Best way to fit 1800mm shelves in a wide alcove?

Hi I would get some 6 or 8 mm stainless bar and chemical fix these into the wall then rest your shelf on the top

Other answers are perfectly in order, yet the best idea for strong shelving without chemical fixing is carpentry designed bespoke solid timber or good quality 18mm MDF (for printing & painting) or prefinished veneered laminate board, and 18mm thickness plywood, timber battening is ideal and best if used with secret or plug fixings. The secret is in the way the battens (preferably) planed timber sections that can be skilfully designed to cosmetically integrate with the shelving material. Try and avoid the d.i.y. sheds as the shelving material tends to be of 15mm thickness. Hope this helps.

i would use tile batern on the three sides, fix the shelves to it on top then fix another piece of battern above the bottom two shelves then hide these by fixing some tongue and groove, making the whole thing look like one. then i'd fit some arcitrave around the edges to hide the side batterns....effectively it would look lkke the top half of a welsch dresser

It all depends on your wall construction. To use on any wall type I would make up an outer frame with a solid back with shelves within..... like a bookcase .