Na(+)/H(+) antiporter that transports sodium from the cytoplasm into the thylakoid lumen in exchange for protons. Contributes to sodium homeostasis and tolerance. Has also Li(+)/H(+) antiport activity under K(+)-free conditions, but not under K(+)-rich conditions. Activity is pH-independent. Induced in response to increased CO(2) concentrations. Expression is under circadian control. Belongs to the monovalent cation:proton antiporter 2 (CPA2) transporter (TC 2.A.37) family.