And that really is the key - crack the energy storage problem and the use of fossil fuels will decline rapidly. A lot of other storage solutions are being tested, too - molten sodium batteries, flywheels, water pumping/gravity storage, thermal storage.In addition to making cars Tesla is becoming more involved with grid battery storage..
In Australia they installed a battery back up system saving the building of new power stations.. solar panels on peoples homes power up the batteries when it isn't needed and the battery system tops up the grid during peak demand. Apparently it has been very successful, was installed in 100 days from contract signing and has reduced power outages... and saved billions of Aussie dollars for new power stations.
Elon Musk famously offered to have it installed within 100 days or it was free.
IMO, this is a leap that will be as important to humanity as the internet - and we are not far off.