What is the operating temperature of the particular PVC conduit?

Very light duty temperature conduit is only rated to ambient (and internal cable) temperature not to exceed 60 deg C, which probably gives a max conductor temperature of  70 deg C at most.See also: https://www.tlc-direct.co.uk/Book/4.5.1.htm

However, there are upper temperature range performance classifications of +90, +105, +120, +150, +250 and +400 deg C also available.

Using the higher temperature conduit (give or take issues with them being available to touch), it's perfectly reasonable to consider 90 deg C.

A real application at this temperature? Well, have a look in BS 7671:2018+A2:2022, Regulation 712.521.101 - especially item (ii) - along with the fact that Regulation 712.523.101 requires an ambient temperature of at least 70 deg C for wiring systems underneath panels - could lead you to consider that, at least for those parts of the  DC cabling, we might be considering 90 deg C conductor operating temperature. (The usual insulated and sheathed single-core Solar DC cable H1Z2Z2-K to BS EN 50618, that doesn't need conduit in most situations, but might for additional mechanical protection, is rated for 90 deg C conductor operating temperature continuous with short-term 20000 hours at 120 deg C for a max ambient of 90 deg C. Still the question as to how we safely terminate but I guess the answer to that is "at some distance from the panels, and/or in expensive heat-resistant terminals".)

So ... could well be DC cabling for solar, but I'm guessing from the info  lyledunn  has given us, that this isn't the case, because there are 3 circuits in the same conduit (so the learner needs to use grouping factor as well) leads us away from that, possibly backing up Lyle's judgement of 'perhaps an ill-considered design solution' - however, there may well be an application out there for which it becomes a distinct possibility.

What is the operating temperature of the particular PVC conduit?

Very light duty temperature conduit is only rated to ambient (and internal cable) temperature not to exceed 60 deg C, which probably gives a max conductor temperature of  70 deg C at most.See also: https://www.tlc-direct.co.uk/Book/4.5.1.htm

However, there are upper temperature range performance classifications of +90, +105, +120, +150, +250 and +400 deg C also available.

Using the higher temperature conduit (give or take issues with them being available to touch), it's perfectly reasonable to consider 90 deg C.

A real application at this temperature? Well, have a look in BS 7671:2018+A2:2022, Regulation 712.521.101 - especially item (ii) - along with the fact that Regulation 712.523.101 requires an ambient temperature of at least 70 deg C for wiring systems underneath panels - could lead you to consider that, at least for those parts of the  DC cabling, we might be considering 90 deg C conductor operating temperature. (The usual insulated and sheathed single-core Solar DC cable H1Z2Z2-K to BS EN 50618, that doesn't need conduit in most situations, but might for additional mechanical protection, is rated for 90 deg C conductor operating temperature continuous with short-term 20000 hours at 120 deg C for a max ambient of 90 deg C. Still the question as to how we safely terminate but I guess the answer to that is "at some distance from the panels, and/or in expensive heat-resistant terminals".)

So ... could well be DC cabling for solar, but I'm guessing from the info  lyledunn  has given us, that this isn't the case, because there are 3 circuits in the same conduit (so the learner needs to use grouping factor as well) leads us away from that, possibly backing up Lyle's judgement of 'perhaps an ill-considered design solution' - however, there may well be an application out there for which it becomes a distinct possibility.