With the pact, Comcast, which has 29 million customers, can realize a 5 percent equity stake if the agreement leads to 30,000 new customers for Sunrun or Comcast spends $10 million on marketing the program, according to the agreement filed with the U.S. Securities and Exchange Commission. Comcast will take up to a 10 percent stake in the company if its marketing leads to 60,000 new residential or commercial customers over the 40-month term of the deal.