The National Renewable Energy Laboratory (NREL) in Colorado is a hotbed of research and innovation.
One field its researchers are looking at is that of biofuels, which can be produced from biomass. Breaking things down, biomass can include anything from algae to wood and manure.
The potential of biofuels is significant. "Biofuels are very important for sustainable transportation," the NREL's Thomas Foust told CNBC's "Sustainable Energy." "Biofuels, designed intelligently, can provide efficiency gains and emission benefits in synergy with their hydrocarbon counterparts for a very sustainable, clean, transportation energy future."
While there is undoubted promise, there are challenges. Foust said that the main hindrances to the progress of second-generation biofuels were the underlying science and technology to "make them efficient as well as high yields and cost effective."
Growth has been a challenge. According to the International Energy Agency, output of conventional transport biofuels, such as sugar and starch based ethanol and hydrotreated vegetable oil, grew by only 2 percent in 2017.
One key project at the NREL is the Co-Optimization of Fuels and Engines initiative, a collaboration between the NREL, the U.S. Department of Energy and a number of other national laboratories.
Its aim is to transform both vehicles and transportation fuels to "maximize performance and energy efficiency, minimize environmental impact, and accelerate widespread adoption."
Away from the NREL and looking at the broader biofuels landscape, the University of Cambridge's Erwin Reisner told CNBC that biofuels were an important part of the energy mix but that there were also limitations.
"Let's take a good example, like Brazil, where we can (use) … sugarcane to produce bioethanol, and this works particularly well because there's low population density in Brazil plus sugarcane is an attractive, efficient crop," he said.
"In the northern hemisphere it's much more complicated because if we look at … corn, for example in the U.S. or soybeans in Europe, we get much less energy out of these beans, we have high population density." Overall, implementation in these markets was more difficult, he added.
Reisner said that an attractive scenario would be to use crops for food production and waste products to produce biofuels. In the years ahead, the adaptation of engines will be crucial.
"Engines can generally be adapted," he explained. "If we look at Brazil, you can buy flexible vehicles, go to your gas station and put in your tank anything from fuel gasoline to pure bio ethanol and any mixture thereof … it's possible with certain legislation to implement this," he added.