Sand Salt Battery with Supercritical CO2 Hydraulic Power Pack for 16 mm BTU of Energy Storage and 1,500 tons Chiller Cooling or 840 kW of Grid Scale Power in one 40 Foot ISO Shipping Container

Optimized Thermal Energy Storage Using Sand and Salt with Thermal Oil Heat Exchange in Shipping Containers

Discover how a standard 40-foot shipping container filled with sand and salt can be transformed into an efficient thermal energy storage unit using a multi-layered thermal oil pipe layout. This setup offers over 16 million BTU of energy capacity with fast charge and discharge performance through 2-inch steel heat exchanger pipes.

By embedding 2-inch steel thermal oil pipes in a layered serpentine configuration within a 40-foot shipping container filled with a sand-salt mix, thermal energy storage can be optimized for rapid heat charge and discharge. This system offers over 16 million BTU of thermal capacity and is ideal for integration with industrial waste heat, solar thermal, or off-peak grid energy.

Optimized Thermal Storage Using Sand, Salt, and Thermal Oil in Shipping Containers

A standard 40-foot shipping container can be repurposed into a powerful thermal energy storage unit by filling it with a 50/50 mix of sand and salt and embedding steel heat exchanger pipes for thermal oil circulation. This configuration leverages the high thermal mass of granular solids and the fluid dynamics of thermal oil to store and transfer heat efficiently.

Thermal Mass and Energy Capacity

The 40-foot container, with internal dimensions of approximately 12.03 meters in length, 2.35 meters in width, and 2.39 meters in height, provides a usable internal volume of about 67.6 cubic meters (2,386 cubic feet). After accounting for pipe volume and flow channels, approximately 66.9 cubic meters (2,362 cubic feet) of the space can be filled with the sand-salt mixture.

Thermal Mass Calculation

Average density of 50/50 sand and salt mix: 1,400 kg/m³ (87.5 lb/ft³)

Average specific heat capacity: 0.205 BTU/lb·°F (0.86 kJ/kg·K)

Total mass: ~93,700 kg (206,675 lbs)

Thermal capacity: ~42,368 BTU/°F (44.7 MJ/°C)

Usable temperature swing (example): 100°F to 500°F (ΔT = 400°F)

Total energy storage:

BTU: 42,368 BTU/°F × 400°F = 16,947,200 BTU

Metric: 44.7 MJ/°C × 222°C = 9,923 MJ (\~2,756 kWh)

Optimized Heat Exchange Pipe Layout

To ensure fast charging and discharging of thermal energy, an optimized pipe layout is required. The system uses 2-inch outer diameter steel pipes arranged in a horizontal serpentine configuration across multiple vertical layers within the container.

Layout Highlights

Approximately 14–15 horizontal layers

Each layer with 5–6 lateral serpentine passes

Total pipe length: ~3,000 feet (914 meters)

Horizontal and vertical spacing: 6–12 inches

Total heat exchanger surface area:

π × 2 in × 3,000 ft = 1,570 ft² (146 m²)

Heat Transfer Capability of 2-Inch Steel Pipes

Using thermal oil as the working fluid (e.g., Dowtherm or Therminol), the embedded steel piping system can achieve high rates of heat exchange.

Example Performance:

Pipe ID: 1.61 inches

Flow rate: 10–20 gallons per minute (GPM)

Thermal oil specific heat: ~0.45 BTU/lb·°F

Thermal oil density: ~7.5 lb/gallon

Heat transfer rate per loop:

Q = mass flow × specific heat × ΔT

At 20 GPM, ΔT = 100°F:

Q = (20 × 7.5) × 0.45 × 100 = 6,750 BTU/min = 405,000 BTU/hr

(≈ 119 kW thermal input/output per loop)

With 3–5 parallel loops, total heat input/output can reach:

BTU/hr: 1 to 2 million BTU/hr

Metric: 293 to 586 kW thermal charge/discharge capacity

Applications and Use Cases

• Industrial waste heat recovery

• Solar thermal energy storage

• Thermal buffering for on-demand steam or hot air generation

• Off-peak electricity-to-heat conversion

• Grid-scale heat storage for power-to-heat-to-power cycles

Conclusion

By leveraging the high thermal mass of sand and salt and optimizing the internal heat exchanger layout with 2-inch steel pipes, a standard 40-foot shipping container can be converted into a modular, high-capacity thermal energy storage system. Capable of storing up to 17 million BTU or 2,756 kWh, and transferring over 1 million BTU/hr, this system is well-suited for industrial, renewable, and grid-level thermal energy applications.

Solar Thermal Battery Drives High-Capacity Chilling for Off-Grid Cooling

Discover how a 40-foot sand-salt thermal battery with concentrated solar input can power thermally or electrically driven chillers, delivering over 1,500 tons of cooling-hours—ideal for off-grid or industrial cooling.

A single thermal battery using sand-salt storage and rooftop solar collectors can provide over 1,500 tons of cooling, delivering up to 127 tons per hour using high-efficiency chillers. This scalable system offers renewable-driven cooling for industrial or remote applications.

Solar Thermal Battery as a Renewable Cooling Source

A 40-foot shipping container filled with a 50/50 sand and salt mixture, equipped with concentrated solar panels and internal thermal oil piping, becomes a robust off-grid thermal battery. When paired with a chiller system—either thermally or electrically driven—it delivers substantial and sustained cooling capacity.

Two Approaches to Cooling

• Absorption Chiller (Thermal-Driven)

• Uses thermal energy directly via lithium bromide absorption system

COP: ~0.7

Cooling output: ~989 tons of cooling-hours

Ideal for locations where electricity is limited

Electric Chiller (Power-Driven)

• Uses power generated from heated supercritical CO₂ driving a turbine

COP: ~6.0

Cooling output: ~1,525 tons of cooling-hours

Delivers up to 127 tons/hour over 12 hours

Cooling Delivery Profiles

System Type 1-Hour Burst 12-Hour Avg 24-Hour Avg

Absorption Chiller 989 tons 82.4 tons/hr 41.2 tons/hr

Electric Chiller 1,525 tons 127.1 tons/hr 63.5 tons/hr

Use Cases

• Data center cooling

• Cold storage in agriculture

• Emergency or disaster zone chilling

• Industrial HVAC in off-grid regions

Conclusion

This integrated solar-thermal battery system delivers flexible, scalable cooling power using stored heat and smart conversion technology. Whether you need high-power bursts or round-the-clock chilling, this solution bridges renewable thermal storage with practical cooling demands.

Thermal Battery Power Output Using ORC or Supercritical CO₂ Turbine Generator at 40,000 BTU/kWh

Explore how a 40-foot container thermal battery filled with sand and salt can generate electricity using an Organic Rankine Cycle or supercritical CO₂ turbine with a heat rate of 40,000 BTU per kilowatt-hour. Includes power output estimates for 1-hour, 12-hour, and 24-hour discharge cycles.

By converting thermal energy stored in a sand-salt thermal battery through an ORC or supercritical CO₂ turbine, a standard 40-foot container can produce nearly 1,250 kWh of electricity. Learn how this system performs over short and long discharge durations using a 40,000 BTU/kWh heat rate.

Thermal Battery Electricity Output Using ORC or Supercritical CO₂ Turbines

A 40-foot shipping container filled with a 50/50 mix of sand and salt can serve as a high-capacity thermal battery. By integrating this system with a turbine generator—either an Organic Rankine Cycle (ORC) or a supercritical CO₂ expander—the stored heat can be converted into usable electricity.

In this analysis, we calculate the expected power generation based on a standard Heat Rate of 40,000 BTU per kilowatt-hour (kWh), which is common for low• to medium-efficiency waste heat recovery turbines.

Stored Thermal Energy

The container holds approximately 16.95 million BTU of usable thermal energy, based on the thermal mass and a temperature swing from 100°F to 500°F:

BTU: 16,947,200

Metric equivalent: ≈ 4,965 kWh of heat energy

Heat Rate and Conversion to Electricity

Using the heat rate of 40,000 BTU/kWh, the maximum potential electric output is:

> 16,947,200 BTU ÷ 40,000 BTU/kWh = 423.68 kWh

This is the total electrical energy that can be extracted if the turbine generator maintains a 40,000 BTU/kWh heat rate.

Output by Timeframe

To understand how this energy can be used over time, we calculate the constant power output for 1-hour, 12-hour, and 24-hour periods.

1-Hour Discharge

Total Power Output: 423.68 kWh

Continuous Output: 423.7 kW

12-Hour Discharge

Total Power Output: 423.68 kWh

Continuous Output: 35.3 kW

24-Hour Discharge

Total Power Output: 423.68 kWh

Continuous Output: 17.65 kW

Summary Table

| Discharge Duration | Total Electrical Output | Average Power Output |

| -----------------| ----------------------| -------------------|

| 1 hour | 423.7 kWh | 423.7 kW |

| 12 hours | 423.7 kWh | 35.3 kW |

| 24 hours | 423.7 kWh | 17.65 kW |

Applications

This system is well suited for:

• Off-grid renewable integration

• Industrial waste heat reuse

• Grid peak shaving

• Energy arbitrage (charging from cheap heat, discharging during high demand)

Conclusion

With a 40,000 BTU/kWh heat rate ORC turbine system, a single thermal battery made from a 40-foot shipping container filled with sand and salt can generate approximately 423.7 kWh of electricity. The power output can be tuned to deliver high peak power for short durations or a stable baseline output over extended periods such as 12 or 24 hours. This setup is scalable and can serve as a cornerstone for thermal energy-to-electricity systems in industrial or grid-scale applications.

More sand/salt containers can be used with one ORC turbine generator system, making this configuration scalable by adding thermal storage containers.

Sand Salt Battery Utilizing Supercritical CO2 to drive a Hydraulic Pump

Concept: using a thermal battery (sand-salt mixture in a 40-foot container) to heat CO₂ to supercritical conditions and then drive a hydraulic pump:

1. Available thermal energy

2. CO₂ heating and expansion capacity

3. Mechanical output in terms of hydraulic horsepower (HP) and gallons per minute (GPM)

4. Feasibility for 1-hour, 12-hour, and 24-hour continuous discharge

1. Thermal Energy Storage Recap

Optimized container setup:

Stored thermal energy:

≈ 16.95 million BTU

≈ 4,965 kWh

≈ 17.9 billion joules (MJ: 17,900)

2. CO₂ Expansion to Drive Hydraulic Pump

Supercritical CO₂ Key Properties:

Critical point: ~31°C (88°F) and 1,070 psi

Operating target: ~500°F (260°C), ~2,000–3,000 psi

Expansion drives turbine or piston, which powers a hydraulic pump

Assume:

CO₂ loop runs through a high-temperature heat exchanger inside the thermal battery

Supercritical CO₂ drives an expander (piston or turbine)

Expander is mechanically coupled to a hydraulic pump

3. Efficiency Assumptions

We’ll break the energy flow into conversion steps:

| Step | Process | Efficiency Estimate |

| ----------| ----------------------------| --------------------|

| A | Heat → CO₂ mechanical energy | 20–25% |

| B | Mechanical → hydraulic energy | 90% |

| Overall | Thermal → hydraulic output | ~20% x 0.9 = 18% |

4. Hydraulic Power Output Calculations

Total available mechanical energy:

18% of 16.95 million BTU =

≈ 3.05 million BTU →

≈ 894 kWh

≈ 3.22 billion joules

Convert to horsepower-hours:

1 HP = 746 watts

894 kWh = 1,198 HP-hours

5. Hydraulic Output Scenarios

We can now divide output over 1-hour, 12-hour, and 24-hour operation windows:

| Duration | Power Output (HP) | Power Output (kW) |

| -------| ----------------| ----------------|

| 1 hour | 1,198 HP | 894 kW |

| 12 hours | 100 HP | 74.5 kW |

| 24 hours | 50 HP | 37.3 kW |

6. Gallons per Minute (GPM) Equivalent

Hydraulic power in HP is given by:

> HP = (PSI × GPM) / 1714

Assume working pressure:

2,000 psi

Solve for GPM:

> GPM = (HP × 1714) / PSI

| Duration | HP | GPM @ 2,000 psi |

| -------| ----| --------------|

| 1 hour | 1,198 | 1,027 GPM |

| 12 hours | 100 | 85 GPM |

| 24 hours | 50 | 43 GPM |

GPM would double if operating at 1,000 psi, halve at 4,000 psi.

Final Assessment

Thermal Battery as Hydraulic Energy Source:

Thermal capacity: 16.95 million BTU

Hydraulic power potential (after 18% conversion efficiency):

~1,198 HP-hours of usable mechanical energy

Discharge Flexibility:

1-hour burst: ~1,198 HP (~1,027 GPM @ 2,000 psi)

12-hour sustained: 100 HP (~85 GPM)

24-hour sustained: 50 HP (~43 GPM)

Use Case Fit

This setup is ideal for:

• Off-grid hydraulic applications

• Peak-time power assist

• Industrial hydraulic presses or pumping

• Load-leveling with thermal energy storage and mechanical output

TEL: 1-608-238-6001 Email: greg@infinityturbine.com

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CONTACT TEL: 1-608-238-6001 Email: greg@infinityturbine.com (Standard Web Page) | PDF