Moving from the present world to one where renewable power dominates our energy economy is going to require some additional technologies. These may include storage, enhanced grid management, and demand-response power management, but they could also include something entirely new. Recently, a paper took a look at a technology I hadn’t realized even existed.

The paper evaluates the potential of what its authors are terming “nighttime photovoltaic power,” and the simplest way of thinking about it is “running solar panels in reverse”: generating electricity by radiating energy away into space. The efficiency is nothing like that of standard photovoltaics and can’t even get there except in unusual circumstances. But as the name implies, it can keep generating power long after the Sun goes down.

Photovoltaics at night

The easiest way to understand this tech is to think of a photovoltaic device in equilibrium with its environment. Here, incoming photons will occasionally liberate an electron, leaving behind a positively charged hole. These can then combine, radiating a photon back out of the device. When operating as a photovoltaic device, there’s a large excess of photons coming in, producing a corresponding excess of electrons and holes that can then be harvested as electricity.