The use of photovoltaic systems with batteries is a well-established practice. Initially, lead-acid batteries were used to store electricity, enabling its use during periods without generation. Off-grid systems widely used this storage technology, as it was, at the time, the most suitable and affordable alternative.
However, it is known that due to characteristics inherent to chemistry and production processes, these batteries are no longer the best option for this type of application.
Intolerance to cyclical operating conditions, greater susceptibility to higher temperatures, excessive weight and size – even for smaller capacities – and the total lack of monitoring and control of operation have always been adverse properties that have contributed to the inefficiency and unreliability of battery systems.
In this context, chemical or mechanical analyses of the Batteries in question, but the lack of adequate monitoring and operational control systems stands out.
Lead-acid batteries are purely electrochemical devices, designed without monitoring or operational control systems. Some models incorporate mechanical safety solutions, such as fire or explosion protection, but lack interfaces or devices capable of informing the inverter of parameters such as state of charge, lifespan, operating conditions, or even confirmation of connection to the system.
With the advancement of technology embedded in inverters over time, these devices have become capable of obtaining, albeit indirectly, certain relevant information about the batteries connected to them.
These inverters monitored parameters such as battery voltage and current, estimating their state of charge. However, because they were indirect and empirical readings, this information was not always accurate, which in some cases compromised system reliability.
With the consolidation of lithium batteries in the market, these devices began to offer greater efficiency, longer lifespan and greater resistance to high temperatures, in addition to incorporating electronic circuits responsible for monitoring, controlling and providing information on the operational status of the batteries.
With the advent of lithium batteries, the possibility of direct communication with inverters also emerged, which contributed to more efficient, safer installations with a higher level of automation.
This communication allows the exchange of crucial information about the battery status, such as charge level (SoC – State of Charge), maximum supported current, alarm status and battery state of health (SoH – State of Health) – thus optimizing the charging and discharging process and protecting the battery, inverter and the system as a whole from damage.
Now, directly and in real time, the battery informs the inverter of a series of data and parameters that allow for more assertive decision-making than before, when everything was indirect or empirical.
The electronic circuit that performs the monitoring is known as BMS (Battery Management System) and is generally a system based on a microprocessor that performs the functions of monitoring the operation and status of the lithium cells, controls the charging and discharging processes of these cells, protects the overall operation of the battery and has the possibility of reporting a series of parameters through a communication port.
These parameters can be transmitted and interpreted by photovoltaic inverters, which use their internal algorithms to identify the ideal operating points for the batteries – such as the most appropriate charging current, the right time to stop recharging to avoid overcharging, checking the state of charge and the amount of stored energy, all directly and accurately.
The advent of communication between inverters and batteries has enabled unprecedented technological and quality advancements. Communication also ensures compatibility between different brands and models of inverters and batteries, as manufacturers can approve their products to work together.
And how does this communication work? Through a physical medium and a communication protocol. The physical medium is where the electrical signals that carry the information will travel. The communication protocol, on the other hand, is the logical organization of how the information will be delivered, ensuring that both the inverter and the battery can interpret it correctly.
It's a bit like communication between people. The physical medium can be written paper, email, speech, gestures, or any other way of sharing information.
Communication protocols are composed of the "grammatical" rules and "vocabularies" that allow one person to understand another. Different communication protocols are often compared to the different languages spoken around the world.
To initiate communication between batteries and inverters, both must have the same physical interconnection medium. Typically, this physical medium is a standard RS-485 communication port or a CAN port.
Both must be compatible with each other. If the battery communicates via a CAN port, the inverter must also communicate CAN. These two standards are the most common for photovoltaic inverters and can be found in various battery models.
The greatest diversity lies in the communication protocol. It's common for each battery or inverter manufacturer to create its own protocol to best suit the needs of its equipment and its interests. There's no standard protocol or one governed by a standard, but it's common to find some that are the most commonly used.
Some inverters adopt the most common market protocols to ensure greater compatibility with different batteries from different manufacturers. The same applies to batteries.
The important thing is that batteries and inverters in the same installation are compatible, that they "speak" the same language, and use the same physical medium. To achieve this, manufacturers of these devices work together to ensure compatibility and proper communication.
When installing a lithium battery with an inverter, it's essential to first verify compatibility between the devices. After this confirmation, the power connections and communication cables are made, which typically use twisted pairs with RJ-45 connectors, similar to those used in computer networks. However, there may be some variations in this standard.
After physically connecting the devices, the inverter must be configured to match the battery model or corresponding communication protocol. Once this step is completed, the system is ready for operation.
Some inverters necessarily depend on communication with batteries to operate, highlighting the relevance and centrality of this interface in the system.
At SecPower's development laboratory, several inverters of different brands and models are received for adjustments and testing to ensure proper communication with the company's batteries.
It's a detailed process that involves numerous tests and procedures, but it's essential for the safety and efficiency of the installations. Today, SecPower batteries, whether low-voltage or high-voltage, are compatible with over 30 inverter brands and models, the main ones sold in the country.
Before using a lithium battery with a photovoltaic inverter, it's essential to first verify compatibility between the devices. This information can be obtained from the manufacturers or their authorized representatives.
The opinions and information expressed are the sole responsibility of the author and do not necessarily represent the official position of the author. Canal Solar.
