Robin Reid The cheapest energy is the one that cost nothing. All vegetation does not pay to grow. All vegetation grows because of sunlight and water. You cannot grow vegetation using coal . Coal is previous vegetation that took millions of years, after it died, to change into coal. Taking that time into account coal is an extremely expensive form of energy. It is just that us humans do not take those millions of years into account in assessing what the true cost is.
Rather than taking years of absorbing sunlight and water for vegetation to grow and waiting millions of years for it to transform into coal that has to be dug up and burnt, we now have the technology to convert sunlight directly into energy, instantly. That is why coal is NOT the cheapest energy.