The BIGGEST problem with clean energy

Vanadium flow batteries could probably be a multi-hour video all by themselves.  They've been around for decades, and Vanadium has the advantage over the other chemistries that it can easily exist in four different charge states, so its used for both the anode and the cathode.  The failure mode of flow batteries is often a membrane breakdown, and with a Vanadium battery, you simply clean up and recharge the material.  No cross contamination.  That said, getting the material in a form the battery needs is expensive, the densities are low, and many other circumstances have contributed to keeping this chemistry in a niche position in the storage market.