Solanium is a rare substance in No Man's Sky obtained via Farming Solar Vine plants at your Home Base or from the same plant in the wilds of planets with High Temperatures.
It's primary uses are in the construction of Explosives which can then be sold for large amounts of units.
Where To Obtain
Here is a planet where Solar Vine grows that only requires the first 2 Portal Glyphs to dial:
It is a moderately Hot planet with a somewhat hellish feel, just about everything is a shade of Red and Orange.
Kind of ridiculous amounts of caves making it a good option for a very large Marrow Bulb operation.
This planet also has Viridium in large amounts.
I have placed a Beacon next to a Drop Pod very close to the Portal to upgrade at your leisure.