Solar Panels Freeze a Bucket of Water by Day to Run Free Air Conditioning at Night

Summers in Florida are terrible, forcing people to get creative in order to stay cool without breaking the bank or overloading the electricity grid. Hyperspace Pirate took on the problem and came up with a clever mechanism that absorbs solar energy throughout the day and stores it as ice for use when cooling is required, bingo.

Three regular 100-watt solar panels are put on the back of a vehicle and simply plug into a normal charge controller connected to a 35-amp-hour lead-acid battery. Once the battery is fully charged, the microcontroller activates an inverter, which powers a miniature refrigerator compressor. That compressor sucks up around 80 to 100 watts and begins to draw heat from a 2-gallon water bucket coated in substantial insulation, as we’re talking one-inch foam panels and a lot of fiberglass wool here.

Hours under the hot afternoon sun transform the entire bucket into a solid block of ice. The phase transition from liquid water to ice manages to store approximately 2.5 million joules of energy in that rather normal container. When the procedure is reversed, these numbers add up to adequate cooling capacity to provide around 700 watts of chilled air for an hour. On the cooling side, a pump circulates a 50-50 mix of water and ethylene glycol via twenty feet of copper tubing coiled deep inside the frozen block. That liquid sucks cold from the ice and drains to a standard automobile radiator with a little fan attached. Only a few watts are required to run the pump and fan, so the battery may continue to provide power even after sunset.

The insulation around the bucket is so strong that heat only leaks in at about 7 or 8 watts. Testing revealed that the ice remained frozen solid for several days, with almost no evidence of melting. The microcontroller’s voltage logging revealed that the compressor was kicking in at 12.9 volts and shutting out at 11.1 volts to keep the battery happy, while solar was still charging. The real-world trial put it through its paces inside the truck cab. Even on a warm day, circulating that refrigerated glycol significantly reduced the inside temperature over a few hours. The entire setup is slightly heavier than a basic battery pack, but it is still suitable for mobile use or small structures where grid ties do not seem like an option.

Scaling up becomes easy from here on out, since adding more solar panels and a larger water tank increases the output to several kW. Cabins and recreational vehicles were already an appropriate fit, both in terms of size and energy requirements. As an added plus, a whole house may use the system as an extra cooling source when it’s really hot outside without having to transfer any excess electricity back to the power company.

Water carries the load rather than all those chemical batteries. So the storage remains compact while the pricing remains affordable. One cubic metre of ice has roughly 93 kilowatt-hours of cooling power and weighs less than a stack of cells. The compressor runs on standard n-butane refrigerant that has been charged into a closed loop. It never interacts with the glycol side. Every last piece was built with off-the-shelf parts, some copper fabrication, and some custom code for monitoring.
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