The manufacturing sector has tons of businesses with just one location and 50 employees. Most of my clients have been in that category. I’ve also worked with multinational corporations, who you definitely can charge a lot more, but the bread and butter is family owned operations who don’t have a marketing or PR department and have no clue who to call when they want pictures, so they usually call the local chamber of commerce or economic development office for advice. That’s why its important to build relationships with those groups, you want them to refer you to those industries.
You ever see the show “How It’s Made”? It’s like that, but more artsy than educational. I haven’t worked with a power company before, but yes, that would also be industrial photography. It’s mostly manufacturing facilities; I’ve done work for a company that builds landing gears for big jets, a company that makes a bunch of different wood products (like wood flooring), several companies that make automotive interiors (ex. the seats for Honda, the dashboards for Nissan), a knife maker, several metalworking companies, a transit bus manufacturer (if you live in a major North American city with public transit, there’s a good chance it was made by this company), even the US Army’s largest tank and small arms repair and overhaul facility, and several other manufacturers. (The shoots I’ve done with the Army are by far my favorite, really cool to see tanks torn down and then reassembled).
Companies use my pictures when they’re looking for clients, they can show them what their facilities look like, what machines they have, what their manufacturing process is, etc. and the pictures look a lot more professional in their PowerPoint than just someone taking a pic with their phone. But yeah, industrial photography is basically pictures of people and machines working to make stuff.