I am about 45 hours in with a friend and we have fully automated Nauvis and Vulcanus. I have about 10 hours on Cubium and feel like I have barely started (barely producing a steady supply of iron and copper). Looking through the recipes available and through FNEI I can't find a scaleable planetside source of power. I am operating on solar panels and accumulators, but it is slow going, sub 10MW. It doesn't appear that any early recipe provides power. 25 steam from Jelly or burning carbon with jelly produced water (from ice) is energy negative. Incinerators won't work because there is no early supply of water. FNEI shows there is a 5K steam recipe further down the tree, but I feel like after so long on the planet I should have been able to to identify a power supply from the planet itself. What am I missing? If people choose to start on this planet, how do they scale the power up?

1. You should have access to Coal Ore as a fuel source; you should be burning that before burning Carbon. Carbon is 2MJ and requires 2 Coal + power to craft if you are automating it; Coal is 4MJ and just comes out of the ground (practically infinite with Big Mining Drills from Vulcanus)
2. Solar Panels should have x2 efficiency on Cubium, not as powerful as Vulcanus, but still better than on Nauvis.
3. If you have been to Vulcanus, you should have access to Cliff Explosives, allowing you to utilize more of the terrain, without being hampered by the cliffs. Along with lack of enemies, means you can effectively place as many Solar Panels as you need.
4. I have not played with Any Planet Start, but not every planet is well suited for it (some people have been able to play on Aquilo using Any Planet Start, so whatever changes are made in that mode, do not necessarily reflect how you should be playing in a normal game)
5. The loop between Jelly Awakening and Carbonic Scaffolding should be providing you with a surplus of both Water and Jelly, without the need of ice melting or steam generation from jelly

EDIT: This video (beginning at 5:47, ending at 11:12) showcases a rather large Cubium base. Though this is taken from somewhat later in the game, they are still utilizing the basic recipes, including the Jelly Awakening and Carbonic Scaffolding recipes mentioned above, along with tons of Solar Panels and Accumulators (this is a constant; but when space is free, there is no reason not to)

Thank you for the detailed response. This was super helpful. I was using carbonic scaffolding but overlooking the jelly awakening for the water. In just a few minutes of play I was able to quadruple my power output. Very much appreciate your help. Great mod, we are having a blast.

Sweet, that's great to hear; glad I was able to help!