 However, the amount of funding and focus of that funding ebbs and flows between the alternative fuels over time due to advances in technology and interest in those fuels.CNG and propane were more popular in the early 2000s, the biofuels ethanol and biodiesel took center stage in the mid-2000s.The U.S. Department of Energy has awarded nearly $460 million through its funding opportunities for hundreds of projects across the country to implement alternative fuels and energy-efficient vehicle technologies.