I, too, have replaced caffeinated coffee with green tea. It helps with the fatigue, and I find relaxation.
I was worried about PCS and green tea, but the following report notes a study (non-human, however) that showed cognitive/memory improvement in neurological functioning of mtbi and green tea:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3205506/
As with all, moderation is key. If I feel like I am having too much green tea, and with our hot weather, I've been drinking cold mugi (wheat) tea or kampoyaku (herbal) tea they sell at Mitsuwa.