3 phase power, and Industrial use power billing rates are typically determined by peak load and power factor. Single phase Residential power has that and many other billing opportunities such as time of day use and Low seasonal rates.
Talking a megawatt though, you would want 3 phase power. A typical 4160/13,800 VAC to 480 VAC transformer though is over 3 MVA in size. Smaller 480 VAC to 120/208 transformers in the range of 30-45 KVA are typically attached to individual breakers on 480 Volt panels supplied by the transformer and they feed your 120/208 volt panels.
Motors are a big reason 3 phase power would be expensive because they have high starting current and poor power factor. Mining RIGS however are different. They can startup slow (one DAG at a time) so peak load wouldn’t be a factor. They also have great power factor … Platinum Plus/Titanium … so billing rates would be among the best. It’s that BIG MVA transformer and running in the lines that would be expensive.
Solar inverters come in both single and 3 phase models, so that’s not an issue as long as you buy the right type. You should probably use a general contractor for solar equipment to get quotes on that 3 phase system. Anyone setting up a solar farm whose size is around 1 MW should use a Solar contractor for many reasons including Cost, Permits, Insurance, etc.
So, to answer your question, Have a Solar Contractor Design & Permit your Solar Farm. They will have more pull with the power company.!
Hope this helps … and 10 seconds with Tails …