The sun over Kawa village, on the western side of Seram island in Maluku, Indonesia, is close and fierce most of the year.
For generations, its fishing families sent boats out for yellowfin tuna and came home with a problem.
The fish spoiled fast, and ice was almost impossible to find.
Ice made in home freezers and bagged in plastic was the main supply, and frequent power cuts left even that unreliable.
Then a machine arrived that used the tropical sun itself to solve the problem, but how exactly does sunlight freeze a fish?
How the sun freezes a tuna
A solar ice maker looks, from the outside, like a compact industrial box with panels tilted at the sky. It reached Kawa as a containerized unit, which cut the assembly work needed on site. Inside, photovoltaic electricity drives a refrigeration cycle with no connection to any grid: current runs a compressor, the compressor pushes refrigerant around a sealed loop, and the loop pulls heat out of water until it freezes.
The clever part is what the machine uses instead of a battery. Thermal energy storage means the ice itself holds the energy. When the sun is strong, the unit freezes more than is needed and banks the surplus as solid blocks. When clouds roll in or night falls, the cold is already made and sitting in the hold.
That design choice was not obvious. The first instinct with any off grid solar system is to store surplus as electricity in a battery bank, but batteries wear out, need replacing and are expensive to ship to a remote island. This design sidesteps that cost entirely.
What the machine replaced
Kawa’s tuna fishers had no cold chain worth the name before the machine arrived. The village sits in West Seram, in Maluku Province, where reliable ice means a boat journey and a fuel bill that eats directly into a catch’s value. The solar ice maker exists to close that gap, so freshly landed yellowfin can reach distant buyers at full quality.
Indonesia is the world’s largest tuna producer, yet remote coastal communities often lack access to a reliable cold chain, which limits their ability to preserve quality and compete in distant markets. The gap between what a fisher lands and what a buyer will pay comes down almost entirely to temperature in the hours after the hook is set.
Before the solar ice maker, post harvest losses were cutting family incomes in ways that no improvement to fishing gear or boat design could fix. The problem was not on the water. It was on the dock.
Nearly 390,000 pounds in a year and what it measured
The facility was inaugurated in Kawa on October 15, 2024, by a UN development body, a German development agency and the International Pole and Line Foundation. It is rated at up to one metric ton of ice a day, running entirely off grid.
Over its first year, the unit produced 176 metric tons of ice, close to 388,000 pounds, with partners putting typical output at about 16 metric tons a month, or roughly 35,000 pounds. That supply served not only Kawa’s fishers but neighboring communities as well.
By replacing diesel generated ice with solar power, the system avoided 4,290 liters of diesel fuel, about 1,130 gallons, and an estimated 40 metric tons of carbon dioxide over the same twelve months.
It also removed an estimated 223,520 single use ice bags, more than two metric tons of plastic that would otherwise have headed for a tropical sea.
The ice is the battery, and that matters elsewhere too
The Kawa unit is the second of its kind in Indonesia, following a solar ice maker that went into operation in Kupang district, East Nusa Tenggara, in 2022. It is the first built specifically around small scale tuna fisheries, where catch size and landing patterns differ sharply from industrial operations. Two further cold storage facilities are now being built for Maluku.
Storing the effect rather than the electricity shows up elsewhere in solar design. Large solar arrays are increasingly paired with other uses of the same ground, and a trailer sized solar desalination unit ran on comparable logic, producing while the sun was up rather than leaning on a battery bank. In Kawa, the medium is frozen water stacked in a hold.
GIZ’s lead for industry decarbonization, Frank Stegmüller, said at the launch that using solar power for cold chain applications meant “cutting emissions and taking steps towards carbon neutral global supply chains.” GIZ reports that fish producers and participating fishers in Kawa have gained around $120,000 in additional income, because chilled catch sells at a higher price.
What the tuna tells you about the machine
The curiosity here is structural. Panels designed to capture heat are being used, through a refrigeration loop, to remove heat from something else entirely. The sun freezes the fish. That inversion is not a paradox, it is engineering, but it is genuinely strange the first time you hold it in your mind.
Affordable, longer lasting ice has improved the quality of fish landed and lets fishers stay out instead of racing home before their supply melts. It has also cut costs sharply by removing the need for externally sourced ice and the travel to find it.
The one honest caveat is scale. Kawa is a prototype, and the 176 metric tons of ice it made in a year serves one village and its neighbors. Replicating it across the thousands of coastal fishing villages along Indonesia’s shoreline would require supply chains, trained technicians and sustained funding that a single pilot does not guarantee. But a prototype that works is a different kind of object than a promise, and in Kawa the ice is already in the hold, and the tuna is cold, and the boat is heading out again.
