Battery-free solar-powered cooling secures resilient and stable infrastructure in extreme off-grid areas

01 July 2026 | Teknologisk Institut, Tribologicentret

The Danish development project "The missing link of the food cold chain: Solar direct drive cooling appliances" has cracked the code to stable, battery-free cooling directly from solar panels. By eliminating the need for traditional batteries and reducing reliance on diesel generators, the project delivers a directly applicable technology that can help strengthen resilience and tactical survivability in the field.
The project has delivered new, documented methods for optimising mobile infrastructure under difficult conditions. By coupling solar energy directly with thermal energy storage, the project has demonstrated how to achieve reliable temperature control without the detour of sensitive and heavy traditional batteries.
Although the technology was originally developed to safeguard food chains in global off-grid regions, the results have proven highly relevant to the defence and emergency services sector. The project's groundbreaking system design addresses three of the military's greatest challenges in the field: logistical complexity, vulnerability to extreme temperatures, and detectable energy signatures.
Ice instead of traditional batteries
Supported by the Energy Technology Development and Demonstration Programme (EUDP), the development project was carried out by a strong consortium consisting of Danish Technological Institute, DTU Construct, Vestfrost Solutions, LS Control, WWF Denmark (World Wide Fund for Nature), and Arla Foods.
The objective was to create a robust solution for areas off the main power grid. The core technological leap in the project is the complete elimination of traditional batteries. Traditional batteries are heavy, expensive, vulnerable to extreme temperatures, and require complex logistics and maintenance.
Instead, the consortium has developed a system where the generated solar power is converted directly into cooling, which is thermally stored in an integrated ice storage – a so-called Phase Change Material (PCM). When the sun shines, the system freezes water or other media into ice within an integrated section of the compartment. This ice acts as a cold storage buffer, keeping the temperature stable when night falls or clouds gather.
Tactical benefits: Stealth and independence
This battery-free technology differs significantly from existing solutions in three crucial areas of direct military relevance:
• Reduction of acoustic and thermal signatures: By replacing or supplementing traditional generators with silent solar panels and quiet, variable-frequency compressors, the physical footprint is dramatically reduced. The thermal signature is lowered during periods when the thermal storage provides cooling, and the active refrigeration system is shut off.

• Resilience under extreme conditions: Traditional batteries (such as lithium batteries) degrade rapidly and lose capacity when exposed to extreme heat or cold. The thermal ice storage in the new system is virtually wear-free and unaffected by harsh climatic conditions. This increases operational reliability during critical missions, where loss of power to medical supplies, food, or sensitive electronics can have fatal consequences.

• Logistical relief: Every litre of diesel saved in a field camp is one less litre of diesel that needs to be transported through potentially hazardous terrain under extreme conditions. By maximising the direct use of solar energy, the logistical burden is significantly eased.
Impressive efficiency in overcast conditions
That the system can function under challenging, real-world conditions is now scientifically documented. Through advanced computer models (digital twins) and physical laboratory tests at Danish Technological Institute, researchers have mapped exactly how efficient the system is.
Using a so-called PI (Proportional-Integral) controller to regulate compressor speed, the project have succeeded in keeping the system running stably, even under highly limited light conditions. Testing of a system with a nominal solar panel output of 800 W shows:
• Early startup: The compressor starts up at a solar irradiance of just 19% of a completely clear sky.

• Full power: Already at 26% irradiance, the compressor reaches maximum speed.

• Survives clouds: The system can maintain stable operation down to an irradiance of just 13% (equivalent to a mere 128 W/m² with an input power of 130 W).
In practice, this means that the system is not just a "fair-weather solution" but is fully functional in changeable weather and moderate cloud cover. Furthermore, environmentally friendly refrigerants with low global warming potential (GWP) are used, aligning with the military's increasing focus on green transition.
From the Kenyan bush to military tenders
The technology is currently being tested under real, challenging conditions in Kenya and the Philippines, with operational data being continuously transmitted home via built-in cellular modems to document durability over time.
However, the project's value extends far beyond the specific test refrigerators. The testing methods, simulation tools, and standards developed by the consortium can be transferred directly to the defence and emergency services sector. The impartial test procedures and documented data enable military procurement officers to set precise, stringent requirements when the armed forces put mobile HVAC (heating, ventilation, and air conditioning) systems out to tender in the future. This minimises the risk of costly technical procurement errors for equipment destined for active operations.
Facts about the project:
• Project name: The missing link of the food cold chain: Solar direct drive cooling appliances

• Purpose: To develop and test a robust, battery-free, and solar-powered cooling system for off-grid areas using integrated system design and thermal energy storage.

• Project period: 2022–2026

• Partner consortium: Danish Technological Institute (project leader), DTU Construct, Vestfrost Solutions, LS Control, WWF Denmark, Arla Foods
The project is supported by the Energy Technology Development and Demonstration Programme (EUDP).
Find more details about the project: www.teknologisk.dk/44239
Contact: Ivan Katic, Danish Technological Institute, email: ik@teknologisk.dk