With more solar inverter manufacturers announce storage solutions, we connected with Lior Handelsman, SolarEdge’s vice president of marketing and product strategy, to tell us more about why the relationship between inverters and batteries is so important.
Solar Power World: Why are inverters and batteries so closely related? What type of relationship do they need to have in a successful solar project?
Lior Handelsman
Lior Handelsman: When combining energy sources in an insightful and intelligent manner, power electronics are needed to perform two important management functions. They must convert energy from different sources—from solar panels, batteries and the grid—then allocate these sources according to different uses such as consumption, storage and grid feed-in. The second important function of power electronics is to provide full visibility into production, consumption and storage needs to properly allocate energy in real time. As the brain of the system, the inverter is the only component that has this information and already contains most of the required electronic hardware.
While of course the quality of the actual battery is important, the inverter is responsible for its functionality. In other words, you can buy a top-of-the-line guitar but if you don’t have a knowledgeable musician to play it then it becomes a decoration. In a PV plus storage system, the inverter controls when the PV is utilized, stored in a battery or transferred to the grid and controls when the battery is charged, idle, or discharged. For example, SolarEdge’s StorEdge solution is programmed to discharge the battery in an optimal manner to meet its programmed goal, such as electric bill reduction, TOU gain, or maximizing backup. The inverter is also responsible for increasing system efficiency, simplicity of design and installation, and safety.
“You can buy a top-of-the-line guitar but if you don’t have a knowledgeable musician to play it then it becomes a decoration.”
SPW: What characteristics must an inverter have to work with batteries? How does this differ from conventional inverters?
Handelsman: Inverter solutions traditionally were responsible for only DC to AC conversion and MPP tracking. As the PV market has matured, inverters have taken on a growing roles in grid interaction, safety monitoring, smart energy management and even reduction of BoS costs. Becoming responsible for managing storage is a natural evolution for inverters in PV systems. To work with batteries, inverters need to know how to read home meters and 
monitor and control batteries. This includes having the capability to charge and discharge the battery according to the set profile and monitor its system status. In addition, inverters that offer backup need to have the capability to operate without the gird or in islanded mode.
SPW: What functions do a meter and auto-transformer provide for a storage solution?
Handelsman: The meter is only needed for daily-cycle, on-grid applications to maximize self-consumption. For instance, a meter is required in Hawaii but not for backup-only applications in other locations. The meter is responsible for monitoring import and export to the grid and load consumption. Based on these readings, the inverter manages PV production and the battery charge/discharge. Without the meter, the inverter does not know if it is pushing energy to the grid or just to the home. Installing a meter also gives the home-owner insight into self-consumption patterns, as the information is displayed in some monitoring platforms.
In the U.S., most home appliances work on 120V, even though the grid operates at 240V. A grid auto-transformer is responsible for converting the 240-V loads to 120V. The grid auto-transformer, located at the connection point to the grid, ensures that the home split phase remains balanced (at 120V) even when residential loads might be unbalanced. For example, with a backup SolarEdge StorEdge system, when the inverter transitions to backup mode it disconnects from the grid and the home moves into islanding mode. When this occurs, the auto-transformer is also disconnected. This means that an auto-transformer is needed to keep the home’s phases balanced. An auto-transformer is only needed in StorEdge solutions that support power back-up.
SPW: How does your company see incorporating storage into your business model?
Handelsman: We focus on integration as a way to lower costs for installers. We also already work with module companies which embed our power optimizers into their panels during manufacturing. This helps to lower installation labor cost and time. In regard to batteries, SolarEdge built its solution to support high-voltage DC batteries because we believe that this is the most efficient and cost-effective way to integrate batteries into a PV system. The StorEdge solution is based on a single SolarEdge DC optimized inverter that manages and monitors PV production, consumption and storage. We were able to design our system so that only one inverter is needed. This means that there is no additional conversion from AC to DC and back to AC. Avoiding unnecessary energy losses in conversion helps decrease system cost. In addition, this allows a simpler design and installation for the installer. Our solution is currently compatible with the Tesla home battery Powerwall. As more HV-DC batteries are made available, we will aim to also support them as well.