The "National Renewable Energy Center" is a telemarketing front for A1 Solar Power, a solar company with several branches throughout California.

Here are two relevant threads from this site:

1) Read the post by "Inside story" on 30 Dec 2013:

http://800notes.com/Phone.aspx/1-707-200-7673/3  

2) Here's a link to a thread in which some members have reported how they have dealt with incessant calls from A1 Solar Power:

http://800notes.com/Phone.aspx/1-707-207-6920