Google is investing $300 million in SolarCity to finance around 25,000 residential solar projects, the solar energy company announced today. SolarCity is the top residential solar system company in the US, but the industry is still in its infancy, and the upfront costs for a solar energy system aren't cheap. To remedy that, SolarCity will install solar panels on residential homes using the funding, and homeowners will pay a monthly fee to the company, instead of spending the well over $20,000 it can cost to have a solar system installed. First reported by Reuters, SolarCity has created a $750 million fund for the projects, the largest ever for a residential solar system. Google previously invested $280 million in SolarCity — which is backed by Elon Musk, who is also the chairman — back in 2011. The company has invested over $1.5 billion in renewable energy projects, but this is its largest single investment to date.