EN 07 - Smart Solar Cooler: Innovative Sustainable Refrigeration

The smart solar cooler is a state-of-the-art device designed to keep drinks and food cold during outdoor activities such as camping, picnics or days at the beach.

Although it is not as efficient in terms of cooling as a fridge that uses a compressor and refrigerant fluid, the focus of the project is on portability and the use of solar energy as an alternative solution.

Built with an adjustable capacity between 20 and 30 liters, it is suitable for both family camping trips and medical brigades transporting vaccines to remote areas of the planet. It has been tested to cool from 24°C to 4°C in less than 30 minutes, maintaining a constant temperature between 4-6°C for a standard load of 12 liters of water.

The cooler uses high R-value insulation, advanced heat sinks with heat pipes and premium thermoelectric cells. Its lightweight, foldable 100 W solar panel makes it easy to transport and install and provides more than three hours of autonomy without the need to recharge the battery. Its intelligent control system allows you to adjust the desired temperature, offering a portable, lightweight and capacity-adjustable solution that makes it a reliable and sustainable cooling option ideal for the applications for which it was designed.

Our design is comprised of three main physical components: the container or cooler, the power and SMART control box, and the solar panel. The cooler not only serves as the physical means to maintain the temperature but also houses the heart of the cooling system, the thermoelectric cell, which converts the electrical potential difference into a semiconductor cell that transforms energy into thermal energy under the Peltier effect principle. It also has an efficient heat dissipation system using a forced ventilation heat radiator and the use of coupled heat pipes to allow more efficient heat dissipation than using conventional heat sinks. In addition, it has been designed to be able to vary the amount of usable cooler space depending on the load. By means of an adjustable door, the user can use the minimum cooler capacity (20 liters) or expand it up to the maximum capacity of 30 (liters). This feature not only reduces heat loss by providing an additional barrier but also allows an already opened beverage to be kept in the cooler's inner antechamber without having to open the cooler completely. The construction material is lightweight and has a thermal resistivity of about 7.5R, which provides excellent thermal insulation capacity once the desired point is reached. In addition, it has a protective reflective coating that reflects sunlight keeping it cool, waterproof and adds not only one but two extra layers of insulation by having a layer of air between the outer shell and the body of the cooler. Net weight is 5.25 lb (2.39 kg).

The control box, with a net weight of 7.24 lb (3.28 kg) stores the 12 volt, 18Ah Lithium Iron Phosphate (LiFePO4) battery. This battery is much more reliable and safer than conventional lithium batteries, with a superior discharge capacity and life span, and much lighter and more tolerant to overheating, making it ideal for the device. In addition, the control box contains the Arduino microcontroller specially programmed to monitor the internal temperature of the cooler and set a set point that turns the thermoelectric cell on/off to save energy when the desired temperature has been reached, functioning as a thermostat. In addition, the control box contains the 12 volt to 5 volt DC voltage converter for powering the LC display and the microcontroller and the battery charge controller that regulates and manages the electrical power that is supplied to the battery by the solar panel protecting the battery from overcharging. In addition, the control code was programmed to maintain the temperature between 6ºC and 7.5ºC, i.e. with a tolerance factor of +1.5ºC to further save the energy savings of the device. However, the set point can be adjusted by the user to set the desired temperature value inside the cooler. This is the SMART capability of the cooler.

The 100W solar panel uses monocrystalline technology to convert light energy from the sun into electrical energy to power the system more efficiently and under better conditions of low solar irradiance. It is also portable, lightweight and foldable. Easy to connect to the device.

The device has been tested for tens of hours both in empty condition (no load) and with the defined standard load of 6 liters (1/3 of the total capacity), corresponding to 12 bottles of water.  It can keep the water bottles below 6°C and even reduce their temperature to 4°C or more. In addition, once the device is completely turned off and unopened, it can maintain the temperature cool for more than 6 hours, reaching thermal equilibrium with the environment in more than 16 hours, which gives it an excellent performance in terms of thermal insulation.

We created this project to provide an affordable, off-grid solution to extend the autonomy of outdoor enthusiasts and medical brigades in remote areas. Our goal was to explore and apply thermoelectric applications, demonstrating that a full-scale working prototype can be built to provide effective small-scale cooling for specific applications. Our potential users are outdoor enthusiasts and health service bodies. Moreover, knowing the difficult conditions that some communities around the world face when living in remote locations isolated from urban centers, we wanted to provide a solution for transporting the vaccines and medicines that medical brigades require when dealing with the epidemic conditions that these communities often face. Furthermore, as outdoor enthusiasts, we wanted to offer a quality product that would allow adventurers or families to enjoy cold drinks in their free time while enjoying the environment and raising awareness about the applications that solar energy can have, even on a small scale, in everyday activities.