The landscape of Bangladesh is lined with tin huts and a practically invisible energy grid. Over 70 percent of the country’s population lives without power, and in a location that approaches 45°C (113°F) in the summer months, that could mean unbearable and dangerous living conditions.

Enter the zero-electricity cooler: Eco-Cooler. Built with re-purposed bottles, the panels use the simple concept that as hot air passes through the wide end of the bottle, it will cool as it is compressed and pushed out of the narrow end into the home. So far, families have seen temperature drops of five degrees after using the devices.

“After initial tests, blueprints of the Eco-Cooler were put up online for everyone to download for free.” Sayed Gousul Alam Shaon, managing partner of the project said in a release. “Raw materials are easily available, therefore, making Eco-Coolers a cost-effective and environmentally-friendly solution.”