Power Circuit Problem - Output DC Voltage is dropping form its supposed value
R9, R10, the voltage feedback divider for the LMR14006 buck converter, should be on net P$2 (right hand side of the 1st 3.3 uH) and NOT on net P$1 (lhs of 3.3 uH). 




At very low loads IC1 will be off most of the time and the voltage across L1 will be low. When you load the output the IC1 feedback pin sees the divided output of the IC1 switch pin  - either full Vin or a D4 diode drop above ground. IC1 either goes insane or if there is enough capacitance on IC1 pin 3 (FB pin) it may see an average DC value.


For a single PV panel you can produce a good approximation to MPPT by holding the voltage at IC1-5 at the optimum voltage for the panels (Vmp). This is typically 80 - 85% of Voc depending on the cells fill factor and can easily be determined in practice or (if you must) from theory. Increasing this voltage slightly with increasing load current produces an even better match to MPPT. 
For multiple panels this approach is "problematic" except when all panels are identical and equally illuminated.

I'm not sure what the input diodes are intended to do. They would serve to isolate the effects of shading on some of the panels. Efficiency losses will be incurred - how much depends on panel voltage. You do not say what Vmp is. AT 12V a diode at the input will lose you around 1V/12V ~= 8%. At 30V that's 1V/30V =~ 3%.

Adding a small capacitor across R9 and R12 will improve transient response of the two converters. Value tbd but probably in the 100's of pF range. 

Components MUST have names on diagrams - L1, L2 etc.