Installing a solar array with battery backup requires some different components than traditional systems. Here is a quick rundown of the components involved in grid-tied PV solar storage system with batteries.
hybrid inverter system
An example of power flow in a hybrid inverter system. The inverter can direct power to a load or the grid if needed, or store it in batteries if not. It can also use power from the grid if needed. -GreatWall
A hybrid inverter (also referred to as a bidirectional or battery-based inverter) is typically a string inverter that can operate bidirectionally. This means it can take DC from the array or the battery, supply AC to the grid or critical load panel, and charge from the PV or the grid. A hybrid inverter can isolate the system from the grid when the grid is down so that the system can still provide power to critical loads without feeding it into the grid. In contrast, when systems with traditional string inverters disconnect when the grid is down, no solar power is able to be generated or used.
The job of a string inverter mainly consists of checking if the grid is online and if PV is being generated, and then converting powering and sending it to the grid. However, hybrid inverters need to be pretty smart, taking an intelligent approach to power management. This is especially important because of changing time-of-use rates which affect the cost of electricity at different times. The inverter needs to determine where the power is coming from and what critical load is needed to manage power from the batteries, array and grid to get the best electricity savings and financial return possible for the system owner.
Battery management system
A battery management system (BMS) helps control parameters such as battery temperature, depth of discharge and state of charge so the batteries aren’t over or under charged, which can affect their life. A BMS is usually a software function internal to a charge controller or more sophisticated charging device.
A BMS is critical when using lithium-ion batteries because there is more risk for thermal issues with this chemistry. When using other batteries, such as lead acid, a BMS can be included but is not critical because there is less risk of thermal issues and the inverter or charge controller can usually handle charging regimes.
Choosing the right battery for a system is essential for optimzing project life and performance, and minimizing maintenance costs and downtime or failure. There are different types of batteries, and manufacturers within each type make their products differently.
Exploring the different types of batteries and asking your manufacturer or distributor the right questions can help you decide which chemistry and manufacturer is right for you. You’ll also want to make sure you size the battery properly to the array and provide proper O&M for the best performance and battery life.