Google continues to invest in renewable energy, announcing Thursday it has invested $300 million in a $750 million SolarCity fund to finance residential solar projects.

This is the company’s largest investment in renewable energy ever, and its second investment in Solar City. In 2011 it invested $280 million in the publicly-traded solar energy company.

“Corporations are starting to realize the importance of using clean energy,” SolarCity chief executive Lyndon Rive said. “Historically the companies that have financed solar deployment have been the big financial institutions and we’ve seen the movement in the sector of tech companies getting into the space and helping to transform a dirty infrastructure to a clean infrastructure.”

Earlier this month Apple announced that it is spending $848 million on a massive solar farm to power its corporate offices and California stores.

“We’re happy to support SolarCity’s mission to help families reduce their carbon footprint and energy costs,” said Siddharth Mundra, renewable energy principal at Google, in a statement. “It’s good for the environment, good for families and also makes good business sense.”

SolarCity’s new fund will be used to cover the cost of installing solar systems on homes in 15 states. SolarCity generally installs the systems at no charge to customers, and then charges the residents slightly less per month for the energy than they’d pay their traditional utility.

“Our number one competitor is the customer not doing anything, just sticking with the monopoly,” Rive said.