A high-temperature thermal "heat battery" (sand / rock / concrete) with an optional Stirling / ORC module that returns electricity on demand.
Product Family
Anchor sand/rock high-temperature heat-battery unit
Modular concrete/block variant
Stirling / ORC heat-to-power (Carnot battery) tier
Controls & optimiser software — core IP, future SaaS
Slovenia
Austria · Italy (North) · Croatia · Hungary
Ukraine (R&D + resilience market)
Anchor technology: Sensible-heat solid media (sand / rock / concrete)
Kresnik
Slovenian solar/fire folk hero — Slovenia-first fallback
Calora
Latin calor = heat — neutral, pan-European
ThermaBank
English thermal + bank — descriptive but generic
Three core value propositions every customer segment cares about.
Arbitrage and peak-shaving shift energy purchase to cheap hours and reduce capacity charges.
Meet RED III, EU ETS and corporate ESG targets with demonstrable carbon reduction.
Optional +P tier delivers heat and electricity through outages — energy security on-site.
Compare sensible, latent and thermochemical media. Order-of-magnitude planning values.
| Material | cp (kJ/kg·K) | Density (kg/m³) | Vol. Heat Cap. (kJ/m³·K) | Max Temp (°C) | Notes |
|---|---|---|---|---|---|
| Water | 4.18 | 1,000 | 4,180 | 95 | Best per-kg; cheap; limited to <100 °C unpressurised |
| Sand / silica | 0.8 | 1,500 | 1,200 | 1,000 | Cheap, abundant, high-temp; air heat-transfer medium |
| Basalt / rock | 0.9 | 2,900 | 2,610 | 1,000 | High volumetric capacity; packed-bed |
| Concrete | 0.88 | 2,300 | 2,024 | 1,200 | Castable, structural; modular blocks |
| Molten salt (solar nitrate) | 1.5 | 1,900 | 2,850 | 565 | Liquid; freezes below ~220 °C |
| Class | Melt Point (°C) | Latent Heat (kJ/kg) | Conductivity (W/m·K) | Notes |
|---|---|---|---|---|
| Paraffin wax | 20–70 | 150–250 | 0.2–0.4 | Organic, flammable, stable |
| Fatty acids | 20–70 | 150–200 | 0.2–0.3 | Organic, less corrosive |
| Salt hydrates | 30–120 | 200–350 | 0.5–1.2 | Inorganic, non-flammable, cheap; may supercool |
| Eutectic salts | 50–250 | 100–250 | 0.5–2.0 | Tunable |
| Class | Storage Density (GJ/m³) | Notes |
|---|---|---|
| Salt hydrate / sorption (e.g. zeolite-water) | ~1.0 | Near-zero standing loss (reactants stored separately); R&D to pilot; seasonal storage |
Q = m · cp · dT
Mass × specific heat × temperature change
Q = V · ρcp · dT
Volume × volumetric heat capacity × dT
Q = m · L
Mass × latent heat of fusion
Q = n · dHr
Moles × reaction enthalpy
Q̇loss = U · A · (Tstore − Tamb)
U-value × surface area × temperature difference
The Carnot battery concept: store electricity as heat, convert it back on demand.
Stores electricity as heat and converts it back to electricity (power-to-heat-to-power).
Term coined
DLR / André Thess, 2018
Origin
Fritz Marguerre patent ~1924
Round-trip efficiency
40–70%
Optimisation study
57% · €0.649/kWh
η = 1 − Tc / Th (Kelvin)
Example: 600 °C hot, 300 K cold → ceiling ≈ 65.6%. Real Stirling: 30–40%.
Key advantage: Can reuse a retired fossil plant's turbine, generator and grid connection.
| Technology | Temp Range (°C) | Scale | Real Efficiency | Maturity | Best Fit | Vendors |
|---|---|---|---|---|---|---|
| Stirling engine | 500–800 | 1–55 kWe | 30–40% | Commercial (niche) | Small CHP, off-grid, resilience | Qnergy, Cleanergy, Microgen, Inresol, STM |
| ORC | 80–350 | 10 kW – MW | 10–25% | Mature | Medium-temp, mid/large sites | Turboden, Enogia, Orcan, Exergy |
| Steam Rankine | >450 | MW–GW | 30–45% | Very mature | Large DH / reused coal turbines | Siemens, GE, reused coal-plant turbines |
| sCO₂ / Brayton | >500 | MW | 35–50% | Emerging | Compact large-scale; watch | Echogen, Hanwha |
| TPV | >1,000 | Modular | 20–40% (lab) | Emerging | Ultra-high-temp, no moving parts | Antora, Fourth Power |
| Thermoelectric (TEG) | Any dT | W–kW | 5–8% | Mature | Sensor/IoT power only | — |
Aluminium PCM 600 °C + Stirling → Bankrupt 2022
The technology works. The lesson: treat +P as an optional CHP/resilience tier, not as a pure power-arbitrage play.
Where the energy to charge the store comes from — solar, wind, thermal/waste heat, geothermal, hydro, biomass and grid surplus.
Electricity → heat via resistive/electrode heaters (~99%) or a heat pump (COP 2–5). Used by PV, wind, hydro and grid-surplus sources.
A hot fluid/stream is stored directly — solar thermal, industrial/data-centre waste heat, geothermal, biomass/biogas CHP. Marginal charge cost often ≈ €0 for waste streams.
| Source | Pathway | Charge cost | Useful temp / quality | Seasonality | Best customer fit | Main limitation |
|---|---|---|---|---|---|---|
| Solar PV (surplus) | P2H | ≈€0–0.05/kWh | any (resistive to 600 °C+) | Summer-peaking, daily | PV owners with heat demand | Daytime only; needs store to time-shift |
| Solar thermal | direct heat | ≈€0 fuel | 60–120 °C (flat/evac), 150–400 °C (conc.) | Summer-peaking | Hotels, spas, agriculture, DH | Collector area; weather-dependent |
| Wind / curtailed renewables | P2H | €0–0.04/kWh | any | Winter-peaking, gusty | Industry, DH near wind | Variable; limited inside SI terrain |
| Off-peak / negative-price grid | P2H | €0.02–0.07/kWh; sometimes <€0 | any | Daily/nightly troughs | Any grid-connected site | Tariff/market access; price risk |
| Industrial waste heat | direct heat | ≈€0 | 80–500 °C+ | Continuous (process-linked) | Glass, metals, food, foundries | Site-specific; HX integration |
| Data-centre waste heat | direct heat (+HP) | ≈€0–low | 30–45 °C (needs HP upgrade) | Continuous | Colocation/edge + DH offtake | Low grade; needs heat-pump lift |
| Geothermal | direct heat | low (pumping only) | 40–150 °C (SI Pannonian belt) | Base-load, stable | Pomurje spas, DH, agriculture | Drilling CAPEX; resource-bound |
| Biomass / biogas CHP | direct heat | low (fuel-linked) | 80–500 °C | Dispatchable/seasonal | Farms, rural DH, sawmills | Fuel logistics; emissions limits |
| Hydro / micro-hydro | P2H | low (cheap baseload/spill) | any | Spring/melt-peaking | Alpine valleys, rural mills | Geography-bound; water rights |
| Grid surplus (curtailment) | P2H | ≈€0 when curtailed | any | Rising with RE share | DH/industry as flexible load | Needs interruptible contract |
Public-source planning ranges (Source #26); validate per site and per year. Geothermal in the Pannonian/Pomurje belt is a genuine regional edge; waste heat (≈€0) is the single best economic charging source.
Store midday PV as heat via an efficient HP; cover evening/winter load; maximise self-consumption.
Homes, hotels, commercial
Soak curtailed/negative-price power; optionally return dispatchable electricity.
Industry, DH, resilience
Buffer summer collection for night/shoulder season; seasonal with pit stores.
Spas, agriculture, DH
Capture low-grade waste heat (≈€0), upgrade temperature, time-shift to demand.
Data centres, food, foundries
Stable geothermal base heat + variable solar top-up, smoothed by the store.
Pannonian spas, greenhouses, DH
Cheap spill-season electricity in; heat + optional power out for resilience.
Alpine/rural microgrids, Ukraine
Design principle. Size the store to the combined charging profile (multiple cheap inputs) and the single dischargeable load. Hybrid charging raises annual cycles and cuts the blended charge price — the two biggest levers on payback. For the +P tier, combine a firm source (geothermal/biomass/hydro) with a variable source (PV/wind) for the most resilient Carnot-battery configuration.
Nine customer segments sized, prioritised and mapped to the right sales motion — each with its best-fit charging sources.
Breweries, dairies, bakeries, food driers, ceramics, plastics, laundries
Pain: Expensive gas/peak power for 60–200 °C process heat; decarbonisation pressure
Charge: process waste heat (≈€0), off-peak/curtailed grid, on-site PV
Direct B2B + EPC; energy-audit-led
Glassworks, foundries, cement, aluminium
Pain: 500–1,500 °C heat + huge waste heat; ETS/CO₂ cost
Charge: high-grade waste heat (≈€0), off-peak/curtailed grid
Direct + EPC; waste-heat-recovery led
Greenhouses, dairy farms, fruit/herb drying, biogas plants
Pain: Winter greenhouse heat; use summer sun / biogas/geothermal waste heat
Charge: biomass/biogas CHP, geothermal, solar PV/thermal
Direct + ag cooperatives; subsidy-led
Hotels, wellness/spas, thermal baths, pools
Pain: Large constant DHW + pool heat; PV self-consumption
Charge: solar thermal, geothermal, PV surplus
Direct + HVAC installers
Offices, retail, schools, hospitals
Pain: Peak-shaving, PV self-use, comfort
Charge: PV surplus, off-peak grid
HVAC/ESCO channel
Velenje, Ljubljana, town DH operators
Pain: Flexibility, peak-boiler avoidance, solar/heat-pump integration, coal phase-out
Charge: curtailed wind/grid, waste heat, solar thermal, geothermal, biomass
Tender/EPC; long cycle
Off-grid sites, microgrids, critical facilities, Ukraine reconstruction
Pain: Blackout resilience; electricity + heat from one store (Carnot battery)
Charge: firm source (geothermal/biomass/hydro) + variable PV/wind
Project/B2B; grant-funded
Colocation, edge sites
Pain: Monetise/offload waste heat to DH or neighbours
Charge: server waste heat (low-grade) + heat-pump lift
Partnership/B2B
Homes with PV + heat pump
Pain: Self-consume PV, shift heating to cheap hours
Charge: PV surplus, off-peak grid
Installer channel + Eko Sklad
| Segment | Store Size | CAPEX (after subsidy) | Annual Saving | Payback | Net Benefit (20yr) | CO₂ Cut / yr |
|---|---|---|---|---|---|---|
| Residential | 20–40 kWh | €2,800–6,300 | €350–900 | 6–10 yr | €5,000–13,000 | 0.5–1.5 t |
| Commercial building | 0.1–1 MWh | €5,600–38,500 | €1,500–9,000 | 5–7 yr | €25,000–150,000 | 3–25 t |
| Hospitality / spa | 0.3–2 MWh | €17,500–84,000 | €4,000–20,000 | 5–8 yr | €60,000–300,000 | 8–45 t |
| Agriculture | 0.5–5 MWh | €21,000–175,000 | €6,000–45,000 | 4–7 yr | €90,000–650,000 | 12–90 t |
| Industrial process heat | 0.5–20 MWh | €14,000–490,000 | €5,000–180,000 | 4–7 yr | €80,000–2,600,000 | 15–500 t |
| High-temp industry | 5–100 MWh | €140,000–2,800,000 | €40,000–900,000 | 3–6 yr | €600,000–13,000,000 | 100–3,000 t |
| District heating / municipal | 5 MWh – GWh | Grant/co-funded | €60,000–3,000,000 | 6–12 yr | €1M–40M | 200–10,000 t |
Assumptions: ~30% subsidy, gross saving €8–12/kWh capacity/year for well-cycled C&I/agri, asset life 20–30 years.
Lower, predictable energy bills
Fast payback (4–8 yr C&I) vs 20–30 yr life
Decarbonisation & compliance
Subsidy capture (~20–40% lower CAPEX)
Resilience via optional +P tier
Higher PV self-consumption
Low operating burden
Brand & sustainability reporting
CAPEX benchmarks, savings formula, unit economics and funding levers.
| Storage Type | Low | High | Context |
|---|---|---|---|
| Sensible solid media (sand/rock/concrete) | €15 | €60 | Industrial heat-battery range |
| Large water pit (seasonal) | €0.4 | €0.6 | Danish pit stores (~€30/m³) |
| Water buffer tank | €1 | €10 | Standard hydronic; cheaper at scale |
| PCM / latent | €50 | €150 | Material-dependent, compact |
| Molten salt (CSP-type) | €20 | €60 | Utility scale |
| Li-ion NMC battery (for contrast) | €150 | €400 | Electricity storage — TES far cheaper for heat |
| LiFePO4 / LFP battery (for contrast) | €110 | €300 | Cheaper, safer Li chemistry; still electricity-only |
Storing energy as heat is ~10–30× cheaper per kWh than Li-ion/LFP when the end use is heat.
TES and batteries are not competitors for the same job — the right choice depends on the output the customer needs. A well-designed site often pairs an LFP battery (electricity) with a TES store (heat).
| Storage option | Stores → delivers | CAPEX basis | Round-trip | Duration | Response | Best-fit job |
|---|---|---|---|---|---|---|
| TES — sensible (sand/rock/concrete) | elec/heat → heat | €15–60/kWhth | 85–93% (heat) | hours–days | minutes | Cheap large-scale & high-temp heat |
| TES + Stirling/ORC (+P) | elec/heat → heat + electricity | +€800–3000/kWe | 40–70% (elec) | hours–days | minutes (warm) | Dispatchable power with heat; resilience |
| LiFePO4 / LFP battery | electricity → electricity | €110–300/kWh | 90–95% | 1–4 h | milliseconds | Electricity backup, fast response, PV self-use |
| Li-ion NMC battery | electricity → electricity | €150–400/kWh | 90–95% | 1–4 h | milliseconds | High energy density where space is tight |
| Lead-acid battery | electricity → electricity | €100–250/kWh | 75–85% | hours | milliseconds | Low-cost short backup/UPS |
| Sodium-ion battery | electricity → electricity | €80–250/kWh | 85–92% | 1–6 h | milliseconds | Emerging low-cost LFP alternative |
| Vanadium / redox flow | electricity → electricity | €250–600/kWh | 65–80% | 4–12 h | <1 s | Long-duration electricity, many cycles |
| Pumped hydro (PHES) | electricity → electricity | €40–120/kWh | 70–85% | 6–20 h | seconds | Bulk grid storage where geography allows |
| Compressed air (CAES) | electricity → electricity (+heat) | €40–150/kWh | 40–70% | 6–24 h | minutes | Long-duration bulk; cavern sites |
| Liquid air (LAES) | electricity → electricity (+heat/cold) | €100–300/kWh | 50–70% | 6–24 h | minutes | Siting-flexible long-duration |
| Flywheel | electricity → electricity | €1,000–5,000/kWh | 85–90% | seconds–min | milliseconds | Frequency/power quality, not energy |
| Green hydrogen / P2G | electricity → fuel/elec/heat | varies | 25–45% (e→e) | days–months | minutes | Seasonal/long-haul, hard-to-electrify |
Decision rule. Need heat (process, DHW, space, district)? → TES wins on cost (10–30×). Need fast electrical backup / 1–4 h power? → LFP wins. Need both heat and dispatchable power / blackout resilience? → TES + Stirling/ORC (+P) — the Svarog differentiator, especially for the Ukraine resilience market. Need seasonal? → water-pit / thermochemical TES (heat) or PHES/CAES/hydrogen (electricity).
AnnualSaving ≈ Ncycles × Qusable × (pdisplaced − pcharge / ηrt) − O&M
Ncycles = cycles per year · Q = usable heat per cycle · p = price per kWh · ηrt = round-trip efficiency
Site
Food producer, ~120 °C process heat
Daily heat
500 kWh
Charge price
€0.05/kWh
Displaced price
€0.09/kWh
Cycles/year
300
Round-trip η
90%
Gross spread
€0.034/kWh
System size
600 kWh
CAPEX @ €40/kWh
€24,000
Annual Saving
€5,100
Payback
~4.7 yr
Single-digit years; improved further by subsidy, CO₂ price and waste-heat charging.
Electricity VT (high)
€0.084/kWh
Electricity NT (low)
€0.070/kWh
Electricity ET (uniform)
€0.077/kWh
Non-household YoY
-16.6%
Gas excise
€0.00086/kWh
District heating
€25–93/MWh
Period: Nov 2024 – Feb 2025, energy component excl. VAT.
Estimate store size, CAPEX, annual savings and payback for a site. Adjust the inputs — results update live.
Net annual saving
€4,687
Payback (after subsidy)
3.6 yr
Store size
600 kWh
CAPEX (before subsidy)
€24,000
CAPEX (after subsidy)
€16,800
Effective spread
€0.034/kWh
Annual heat throughput
150,000 kWh
Gross annual saving
€5,167
O&M cost / yr
€480
Payback (before subsidy)
5.1 yr
~20-yr net benefit
€76,940
AnnualSaving ≈ Ncycles × Qdaily × (pdisplaced − pcharge / ηrt) − O&M
Same formula as §6 Economics. Order-of-magnitude planning estimate — validate per site (tariffs, load profile, subsidy eligibility).
Top 10 named Slovenian prospects with entry angles and priorities.
| # | Company | Segment | Why | Size | Entry Angle | Priority |
|---|---|---|---|---|---|---|
| 1 | Pivovarna Laško Union Heineken |
Brewery / food | Large constant 60–100 °C process heat & DHW; ESG targets; relatable reference | 1–10 MWh | Energy audit → process-heat pilot | High |
| 2 | Perutnina Ptuj MHP (Ukraine) |
Food / poultry | Big steady heat demand; Slovenia↔Ukraine bridge | 2–15 MWh | Corporate decarbonisation + bridge story | High |
| 3 | Steklarna Hrastnik | Glassworks | 1,000 °C+ furnaces, huge waste heat; high CO₂/ETS cost | 5–50 MWh | Waste-heat capture + high-temp store | High |
| 4 | Sava Hotels / Terme 3000 | Hospitality / spa | Constant pool + DHW heat; geothermal; PV self-consumption | 0.5–3 MWh | DHW/pool buffer + geothermal coupling | High |
| 5 | Paradajz (Lust) / Ocean Orchids | Agriculture | Year-round greenhouse heat; geothermal + summer-sun storage | 0.5–5 MWh | Seasonal/geothermal heat store; subsidy-led | High |
| 6 | Ljubljanske mlekarne Lactalis |
Dairy / food | Pasteurisation + CIP hot water; steady load | 1–8 MWh | Process-heat + waste-heat pilot | Medium |
| 7 | Talum | Aluminium | Energy-intensive; large waste heat; decarbonisation pressure | 10–100 MWh | Waste-heat → store → CHP/power | Medium |
| 8 | KP Velenje / HSE-TES (Šoštanj) HSE |
District heating / coal exit | Flagship coal-to-Carnot-battery; reuse turbines + DH grid | 10–1,000+ MWh | Just-transition flagship | High |
| 9 | Energetika Ljubljana | District heating | Large DH operator decarbonising; storage for flexibility | 10+ MWh | DH flexibility / integration tender | Medium |
| 10 | Thermana Laško / Terme Olimia / Terme Čatež | Hospitality / spa | Multiple spa sites = repeatable SKU | 0.3–2 MWh | Repeatable spa DHW/pool product | Medium |
Reuse turbines, generator, grid + existing DH network. EU just-transition funding. Flagship reference.
MHP ownership links Slovenian C&I market and Ukrainian opportunity through one relationship.
Reference vendors, regional partners and academia for R&D collaboration.
Sand battery (~600 °C, ~100 MWh)
Closest proof-of-concept to anchor product
Recycled granulate to ~1,300 °C
High-temp benchmark / possible licensor
Firebrick heat battery
Industrial decarbonisation benchmark
bGen crushed-rock modular TES
Modular commercial benchmark
Miscibility-gap alloy blocks
Novel media benchmark
Concrete Heatcrete modules
Concrete-module benchmark
Aluminium PCM 600 °C + Stirling
Heat-to-power precedent; defunct 2022 (lesson)
Stirling
ORC
Steam
sCO₂ / Brayton
TPV
Insulation supplier
Heat-pump manufacturer
High-temp heat pumps
ORC heat-to-power partner
Inverters / power electronics
Valves / controls
Faculty of Mechanical Engineering
National research institute
NAS Ukraine — thermal research
Power machinery & systems (NAS)
Igor Sikorsky KPI
National University
Citations and data sources behind every figure on this page.
| # | Category | Title | Source | Use |
|---|---|---|---|---|
| 1 | EU policy | European Commission — Heating and cooling | energy.ec.europa.eu | H&C share of energy; renewable share; EU H&C Strategy |
| 2 | EU data | Eurostat — Energy consumption in households | eurostat.ec.europa.eu | Space + water heating ~77.1% of household final energy (2024) |
| 3 | EU data | Eurostat — Electricity & gas price statistics | eurostat.ec.europa.eu | Non-household electricity price change SI -16.6% YoY |
| 4 | EU policy | Renewable Energy Directive (RED III) | EU/2023/2413 | Binding annual increases in renewable H&C; waste-heat provisions |
| 5 | Slovenia | Government of Slovenia / Agencija za energijo | gov.si | Regulated household tariffs; excise; market transition Mar 2025 |
| 6 | Slovenia | Eko Sklad | ekosklad.si | Grants/loans; subsidy increase Jun 2026; green-transition tax relief |
| 7 | Slovenia | District-heating statistics (SI) | — | ~22% coverage; 47/210 municipalities; ~1.7 GW; DH prices €25–93/MWh |
| 8 | Slovenia | HSE / TES (Šoštanj) | hse.si | Coal phase-out (~2033); Velenje DH network |
| 9 | Technology | Polar Night Energy | polarnightenergy.fi | Commercial sand battery (~600 °C, ~100 MWh, ~90% round-trip) |
| 10 | Technology | Wikipedia — Carnot battery | wikipedia.org | Definition; Thess/DLR 2018; round-trip 40–70%; study 57% |
| 11 | Technology | Wikipedia — Stirling engine | wikipedia.org | External-combustion regenerative engine; micro-CHP since 2003 |
| 12 | Technology | Azelio (Sweden) | — | Aluminium-PCM 600 °C + Stirling; bankruptcy 2022 (lesson) |
| 13 | Technology | Industrial heat-battery vendors | — | Rondo, Kraftblock, Brenmiller, MGA Thermal, EnergyNest |
| 14 | Technology | Heat-to-power vendors | — | ORC & Stirling vendor landscape |
| 15 | Technology | Danish seasonal pit stores | — | Vojens, Marstal (~€30/m³; ~90–92% seasonal efficiency) |
| 16 | Ukraine | Horizon Europe | ec.europa.eu | Ukraine association since June 2022 (consortium eligibility) |
| 17 | Ukraine | EU Ukraine Facility / EU4Energy / EBRD / USAID / MIGA | — | Reconstruction funding & war-risk insurance |
| 18 | Ukraine | Candidate research partners | — | Institute of Engineering Thermophysics; Pidhorny Institute; KPI; Lviv Polytechnic |
| 19 | Materials | Standard engineering references | — | cp, density, latent heat values for storage media (planning values) |
| 24 | Technology | Battery storage benchmarks (LiFePO4/LFP, NMC, lead-acid, sodium-ion) | IEA / NREL ATB / BNEF | CAPEX, round-trip, cycle life & safety for storage comparison (§6.1.1) |
| 25 | Technology | Long-duration & mechanical storage (PHES, CAES, LAES, flywheel, flow, H₂) | IEA / IRENA / DOE-PNNL | CAPEX, round-trip, duration & maturity for storage-alternatives matrix |
| 26 | Technology | Charging-source / renewable-resource references | JRC PVGIS / Global Wind Atlas / EGEC | Charge cost, temperature, seasonality & regional fit for charging sources (§8.3–§8.4) |