Pragmatic Principle 15: Iron Law of Power Density

Robert Bryce makes a persuasive argument that ultimate problem with wind and solar resources is simply a matter of  “basic math and simple physics” associated with the Iron Law of Power Density

Bryce explains that there are a couple of facets to the Iron Law of Power Density.  The first is the effect on resources needed and the second is the area needed to produce power.   He describes the effect on resource intensity:

The shape and size of our energy systems are not being determined by political beliefs about climate change. Instead, those systems are ruled by the Iron Law of Power Density which says: the lower the power density, the greater the resource intensity. This can easily be seen in the graphic below. It includes a screen grab from a 2021 International Energy Agency report on the mineral intensity of various methods of electricity generation. The mineral intensity of offshore wind, including huge amounts of copper and zinc, is shocking: roughly 15,400 kilograms per megawatt of generation capacity. That is roughly 13 times more than the amount needed for natural gas-fired generation (1,148 kg) and six times more than what’s needed for a coal plant (2,479 kg).

Bryce points out that this is part of the reason that there are cost issues associated with offshore wind development:

As Howard Rhodes of EnergyPortal.eu explained earlier this month, the offshore sector is facing “a financial crisis as costs continue to rise. Inflation in components and labor costs, along with rising interest rates, has led to a 57% increase in the costs associated with U.S. offshore wind projects since 2021.” Soaring commodity prices have also increased the cost of making onshore wind turbines. By one estimate, the cost of building a wind turbine has surged by 38% over the past two years.

Bryce explains why the area needed to produce power is an important component of the Iron Law of Power Density. 

Power density is the measure of energy flow that can be harnessed from a given area, volume, or mass. Power density is a measure of how many watts we can get per square meter, liter, or kilogram from a given source. This article focuses on areal power density. Proving why low-power-density sources are the wrong choice for modern society takes only a modicum of effort.

Let’s start by looking at corn ethanol and other biofuels, which have a power density of about 0.1 watt per square meter. Counteracting that paltry power density requires lots of other resources, including fertilizer, diesel fuel, water, and staggering amounts of land. In 2021, Dave Merrill, a reporter and data analyst at Bloomberg, reported that “Two-thirds of America’s total energy footprint is devoted to transportation fuels produced from agricultural crops, primarily corn grown for ethanol. It requires more land than all other power sources combined.” Merrill determined that biofuels require the cultivation of about 80,000 square miles of cropland. That’s an area bigger than the state of Nebraska.

Bryce summarizes the land-use implications:

The only way to substantially increase the production of wind and solar energy is by seizing more and more land, (or ocean) so they can be covered with more and more steel, concrete, copper, and silicon. As I reported in these pages on August 4, in “Massive Riots, Renewable Resentments,” the backlash against the encroachment of large wind and solar projects is real, it’s global, and it’s growing. As can be seen in the Renewable Rejection Database, the total number of rejections and restrictions on wind and solar in the U.S. now totals 575.

This is an important addition to my list of pragmatic environmental principles.  Power density affects the resources needed to develop the resource.  Its importance is confirmed as the costs of wind developments have increases significantly recently.  In addition, power density means that much more land is needed to develop wind and solar resources.