Berlin-based climate research institute Mercator Research Institute on Global Commons and Climate Change (MCC) has released a new study indicating that, in the last decade, the cost of solar power has dropped by 87 percent, and the cost of battery storage by 85 percent.
They’ve been deployed substantially since then. Basically as fast as factories can produce them. Residential rooftop installations are the most expensive way to do solar, so if that’s what you’re thinking of, that’s why. The real savings is in covering a huge field.