Solar water heater vs Heat pump for heating water?
I see 5 questions:

1) Solar hot water in the morning and on cloudy days.  Your usage pattern is worst-case since maximum solar energy availability is soon after your usage.  So you will need a storage tank that can keep the water hot until you need it.  Lots of variables here so your best bet is to consult an insulated tank supplier in your area.  As far as cloudy days, you're either going to have to upsize the tank considerably (probably not feasible) or plan on installing a backup hot water heater.

2) Power consumption of heat pump based hot water heaters.  These can be 2-3 times more efficient that a standard resistance heating water heater.  The formulas for calculating energy to raise a liter of water 1 degree are straightforward and you can do that yourself.  But keep in mind that most of these units also have resistance backups when demand exceeds capacity of the heat pump and that can reduce your savings.  Also remember that these effectively cool the room they are in and that can impact your heating costs.

3) Reliability.  Heat pump units are more complex that solar units and it's likely will require more maintenance and not last as long.  But depending on the solar unit you choose, there may be reliability and longevity issues with that as well.  Check with your supplier for their warranties.  Also keep in mind that you will have a pump with the solar unit that may need maintenance.

4) Maintenance costs.  See above but it's difficult to say without specifics and even then it's a lot of guesswork.  You need to rely on the data provided by the supplier of your specific equipment and, as you know, your experience may vary.

5) Insulated pipes.  In either case YES, you will want to insulate the hot water pipes to conserve as much of the heat energy as possible.