text: Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
  ### Context:
  CREATE TABLE table_name_58 (year_commissioned INTEGER, gross_head__metres_ INTEGER)
  ### Question:
  What is the Year Commissioned of the power stationo with a Gross head of less than 18?
  ### Answer:
  SELECT AVG(year_commissioned) FROM table_name_58 WHERE gross_head__metres_ < 18