Finding alternate sources of energy is a constant concern for scientists and one of the latest developments involves the INTA Project from Argentina's National Institute of Agricultural Technology. It revolves around a plastic backpack that attaches to cows in order to collect their, well, farts. The natural gas of cows is jam-packed with methane. Extracting about 300 liters a day, the INTA Project can run a car or fridge for 24 hours.
To achieve this, tubes from the INTA Project's backpack are inserted into the cows' rumens (their biggest digestive tract). Interestingly, the project is not ongoing. It is simply being conducted to show that it is possible to collect methane from cows and use it for energy, but not necessarily for mainstream systems.