The system is modular and couples 20th century technology with the latest development in materials to provide the lowest cost Watt of solar cooling available.



Solar Polar has developed a solar cooling system that will bring cooling to the 1.6 billion people without mains electricity.

This technology will cheaply cool the produce from marginal farmers reducing the 50% food waste, improving the quality of the produce they sell and allowing them to grow higher value crops, alleviating poverty, hunger and greenhouse gas emissions from rotting produce.

If food waste were a country it would be the third largest emitter in the world!

Project Status

The technology has been developed and verified at our lab at Imperial College and the initial results have been the subject of a paper; “Testing and simulation of a solar diffusion-absorption refrigeration system for low-cost solar cooling in India”. ISES Solar World Congress, 29 Oct – 02 Nov, 2017, Abu Dhabi, UAE. Authors: James Freeman, Ahmad Najjaran, Robert Edwards, Michael Reid, Richard Hall, Alba Ramos, Christos N. Markides.

The technology has reached TRL7. We are currently rolling out field trials/demonstrator systems in India and the UK. The first is at Anna University in Chennai and the second is under construction in Ahmedabad near our manufacturing partners in India. The third is being set up on a farm in the UK. This demonstrator/fireld trial project is being conducted with the assistance of Innovate_UK as part of their Energy Catalyst programme. A previous Innovate UK programme allowed us to bring the project from TRL4 to TRL6 and to establish the business case and route to market that we are now pursuing.

The technology has one granted patent, one patent pending and another to be filed this month.


The product is a solar refrigeration product. Solar heat is collected using high efficiency solar thermal collectors.

A Diffusion Absorption Refrigeration (DAR) based refrigeration system is used to produce cooling directly from the heat of the sun thus collected. The DAR system is very similar to the type of refrigerator used in hotel minibars and is a direct descendant of the gas fridges of the first half of the last century that ran off a small gas flame. They are still used today in caravans and houseboats.

The cooling produced from the DAR system is fed into refrigerated spaces for agricultural produce thus preserving the produce, keeping it in good condition and pre-cooling it for onward transport.

Innovative Aspect

The system is modular and couples 20th century technology with the latest development in materials to provide the lowest cost Watt of solar cooling available.

The reason this technology has not been previously considered is that it relies on a physical effect called the bubble pump to work and that effect relies on capiliary action. The result is that the upper limit to the cooling power is 200W. 

The advance is to develop a way of making the unit modular so more than 200W can be produced by adding modules into an effective “battery of cooling” The second innovation is to use the latest nano-materials to get more ore the available solar energy converted to cooling than previously possible.


Focusing on India for the time being. 400million of the Indian population don’t have access to mains electricity. Most of those people are small farmers (average farm size 2.4 hectares.)

These small farmers cannot afford the diesel for the generators needed to power on-farm pre-cooling so their customers cannot use refrigerated trucks to take them to market. (refrigerated trucks can only keep already pre-cooled produce cool) As a result, the farmers have to sell their produce as soon as it is harvested and it then travels to market on open trucks where at destination rotten produce has to be removed before the food can be sold. As a result in 2015 48% of the food grown in India rotted before it got to market.

With affordable solar cooling, no diesel is needed. Refrigerated trucks can pick up the food and the farmers can sell top quality food over a period of time when prices are optimal. Food reached the market unharmed, there is no time and produce wasted in sorting out rotten produce and the customer will pay more for better quality food.

As an illustration of the economic effects of not having a proper cold-chain due to lack of pre-cooling, India imports 140 thousand tonnes of apples from Spain (mostly to Mumbai) because there is an unbroken cold-chain between the tree in Spain and the supermarket shelf in Mumbai. Millions of tonnes of apples are produced in north-western India but only a small fraction of them get as far as Mumbai.


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