The board may:
a. Investigate upon its own initiative or upon complaint in writing any matter concerning any public utility;
b. Appraise and value the property of any public utility whenever in the judgment of the board it shall be necessary so to do for the purpose of carrying out any of the provisions of this chapter. In making such valuation the board may have access to and use any books, documents or records in the possession of any department or board of the state or any political subdivision thereof.