Did Solar Impulse flight in commercial airspace and have kind of type 23 certification?
To answer the question presented in the title, I looked to Wikipedia for details on the flight(s) of Solar Impulse. According to Wikipedia, Solar Impulse 2 (HB-SIB) circumnavigated the Earth’s Northern Hemisphere in 17 legs/flights. Of those 17 legs, 14 legs had maximum altitudes above 18,000 feet MSL. In the U.S., Class A airspace is between 18,000 and 60,000 feet MSL. It is not considered “commercial” airspace. It is accessible to any aircraft with a Mode C transponder and ADS-b, including experimental aircraft. And, even this requirement can be waived with prior approval.


  91.135 Operations in Class A airspace.
  
  Except as provided in paragraph (d) of this section, each person operating an aircraft in Class A airspace must conduct that operation under instrument flight rules (IFR) and in compliance with the following:
  
  (a) Clearance. Operations may be conducted only under an ATC clearance received prior to entering the airspace.
  
  (b) Communications. Unless otherwise authorized by ATC, each aircraft operating in Class A airspace must be equipped with a two-way radio capable of communicating with ATC on a frequency assigned by ATC. Each pilot must maintain two-way radio communications with ATC while operating in Class A airspace.
  
  (c) Equipment requirements. Unless otherwise authorized by ATC, no person may operate an aircraft within Class A airspace unless that aircraft is equipped with the applicable equipment specified in §91.215, and after January 1, 2020, §91.225.
  
  (d) ATC authorizations. An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned. In the case of an inoperative transponder, ATC may immediately approve an operation within a Class A airspace area allowing flight to continue, if desired, to the airport of ultimate destination, including any intermediate stops, or to proceed to a place where suitable repairs can be made, or both. Requests for deviation from any provision of this section must be submitted in writing, at least 4 days before the proposed operation. ATC may authorize a deviation on a continuing basis or for an individual flight.


For further details about the aircraft, it’s custom autopilot and flight controls, and the actual flight Itself, visit https://aroundtheworld.solarimpulse.com/adventure .