yes the bentlys are ok for already clean stuff or high work, but i wouldnt want to use one again on a conservatory roof.
I think water pressure would be able to, but not how i was thinking, i dont think it would be very consistent. imagine like a paint roller on a pole, that kind of design but with bristles all the way around the tube, and a bit larger, with a gap i the middle with the chain to electric motor to power it. then you would only have to push it up and down each panel and the motor will do all the scrubbin for you. UPVC solvent cleaner is very good, having that too would really speed things up.
Done a job doing the soffit boards and gutters from a 25ft pole, and bently to keep it light still quite difficult and allot of strain to scrub upwards with the pole bent etc.. Come up well though.
Last conservatory the gutters were all frozen up, so i ended up taking the whole guttering sections off to clean.