This article "Benchmarked: The Most Power-Efficient Ubuntu 19.04 Flavor Will Surprise You" from forbes.com compares the power usage of different flavours of Ubuntu 19.04.
On top, and no surprise to me, is our favourite flavour: Ubuntu MATE! And Martin Wimpress @wimpy gets a mention and a few quotes, as well he deserves.
Personally I've always suspected this result, as one of the first daily drivers of Ubuntu MATE from Martin's early PPA on a Core 2 Duo! I never did any repeatable tests, but even back then it was the only flavour that would run with anything like same performance as the (unsupported) Ubuntu 10.10 that it had to replace.
Kudos to @wimpy and those that assist and support him!