The LENR (Low Energy Nuclear Reactions) field is really hot right now.
COPs of 6-20x (and sometimes more) are being reported.
Several labs have been burned to the ground who experimented with it and had a run-away reaction that was not expected.
Whether it's Fusion or Transmutation or something else, the results are real and we are seeing heat anomalies that can't be explained, in table-top devices that use Ni nano-powder, some catalysts, a loading current and heat, and nothing particularly radioactive or difficult to procure.
Also findings of direct EMF generation were reported recently, which could potentially bypass the heat-to-electricity step and the wasted energy in the Carnot cycle altogether.
LENR is a fundamental shift in the energy storage density the author is talking about.