Why Solar Panels Can’t Get Much More Efficient (And That’s Okay!)

Shockley-Queisser and the limits to converting sunlight into electricity

Ground-mount solar panels in Jurupa Valley, CA. Image by US Department of Energy (US government work).
LEDs and solar cells are just the inverses of each other! Left side of figure US government work; overall figure by the author.
Periodic table of elements and the first few rows highlighted: As we move across columns from left to right, we add electrons to the element’s outermost shell, until a stable, full valence is reached on the right. By virtue of their position in a common column, carbon and silicon have similar chemistries. Periodic table adapted from https://pubchem.ncbi.nlm.nih.gov/periodic-table/ (US government); overall figure by the author. All remaining figures by the author.
The left-hand figure gives the solar spectrum in terms of wavelengths hitting the surface of the Earth (as well as the “top of the atmosphere”). On the right side, the energy of a photon with any given wavelength is indicated by the blue curve: Any electron with a wavelength above about 1,150 nm carries less than 1.1 eV, and so its energy is lost. For electrons with shorter wavelengths, only 1.1 eV is used for photoexcitation, and so the energy gap between 1.1 eV and whatever the photon carries is wasted. The inscribed spectrum is simply for reference (not to scale).
Energy losses and “spectral efficiency” based on a standard solar spectrum and a band gap energy of 1.1 eV.

Key Points

References

Academic with a background in medicine, mathematics, and engineering (MD,PhD). Interested in agriculture and how consumption drives global environmental change.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store