The U.S. code pertaining to the Department of Energy is in title 42, chapter 84.
A free U.S. Code can be found online at the Office of Law Revision Council United States Code page, as well as the Legal Information Institute.
A simple list of the Department of Energy administers can be found here.
Access to Annotated State Code and Regulations
Westlaw and Lexis provide access to annotated state code; the annotated codes are found within each states' page.
State Administrative Code Collections
Lexis: State page > Administrative Materials, Codes and Regulations
Westlaw: State page > Regulations
Freely Available Collections
States and municipalities' websites typically provide access to state code and regulations.
Legal Information Institute: State Statutes Related to Utilities and Transportation.
This page provides links to the full text of state utilities law statutes that are freely available on the web. The currency of linked statutes varies.