The ultimate source of energy for atp synthesis in chloroplasts is

the sun

Explanation:The sun is the ultimate source of energy for virtually all organisms. Photosynthetic cells are able to use solar energy to synthesize energy-rich food molecules and to produce oxygen.

sunlight

Explanation:

The primary and accessory  pigments in chlorophyll are collectively assemble as photosystems I and II, and this is the region of trapping of light energy in leaf chloroplasts.

The process of photolysis of water, which splits water into electrons, protons, and H+ marks the beginning of photosynthesis, and therefore the entry point of sunlight into photosynthesis.

The process of ATP synthesis in plants takes place by photo-phosphorylation which can be cyclic or non-cyclic. Light is captured by photo systems, and passed to primary pigment in chlorophyll, which is excited.The  excited electrons in chlorophyll  molecule  move to higher energy levels, in cascade from one higher energy levels to another until it leaves the chloroplast molecule.(Photoactivation)

The lost electron   is replaced  by electron acceptor for  chlorophyll in Cyclic photo-phosphorylation, and by electron from photolysis for primary pigments in non-cyclic photo-phosphorylation.

It is during this  process of transfer of electrons from one higher energy levels to another that Energy for the synthesis of ATPs by chemiosmsosis occurs.Where ATPase synthase catalysed ADP with inorganic phosphate to give ATPs, to be used in Calvin Cycle.Thus the ultimate sources is the sunlight used for exciting the electrons and it transfers,