Which Battery is Best for Utility Surcharge Avoidance?
The inverter chosen to avoid utility surcharges by supplying supplemental energy will be the driver for battery selection. Solar integration will be mandatory in some utility jurisdictions. The battery will need to handle micro cycling and partial state of charge operations. Efficiency and energy density will be critical. Safety certifications will be mandatory in many jurisdictions.
Many of the same inverters that provide Whole Home Backup also incorporate grid support functions. The same criteria will drive the choice of battery used by these systems for the whole home application. These battery systems will all be 48V.
High-frequency grid-tie inverter systems that target residential self-consumption and avoidance of time-of-day usage charges are generally sold as an integrated package with a preselected high-energy density battery. For system efficiency, these batteries are predominately high-voltage lithium and are specifically designed to match the very high DC input voltage of the inverter (400V ~ 500V). These inverters typically provide minimal backup run time and no surge support. Therefore, a battery with a high surge current is not required, and moderate discharge and charge current rates are usually sufficient. High-voltage batteries for this application will be maintenance-free and require a secure enclosure with restricted access due to the high voltage. Monitoring of lifetime battery energy throughput will be of significant value to homeowners and grid management companies. Lead-acid batteries no longer feature these types of inverters.