Here "cost" is a euphemism for stupendous amounts of energy. Producing it would take up a lot of land in PV panels. That'll only give you a little extra forest and entire agricultural states covered in PV and vertical farming towers instead. I could imagine some rich, arid countries trying this but not ones with fertile soil and rain. It's hard to compete with the free fusion reactor floating up there.
From the appendix¹ (assuming I am reading this right):
Value of production 405,329$/year
Cost of energy 15,987,286$/year
Area of field for equivalent yield 6,333,272m²
Land Area Required for PV Array 4,157,293m²