  In this work, we assess the potential detectability of solar panels made of
silicon on an Earth-like exoplanet as a potential technosignature.
Silicon-based photovoltaic cells have high reflectance in the UV-VIS and in the
near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is
used to provide the 2022 human energy needs with a land cover of ~2.4%, and
projecting the future energy demand assuming various growth-rate scenarios, we
assess the detectability with an 8 m HWO-like telescope. Assuming the most
favorable viewing orientation, and focusing on the strong absorption edge in
the ultraviolet-to-visible (0.34 - 0.52 um), we find that several 100s of hours
of observation time is needed to reach a SNR of 5 for an Earth-like planet
around a Sun-like star at 10pc, even with a solar panel coverage of ~23% land
coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast
amounts of energy. Even with much larger populations than today, the total
energy use of human civilization would be orders of magnitude below the
threshold for causing direct thermal heating or reaching the scale of a
Kardashev Type I civilization. Any extraterrrestrial civilization that likewise
achieves sustainable population levels may also find a limit on its need to
expand, which suggests that a galaxy-spanning civilization as imagined in the
Fermi paradox may not exist.
