Small, cheap to build, and thrifty with both power and hydrogen. If you've got hydrogen overwhelming your builds why not convert the excess to deuterium -- you'll need a LOT of it later in the game for science. Or, make deuterium fuel rods to power Icarus or your industry.
Requires two red science technologies: Fractionation and MkIII belts. And one yellow science tech: Automatic Pilers. The pilers tech requires only 50 yellow science so this really is an early option for making deut!
The build assumes no ILS/PLS stacked output since that's unlocked in the late game. It still achieves almost full fractionator capacity using pilers; see second picture for the stats. Proliferating the hydrogen can increase deut production at the cost of more power consumed. It's optional.
This build also uses splitters to prioritize completely filling each fractionator in series to maintain good power economy when the H2 supply is low or intermittent. It's robust and recovers automatically from intermittent H2 supply, blocked output and power outages.