Karnot iSTOR P58 Thermal Battery
Thermal storage solution for decarbonising heating and hot water
The Karnot iSTOR P58 provides highly efficient, low-carbon heating for commercial buildings and industrial processes. Up to three times smaller than the equivalent hot water based thermal store, the iSTOR P58 is a space-saving alternative to water tanks and buffer vessels used in buildings for buffering heat.
Key Features & Advantages
Engineered for maximum energy density and operational flexibility — the iSTOR P58 delivers powerful thermal storage in a compact, efficient package.
High Energy Density
Delivers a nominal storage capacity of 80 kWh in a compact form, making it an ideal replacement for bulky hot water tanks.
Powerful & Flexible Output
Features two independent hydronic circuits (High Power and Low Power) that can be configured to suit any application and load requirement.
Rapid Charge & Discharge
High flow rates allow the battery to be charged quickly from any heat source and to deliver high-temperature hot water on demand.
Minimal Standby Loss
Engineered for maximum retention, with a low standby energy loss of just 3.0 kWh per 24 hours.
Technical Specifications
Comprehensive specifications for system design and installation planning.
Performance & Capacity
| Nominal Storage Capacity | 80 kWh273 kBTU |
| Standby Stored Energy Loss Rate | 3.0 kWh / 24h10.2 kBTU / 24h |
| Design Discharge Outlet Temperature | 54°C129.2°F |
| Charging Source Temperature | 65°C to 80°C149°F to 176°F |
Operational & Physical
| Max Flow Rate (High Power Circuit) | 50 L/min13.2 gal/min |
| Max Flow Rate (Low Power Circuit) | 40 L/min10.6 gal/min |
| Maximum Working Pressure | 1.6 MPa (16 bar) |
| Dimensions (W × D × H) | 1200 × 1000 × 1470 mm47″ × 39″ × 58″ |
| Weight | 1,402 kg3,091 lbs |
Additional Advantages
Beyond core performance, the iSTOR P58 delivers system-wide benefits that transform how you manage thermal energy.
System Benefits
- Charges from multiple energy and heat sources
- Decouples heat sources from heating demands
- Offers demand side management and shifts heating loads to cheaper off-peak tariffs
- Reduces pre-heat time required in buildings
- Modular and scalable — thermal batteries can be connected in series or in parallel to increase heat storage capacity
- Combines with HVAC&R equipment, and integrates solar thermal and solar PV systems with existing heating plant
Lower Costs
A Karnot iSTOR P58 thermal battery is clean and fast to install. There's no need to increase the size of expansion vessels nor the volume of water treatment chemicals. Running costs are also low because mandatory annual maintenance and inspections are not required.
Note: As an innovative company committed to continuous improvement, our products are subject to change without prior notice. Always refer to the latest version of this document.
Ready to Optimise Your Thermal Storage?
Contact our technical team for system design assistance and detailed project specifications.
Contact SalesFrequently Asked Questions
Quick answers to the questions most commonly raised by engineers and facility managers evaluating the iSTOR P58.
What is the Karnot iSTOR P58 thermal battery?
The iSTOR P58 is a high-density phase change material (PCM) thermal battery with 80 kWh nominal storage capacity. It stores energy as heat rather than electricity, charging from a heat pump or other heat source at 65–80°C and discharging hot water at 54°C through two independent hydronic circuits. Footprint is 1200×1000×1470 mm and weight is 1,402 kg.
How is a PCM thermal battery different from a hot water tank?
A PCM thermal battery stores energy in a phase change material that absorbs and releases large amounts of heat at a near-constant temperature, giving up to 3× the energy density of an equivalent water tank. The iSTOR P58 holds 80 kWh in a 1.2 m³ cabinet — a water tank would need roughly 3 m³ for the same usable energy. Standby loss is also lower at 3.0 kWh per 24 hours, and there is no annual maintenance or water treatment chemistry to manage.
Why use a thermal battery instead of a lithium battery for heating loads?
For sites whose load is heating, cooling, or hot water (most industrial and commercial sites in the Philippines), storing energy as heat directly is typically 5–10× cheaper per kWh than storing it as lithium electricity and then converting it back. There are no rare earths, no fire risk, no chemistry that degrades, and no thermal runaway concerns at high tropical ambient temperatures.
How does the iSTOR P58 pair with a Karnot iHEAT heat pump?
The iHEAT R290 heat pump charges the iSTOR P58 through its high-pressure circuit at 65–80°C, typically during daytime solar generation or off-peak tariff windows. The stored heat is then discharged through the low-pressure circuit at 54°C to meet hot water or space heating demand on the customer schedule. This decouples generation from demand and lets the heat pump run at its most efficient operating point.
Is the iSTOR P58 suitable for tropical Philippine conditions?
Yes. The PCM medium is non-flammable and unaffected by high ambient temperatures, and the system is rated to 1.6 MPa (16 bar) working pressure. Unlike lithium-ion batteries, there is no thermal runaway risk in Philippine ambient conditions, which makes the iSTOR P58 well-suited to plant rooms, factory floors, hotel basements, and other commercial installations across Luzon and Visayas.
Can multiple iSTOR P58 units be connected together?
Yes. The iSTOR P58 is modular and scalable. Multiple units can be connected in series or in parallel to increase total heat storage capacity. This allows the system to be sized to the actual customer load profile and expanded later as demand grows, without replacing existing equipment.
What maintenance does the iSTOR P58 require?
The iSTOR P58 has no mandatory annual maintenance or inspection requirement. There is no expansion vessel sizing to increase, no water treatment chemistry to manage, and no pressurised gas charge to monitor. Running costs are minimal compared to traditional water-based thermal stores.