Is it possible to generate electricity from the heat emitted by sunbaked desert sand?

While the idea of harnessing electricity from the heat of sunbaked desert sand may seem promising, it is not feasible on a large scale. The heat is typically diffuse and not concentrated enough to be useful. However, recent advancements in technology offer potential solutions to store and utilize this heat.

Theoretical Limitations and Practical Insights

The heat emitted by sunbaked desert sand, though intense at the surface, is too diffuse to be efficiently collected and utilized for electricity generation. Sand is a good insulator, and any stored heat would quickly dissipate. While the surface of the sand can reach high temperatures, the heat is only skin-deep, making it a poor candidate for direct power generation.

Instead of attempting to utilize this heat directly, researchers are exploring more targeted approaches. One such method is utilizing concentrated sunlight to heat materials to very high temperatures. This strategy allows for a more effective and efficient conversion of thermal energy into electrical power.

Storing Wind and Solar Power with Silica Sands

A significant breakthrough in this field was made by researchers at the National Renewable Energy Laboratory (NREL). They proposed using sunbaked desert sand, specifically silica sand, as a medium for storing excess wind and solar power. This material is not only readily available and inexpensive but also stable and non-reactive.

The proposed technology, called Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle (ENDURING), was designed to address the scalability and cost challenges of traditional energy storage methods. NREL researchers theorize that silica particles can be heated to high temperatures and stored for extended periods, providing a continuous source of heat for industrial and chemical processes as well as power generation.

Technical Details of the ENDURING System

The baseline system designed by NREL can store a capacity of up to 26,000 MWh, with costs ranging from $2 to $4 per kWh. The technology works by heating silica particles through an array of electric resistive heating elements to around 1200 degrees Celsius. These particles are then deposited in insulated concrete silos for thermal energy storage.

When energy is needed, the hot particles are gravity-fed through a heat exchanger, which heats and pressurizes a working gas. This gas drives turbomachinery and spin generators to create electricity for the grid. Once discharged, the spent particles are again stored in insulated silos until conditions and economics allow for recharging.

This system offers a scalable solution that can be deployed almost anywhere, making use of existing infrastructure such as retired coal and gas-fired power plants. The cost-effectiveness and potential for large-scale deployment make it a promising option for addressing energy storage needs in both urban and rural areas.

Alternative Methods: Falling-Particle Receivers and Brayton Cycle

Another approach involves the use of falling-particle receivers, which directly heat sand or manufactured particles using a beam of concentrated sunlight. The particles are heated as they fall through open air and stored in an insulated bin. These heated particles pass through a particle-to-working-fluid heat exchanger, simulating a high-efficiency Brayton cycle using supercritical carbon dioxide (sCO2) with an exit temperature of 720°C.

This method presents a more efficient way to convert thermal energy into useful power. The silica sand-based solution, while currently in the testing phase, shows significant potential for large-scale energy storage applications.

Conclusion

While the direct conversion of heat from sunbaked desert sand into electricity is not practical, innovative approaches such as silica sand-based thermal energy storage offer promising solutions for storing and utilizing renewable energy. These technologies not only address the scalability and cost challenges of traditional storage methods but also provide a sustainable and cost-effective way to meet the growing demands of the energy grid.