The main reason is pretty simple: solar PV is different from every other source of electricity, in ways that make it uniquely well-suited to 21st-century needs. (Among those needs I count abundance, resilience, and sustainability.)

Every other commercial source of electricity — besides solar PV — generates energy through roughly the same means: by spinning a turbine.

Coal plants, gas plants, nuclear plants, and concentrated solar power plants are all just different ways of boiling water to produce steam that spins a turbine. Wind power harnesses the wind to spin a turbine. Hydropower dams use flowing water to crank a turbine. These spinning turbines, in turn, provide mechanical force to an electric generator, which translates it into electrical current (this is done by moving electrical conductors through magnetic fields — see Faraday’s Law).

Solar PV works differently: it converts sunlight directly into electricity. Photons of light excite the surface of a semiconductor, knocking electrons loose to become part of a charged electrical field, generating electromotive force that can be tapped by wires. (See: the photovoltaic effect.)

This difference sounds technical, but it is enormously consequential. It brings three obvious advantages, often touted by solar proponents.

First, a solar cell has no moving parts, so operation and maintenance costs tend to be very low. It has to be kept clean, but that’s about it.

Second, a solar cell requires no fuel — so fuel costs are zero. Once the initial investment is paid off, and subtracting modest O&M costs, the power produced is free.

And third, a solar cell generates power without any pollution.