Trying to get my head round solar input values?

[Solarfun4jim]

Looking at the comparison graphic below, i've heard several times that charging at a lower voltage threshold will take much longer to charge a battery bank. Can someone explain how this comes about, since the same 'overall wattage' is being input.
Edit...cells would be 280Ah and 1C charge = 280A(thus in both instances, very low C charge ratings)

 

[Ivar Ivarson]

During charging, you're driving an electro-chemical reaction 'backwards' than when you discharged the battery. The higher the 'pressure' [the usual metaphor for voltage] the faster the reaction goes. As for the amperage end of your question, I've no clue.

 

[nosys70]

the energy has to spread into the battery. it is like watering a garden
When you put too much water (or too fast) , the water accumulate before penetrating.
it can create "rivers" and leave marks in the earth while other parts could stay dry.
that is why the usual spec for charging a battery is around 0.3 to 0.5C.
But some batteries are built to accept fast charge up to 2C.

 

[Solarfun4jim]

the energy has to spread into the battery. it is like watering a garden
When you put too much water (or too fast) , the water accumulate before penetrating.
it can create "rivers" and leave marks in the earth while other parts could stay dry.
that is why the usual spec for charging a battery is around 0.3 to 0.5C.
But some batteries are built to accept fast charge up to 2C.

So, i take it, this means that the 17.1A is absorbed much quicker due to the higher potential difference (in set up 2) than the 18.38A can be absorbed in set up 1, despite being a higher Amperage.
Thanks guys.