Underhyped Tech - Thermal Energy Storage

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Written By Frontier Tech Hub

This is a deep dive into one of our nine underhyped frontier technologies for development.
The full exploration will be released on April 23rd. Sign up to the launch event here.

Capturing and reusing heat for cleaner energy and resilient power

Not all energy needs to be electric. Thermal Energy Storage (TES) captures heat—often from the sun or industrial processes—and holds onto it for later use. That stored heat can cook meals, keep vaccines cool, or warm homes through the night. In places where electricity is unreliable or expensive, TES offers a low-cost, low-tech alternative. It’s especially promising in off-grid and peri-urban settings, where adaptable, durable energy solutions are needed most. This piece explores how TES works, where it’s already making a difference, and why it deserves more attention in climate and development planning.

  • Thermal Energy Storage (TES) systems capture and store heat for later use, helping communities manage energy more efficiently. These systems absorb excess heat from solar energy, industrial waste, or phase change materials (PCMs) and release it when needed for cooking, refrigeration, or heating.

    Small-scale, decentralised TES applications using PCMs, underground heat storage, rock beds, vegetable oils, molten salts, and sand-based systems provide low-cost and locally adaptable alternatives for cooking, cooling, and heating in rural and peri-urban settings​.

    Some of these systems enable reliable energy access without requiring complex infrastructure, making them a viable alternative for improving energy security and resilience in off-grid and energy-scarce communities in the Global South.

    • Solar Heat Capture: Stores surplus heat during the day for night-time or cloudy-day use.

    • Off-Grid Cooking & Heating: Retains solar or biomass heat to provide continuous energy for cooking, reducing fossil fuels, firewood and charcoal dependency in rural communities.

    • Cold Storage for Agriculture & Health: Keeps food, dairy, and medicines cool without requiring uninterrupted electricity.

    • Disaster-Resilient Energy Storage: Provides backup heating and cooling in emergencies where electricity access is disrupted.

    • Integration with Solar Water Heating: Enables efficient water heating without requiring batteries or grid connections, supporting clean energy transitions.

  • Despite the urgent need for affordable, reliable energy in remote and low-income communities, energy storage solutions often focus on batteries rather than thermal storage. TES offers a cost-effective alternative for heat-intensive applications such as cooking, refrigeration, and passive heating, reducing dependence on fossil fuels and electricity grids. However, adoption is limited by a lack of awareness, and insufficient research on low-tech, locally adaptable.

    • Decentralised Energy Access: TES stores excess solar thermal energy, ensuring availability during night-time and off-sunshine hours​, ensuring energy availability in remote areas.

    • Passive Heating and Cooling: Sand batteries and low-cost PCM-based materials can regulate indoor temperatures in homes and small-scale productive settings​.

    • Affordability & Local Manufacturing: Many TES materials, such as salt, sand, or repurposed industrial waste, are abundant and locally available​.

    • Higher Reliability: Unlike electric batteries, TES systems are less affected by ambient temperatures and can operate with nearly 100% depth of discharge, reducing wear and extending lifespan.

    • Durable and Low-maintenance: TES systems have minimal maintenance needs and often last between 7 and 15 years, significantly outlasting conventional batteries.

    • Technical Expertise for Implementation: Installation and maintenance require trained personnel, which can be a barrier in rural areas.

    • Material Availability and Sustainability: Some TES solutions rely on materials that have environmental extraction concerns or face supply chain limitations.

    • Heat Loss & Efficiency Issues: Thermal losses occur in poorly insulated TES systems, reducing efficiency in real-world applications​.

    • Costly Phase Change Materials: For advanced PCMs and high-performance insulation materials​.

    • Size & Space Requirements: Certain TES systems require large volumes of material, limiting deployment in dense urban areas.

    • Scalability Challenges: While useful for individual households or community-scale setups, TES systems often require customized designs based on climate and local resources​.

    • Advances in Phase Change and Low-cost Materials: More affordable PCMs and heat storage solutions are being developed.

    • Policy Support for Renewable Heat Solutions: Governments and NGOs promoting just energy transitions can drive TES adoption in rural communities.

    • Integration with Renewable Systems: TES complements solar thermal and biomass solutions, making off-grid energy more reliable.

    • Community-led Initiatives and Knowledge-sharing: Involving local cooperatives and micro-financing models improves TES adoption​.

    • Local Manufacturing & Upcycling: Repurposing materials such as sand, salt, or recycled metal for thermal storage makes TES more viable in LMICs.

    • Capacity Building: Providing training for local entrepreneurs and technicians enhances TES adoption and long-term sustainabilit

    • Sustainable Housing & Construction: Embedding TES in bioconstruction, low-cost housing and passive solar designs improves thermal comfort​.

    • Limited Funding and Financial Incentives: Most TES research and pilot projects are concentrated in high-income countries, with minimal investment in LMICs​.

    • Lack of Policy: Few incentives exist for community-scale TES projects, limiting adoption​. Many policymakers are unfamiliar with TES applications in energy planning.

    • Limited Awareness and Adoption: TES is less known compared to battery storage, requiring extensive training for community-level adoption​.

    • Material Supply Chain Constraints: Some advanced TES solutions require high-cost or scarce materials, or international supply chains, limiting their accessibility​ in remote areas.

    • Competing Storage Technologies: Lithium-ion batteries, lead-acid batteries, and grid-based electrification receive more funding and policy support than TES​.

    • Social and Behavioral Adoption Challenges: Shifting cooking and heating habits requires cultural acceptance and long-term user engagement​.

Curious examples: what’s already happening?

Case Study no. 1

Sand Battery for Community Heating in Finland - Pilot

  • Many communities worldwide, especially in colder climates, struggle with affordable, sustainable heating solutions. Traditional district heating often relies on fossil fuels like oil and woodchips, leading to high carbon emissions and resource depletion. Additionally, renewable energy sources like wind and solar are intermittent, requiring efficient storage solutions to harness their full potential.

  • Polar Night Energy has developed a large-scale sand battery in Pornainen, Finland, to store excess energy from solar and wind power as heat. This innovative system will:

    ✔️ Store up to 100 MWh of thermal energy using crushed soapstone, a by-product of Finnish fireplace manufacturing.

    ✔️ Replace oil-based heating, reducing carbon emissions by nearly 70%.

    ✔️ Maintain heat at 500°C for weeks or even months, providing a stable and continuous heating supply even in winter.

    ✔️ Integrate with the district heating network, supplying homes, offices, schools, and libraries with sustainable heating.

    • Cuts 160 tonnes of CO₂ emissions annually, aligning with Pornainen’s carbon neutrality goals.

    • Reduces woodchip burning by 60%, conserving biomass resources.

    • Provides a cost-effective and scalable thermal energy storage solution, setting a precedent for future low-emission district heating systems.

    • Demonstrates the viability of widespread sand battery adoption in communities worldwide, particularly in regions with seasonal heating needs.

  • More information here.

    Image: The sand inside the silo at the Vatajankoski power plant in Kankaanpää can store heat at around 500C for several months. Credit: Polar Night Energy.

 

Case Study no. 2

Solar-Biomass Hybrid Dryer with Thermal Energy Storage for Rural Communities - Product/Service

  • In many rural and tribal communities, food preservation is a challenge due to a lack of reliable drying infrastructure. Traditional sun-drying is inefficient, weather-dependent, and can compromise food quality. Additionally, electric dryers are often inaccessible due to unreliable power supply and high energy costs.

  • The Solar-Biomass Hybrid Dryer developed by TERI integrates Thermal Energy Storage and a Biomass-based Heat Exchange (B-HE) system with a solar dryer for continuous and efficient food drying. This innovation:

    ✔️ Has a 50 kg per batch fresh produce capacity, extending the shelf-life of dried food.

    ✔️ Uses less than half a unit of electricity for 10 hours of operation, significantly reducing energy costs.

    ✔️ Features a controller for optimised drying conditions, improving product quality.

    • Empowers rural women, and tribal communities by creating sustainable livelihoods.

    • Reduces food spoilage and post-harvest losses, improving food security.

    • Provides an energy-efficient, cost-effective alternative to traditional drying methods.

    • Promotes climate resilience by reducing dependence on fossil fuels and ensuring year-round food processing.

  • More information here.

    Image: The hybrid dryer system is integrated into a movable base for flexibility and accessibility. Credit: TERI.

Other interesting cases

Solar cooker incorporating heat storage and PCM (Spain) - Prototype
Parabolic solar cookers with PCM storage allow cooking at night, reducing wood and charcoal use​.

Decentralised solar-powered cooling systems (Pakistan) - Review
Food conservation units extend food shelf life and improve farmers’ bargaining power​.

Open-Source Models for Sand-Based Thermal Energy Storage (USA) - Prototype
Researchers presented a new open-source modelling package for particle-based silica-sand thermal energy storage (TES) in the Modelica language.

Solar Cookers with TES (Uganda) - Product/Service
It helps to combat the widespread deforestation that is occurring in the country.

PCM-Based Refrigeration in Kenya (Kenya) - Pilot
Deploying low-cost refrigeration for the fisheries industry in Kenya.

Experimental testing on the performance of solar dryers (​​Ethiopia) - Prototype
Exploring indirect solar dryers.

Rock-based TES for Rural Heating (Morocco) - Research
Research on using locally sourced rocks for heat storage.

Storing energy for hundreds of years (Sweden) - Product/Service
TEXEL’s TES tech stores electricity as thermal energy and can maintain this stored energy for exceptionally long periods with minimal energy losses. 

​​Financial Analysis of Low-Temperature Solar Thermal Energy Storage Systems (Colombia) - Research
A study to supply hot water and heating for rural households.

Future scenarios: what might happen in 2035?

As part of our exploration of these nine underhyped technologies, our partners at Pluriversa conducted a foresight exercise to consider possible futures and anticipate the challenges and opportunities within each technology. The exercise produced four scenarios for the year 2035, which you can read here, along with speculative use cases - with different potential outcomes - for each technology. Read on to explore potential future scenarios involving thermal energy storage.

2035: High-Efficiency Ambient Energy Generation

Researchers from top departments in physics from all over the world were able to develop a high-efficiency thermal storage material. The surface of the material is a superconductor that absorbs intensive amounts of energy under the right circumstances.

It is so powerful that the first energy generators built with thermal storage have been able to extract heat from the environment, cooling down external temperatures. This is something that has become very useful in areas affected by considerable increases in temperature. The machine does this process in a way that the energy produced is considerably more than the energy consumed.

The technology works best in certain climates. However, engineering calculations indicate a wait time of 2-3 years before it improves, although some consider this to be extremely optimistic.

2035: Black Market Ambient Energy Trading

Like with most revolutionary technologies, thermal energy storage has had unexpected consequences. Illegal traders are using them in combination with ambient energy generators in environmentally fragile places, and the consequences are dramatic.

Traders sell the extracted energy in the global energy black market with a generous return on investment, making the business very attractive. Entire criminal organisations have been formed around the technology. The energy produced, with prices below formal energy markets, is quickly sold without leaving any trace behind.

Regulating the use of high-efficiency thermal storage materials has become one of the major challenges for countries everywhere in the world.

Final thoughts

If you’re working in energy access, agriculture, health, or sustainable housing, TES might offer a simple but powerful addition to your toolkit. The real opportunity lies in using local materials and knowledge to create solutions that last.

Some ideas to explore next:

  • Could sand or salt-based storage improve thermal comfort in off-grid homes?

  • Might solar heat be stored for cooking or cold storage where electricity is scarce?

  • Are there ways to integrate TES into local housing, food, or health projects?

  • Could community-led repair or upcycling initiatives support long-term adoption?

TES isn’t new—but it might be newly useful in places looking for affordable, resilient energy options.

This is a deep dive into one of our nine underhyped frontier technologies for development.
The full exploration will be released on April 23rd. Sign up to the launch event here.

Frontier Tech Hub

The Frontier Tech Hub works with UK Foreign, Commonwealth and Development Office (FCDO) staff and global partners to understand the potential for innovative tech in the development context, and then test and scale their ideas.

https://www.frontiertechhub.org/
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