The TP4056 has a Vinmax of 8V and can be safely operated, if desired, at 6V input.
TP4056 datasheet here
PV panel voltage regulation:
A reason to limit Vin is that the IC will charge at a decreasing maximum current as Vin increases due to thermal dissipation issues. Charging specifications are given at Vcc = 5V (datasheet page 1) so limiting Vin to 5VDC makes sense. Due to the non-critical voltage requirement, a zener diode of suitable wattage could be used (option A below). If tighter Vin control is wanted, a simple shunt regulator will suffice - eg a TL431 driving a shunt transistor (P Channel MOSFET or PNP BJT) (option B below).
Components are sized for regulation at 5V, 2 watt.
simulate this circuit – Schematic created using CircuitLab
TP4056 modules are relatively low cost (your price is OK but they can be substantially lower than your example if you buy 10 from some sites). It is better to use one module per battery although more than one battery can be connected in parallel with a variable degree of success. If connecting more than one battery, ENSURE that they are balanced first - connect them together via say a 10 Ohm resistor if voltages are about equal and maybe charge them individually first and then parallel them.
Paralleling batteries of different mAh capacity is potentially doable but is inadvisable unless there is some good reason to do so. As above, equalise voltages first.
There are two main styles of TP4056 modules available - those with a low voltage load cutout (which you have cited) and those without the cutout circuitry. Those with the cutout are much preferred in simple circuits where the user does not manage the load and battery, as they prevent cell overdischarge and battery damage or destruction.
Battery protection circuitry:
The diagram below shows a TP4056 charger plus a DW01A battery management IC and FS8205A dual MOSFET. The DW01A disables the path to B- when various conditions are not met. The TP4056 already provides charging and overvoltage control, so in normal use the main specification is battery undervoltage protection, preventing a load from discharging the battery below a safe level. On TP4056 modules with Out+ B+ B- and Out- terminals, the two extra ICs are the DW01A and the dual MOSFET.
Very useful TP4056 & DW01A related application note here
PV PANELS:
The PV panels you cited are encapsulated in epoxy resin. This is potentially acceptable for occasional outdoor exposure. If they are to be used outdoors on a semi-permanent basis, you can expect a lifetime of as little as a summer (say 3 months), typically about a year, and in exceptional circumstances, a few years.
A far better choice is "PET" encapsulated panels (or, less liable to be found, a fluorocarbon plastic encapsulation). Depending of manufacturing quality, a PET panel may give in excess of 10 years of full time outdoor use.
eg PET PV panel 6V 1.5W $US3.06 free shipping - quality unknown but LOOKS reasonable.
PET (Polyethylene Terephthalate) is the same plastic used in softdrink bottles. It is laminated to the PV material and PCB backing using EVA laminating plastic (as also used in standard glass-fronted PV panels.) PET chemical bonds resist breakdown by UV light, whereas epoxy resin carbon-carbon bonds are susceptible to UV degradation leading to frosting and crazing of the surface over relatively short time periods.
Sunshine hours and related statistics for Esbjerg, Denmark from www.gaisma.com
