Robust and Reliable Connectors for Residential Energy Storage Systems

By Bill Ahumada | April 29, 2025

Residential energy storage systems (RESS) are one of the growing ways to realize this vision. Designed for use in homes, a RESS stores excess energy generated by renewable sources, such as solar panels, for use on demand when a residence needs it.

The All Electric Society (AES) envisions a world where renewable electrical energy is universally accessible, abundant, and economically viable as the predominant energy source. Making this vision a reality will require the electrification, interconnection, and automation of all economic sectors and infrastructure.

Introduction to residential energy storage systems

A RESS usually consists of a renewable energy source, batteries, inverters, and control systems. The synergy of these components enables the complete system to generate energy, store that energy efficiently, and utilize it strategically during periods of high demand, power outages, or when renewable sources are not actively generating electricity (Figure 1).

Figure 1: Residential energy storage systems are comprised of a renewable energy source, batteries, inverters, and control systems.

Solar panels are the primary renewable energy source for residential systems. The panels harness energy from the sun and convert it into electrical energy. That energy can then be pushed into an energy storage system located in the residence. Batteries, the heart of the system, store the excess energy efficiently. Lithium-ion batteries, known for their high energy density and cycle life, are commonly used. Other technologies, such as lead-acid or lithium-iron-phosphate batteries, may also be utilized based on specific requirements.

System needs in the market for residential products

A good RESS ensures optimal performance, reliability, and user satisfaction. In addition, a system should be aesthetically pleasing, installation-friendly, expandable, and affordable.

A RESS’s visual appeal and design play a crucial role in system adoption. These systems are often installed in visible areas of homes, such as garages, sidewalls, and living spaces. Therefore, considerations for space requirements, design, and appearance are vital.

Complex installations can involve lengthy installation times and high labor costs, which drive up the system’s price. Because of this, easy RESS installation is essential. This involves compatibility with existing infrastructure, including solar panels, inverters, and home electrical systems. A system that seamlessly integrates with these components reduces the need for extensive modifications and time for installation, making the technology financially feasible for a broader range of homeowners.

Modular energy storage systems that are easy to install offer homeowners the flexibility to start with a smaller capacity and scale up as needed. This adaptability particularly appeals to consumers who prefer to gradually invest in an energy storage solution or adjust their system to changing energy requirements.

Cost is a significant factor in the adoption of RESS, as it usually represents the most substantial portion of the complete system. To encourage widespread adoption, manufacturers and developers must ensure that RESS is cost-competitive. This involves optimizing manufacturing processes, using cost-effective materials, and exploring innovations that reduce overall system costs without compromising efficiency and reliability.

Stackable energy storage system

The stackable energy storage system (SESS) is the most common RESS style. These systems are modular, scalable, and stackable. Electrical connectors serve as the linchpin for seamless integration, efficiency, and safety across various parts of the energy storage system. Choosing the right connectors is important to ensure the system’s reliability (Figure 2).

Figure 2 (00077979): Stackable energy storage systems are popular due to their modularity, scalability, and stackability.

Addressing the connector needs of the RESS

Battery modules are the most crucial component of RESSs. They are a collection of battery cells connected in series or in parallel. The combined cells store electricity as chemical energy, most commonly Lithium-ion, so it can be used when needed. The battery modules are coupled with a battery management system (BMS) to support and maintain efficient operation of the battery system.

Together, these components monitor the battery cells to ensure they are operating within their prescribed operating windows for the state of charge, voltage, current, and temperature. They also monitor and control charging, discharging, and safety features like temperature regulation. High-quality connectors can manage the signal and data transmission of the monitoring and controlling functions of these devices. Robust board-to-board connectors are ideal for the compact size and limited space within these devices. Board-to-board connectors with pin headers and sockets in 1.27 mm and 2.54 mm pitches can offer design flexibility. In addition, they offer numerous configurations: mezzanine, coplanar, and mother-daughter connections (Figure 3).

Figure 3: Due to the compact size and limited space within these devices, connections like the Phoenix Contact FQ series board-to-board connectors are ideal. The pin headers and sockets are available with 1.27 mm and 2.54 mm pitch.

Intermodule connectors facilitate communication and power transmission between stacked battery modules. These connectors are integral to the modular design, allowing for the dynamic expansion or reduction of the system based on energy storage requirements. Specialized connectors maintain a secure and stable alignment and arrangement of battery modules, which the stacking mechanism requires.

The ideal connectors should incorporate features such as sealing to provide weather and corrosion resistance, which contributes to the longevity and reliability of the system; float, to address the possible misalignment that can occur when stacking the battery modules; and possibly disconnect/connecting under load, which could be required for safety during maintenance and system conditioning.

Battery pole connectors can reliably support power requirements. These connectors can accommodate voltages up to 1500 V DC and 350 A. UL 4128 approval and IP67 degree protection ensure the connectors will meet application requirements. Some of these connectors can freely rotate 360°.

To communicate and transmit data between the BMS and other components, RESSs use common protocols, such as Modbus, CAN bus, and RS-485. Instead of using an individual connector for power, another for data, and yet another for signal connections, hybrid connectors are a growing trend (Figure 4).

Figure 4 (00179196 – white paper version): Phoenix Contact’s Battery Pole Connectors are rated for voltages up to 1500 V DC and up to 350 A. The BPC meets UL4128 and provides IP67 degree protection.

A hybrid connector, capable of handling power, signal, and data communication within a single interface offers several benefits that can enhance the versatility of stackable RESS. These connectors streamline the overall system setup, reducing complexity, optimizing space, and contributing to cost savings. Finally, consideration should be given to the utilization of UL-certified connectors, which comply with standards such as UL 9540 for energy storage systems and UL 4128 for intercell connectors. These approvals underscore safety and reliability, which ensures adherence to industry standards and regulations (Figure 5).

Figure 5: A hybrid connector, capable of handling power, signal, and data communication within a single interface, offers several benefits that can enhance the versatility of stackable RESS.

Addressing connector needs with the key features and requirements mentioned is essential for the successful development and deployment of residential energy storage systems. Manufacturers and developers must consider critical factors such as aesthetics, easy installation, scalability, customization, and cost competitiveness. By meeting these requirements, they can create efficient, reliable, and well-suited RESS solutions that align with the evolving needs of homeowners and the dynamic energy market. This strategic approach ensures the growth and integration of the RESS market, as it continues to support sustainable and independent energy solutions.

Learn more about battery storage solutions at Phoenix Contact.