Efforts to ween the economy off of fossil fuels and onto more renewable energy to address climate change face significant technological hurdles beyond the economic impacts of such a transition.
When considering the environmental costs and benefits of shifting away from fossil fuels – particularly in the transportation and industrial sectors of the economy – we must take into account each energy source's full life cycle.
The truth is that fully transitioning to a renewable energy economy will require a tremendous, and some argue an unsustainable amount of raw materials and land.
Renewable energy sources have a lower energy density than fossil fuels, so they often require more energy to capture the same amount of power from other sources per volume.
Gasoline, for example, is ten quadrillion times more energy-dense than solar radiation, one billion times more energy-dense than wind and water power, and ten million times more energy-dense than human power.
The result of this is that there are fundamental limits to how much energy we can extract from renewables compared with the amount of land area required for production. In many cases, the environmental impact of relying on more renewable energy may be the same or greater than extracting and burning oil, natural gas, or even coal.
To meet the most aggressive goals set by decarbonization advocates to address climate change, we’re talking about the full electrification of every sector of the U.S. economy, including manufacturing and transportation which together account for more than 70 percent of the petroleum used in 2019.
The transportation sector accounted for 28.2 quadrillion British thermal units (quads) of energy consumption in 2019, according to the Energy Information Administration. Transportation is the biggest energy consuming sector and has been since 2000. The vast majority of the energy used in transportation – 91 percent in 2019 – continues to come from petroleum. Renewables, mainly in the form of biofuels, account for 5 percent.
The industrial sector used 26.3 quads of energy last year with natural gas providing 40 percent of the energy input and petroleum 34 percent. A total of 9 percent of the energy consumed in the industrial sector – including manufacturing, agriculture, forestry, mining, and construction –came from renewables in 2019.
Several life-cycle analyses published in recent years confirm that wind, solar, and hydropower regularly require more raw materials, including iron, copper, aluminum, and cement per unit of energy produced than coal- and gas-fired electric generation.
Austrian researcher Edgar Hertwich found in a report co-written with an international team that solar photovoltaics (PV) can require 10 to 40 times more copper per megawatt-hour than fossil fuel-fired plants. Onshore wind generation can need five to 15 times more iron.
Mark Jacobson, a civil and environmental engineering professor at Stanford University, estimates that converting the global power sector to renewable energy would require nearly 4 million 5-megawatt wind turbines and about 90,000 utility-scale solar power plants of 300 MW each, plus 1.7 billion rooftop solar systems.
The total footprint required for 4 million wind turbines is about 50 square kilometers – the size of Manhattan – but the spacing needed between each turbine also must be taken into account.
Based on an estimated 50-square meter per megawatt-hour of annual production, including spacing and onshore wind production in the International Energy Agency’s (IEA’s) “Sustainable Development Scenario” – about 7,000 terawatt-hours in 2040 – would require a land area roughly the size of Germany.
Similarly, at 15 to 20-square meters per megawatt-hour (MWh) of annual output, generating the IEA’s Sustainable Development Scenario’s 7,200 TWh in 2040 would use 110,000-140,000 sq km of panels – equal to the land area of Greece – including around 60 percent of utility-scale capacity and 40 percent of rooftop generation.
These additional mining and land-use requirements are not inconsequential and raise questions about the true life-cycle environmental costs of renewable energy.
Life-cycle analysis of energy technologies gives a better idea of carbon dioxide emissions, including indirect emissions caused by the production of materials, manufacturing of equipment, and construction of plants. It shows, in particular, that renewable sources are not carbon-free.
A recent report by scientists from University College London found that renewable technologies become “relatively less attractive” once indirect emissions are taken into account.
The life-cycle emissions of wind amount to just 15 kilograms of carbon dioxide per MWh according to the National Renewable Energy Laboratory (NREL), versus 20 kg/MWh for hydropower, 25 kg/MWh for nuclear and a more substantial 60 kg/MWh for PV, which requires energy-intensive manufacturing.
This is still much better than combined-cycle gas turbines at 465 kg/MWh and coal at 1,050 kg/MWh. But the sun does not always shine; the wind does not always blow, and, as NREL notes, there are questions about whether battery storage can provide peak capacity in power grids, for the parts of the day when electricity use spikes.
That is why the world is not rushing to shun natural gas for its future power needs, even under low-carbon scenarios. Gas remains a secure provider of “baseload” power — the minimum amount of electricity needed to satisfy demand at any given time.
Natural gas is also extremely cost-competitive. The sharp drop in renewables costs in recent years has been impressive. Still, following the demand shock from the coronavirus pandemic, natural gas is back to being the cheapest option for new power generation in most of the world.
The IEA says global natural gas consumption is headed for an estimated 4 percent drop in 2020, and sees risk of “prolonged overcapacity” as the build-up in new gas and LNG export capacity from past investment decisions outpaces slower than expected demand growth.
Natural gas as is not only cheap; it also has the potential to be far cleaner than current technology.
International oil companies, many with 2050 net-zero carbon emission goals, are moving to address methane emissions from gas flaring to reduce life-cycle emissions. Some companies are also investing in “green gas” — natural gas produced from hydrogen or biogas — to further reduce their carbon footprint.
Most of the post-2021 growth in gas demand is expected to occur in Asia, led by China and India, where gas benefits from strong national support. These countries, where energy demand is growing fastest than the rest of the world, are looking at a combination of gas and renewables to meet their commitments under the 2015 Paris Climate Accord.
It’s important to remember that these emerging economies are focused on raising living standards first and environmental protection second. Natural gas is the obvious choice — it’s cheap and abundant. With increasing improvements to its environmental performance, natural gas should continue play a major role in meeting energy demand globally.
