One of the main challenges of using lithium batteries in solar energy systems is to ensure compatibility with inverters. Inverters are a crucial component of solar systems, since they convert the direct current (DC) electricity produced by the panels into alternating current (AC) electricity that can be used in homes and businesses. The incompatibility between lithium batteries and inverters can reduce efficiency or even cause system failure. In this scenario, the total energy efficiency of your solar system may be lower than that of a perfectly sized inverter or smaller, especially if it is very oversized.
This is important to keep in mind, especially since using the smallest inverter (depending on the installer) will offer you greater efficiency, but it will also set the size of the system. If we use the previous graphic as an example, if the size of the inverter is reduced, the maximum output power of the system (in kilowatts — kW) will be determined by the size of the inverter. For that reason, lithium batteries with the right BMS communications with the inverter are a much better option and, in the long run, much cheaper. If the battery bank is too large and the charging capacity of the inverter is too small, the battery will not reach a full charge cycle.
I tried to find the efficiency curve of the SMA Sunny Boy 3000US, but I could only find the curve of the 4000US, which is an inverter intended for larger systems with more capacity in the matrix. So, if per night you consume 2.4 kWh of electricity, then you need to install 2 batteries of 100 Ah (12 V), but here we must take into account that it is undesirable for the batteries to be discharged to 100%, and better not more than 70%-50%. V-TAC batteries are compatible with a wide range of inverters, including those from other brands, and offer a number of benefits, such as a lightweight design and easy installation. In fact, SMA, the largest inverter manufacturer in the world and a leader in Australia, recommends this practice.
The incompatibility between lithium batteries and inverters can reduce efficiency, increase maintenance and repair costs, and even fail the system. It can also help ensure that the inverter can fully charge the lithium batteries and manage their voltage and current requirements. In comparison, grid-interactive inverter-battery chargers, such as the Selectronic SP PRO and the Victron Multiplus, can be operated with solar inverters or with MPPT solar charge controllers in configurations coupled to alternating or direct current. Therefore, it is important to ask the installer about the performance of your system if an oversized inverter is suggested (for example, if an inverter is undersized, this should occur within certain parameters, which accredited solar installers will be familiar with).