For photographic images, dithered PNGs have worse quality:size ratio than JPEGs. If you want small files and are willing to sacrifice quality you can turn the JPEG compression up or reduce the resolution.
https://solar.lowtechmagazine.com/2023/06/rebuilding-a-solar...
https://solar.lowtechmagazine.com/about/the-solar-website/ (Lots of comments at the bottom about image compression)