Complex Made Simple

How sand is now a treasured tool for saving energy

Have you ever walked on a sandy beach barefoot, on a hot summer day, and nearly burned your feet? Well, that finally gave rise to new renewable energy technologies

ENDURING takes excess energy generated from wind and solar power and uses it to superheat silica sand Heliostats captures sun rays, reflects them onto a large mirror, and redirects them into a steel container filled with sand Echogen says its system will deliver a cost of storage of $50-$60/MWh

Have you ever walked on a sandy beach barefoot, on a hot summer day, and nearly burned your feet? Well, that finally gave rise to new renewable energy technologies.

ENDURING

One of the main Achilles’ heels of renewable technology is finding a reliable storage of excess energy when generation exceeds demand.

Researchers at the National Renewable Energy Laboratory (NREL) have recently unveiled their new thermal energy storage technology that uses hot sand to store energy, just like a battery.

Called the “Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle,” or ENDURING for short, this could prove to be a game-changer for making renewable technology far more reliable in the future.

The system takes excess energy generated from wind and solar power and uses it to superheat silica sand.  This new system feeds sand through a heater that then heats the sand particles to in excess of 1,200°C. 

Diagram of the ENDURING system. Source NREL

Once the sand is heated, it is then fed into an insulated silo made of concrete for storage. When the stored energy is needed again, the sand is fed into a heat exchanger than then pressurizes gas to power turbomachinery and spin generators to produce electricity again.

The beauty of this system is that it can be hooked up to the grid and can be placed on decommissioned coal or gas plants.  ENDURING could help phase out coal and natural gas plants.

According to the NREL, even a single ENDURING system should be able to store as much as 26,0000 MWh of thermal energy. A megawatt of capacity will produce electricity that equates to about the same amount of electricity consumed by 400 to 900 homes in a year. 

Similar technology spreads to Italy

An Italian firm, Magaldi Group, is also using sand as a storage system to eventually concentrate solar energy.

Heliostats captures sun rays and reflects them onto a large mirror, which then redirects the sunlight into a cylindrical steel container filled with sand. Here, sand is exposed to temperatures of over 600°Celsius. The hot sand then produces steam which generates electricity. The company aims to expand over Italy and all other countries.

The system allows for energy to be produced also at night time and uses materials that are compatible with the environment, which makes it eco-friendly. One system can make up to 500 kWh of power.

Other energy-storing combinations using sand

An innovative thermal energy storage system that uses sand, water, and carbon dioxide as its core components promises to be among the lowest-cost long-duration options available for renewable energy backup.

Ohio-based Echogen says its PTES (Pumped Thermal Energy Storage) system will deliver a cost of storage of $50-$60/MWh for a 100MW facility once it reaches commercial maturity around 2030 when prices would equally apply for eight or 100 hours of storage.

By comparison, a four-hour 100MW/400MWh lithium-ion battery system currently incurs a cost of $132-245/MWh, according to investment bank Lazard.

Long-duration energy storage market leader Highview Power offers a comparably low cost for its liquid-air system, which is currently about $100/MWh for a 100MW system and could fall to $50/MWh by 2030.

Echogen says its own calculations show that the cost of its PTES system will be 20-30% lower than Highview’s at 100MW/1GWh on a like-for-like basis, largely due to lower-cost equipment and the lower complexity of its system.

Like other thermal energy storage systems, Echogen’s converts electricity to heat, which is stored for hours or days until required and converted back to electricity when required.

Echogen’s system uses electrical power to move heat from a cold reservoir filled with water/ice to a hot reservoir containing grains of sand using a heat pump. The heat is stored in the sand until needed and then is run through a heat engine to generate electricity as and when required.