Biofuels are liquid fuels derived from biomass such as cereals, sugarcane, soy, palm oil, and other agricultural crops. They are intended to serve as a substitute for conventional fossil fuels in transport and energy production. Historically, biofuels gained prominence in the early 2000s as a low-carbon alternative to petroleum, particularly in countries like the United States, Brazil, and the European Union, where crops like corn and sugarcane were processed into ethanol and biodiesel.

The use of biofuels aimed to reduce dependency on imported oil, promote energy security, and curb greenhouse gas emissions. However, while biofuels contributed around 4% of global transport energy demand, their climate benefits have been debated because emissions from cultivation, land use changes, and fuel production can offset the gains. Moreover, the opportunity cost of using fertile land for fuel instead of food or reforestation adds another dimension to their sustainability challenge.

The opportunity cost of land is a critical consideration because agricultural land used for biofuel production could alternatively be used for food crops, reforestation, or renewable energy generation. While biofuels occupy roughly 32 million hectares of land globally, this land could potentially generate much higher energy returns if used for solar panels or other renewable energy projects.

From a climate perspective, freeing land from biofuel crops allows for carbon sequestration through rewilding or afforestation, which may provide greater environmental benefits than growing fuel crops. Additionally, dedicating the same land to solar energy could produce around 32,000 TWh per year—23 times more energy than the current output of liquid biofuels—demonstrating that land use decisions have significant implications for sustainable energy and climate mitigation strategies.

Land currently used for biofuels could be repurposed for solar energy production, which can then power electrified transport. If solar panels were installed on 32 million hectares of land currently devoted to biofuel crops, they could generate approximately 32,000 TWh of electricity annually. This is enough to meet the world's entire electricity demand, indicating the massive potential of solar deployment.

With the rising adoption of electric vehicles (EVs), this solar electricity could be used to power all cars and trucks globally, which require roughly 7,000 TWh per year. Even using only one-quarter of this solar energy could electrify all road transport, leaving the remaining land for other purposes such as food production, limited biofuel crops, or rewilding. This approach highlights the synergy between renewable energy generation and electrification of transport for decarbonisation.

Biofuels are inherently less efficient than solar energy due to the low conversion rate of sunlight into biomass through photosynthesis. Plants generally convert less than 1% of sunlight into usable energy, and additional losses occur during processing and conversion into liquid fuels. Even high-performing crops like sugarcane are far less efficient than solar panels, which convert 15–20% of sunlight into electricity, with some designs achieving up to 25%.

In contrast, electricity generated from solar panels can directly charge electric vehicles, minimizing energy losses associated with growing, harvesting, and processing crops into fuels. Consequently, while biofuels occupy large tracts of land for relatively modest energy output, solar panels can generate significantly more energy on the same land area, offering a more scalable and climate-effective approach for decarbonising transport.

Replacing biofuel crops with solar panels has several advantages. First, it dramatically increases energy efficiency and output; solar panels could generate 23 times more energy than current biofuels on the same land area. Second, it supports electrified transport, which is emerging as a major decarbonisation strategy for road vehicles. Third, it frees land for alternative uses, including food production, biofuel for aviation, or rewilding for carbon sequestration.

However, there are limitations. Solar power is intermittent and requires energy storage and grid infrastructure to ensure reliable availability. Transitioning to solar-based electrification also depends on widespread adoption of electric vehicles, which is still gradual. Land use changes can have socio-economic impacts on farmers dependent on biofuel crops for livelihood. Therefore, while solar offers significant efficiency and climate benefits, a balanced, multi-use strategy that considers food security, energy reliability, and socio-economic impacts is essential.

Brazil is a prominent example where sugarcane-based ethanol plays a major role in transport energy, accounting for a substantial share of domestic fuel consumption. Similarly, the United States relies heavily on corn-based ethanol, and the European Union produces biofuels from cereals and rapeseed. These crops occupy millions of hectares of fertile land, with Brazil alone dedicating significant sugarcane plantations to ethanol production.

While these biofuels contribute to energy security and emission reductions, the land use has trade-offs. Large-scale cultivation can compete with food production, drive deforestation, and limit carbon sequestration opportunities. As demonstrated in global analyses, the 32 million hectares used for biofuels could alternatively produce 32,000 TWh of electricity via solar panels, highlighting the opportunity costs of land allocation decisions and the need to balance climate, energy, and food priorities.

Converting half of biofuel cropland, roughly 16 million hectares, to solar energy could produce around 16,000 TWh of electricity annually. This is more than twice the total energy currently derived from all biofuels globally and could fully meet global road transport electricity demand, which is estimated at 7,000 TWh per year. The remaining land could continue to produce biofuels, support food production, or be rewilded to sequester carbon.

The carbon impact would be substantial. By generating electricity directly from solar and using it to power electric vehicles, the inefficiencies and emissions associated with crop cultivation, harvesting, and fuel processing would be avoided. Additionally, EVs powered by solar reduce tailpipe emissions, contributing significantly to climate mitigation. Such a strategy demonstrates a practical pathway to maximize energy output, enhance land-use efficiency, and accelerate transport sector decarbonisation while balancing other land use priorities.