Hybrid Sand Thermal Battery for Heat Storage by Solar PV or Wind and for Thermal Oil Heat and ORC Power Generation Heat to Electricity and Desalination with Graphene Coated Sand Add On

Revolutionizing Energy Storage and Water Purification: The Sand Thermal Battery Hybrid

As the world transitions toward sustainable energy solutions, the challenge of energy storage and water desalination remains at the forefront. Traditional battery storage systems, such as lithium-ion and flow batteries, are often expensive, resource-intensive, and limited by degradation over time. A novel approach, the Sand Thermal Battery Hybrid, offers a sustainable and multi-functional solution by combining solar photovoltaics (PV), concentrated solar energy, thermal oil circulation, and desalination into a single, highly efficient system.

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Concept Overview: How the Sand Thermal Battery Hybrid Works

This innovative system is designed to store and utilize solar energy, generate electricity, and desalinate water within a single infrastructure. The design consists of a vertically stratified, insulated sand battery holding tank with key functional layers:

1. Bottom Layer – Solar PV-Driven Resistive Heating:

• Solar PV panels provide electricity to power resistive heating elements embedded in the bottom of the tank.

• This heat is absorbed by the sand, ensuring continuous energy storage even when sunlight is unavailable.

2. Middle Layer – Metal Tubes with Circulating Thermal Oil:

• Heat transfer is optimized with metal tubes that circulate thermal oil, allowing stored heat to be used in applications such as:

• Direct heating for industrial or residential purposes.

• Power generation via an Organic Rankine Cycle (ORC) turbine to produce electricity.

3. Top Layer – Saltwater Spray Nozzles for Desalination:

• Saltwater is sprayed over the heated sand, generating steam that rises through an insulated chamber.

• The steam is collected and condensed into fresh water outside the thermal battery.

• Leftover salt from desalination remains in the sand, enhancing thermal conductivity and efficiency of the system.

4. Standby Heating – Fresnel Lens Concentrated Solar Energy:

• Large Fresnel lenses focus sunlight onto the sand through insulated glass, providing an alternative heat source when PV electricity is unavailable.

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Three Core Functions of the Sand Thermal Battery Hybrid

This system combines multiple energy and water solutions in one, making it a game-changing technology for sustainable infrastructure.

1. Efficient Thermal Energy Storage

By utilizing both solar PV and concentrated solar heating, the system can store thermal energy effectively within sand. Unlike conventional lithium-based batteries, sand is abundant, non-toxic, and does not degrade over time. The addition of salt improves the heat retention capacity, allowing for higher efficiency in energy storage.

2. Renewable Power Generation via ORC Turbines

The stored heat can be used to power an Organic Rankine Cycle (ORC) turbine generator, converting the thermal energy back into electricity. This process enables grid-independent power production, especially in off-grid locations or industrial applications that require sustainable power generation.

3. Integrated Water Desalination for Freshwater Production

By leveraging high-temperature sand, this system can generate steam to produce fresh water from saltwater sources. The remaining salt is absorbed into the sand, enhancing its thermal storage efficiency rather than becoming a waste product. This feature makes the system highly valuable for coastal regions, desert areas, and islands where both water and energy are scarce.

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Key Advantages Over Conventional Energy and Water Solutions

| Feature | Sand Thermal Battery Hybrid | Lithium-Ion Batteries | Traditional Desalination (RO/Thermal) |

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

| Energy Storage Lifespan | Indefinite (No chemical degradation) | 5-15 years (Capacity fades over time) | N/A |

| Material Availability | Abundant (Sand & Salt) | Limited (Lithium, cobalt, nickel) | High for RO membranes |

| Thermal Storage | Uses sand & salt to retain heat | N/A | N/A |

| Electricity Generation | Can power ORC turbines | Direct discharge only | N/A |

| Water Desalination | Uses stored heat for steam desalination | N/A | Requires dedicated power sources |

| Environmental Impact | No hazardous waste, recyclable materials | Battery disposal issues, mining impact | High brine discharge in RO systems |

| Cost Efficiency | Low-cost materials, no replacement needed | Expensive materials, recurring costs | Energy-intensive, high operating costs |

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Potential Applications and Global Impact

1. Off-Grid and Remote Power Solutions

• The hybrid nature of the system allows it to function as both an energy storage unit and a power generator, making it ideal for remote villages, military outposts, and disaster relief operations.

2. Sustainable Industrial Heating

• Many industrial processes require high-temperature heat, which this system can provide using stored solar energy.

• Applications include metal processing, chemical production, and textile manufacturing.

3. Water Security in Arid Regions

• The integrated desalination function makes this system highly valuable in regions suffering from water scarcity.

• Islands and coastal communities could reduce their reliance on fossil-fuel-powered desalination plants.

4. Carbon-Free Grid Support

• This system could work in tandem with renewables like wind and solar farms to provide dispatchable energy without relying on chemical batteries.

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Challenges and Areas for Further Development

While the Sand Thermal Battery Hybrid presents a promising solution, there are challenges to address:

1. Optimizing Thermal Efficiency

• Research is needed to fine-tune the mixture of sand and salt for the highest heat retention properties.

2. Scaling the Desalination Output

• While the concept is sound, increasing efficiency in steam generation and condensation could improve freshwater yield.

3. Cost-Effective Manufacturing and Deployment

• Large-scale implementation will require cost-effective insulation materials and optimized designs to maximize efficiency.

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Conclusion: A Breakthrough in Renewable Energy and Water Security

The Sand Thermal Battery Hybrid represents a multi-functional, sustainable solution that combines energy storage, power generation, and desalination into one efficient system. By leveraging abundant materials like sand and salt, and utilizing solar PV, concentrated solar heating, and ORC technology, this approach provides a low-cost, long-lasting alternative to conventional batteries and desalination plants.

With further research and development, this hybrid system could become a cornerstone of renewable infrastructure, particularly in areas facing energy and water shortages. As the demand for sustainable and resilient solutions grows, the Sand Thermal Battery Hybrid could play a critical role in achieving energy independence and water security worldwide.

Comparing Sand Thermal Battery Desalination vs. Reverse Osmosis with Solar PV Panels

As water scarcity and energy sustainability become pressing global concerns, innovative desalination methods are emerging to provide fresh water from seawater. Two promising approaches include sand thermal battery desalination and reverse osmosis (RO), both powered by solar photovoltaic (PV) panels. This article examines the design, efficiency, costs, and viability of these systems.

System Overview

1. Sand Thermal Battery Desalination

The sand thermal battery is a low-cost and low-maintenance desalination method that uses solar energy to store heat and evaporate seawater. The system consists of an insulated steel drum filled with sand, resistive heating elements powered by solar PV panels, and a Fresnel lens for standby heating. The process works as follows:

• Solar PV panels power heating elements at the base of the sand battery.

• Sand retains heat, reaching temperatures of 240°C after six hours of charging.

• Saltwater is sprayed onto the heated sand, generating steam.

• The steam is condensed into fresh water outside the system.

• The remaining salt mixes with the sand, improving thermal storage efficiency.

This system operates passively, requiring no moving parts or external power beyond solar energy.

2. Reverse Osmosis Desalination

Reverse osmosis (RO) is a widely used desalination technology that relies on high-pressure pumps to push seawater through a semi-permeable membrane, removing salt and impurities. The system includes:

• Solar PV panels generating electricity to power the RO system.

• A high-pressure pump forcing seawater through membranes.

• A filtration system removing salt and contaminants.

• A freshwater collection tank.

While RO is highly efficient, it requires continuous power, filter replacements, and maintenance.

Comparison of Performance and Efficiency

Water Output and Energy Efficiency

| System | Fresh Water Output (Gallons per Day) | Energy Efficiency |

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

| Sand Thermal Battery | 6.05 gallons | Converts heat directly, but has low water output. |

| Reverse Osmosis (RO) | 1,245 gallons | Uses electricity efficiently to produce a large volume of water. |

• The RO system produces over 200 times more water per day than the sand thermal battery.

• The sand thermal battery operates without electricity once heated, while RO relies on continuous electrical input.

Capital Cost Comparison

| Cost Factor | Sand Thermal Battery | Reverse Osmosis (RO) |

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

| Sand Battery System (Including Barrel, Insulation, Piping) | $500 | N/A |

| RO System Equipment | N/A | $3,000 |

| Solar Panels (5 @ $199.78 each) | $998.90 | $998.90 |

| Solar Panel Installation | $200 | $200 |

| RO Installation | N/A | $500 |

| Total Initial Cost | $1,698.90 | $4,698.90 |

• The sand thermal battery is 64% cheaper than the RO system in terms of initial setup cost.

• The RO system requires specialized equipment, leading to a higher upfront investment.

Maintenance Costs

| System | Annual Maintenance Cost |

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

| Sand Thermal Battery | $0 |

| Reverse Osmosis (RO) | $300 |

• The sand thermal battery has no moving parts or filters, making maintenance negligible.

• RO systems require regular filter replacements, membrane cleaning, and servicing, leading to ongoing costs.

Long-Term Cost Projection

| Timeframe | Sand Thermal Battery (Total Cost) | Reverse Osmosis (Total Cost) |

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

| Year 1 | $1,698.90 | $4,698.90 |

| Year 5 | $1,698.90 | $6,198.90 |

| Year 10 | $1,698.90 | $7,698.90 |

• Over 10 years, the sand thermal battery maintains a fixed cost, while RO system costs increase to nearly $7,700 due to maintenance.

• The sand battery is 4.5 times cheaper in total ownership cost over a decade.

Which System is the Better Choice?

Choose the Sand Thermal Battery If:

• You need a low-cost, low-maintenance desalination solution.

• You have limited access to electricity or require a fully off-grid system.

• A small, passive water source is sufficient for needs such as remote communities, disaster relief, or desert environments.

Choose Reverse Osmosis If:

• You need large-scale freshwater production.

• You can afford higher upfront and maintenance costs.

• A steady supply of drinking water is required, making efficiency more critical than capital cost.

Conclusion

The choice between a sand thermal battery desalination system and a reverse osmosis system depends on cost, efficiency, and water needs. The sand thermal battery offers an affordable, off-grid solution, while reverse osmosis provides significantly higher water output at a higher financial investment.

For small-scale, low-tech, and sustainable desalination, the sand thermal battery is an excellent choice. However, for large-scale, high-efficiency desalination, RO remains the superior technology despite higher costs.

Both solutions demonstrate how solar energy can be harnessed to address water scarcity and sustainable energy challenges worldwide.

Compare Cost Per BTU of Solar PV to a Heat Pump

To calculate the cost per BTU using solar PV panels and compare it to a heat pump with a COP of 4.0, let's define some key assumptions:

Solar PV Cost per BTU

1. Solar PV Efficiency: ~20% (typical for commercial panels)

2. Installed Cost of Solar PV: $1.50 per watt (approximate value for utility-scale solar)

3. Lifespan of Solar Panels: 25 years

4. Capacity Factor: 20% (realistic for most locations)

5. Energy Production Over 25 Years:

• 1 watt of installed capacity = \( 1 \times 0.2 \times 24 \times 365 \times 25 = 43,800 \) watt-hours

• 1 watt-hour = 3.412 BTU

• Total BTU over 25 years: \( 43,800 \times 3.412 = 149,514 \) BTU per installed watt

Cost per BTU for Solar PV:

\[

\frac{\$1.50}{149,514} = 0.00001004 \text{ USD per BTU} \text{ (or 0.001 cents per BTU)}

\]

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Heat Pump Cost per BTU (COP 4.0)

1. COP = 4.0 means 1 kWh of electricity produces \( 4 \times 3,412 = 13,648 \) BTU of heat.

2. Electricity Cost: Assume $0.10 per kWh (utility-scale average)

3. Cost per BTU:

\[

\frac{\$0.10}{13,648} = 0.00000733 \text{ USD per BTU} \text{ (or 0.00073 cents per BTU)}

\]

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Comparison

| Source | Cost per BTU (USD) | Cost per BTU (cents) |

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

| Solar PV | 0.00001004 | 0.00100 |

| Heat Pump (COP 4.0) | 0.00000733 | 0.00073 |

• A heat pump with a COP of 4.0 is about 27% cheaper per BTU compared to direct electricity from solar PV.

• This is because the heat pump multiplies energy efficiency by extracting heat from the environment.

Would you like further breakdowns, such as for different COP values or electricity costs?

Heat Pump Temperature

The highest temperature a CO₂ heat pump can achieve depends on system design, pressure, and heat exchanger efficiency. Transcritical CO₂ heat pumps operate at high pressures and can reach much higher temperatures than traditional refrigerants.

Key Factors Determining Maximum Temperature:

1. Transcritical Operation – Unlike traditional refrigerants, CO₂ operates above its critical point (31°C, 7.38 MPa), allowing it to reach very high discharge temperatures.

2. Compressor Design – High-efficiency, high-pressure compressors enable higher temperature outputs.

3. Gas Cooler Efficiency – Instead of a condenser, CO₂ systems use a gas cooler to extract heat efficiently.

Maximum Achievable Temperatures

• Commercial CO₂ heat pumps: ~90–120°C (194–248°F)

• Industrial CO₂ heat pumps: ~150°C (302°F)

• Lab-scale or extreme pressure systems: 200°C+ (392°F+)

Examples of High-Temperature CO₂ Heat Pumps

• Mitsubishi Q-ton: ~90°C (194°F)

• Mayekawa CO₂ Heat Pumps: ~120°C (248°F)

• Advanced Industrial Systems: Up to 150°C (302°F)

Theoretical Limitations

• Discharge temperature depends on compression ratio

• High pressures (~10 MPa or more) are required for extreme temperatures

• Heat exchangers must handle high-temperature, high-pressure CO₂ safely

Would you like to explore how to optimize a CO₂ heat pump for a specific application?

Temperature to Convert Sand into Sand Coated with Graphene

To convert sand and sugar into graphene-coated sand using the batch method with sugar at the bottom and biochar on top, the process requires pyrolysis and graphitization temperatures. Here’s a breakdown of the required temperature range:

Key Reactions & Temperature Requirements:

1. Carbonization of Sugar → Amorphous Carbon (200–400°C)

• Sugar thermally decomposes into carbonaceous material at ~200–400°C.

• Intermediate stage: formation of hydrocarbons and tars.

2. Graphitization of Sugar-Derived Carbon → Graphene (800–1000°C)

• At 800–1000°C, amorphous carbon from sugar rearranges into graphene-like structures.

• Requires a catalyst (e.g., sand containing silica or iron impurities) or slow pyrolysis.

• 900°C+ improves the quality and conductivity of graphene.

3. Silica-Sand Interaction → Graphene Coating on Sand (900–1100°C)

• At temperatures of 900–1100°C, the carbon source (sugar-derived carbon) reacts with the silica (SiO₂) from sand.

• This enables the graphene layer to bond to the sand surface.

• If biochar has trace iron, nickel, or magnesium, it can act as a catalyst for graphene formation.

Optimal Process Temperature:

• Recommended: 1000–1100°C for strong graphene bonding and high-quality graphene layers on sand.

Harnessing Solar PV and Sand Battery Technology for High-Temperature Applications

Introduction

The combination of solar photovoltaic (PV) energy and sand battery technology has the potential to provide high-temperature heat storage and utilization. One promising application is the production of graphene-coated sand, which requires temperatures between 900 and 1100 degrees Celsius. This article explores the feasibility of using a solar PV-powered sand battery to achieve these high temperatures and the necessary optimizations to make the system effective.

Understanding Sand Battery Technology

A sand battery stores thermal energy by converting electricity into heat, which is then retained within a high-temperature silica sand medium. Traditional applications of sand batteries, such as those developed by Polar Night Energy, have demonstrated heat retention at temperatures up to 600 degrees Celsius. However, with optimized design and power input, sand batteries can potentially reach 1000 degrees Celsius or more, making them suitable for advanced thermal applications like graphene-coated sand production.

Temperature Requirements for Graphene-Coated Sand

The process of coating sand with graphene involves several key steps:

• Carbonization of Sugar (200-400 degrees Celsius): Sugar thermally decomposes into amorphous carbon, forming an initial carbon layer on the sand.

• Graphitization (800-1000 degrees Celsius): The amorphous carbon rearranges into graphene-like structures.

• Silica-Sand Interaction (900-1100 degrees Celsius): At high temperatures, the carbon interacts with the silica surface of the sand, bonding to form a stable graphene layer.

Can a Solar PV-Powered Sand Battery Reach 900-1100 Degrees Celsius?

Achieving these temperatures with a sand battery requires specific enhancements:

1. High-Temperature Heating Elements

• Resistive heating elements made from nickel-chromium (NiCr) or molybdenum disilicide (MoSi₂) can handle temperatures exceeding 1000 degrees Celsius.

• Induction heating can be used if the sand contains ferrous impurities, enabling faster and more uniform heating.

2. Improved Thermal Insulation

• The use of high-temperature ceramic insulation, such as alumina or zirconia, can reduce heat loss and maintain stable high temperatures.

• A well-insulated sand battery can retain heat for extended periods, ensuring efficient thermal energy utilization.

3. Increased Power Input and Heating Time

• A higher power input from solar PV arrays will accelerate heating.

• Larger thermal mass (more sand) requires longer heat-up times but provides more stable thermal energy storage.

4. Optimized Heat Transfer Mechanisms

• Uniform heat distribution is essential to ensure even graphene formation on sand particles.

• A controlled atmosphere, such as an inert gas environment (argon or nitrogen), can help prevent oxidation and improve graphene quality.

Comparing Solar PV and Alternative High-Temperature Heating Methods

While a solar PV-powered sand battery is a feasible solution, alternative approaches may enhance efficiency:

• Concentrated Solar Power (CSP): Can achieve temperatures exceeding 1500 degrees Celsius and may be integrated with a sand battery.

• Direct Induction Heating: Provides faster heating compared to resistive elements, reducing overall energy consumption.

• Hybrid Systems: Combining a sand battery with carbon-based heating, such as biochar-assisted conductive heating, could improve efficiency and heat transfer.

Conclusion

A solar PV-powered sand battery can potentially reach 900-1100 degrees Celsius with proper system design and optimization. Key factors include high-temperature heating elements, enhanced insulation, increased power input, and optimized heat transfer. By leveraging advancements in thermal energy storage and solar PV technology, it is possible to create a scalable and sustainable solution for high-temperature applications such as graphene-coated sand production. Ongoing research and development will be essential to refine the efficiency and economic viability of this approach.

Benefits of a Sand Battery

A sand battery is not an efficient candidate for electricity generation using an Organic Rankine Cycle (ORC) system, as the required heat rate of 40,000 BTU/kWh means significant losses when converting stored thermal energy back into electricity. However, sand thermal batteries have several advantages in other applications where heat, rather than electricity, is the primary output.

Key Benefits of a Sand Thermal Battery

1. High-Temperature Energy Storage

• Sand can store heat at temperatures up to 1000–1200°C, making it ideal for applications requiring direct thermal energy rather than electricity.

• Unlike phase change materials (PCMs), sand does not degrade over time, making it a durable storage medium.

2. Low Cost and Readily Available Material

• Sand is abundant, inexpensive, and non-toxic, unlike lithium-ion batteries or other exotic thermal storage materials.

• It does not require rare metals or complex processing for use in energy storage.

3. Long-Term Heat Retention

• With proper insulation, a sand battery can store heat for days or even weeks with minimal losses, making it suitable for seasonal energy storage in cold climates.

4. Efficient for Industrial Process Heat

• Many industrial processes, such as steel production, cement manufacturing, and chemical processing, require direct heat rather than electricity.

• A sand battery can efficiently provide process heat without the energy losses associated with converting heat into electricity.

5. District Heating and Space Heating Applications

• In regions with cold climates, sand batteries can store excess solar or wind energy and provide district heating or residential heating during winter months.

• This approach is more efficient than converting heat to electricity and back to heat.

6. Grid Load Balancing and Demand Management

• A sand battery can store excess renewable energy during periods of low electricity demand and release heat when needed, helping to stabilize the grid.

• It can reduce reliance on fossil-fuel-based heating systems, thereby lowering carbon emissions.

7. Scalability and Modularity

• Sand battery systems can be modularly expanded to meet various heat demands, making them a flexible option for energy storage.

• Unlike chemical batteries, they do not degrade with charge cycles, providing long-term storage solutions.

8. Resilience and Off-Grid Applications

• In remote locations or off-grid setups, sand batteries can store energy from solar PV or wind turbines for later use in heating applications without needing grid infrastructure.

Conclusion

While sand batteries are not ideal for electricity generation via ORC systems, they excel in direct heat applications such as industrial heating, district heating, and seasonal thermal storage. Their low cost, durability, and efficiency in thermal energy retention make them a viable alternative to chemical batteries in heat-based energy storage scenarios.

Would you like to explore specific applications for a sand thermal battery in your projects?

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

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