Sand Battery Explained

3 min read

When it comes to renewable energy the recurring problem is intermittency, which basically means that the energy supply is fluctuates a lot during a 24-hour period. This is why backup power is essential for renewable energy applications. These backup power solutions usually come in lithium-ion or lithium phosphate batteries, but there are new battery technologies on the rise, such as Thermal Energy Storage (TES) devices.

TES devices are batteries that store energy in the form of heat. They are charged by passing electricity in a heating component planted in the thermal medium. The thermal medium can be water, sand or similar substances. The heat energy can then be discharged on later day through a cooling process.

TES systems tend to have a high Round-trip Efficiency Rate (RTE) – the percentage of electricity put into storage that is later retrieved. A 100% RTE would mean that every unit of energy stored could be retrieved later for use. 

Why Sand for RTE?

• Sand has a low specific heat. Sand doesn’t need a lot of energy to heat up quickly as its high density allows it to store thermal energy for longer.
• No chemical reactions. Sand batteries are low maintenance and therefore have a long lifespan.
• High heat temperature. Sand can be heated above the boiling point of water and can also hold on to that heat energy at an RTE of above 90%.
• Cheap. Sand can be purchased for extremely low prices.
• Easy to get. It is easier to get large amounts of sand than water or other fossil fuel materials such as
• Non-toxic. Sand does not contain toxins such as asbestos.
• Non-flammable. Sand is not flammable like lithium-ion batteries. In fact, sand is one of the best fire extinguishers.

Sand battery applications

Polar Night Energy in Finland developed a sand battery for commercial use. The company heats the sand using renewable energy and then sends the heat in the form of air, hot steam, and hot water with temperatures of up to 400–500⁰C to homes. The sand TES device sits in a powerplant and is used to power homes, offices, and the municipal swimming pool. The sand can keep the heat potentially for months.

Abu Dhabi based company, Batsand, places sand-filled storage vessels underground in the yards of homes to save space. This is similar to the positioning of a sceptic tank. This TES device is aimed at 300-400m² buildings and store 10 680 kW/h of energy. This comes with a recommended 30+ kW of solar panels on the building’s roof. 

Netherlands based Newton Energy Solutions (NES) have a TES that combines the functions of a TES, a geyser, and a buffer tank. It can serve as large battery and a geyser simultaneously, removing the need for a traditional geyser. NES uses special vacuum insulation and thin tank walls to hold more water and more heat than other devices of the same weight. This system comes with an option of a 214 litre 20 kWh capacity or a 320 litre 29 kWh capacity. NES says that their smaller version can heat 600 litres of tap water to 40⁰C. To cap it all off, NES says that the device is made from fully recyclable materials.

Challenges with TES

• Size – TES batteries can be up to 7 metres high, with some of the smallest batteries measuring 40m³ making them is not ideal for residential use. Larger applications also cool down slower, meaning that they retain heat for longer. This makes larger applications that serve hundreds of homes more ideal than single systems that serve one home.
• Lost power – although the RTE of TES devices are high, it becomes lower when converting the heat into electricity. This is because a small but significant amount of energy is lost during the conversion from heat energy to electricity.
• Affordability – the smaller NES device is priced at around €5 000 – €6 000 (R101 913,00 – R122 295,60). This is without adding a renewable energy application to harvest the energy. Batsand’s smaller 14 kW system goes for €7 200 (R146 746,80) but inflates to €17 000 (R346 485,50) with installation.

Quick sand battery explanation

TES devices work best together with renewable energy applications such as wind and solar. Solar panels can collect energy from the sun, and then the TES device can store that heat energy for water heating and air conditioning, and it can take pressure off of the lithium batteries that come with the solar panels, allowing them to cool down more which makes them last longer.

Once the cost for all this equipment and installation goes down, this blended energy technology solution should be something that most people consider when looking for alternative energy. If TES technology gets to the point that it can store heat energy and convert it to electricity economically, it could be a no-brainer solution. 

What do you think of TES systems/devices? Do you think this could be one of the solutions that could finally help renewable energy confidence? Share your thoughts by replying to this email!

For more information on sand batteries, or any other renewable energy related articles, view the other blog posts on my website and be sure to open my weekly emails every Tuesday at 9AM CAT. Please also share this newsletter with your friends and collogues working in the renewable energy sector.

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