a square glass brick with solar cells inside
https://files.mastodon.social/media_attachments/files/113/765/304/300/753/214/original/1810148376249524.webp
These ones (amusingly) do remind me of the 1980's glass brick wall fad, but they are used to replace windows or other glass in office blocks, buildings, and even bus stops. The inventors at Build Solar think they look better than solar panels and take up less space, so could be an alternative to current building materials.
Image Source: https://www.bbc.co.uk/newsround/64582127
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