After unveiling residential 'solar roof' these days, Musk is going further. The company will not just build and sell its own line of solar panels to combine with its battery storage system but they have made a big sales pitch. 

After Musk was joined on a 40 minute conference call by SolarCity CorpSolarCity Corp (SCTY.O), they agreed to Tesla Motors Inc's (TSLA.O) $2.6 billion offer to buy the solar panel installer. The electric car maker released a projection that it says shows SolarCity will add $1 billion in revenue to Tesla's balance sheet in 2017. SolarCity will also pile more than $500 million in cash into Tesla over the next three years, Tesla said in a released statement.The deal, which has dragged on Tesla's stock, has been legitimately questioned by analysts and corporate governance experts. 

SolarCity has come under pressure from rivals offering low-cost solar energy from large, utility-scale installations, and because some state governments have reined in subsidies that encouraged rooftop solar, but Musk touted SolarCity's plans to offer entire roofs made of solar panels made to look like shingles. 

Even if Tesla is facing a gargantuan task in manufacturing and launching its mass-market Model 3, which Musk says will hit the market at the end of 2017, Tesla sought to defend SolarCity's financials.