Would these coatings be useful in solar panels? Does the energy trapped/absorbed by these CNTs turn into heat and does it transfer easily to the material its applied to?
Going from 99% black to 99.999% black turns out not to represent that much more efficiency. It's the difference between absorbing 99 of 100 joules of energy vs 99.999 of 100 joules of energy; unless the rest of your system is effectively 100% efficient, it may not even be a noticeable change. It is very likely that other engineering concerns, not least of which is price, is going to dominate this question.
The article does mention that it's more durable than vantablack, so perhaps more suitable for a space-based project (if it turns out a really black material is useful for a solar panel of sorts).