Solar and wind power have come a long way, so much so that you’ll start to see many more huge battery-storage systems around, such as those proposed for Brighton and Roslindale/Hyde Park. They don’t hold that much power right now, but they’ll keep getting better. … One non-clean-energy concern in this otherwise welcome clean-energy development: what chemicals are in these batteries? … The Globe wrote about a planned Everett battery-storage system in May.