How does a sand battery work? 

You’d be forgiven for not even knowing sand batteries exist. When we hear the word battery we picture the electricity-storing devices used to power smartphones, computers, cars and air conditioning remote controls. But batteries can be understood as any device that stores energy.

The batteries we typically think of store chemical energy that can be converted into electricity for use as a power source. But heat is also a form of energy that can be stored and used. The value of this thermal energy is particularly profound when one learns that more than 52% of all energy used worldwide is for heating and cooling. In addition to creating comfortable indoor climates, warming showers, and cooking food, heat is essential for nearly every industrial process, from applying color to plastic trinkets to processing agricultural goods. Regardless of where the energy comes from, the end goal is often pure and basic heat, with electricity often just an intermediary.

Imagine the heat on the bottom of your feet when walking across a sandy beach at midday.

What is a Sand Battery?

What does sand have to do with thermal energy? Think about walking across a beach at midday and you’ll realize how sand is an incredibly efficient material for retaining thermal energy and once warmed, and with proper insulation, it can remain hot for six months. A sand battery is essentially a large encased, insulated mound of sand with internal physical and chemical components that support heating and heat conduction. Energy is transferred into the sand battery from conventional sources including solar panels, generators or a fossil fuel-reliant electricity grid to heat the sand. The battery then retains that thermal energy until it is needed as direct heat or transformed to other forms such as kinetic energy via steam.

Alternō sand battery (far left) with accompanying equipment.

There are numerous uses and advantages of sand batteries. Consider, for example, Vietnam’s large coffee farms. Before roasting the beans, farmers often rely on sunlight to dry them, which puts the entire process at at the mercy of capricious weather patterns. Otherwise, the farmers can dry them with the assistance of carbon-spewing combustin engines. Sand batteries attached to solar panels, however, can provide the coffee farmers with consistent and regular heat that doesn’t release greenhouse gases. Sand batteries can be easily adopted by most industries that employ massive amounts of unseen heat. Textile factories, for example, require heat to iron fabrics while car manufacturers dry paint with hot air. Sand batteries in these situations don’t reduce the quality of the work but drastically cut down on harmful emissions and overall environmental impacts. 

Vietnamese farmers typically dry their coffee beans before roasting in the open air or in large greenhouses.

Sandbatteries Developed in Vietnam

Hải Ho has long been aware of the dangers of climate change that result from environmentally destructive behavior. “I watched the Inconvenient Truth in 2008 and since then I’ve been a bit of a doomsday prepper,” he shared with Saigoneer during our visit to his Thủ Đức factory. “My house is right on the beach in Đà Nẵng, so I saw with my own eyes the storms getting bigger and bigger and then I looked at the data.”  

Hải’s concern for the future of the planet’s environmental health and the particularly poignant impact on Vietnam led him to establish a sustainable travel company in 2011. Everything was going well until Covid and the business understandably hit a standstill. During the lull, and motivated by a desire to be the change he hoped to see in the world, he moved to remote Bảo Lộc and built a fully off-the-grid home. This is where he saw the applications for sand batteries in Asia setting

After moving into his self-sufficient home, Hai quickly discovered the limits of powering it via solar panels connected to a lithium battery that stored energy to use at night.  “You can use an aircon, you can turn on the fan, you can turn the computer; easy peasy. But the moment you press a button to heat up a water heater or the water kettle, it crashes,” he explained. It takes five times as much energy to heat water as it does to run an air conditioner, and this is simply more than a lithium battery can manage. Moreover, in addition to their limited capacity, lithium batteries lose their full storage potential quickly and are always at risk for dangerous malfunctions when exposed to the elements. 

Alternō sand battery operated by the Alternō team in their factory.

Hải shared his frustrations about lithium batteries' inability to satisfy routine, daily heating needs on his social media. Friends quickly shared details about sand batteries and by 2021 Hải and his co-founders Nguyễn Quốc Nam  launched Alternō. After successful participation in an accelerator program, by 2024 they were working with large corporations including global food conglomerates to install sand batteries as part of holistic technology integration to meet heating needs while reducing emissions.

Alternō battery installed for a client.

Alternō provides businesses with sand batteries designed and constructed in-house as well as supports their clients in selecting and installing appropriate energy source systems. For example, Alternō can provide guidance for choosing the most suitable solar panels for use in coordination with their sand battery. Or, as is sometimes the case, the upfront costs of a clean energy source are not realistic and the Alternō team will help connect the battery to a traditional fossil fuel-burning source. Sand batteries do not produce energy in and of themselves, and will thus always be a piece in the larger puzzle of how to meet energy demands in the most feasible, sustainable way. There is always room for compromise when working on this puzzle. 

In addition to a lack of awareness, the biggest challenge for sand battery adoption is their cost. Hải admits that even though his off-the-grid home revealed to him the potential of sand batteries, he can’t actually afford one himself. At approximately 20,000 USD they are not realistic for individual or small business use. And anyway, Hải’s ultimate goal is to have as much of an impact on global emissions as possible, which necessitates working with multinational corporations and huge factories, particularly because they spend half of their fuel costs on heating.

Many small scale business operations in Vietnam still rely on burning wood or fossil fuels to generate heat.

Just because big conglomerates have the cash needed for sand batteries doesn’t mean they are eager to spend it. Thus Hải has learned that he must offer financing options when approaching large companies. Their curiosity about sand batteries gets them in the door, but it’s Alternō’s ability to connect clients to sustainable energy solutions while offering financing options that get contracts signed. To date, their success can be understood as the world most affordable thermal energy storage solution. 

Sand Batteries are Not a Silver Bullet … and That is Okay

It was surprising at first to hear that Hải sometimes connects Alternō sand batteries to fossil fuel burning sources as those produce the carbon emissions he is working so hard to reduce. But the more Hải explained his approach to combatting global climate change the more it made sense. While he is an ardent believer who prioritizes the mission of saving the planet from the monster of climate change, he is realistic. “Why are we waiting for a silver bullet? To kill the monster. But in the meantime we have to fire every single kind of bullet we have to slow it down; to buy time for someone to invent the silver bullet,” he explains. “What we do is small, it’s not magic, but maybe it will slow things down so instead of a category 5 storm we experience a category 4 storm. Or maybe it extends disaster from happening in 2030 to happening in 2032 and during that time someone invents something that saves us.” 

Alternō presented at the Powering a Sustainable Future event.

Hải became animated when speaking about the other ideas he’s learned about at events while promoting Alternō. From paper batteries to wind turbines on the sides of buildings to tabletop nuclear fusion, many people are crafting “bullets” to slow down climate change like Alternō. Such a situation reveals an important reality about sustainable actions: no singular solution or action will solve everything. Even the most passionate individuals like Hải can only hope to contribute to the larger set of solutions. Hải serves as a great example of how the size of the problem doesn’t have to discourage one from working on those small contributions. 

The Alternō headquarters complete with sand batteries in the open space.