No "regeneration" of energy, but if you start your ride in the morning with the battery chilling in a garage (cell temperature ~70F) and then you park it in direct sunlight for several hours (cell temp 100-120F), then you may have slightly more energy available. It's not "free" - the maximum energy will reduce again when you park it and it cools overnight, but it may be real. You may be able to get another mile or two of range riding in the afternoon vs riding in the morning.
Battery SOC is a weird thing. Cell temperature, voltage, coloumb counting, wear, etc all factor into determining how much energy is actually available. People write PHD dissertations on how to accurately gauge available energy. In practice this is usually done either by using a lookup table or by counting coloumbs in / out of the battery, resetting after a top balance.