Fossil fuels still supply about 86% of the world’s total energy, even though renewables generated a third of global electricity in 2024. The gap between those two numbers tells most of the story: electricity is only one slice of energy use, and replacing fossil fuels in transportation, heating, and heavy industry is far harder than adding solar panels to a grid. The reasons we haven’t switched are a tangle of physics, economics, infrastructure, and politics.
Renewables Cover Electricity, Not Energy
One of the most common misconceptions is conflating electricity with energy. Electricity powers your lights, appliances, and increasingly your car. But energy also includes the jet fuel in a 747, the natural gas heating a home in January, and the coal baking limestone into cement at 1,700°C. Renewables met just over 8% of total global energy demand in 2024. The other 78 percentage points of that fossil fuel share come from sectors where plugging into the grid isn’t straightforward or, in some cases, isn’t yet possible.
The Energy Density Problem
A kilogram of gasoline contains about 12,200 watt-hours of energy. A kilogram of the best lithium-ion battery holds roughly 150 watt-hours, about 80 times less. For a car making short daily trips, that tradeoff is manageable because electric motors are so much more efficient than combustion engines. For a cargo ship crossing the Pacific or a long-haul truck carrying 40 tons of freight, the math gets brutal. You’d need a battery so heavy it eats into the payload, which is why shipping and aviation still run almost entirely on liquid fuels.
Diesel is similarly energy-dense at 12,700 watt-hours per kilogram. These fuels pack an extraordinary amount of energy into a small, portable, stable package that can be pumped, piped, and stored cheaply. No battery technology available today comes close to matching that convenience for applications where weight and volume matter.
Intermittency and Grid Reliability
Solar panels only produce electricity when the sun shines. Wind turbines only spin when the wind blows. This isn’t a slogan; it shows up clearly in capacity factor data. According to the U.S. Department of Energy, solar plants produced power at about 23% of their maximum rated capacity in 2024, and wind plants at about 34%. By comparison, natural gas plants ran at roughly 60% and coal at 42%, with the lower coal number reflecting deliberate scaling back rather than an inability to run.
The practical consequence is that a grid powered entirely by wind and solar needs massive energy storage to cover nights, calm days, and winter weeks with low sun. Grid-scale battery storage is growing fast, but it remains a small fraction of what would be needed to back up an entire national grid for hours or days at a time. Until storage catches up, fossil fuel plants (especially natural gas) serve as the backup that keeps the lights on when renewables drop off.
Steel, Cement, and Extreme Heat
Some industries don’t just need electricity. They need intense, sustained heat and specific chemical reactions that fossil fuels currently provide. Steelmaking heats iron ore to between 1,700°C and 3,000°C in the presence of carbon from coal-derived coke. The carbon isn’t just fuel; it chemically strips oxygen from the iron ore. Producing a ton of steel releases about 1.8 tons of CO₂.
Cement is similarly locked in. Calcium carbonate is heated in a kiln, and the chemical reaction itself releases CO₂ regardless of the heat source. Each ton of cement produces roughly a ton of CO₂ equivalent. Both materials cost less than $150 per ton to manufacture with conventional methods, making them extraordinarily cheap and extraordinarily hard to replace. Experimental alternatives like molten oxide electrolysis for steel and electric kilns for cement exist, but none operate at commercial scale yet.
The Cost Picture Is Shifting
For new power plants, renewables have already won the cost race in most places. The U.S. Energy Information Administration estimates that utility-scale solar entering service in 2030 will cost about $37.58 per megawatt-hour, compared to $64.55 for a new natural gas combined-cycle plant. Solar is cheaper than gas on average and in most U.S. regions, even without tax credits.
But cost per megawatt-hour for new builds isn’t the whole picture. The world already has trillions of dollars of fossil fuel infrastructure: pipelines, refineries, tanker fleets, gas distribution networks, and power plants with decades of operational life remaining. Shutting down a functioning gas plant to build a solar farm that’s cheaper per unit of new electricity still means writing off the remaining value of that plant. Utilities, investors, and governments are reluctant to strand those assets, which slows the transition even when the economics of new construction favor renewables.
Subsidies That Tilt the Playing Field
Fossil fuels receive enormous financial support worldwide, much of it invisible. The International Monetary Fund calculated that global fossil fuel subsidies totaled $7.4 trillion in 2024. Of that, $725 billion was direct fiscal support: governments keeping gasoline or electricity prices artificially low. The remaining $6.7 trillion represents what the IMF calls implicit subsidies, essentially the health and climate costs of burning fossil fuels that don’t show up in the price. Air pollution and climate change account for about three quarters of that hidden total.
These subsidies make fossil fuels appear cheaper than they actually are. When the price of gasoline doesn’t reflect the cost of the respiratory illness it causes or the climate damage from its emissions, consumers and businesses have little financial incentive to switch. Removing or restructuring these subsidies would dramatically change the relative cost of fossil fuels versus clean alternatives, but doing so is politically difficult because it means higher energy prices in the short term.
Mineral Supply Constraints
Scaling up renewables requires mining. Building a wind plant uses about nine times more minerals than building a gas-fired plant of the same capacity. Lithium for batteries, rare earth elements for wind turbine magnets, and copper for electricity transmission all need to be extracted, refined, and processed, and the supply chains for these materials are concentrated in a handful of countries.
This doesn’t mean the transition is impossible. The total environmental footprint of mining these minerals is smaller than the ongoing extraction of coal, oil, and gas. But it does mean the transition faces real bottlenecks. Opening a new lithium mine takes 7 to 10 years from discovery to production. If demand for batteries and turbines outpaces mineral supply, it creates delays and price spikes that slow deployment.
Why the Transition Is Happening Anyway
Despite all these barriers, the shift is underway. Renewables are the fastest-growing energy source globally. Solar panel costs have dropped more than 90% since 2010. Electric vehicle sales are climbing steeply. The reasons we still use fossil fuels are real, but they’re increasingly economic and logistical rather than technological. The core challenge now is speed: replacing 86% of the world’s energy system involves rewiring not just power grids but industrial processes, transportation networks, heating systems, and the financial structures built around them. That’s a project measured in decades, not years, and it explains why fossil fuels remain dominant even as the alternatives get cheaper and better.