DIY solar cooling system freezes water by day, cools homes at night
Air conditioning accounts for roughly 10 percent of global electricity consumption, and that figure is rising fast.
To address this challenge, a Florida resident created a functional off-grid cooling system built entirely from off-the-shelf parts — and the physics behind it are surprisingly compelling.
How the system works
The setup begins with three standard 100-watt solar panels mounted on a vehicle. These panels feed electricity to a charge controller, which manages how the battery is charged to prevent overcharging.
The charge controller is connected to a 35-amp-hour lead-acid battery, a type of rechargeable battery commonly used for energy storage.
When the battery is fully charged, a microcontroller—an electronic device programmed to control other devices—triggers an inverter that converts the battery’s direct current (DC) power to alternating current (AC) power.
This powers a miniature refrigerator compressor running on R600 refrigerant, another name for n-butane, a type of refrigerant sealed in a closed loop system.
That compressor draws heat from a 2-gallon water bucket wrapped in about 1-inch foam panels and fiberglass wool insulation, which slows heat transfer.
Over several hours of direct Florida sun, the compressor cools the water, turning the entire bucket into a solid block of ice. This process stores approximately 2.5 million joules of thermal energy—in the form of heat—in an ordinary plastic container.
Heat leaks back in at around 7 to 8 watts through the insulation, so the ice stays frozen for several days with minimal loss, well beyond a single night’s cooling requirement.
Releasing the cold on demand
The cooling side works through a separate glycol loop. A small pump circulates a 50/50 mix of water and ethylene glycol through 20 feet of copper tubing coiled inside the frozen block.
The fluid absorbs cold from the ice and flows to a standard automotive radiator fitted with a small fan, pushing chilled air into the surrounding space.
The pump and fan together draw only a few watts, so the battery can run them well after sunset without significant drain. In real-world testing, the system cooled a truck cab significantly over a couple of hours on a warm day, validating the concept.
Discharge capacity is roughly 700 watts of effective cooling per hour — comparable to a small window air conditioner — delivered with almost no electricity at the point of use.
Why ice beats batteries for this job
The energy density of ice as a thermal storage medium is impressive. One cubic meter of ice holds about 93 kilowatt-hours of cooling capacity, comparable in energy to a large chemical battery pack but at a fraction of the cost and without degradation over charge cycles. Water never loses its latent heat of fusion no matter how many times it freezes and thaws.
The compressor handles the energy-intensive freezing step during peak solar hours, when panels would otherwise throttle back or dump excess power.
The stored cold is then released passively, shifting the cooling load to when it is needed — evening and night — without drawing from the grid.
Scalable and practical
The system’s architecture scales straightforwardly. A larger water tank and additional solar panels increase output proportionally, with one cubic meter of ice providing enough cooling for a small house.
The creator notes the concept suits cabins, RVs, and off-grid structures particularly well — anywhere grid ties are impractical or expensive.
Every component — panels, battery, compressor, copper tubing, radiator — is commercially available. The microcontroller code automatically handles voltage-based compressor cycling, protecting the battery while maximizing freeze time.