As our population grows and we use more natural resources than ever, the issue of renewable energy sources becomes ever more pressing. Innovation isn’t only important in the business world, it’s also crucial for ensuring the future of our planet. Fortunately, many innovative and uber-smart scientists have been on the task of experimenting and analyzing data to developing new, cleaner energy sources that may eventually replace fossil fuels like coal, gas and oil. Though solar and wind power get a lot of attention, there’s a lot more out there when it comes to renewable energy sources. Here are 5 of the most innovative—though these are far from the only odd options that have been explored.