[vmh1928]

Pre-internet people subscribed to specialized periodicals. Home Power and Mother Earth News were two. Both were filled with case studies and DIY projects and the back pages had "send $5 for plans to build your own low-head hydro." I'm sure there were more publications (Stewart Brand's publications come to mind, Whole Earth Catalog and CoEvolution Quarterly for two.) The archives of Home Power (1987 - 2018) are here: https://www.homepower.com/

Popular Mechanics and other "Popular xxx" magazines are also examples. If you were lucky your local library subscribed so you could read them there (hopefully people hadn't stolen the issues or ripped pages out.)