questions
- Is there a co-located heat sink or source that PTES can leverage?
- Are there space and permitting conditions suitable for an industrial-like plant?
- Does the grid need 6–20 hour flexibility at the same node?
7.2 Quantitative steps
- Map expected charge/discharge profiles and heat loads.
- Estimate CAPEX and OPEX for heat pumps, heat engines, and storage.
- Run LCOS and net present value (NPV) scenarios including heat revenues or avoided costs.
- Compare outcomes to alternatives: batteries, pumped hydro, thermal storage with separate power assets.
8. FAQ: common questions on PTES
How does PTES differ from simple thermal storage plus a power plant?
PTES explicitly uses a heat pump to charge thermal reservoirs and a heat engine cycle to recover electricity, closing the loop as a storage system. Simple thermal storage plus a separate power plant may not be optimized for round-trip efficiency or integrated dispatch.
What round-trip efficiency should planners assume?
For planning studies, using a range of roughly 40 to 60 percent AC–AC is reasonable for most PTES concepts, depending on temperature levels and integration. Sensitivity analysis around this range is important.
Is PTES bankable today?
PTES is at an advanced demonstration stage, with a smaller reference base than pumped hydro or batteries. Bankable projects are likely to involve strong counterparties, vendor guarantees, and in some cases support from public funding or regulated asset frameworks.
Where does PTES fit relative to other LDES options?
PTES is most compelling where thermal integration is valuable and where pumped hydro or cavern storage are unavailable. It complements, rather than replaces, batteries, flow systems, and hydrogen-based storage.
What project timelines are realistic?
Expect roughly 4–8 years from early feasibility to commissioning, depending on permitting, integration complexity, and whether PTES is part of a broader site upgrade.