Curiosity Box

Go to http://curiositybox.com/hyperspacepirate and use code HYPERSPACEPIRATE to get 40% off your first month until March 31. In this video I'll be showing how I store solar energy as ice in a "thermal battery" that can be stored and used later for air conditioning. Three 100W photovoltaic panels are mounted in the back of my truck and connected to a charge controller and 12V battery which runs a refrigeration compressor through an inverter connected to the 12V source. The compressor consumes approximately 80-100W of power, and freezes a 2 gallon (7.5 liter) bucket of water surrounded by thick insulation. With the water completely frozen, 2.5 megajoules of energy is stored in the phase change from liquid to solid, which could provide about 700 watts of cooling for an hour. Using the ice block for cooling is accomplished by pumping 50/50 ethylene glycol antifreeze through a long coil of copper tubing buried in the ice block and then through a radiator with a fan to provide cooling. The pump and fan only consume a few watts, so they can be run off the internal battery in the system for several days without a problem. I originally intended to monitor current and voltage for both the solar panels and the 12V supply, but the ACS712 current sensors I used started getting cooked at around 15 amps (despite just being hall effect sensors), and the charge controller has the solar panels isolated from the 12V source (presumably via some transformer with PWM switching), so I couldn't directly measure it with my arduino. So the only metric I was able to record was the voltage of the 12V source and whether or not the refrigeration compressor was running. The compressor is controller by an arduino that turns it and the condenser fan on at 12.9V and shuts it off at 11.1V. The arduino also logs the voltage of the 12V source to an SD card. Overall this was a big success, with the only drawback being the weight of the system due to the thermal reservoir, compressor, and battery. I was able to freeze the water during the afternoon and it provided me several hours of cooling in the evening after the sun went down. The weight, size, and power consumption of the system make it perfect for something like an RV or camper or small cabin. This system is more suited to a home/building and I'm fully confident that with more solar panels and a larger reservoir it could be scaled up to several kilowatts for a whole-house system to serve as an auxiliary air conditioner, allowing energy savings without needing to tie the solar panels into the grid.