It does nothing much to coal efficiency. Most coal based generators run
24/7 at their rated output anyway, since it makes no sense to run anything with a higher marginal cost while there is unused coal generation capacity.The motivation for shifting peak loads is to flatten the load curve, with the result that more of the load is base load. Since the cheapest way of supplying base load is through the use of coal based generators, flattening the load curve results, in due course, in more of the total energy output coming from coal based generators, and thus more CO2.
Sylvia.