How does consciousness arise if not via electrical activity?
Electrical activity itself is not sufficient. Wikipedia is not a definitive answer here but it is a start at what your myriad problems are here:
Consciousness is subjective experience or awareness or wakefulness or the executive control system of the mind.[1] It is an umbrella term that may refer to a variety of mental phenomena.
Consciousness in medicine (e.g., anesthesiology) is assessed by observing a patient's alertness and responsiveness, and can be seen as a continuum of states ranging from alert, oriented to time and place, and communicative, through disorientation, then delirium, then loss of any meaningful communication, and ending with loss of movement in response to painful stimulation.
Consciousness in psychology and philosophy has four characteristics: subjectivity, change, continuity and selectivity.[1][6] Intentionality or aboutness (that consciousness is about something) has also been suggested by philosopher Franz Brentano. However, within the philosophy of mind there is no consensus on whether intentionality is a requirement for consciousness.
You'll note that the medical definition isn't helpful, since that has to do with being alert, not with being self-aware. That leaves psychology (not medical psychiatry) and philosophy, each of which would clearly tell you that things like rocks and gaseous masses are not conscious, and (hate to tell you this) but rocks and gaseous masses are the primary forms of visible matter in this universe.
humans the world over since dawn of recorded history have reported having a relationship with something they call "God". Unless they're all nuts, there must be a "cause" for that experience.
Belief in the supernatural did not necessarily arise in humans in numerous places at different times in different, distinct episodes. Such beliefs are more likely to have originated with a small group of proto-humans, millions of years ago, and as those people spread out and diversified and eventually settled in places all over the world, their beliefs in the supernatural changed, evolved, became more sophisticated, but also widely diversified. Yet, if you'll read "The Hero with A Thousand Faces", you'll see that there are numerous similarities amongst different myths and religions. This isn't necessarily evidence of a universal truth, but certainly points to common origins in our beliefs.
People all around the world used to believe the earth was flat. For thousands of years (for certain) and more likely millions of years (extending back to unwritten history), people believed the world was flat (and, not surprisingly, many also believed that their particular land and people lived in the middle of that flat world). Sure, there might have been some that didn't believe this, that thought maybe it was a different shape... but they'd have been the overwhelming minority.
And in the same vein, those same people believed that the sun was rising on one side of the immobile flat earth, traveling through the sky, then setting on the other side of the flat earth, then traveling behind the other side of the flat disc to rise again on the other side.
Did the fact that an overwhelming number of people all over the world believed those things make those things real or true?
We don't understand hardly anything about solar activity. What little we do know makes it very clear that it's not simply a fusion process responsible for the atmospheric heating
You're right, grammatically - we DON'T understand "hardly anything" about solar activity. We understand a great deal about the sun. It is fueled, pretty simply, by fusion in its core. The heat and energy of that fusion is carried from the core to the surface via convection. The surface radiates energy.
You're perhaps thinking of specific types of solar activity, such as sun-spots. Yes, we don't understand those things nearly as well as we could. But those things have little to do with the basic process of radiant heat generation caused by fusion in the sun's core.