Renewable Sources

The resource comes back; the machine that harvests it does not. Covers: Biomass — Burning What Grows Back and Marine Energy — Tides, Waves and Salt.

The resource comes back; the machine does not

The sun will rise again tomorrow, the wind will keep blowing, and water will keep falling under gravity long after any coal deposit or uranium mine runs dry: in that strict sense, these sources are inexhaustible on a human timescale. But that feature of the resource does not automatically carry over to the machine that converts it into electricity. A solar panel, a wind turbine, a hydroelectric dam or a geothermal well are built from finite materials — silicon, steel, copper, concrete, rare earths in some designs — occupy specific territory, degrade over time, and have to be replaced, repaired or decommissioned like any other piece of industrial infrastructure. Confusing the inexhaustibility of the resource with the inexhaustibility of the technology is the underlying error this section wants to correct.

Six machines, six ways of touching the land

The six sources in this section convert a natural resource into electricity through physically very different mechanisms, and each one leaves a different territorial and material footprint: solar PV converts light directly into current through semiconductors; wind extracts kinetic energy from air with blades that spin a generator; hydropower harnesses the potential energy of dammed or moving water; biomass releases, when burned, the chemical energy that photosynthesis captured months or years ago, not millions of years ago; geothermal extracts heat stored underground; and marine energy — still the least mature of the six — tries to capture the energy of tides and waves with devices that must survive the harshest environment of all: the open sea.

Diffuse by nature, not by design

Except for geothermal and, to a lesser extent, reservoir hydropower, these sources share a structural physical trait: the energy they harness arrives spread over a large surface — sunlight, wind, waves — instead of concentrated in a fuel that can be shipped by truck or tanker. That diffuseness is not an engineering flaw fixable with better technology, but a direct consequence of how solar and gravitational energy reach the Earth's surface: that is why capturing an amount of energy comparable to a thermal plant almost always requires far more land for collection. That is exactly the comparison this section's data pages quantify for each source.