Sunrun’s move into grid services is an outgrowth of its increasing emphasis on adding batteries to its residential solar systems. Storage can increase value for customers in certain markets where storing solar energy can be more lucrative than sending it back to the grid under changing net metering regimes. It’s also a way for Sunrun and other residential solar and inverter players like Tesla, Vivint Solar, SolarEdge and Enphase to boost revenue from each installation.