The entire 20-page study is worth reading. Here I highlight some of the report’s key points regarding batteries, Moore’s Law, and the physical limitations of wind turbines and solar photovoltaics.
“Availability”—having energy when you want it—“is the single most critical feature of any energy infrastructure.” The pervasive non-availability of energy is what chiefly hobbled economic and social progress in pre-modern times. The comparative ease and low cost of storing fossil fuels and other conventional energies is “why, so far, more than 90 percent of America’s electricity, and 99 percent of the power used in transportation” come from those sources.
Climate campaigners claim battery technology will soon make renewable electricity available to all with little or no fossil-fuel backup. However, the expense would be formidable. It costs less than $1 a barrel to store oil or energy-equivalent quantities of natural gas and coal, but battery storage of the same amount of energy “costs roughly $200.” In other words, “the cost to store energy in grid-scale batteries is . . . about 200-fold more than the cost to store natural gas to generate electricity when it’s needed.”
Batteries are getting cheaper and lighter, but not enough to economically replace fossil fuels for machines that move large numbers of people, grow food, or mine minerals and raw materials. For example, “the energy equivalent of the aviation fuel actually used by an aircraft flying to Asia would take $60 million worth of Tesla-type batteries weighing five times more than that aircraft.”
Faced with such impediments, some new energy economy enthusiasts claim renewables are on the verge of the same sort of accelerating efficiency gains that occurred in the information technology sector, as predicted by Intel co-founder Gordon Moore in 1965.
That is not happening. As Varun Sivaram, chief technology officer of India’s largest renewable energy company, observed in April 2015:
Earlier this month, Moore’s law—the prediction that the number of transistors on an integrated circuit would double every two years—turned 50 years old.
It so happens that the silicon solar panel, the dominant variety in the market today, is about the same age—roughly 52 years old. And over the last half-century, while the computing power of an identically sized microchip increased by a factor of over a billion, the power output of an identically sized silicon solar panel more or less doubled.
Here’s how Mills puts the same point: “If photovoltaics scaled by Moore’s Law, a single postage-stamp-size solar array would power the Empire State Building. If batteries scaled by Moore’s Law, a battery the size of a book, costing three cents, could power an A380 to Asia.”
Why doesn’t Moore’s Law apply to the energy sector? Miniaturization dramatically increased the power of integrated circuits and decreased the cost of computational devices. However, miniaturizing renewables would turn them into children’s toys. To collect enough of nature’s diffuse energy to power a modern society, wind turbines and solar arrays must be huge. Unsurprisingly, the size, mass, and industrial footprints of renewable facilities increased over time.
Moore’s law does not apply because the “challenge in storing and processing information using the smallest possible amount of energy is distinct from the challenge of producing energy, or of moving or reshaping physical objects.” Mills elaborates:
The world of logic is rooted in simply knowing and storing the fact of the binary state of a switch—i.e., whether it is on or off. Logic engines don’t produce physical action but are designed to manipulate the idea of the numbers zero and one. Unlike engines that carry people, logic engines can use software to do things such as compress information through clever mathematics and thus reduce energy use. No comparable compression options exist in the world of humans and hardware.
The cost of renewables has declined 10-fold in recent decades. However, as with fossil fuel combustion, which also achieved rapid efficiency gains when first commercialized, the “path of improvement” for renewables has begun to exhibit “diminishing returns.” That is inevitable given the inherent “physics-constrained limits of energy systems.” Mills explains:
Solar arrays can’t convert more photons than those that arrive from the sun. Wind turbines can’t extract more energy than exists in the kinetic flows of moving air. Batteries are bound by the physical chemistry of the molecules chosen.”
For combustion engines, the Carnot Efficiency Limit dictates a theoretical maximum conversion of heat into useful work of about 80 percent. Today’s best hydrocarbon engines achieve about 50-60 percent conversion efficiency, so there’s “still room for improvement” but nothing like the “revolutionary advances” achieved in the early “decades after invention.”
For wind, the Betz Limit holds that a spinning blade can capture no more than about 60 percent of the kinetic energy of moving air. “Modern turbines already exceed 45 percent conversion.” Hence, a further “10-fold improvement is not possible.”
Similarly, for photovoltaic cells, the Shockley-Queisser Limit determines that PVs can convert no more than about 33 percent of photons into electrons, and modern PVs achieve more than 26 percent efficiency. Thus, there are also “no 10-fold gains left” for PVs.
Mills concludes “there is no possibility of a near-term transition” to a new energy economy. Coal, oil, and natural gas “are the world’s principal energy resource today and will continue to be so in the foreseeable future.”