In the current wave of promoting energy transition and achieving carbon neutrality, solar inverters and battery energy storage systems (BESS) play a pivotal role. Solar inverters are responsible for converting the direct current (DC) generated by solar panels into alternating current (AC) that can be used by households, industries, and the grid. Meanwhile, energy storage systems can effectively store excess electricity, enabling functions such as load regulation, peak shaving, valley filling, and backup power supply. This article explores the architectural composition of solar inverters and battery energy storage systems, as well as the related solutions offered by Littelfuse.
Solar inverters and battery energy storage systems as key alternative energy solutions
Solar inverters and battery energy storage systems have become important alternative energy solutions today. Architecturally, they can be divided into AC-coupled solar systems and DC-coupled solar systems. AC-coupled solar systems use dual inverters, consisting of a bidirectional inverter with batteries and a solar inverter, providing higher flexibility and easier installation, especially suitable for retrofit projects, while retaining grid-tied inverters. However, their efficiency is lower because the energy used by the batteries requires multiple inversions and requires multiple components such as multiple medium-voltage transformers and inverters. For existing photovoltaic (PV) systems, they are cost-effective.
DC-coupled solar systems use a single inverter to power the load and are unsuitable for retrofit projects, requiring replacement of existing inverters and, in many cases, reconfiguration of PV array wiring. However, their efficiency is higher because the power does not require multiple inversions, fewer components are needed, and the short cables between the BESS and the PV system reduce losses. However, their costs are higher, and installation in existing PV systems is complex.
Solar inverter topology types can be divided into microinverters, string inverters, multi-string inverters, and central inverters. Microinverters have a rated power of up to 300 W and are mainly used in residential buildings, with an output voltage of 230 VAC, single-phase, featuring self-consumption characteristics. String inverters have a rated power of 1 kW to 10 kW, primarily for residential use but can also be grid-connected, with an output voltage of 230 VAC, single-phase. If power optimizers or DC optimizers - DC-DC converters with Maximum Power Point Tracking (MPPT) functionality - are used in combination with string inverters, the overall efficiency of the solar system can be improved. MPPT functionality is performed at the individual PV panel level to ensure all PV panels operate at their maximum power point.
Multi-string inverters have a rated power of 30 kW to 200 kW, mainly for commercial, industrial, and utility applications, with an output voltage of 400 VAC, three-phase, featuring self-consumption and distribution grid compatibility. Central inverters have a rated power of up to several megawatts, mainly used in medium-voltage grids and PV power farms, with an output voltage of 400 VAC to 690 VAC, three-phase.
Comprehensive and high-quality solar inverter and BESS solutions
Littelfuse offers a wide range of product lines for solar inverters and battery energy storage systems (BESS), including input protection components such as fuses, metal oxide varistors (MOV), surge protection devices (SPD), and ground fault relays; components for DC-DC converters such as MOSFETs, gate drivers, transient voltage suppression (TVS) diodes, and temperature sensors; components for DC-AC inverters such as IGBT modules, gate drivers, TVS diodes, and temperature indicators.
Additionally, there are components for output protection such as fuses, MOVs, surge protectors, and AC ground fault relays; components for auxiliary power supplies such as MOSFETs, gate drivers, and TVS diodes; and components for BESS such as fuses, TVS diodes, TVS diode arrays, arc flash relays, SPDs, and ground fault relays, as well as components for communication interfaces such as TVS diode arrays and multilayer varistors (MLV). The product variety is quite diverse.
If categorized by inverter type, Littelfuse's potential products for microinverters include MOSFETs (Trench Gate Gen2, Ultra-junction X2) or IGBTs (600-650 V Trench), TVS diodes (SMCJ, SMDJ, SMBJ), negative temperature coefficient (NTC) thermistors (RA, RB, KR), silicon carbide (SiC) Schottky diodes (650V diodes), MOVs (TMOV, UltraMOV, LA), fuses (215), gate drivers (IXD_6xxSI), TVS diode arrays (SP3130, SP712, SP2555NUTG), or MLVs (MLA, MHS), etc.
Littelfuse's potential products for power optimizers include MOSFETs (Trench Gate Gen2), TVS diodes (SMCJ, SMDJ, 1.5SMC, SMBJ), NTC thermistors (RA, RB, KR), gate drivers (IXD_6xxSI), TVS diode arrays (SP3130, SP712, SP2555NUTG, SM712), or MLVs (MLA, MHS).
Littelfuse's potential products for string inverters include MOVs (UltraMOV, LA, SM20, TMOV), MOSFETs (Trench Gate Gen2, Ultra-junction X2), TVS diodes (SMCJ, SMDJ, SMBJ), SiC Schottky diodes (650V diodes), NTC thermistors (RA, RB, KR), IGBTs (600-650 V Trench), fuses (Class J, Class RK5, KLKD), gate drivers (IXD_6xxSI, IX4351NE), TVS diode arrays (SP3130, SP712, SM712, SP2555NUTG), MLVs (MLA, MHS), etc.
Littelfuse's potential products for multi-string inverters include fuses (SPF, SPFI, SPXV, SPXI, Class T, Class J), SPDs (SPD2 PV, SPD type 2), SiC MOSFETs (LSIC1MO120E0120, LSIC1MO170E1000), MOSFETs (high-voltage series), SiC diodes (1200 V diodes), IGBT modules (MIXA, MIXG), high-speed fuses (L75QS), TVS diodes (SMBJ, SMF), MOVs (UltraMOV, LA, SM7), gate drivers (IX4351NE), TVS diode arrays (SP3130, SP712, SM712, SP2555NUTG), MLVs (MLA, MHS).
Littelfuse's potential products for central inverters include inline fuses (SPXI, SPFI), fuses (SPXV, SPNH, LFPXV, SPF, Class J, Class RK5, Class L), SPDs (SPD2 PV, SPD type 2), DC disconnect switches (LS7xx, LS6xx), SiC MOSFETs (LSIC1MO120E0120, LSIC1MO170E1000), MOSFETs (high-voltage series), SiC diodes (1200 V diodes), IGBT modules (MIXA, MIXG), high-speed fuses (PSR, PSX), TVS diodes (SMBJ, SMF), AC ground fault relays (EL-731), DC ground fault relays (EL-731, SE-601), gate drivers (IX4351NE), TVS diode arrays (SP3130, SP712, SM712, SP2555NUTG), MLVs (MLA, MHS).
Littelfuse's potential products for BESS include fuses (501A, 881, TLS, JLLN, CNN, 885, Class J, Class RK5, Class L), TVS diodes (TPSMC, SZ1SMC, SZ1.5SMC, TPSMB, SZ1SMB, SZP6SMB, TPSMA6L, SZ1SMA, TPSMB), temperature sensors (USP16673, RB), SMD or inline fuses (438A, 441A, 521, 483A), TVS diode arrays (AQ05C, AQ24CAN), high-speed fuses (PSR, PSX, ESR), MOSFETs (X3 Class), gate drivers (IXD_6xxSI), high-voltage DC contactor relays (DCNxx), arc flash relays (AF0100), DC disconnect switches (LS7xx, LS6xx), SPDs (DC link/AC link) (SPD type 2), ground fault relays (SE-601), IGBT modules (MIXA, MIXG).
Comprehensive safety standards for solar inverters and BESS
Solar inverters and battery energy storage systems (BESS) are subject to numerous safety standards, including IEC 61683 - Power conditioners - procedure for measuring efficiency, which describes guidelines for measuring the efficiency of power conditioners used in standalone and utility-interactive PV systems. IEC 62109-1- Safety of power converters for use in photovoltaic power systems - Part 1: General requirements. This part of IEC 62109 applies to power conversion equipment (PCE) used in PV systems that require uniform safety levels. This standard specifies the minimum requirements for the design and manufacture of PCE to protect against hazards such as fire, energy, electric shock, mechanical, and other risks. IEC 62109-2 - Safety of power converters for use in PV power systems - Part 2: Particular requirements for inverters. Part 2 of IEC 62109 covers particular safety requirements for DC-AC inverter products used in PV power systems. These three standards apply globally.
UL 1741 - Inverters, converters, controllers, and interconnection system equipment for use with distributed energy resources. These requirements cover inverters, converters, charge controllers, and interconnection system equipment (ISE) for standalone or grid-connected power systems. UL 9540A - Standard for test method for evaluating thermal runaway fire propagation in battery energy storage systems. This document evaluates the fire characteristics of battery energy storage systems experiencing thermal runaway. These two standards apply to North America.
EN 50524 - Data sheets and nameplates for PV inverters. This document aims to provide essential information for configuring safe and optimal PV inverter systems. EN 50530 - Overall efficiency of PV inverters. This standard provides a procedure for measuring the maximum power point tracking (MPPT) accuracy of inverters used in grid-connected PV systems. These two standards apply to Europe.
High-speed square-body semiconductor fuses can increase BESS capacity and reduce operating costs
PSR high-speed square-body semiconductor fuses can increase the capacity of BESS, thereby reducing utility operating costs and enabling longer reliance on battery energy storage systems to meet peak power demand. To achieve this, integrators can add more battery banks to their BESS or switch from flow battery solutions to higher-capacity lithium-ion batteries.
However, the higher power density in new BESS may lead to larger fault currents. At high power levels, a fault can cause catastrophic damage or even personal injury. BESS requires higher levels of circuit protection, posing design challenges. If fuses with higher short-circuit current interruption ratings than those currently used in BESS can be found, more battery banks can be added to the BESS. Additionally, to protect sensitive electronic components used in BESS power converters, the fuses must be capable of rapid interruption.
The Littelfuse PSR series of high-speed square-body semiconductor fuses offer the highest short-circuit current ratings: 150 kA DC and 200 kA AC interruption ratings. Higher ratings can also reduce the number of combiner boxes, lowering costs and design complexity. The PSR series fuses act faster and have higher short-circuit current interruption ratings. Other advantages of the PSR series fuses include flexible form factors and installation options. The PSR fuse series can directly replace commonly used block-type form factor fuses, avoiding the cost of major design changes. To adapt embedded PSR fuses to parallel busbar mount configurations, Littelfuse's L-bracket design can be used.
By using Littelfuse PSR series fuses, the number of combiners per container can be reduced by one, and two additional battery units can be added. This increases the capacity of the current BESS container by 7%, enabling utilities to rely on battery energy storage systems for longer periods during peak power demand and reducing operating costs.
Conclusion
The integration of solar inverters and battery energy storage systems not only improves energy utilization efficiency but also brings new opportunities for distributed energy management, grid stability, and energy autonomy. With continuous advancements in power electronics, battery management systems (BMS), communication protocols, and artificial intelligence, future solutions will trend toward higher efficiency, greater intelligence, and modularity. The Littelfuse solar inverter and BESS solutions introduced in this article can help customers build highly reliable, high-performance, and cost-effective integrated solar and storage systems, contributing to the sustainable vision of green energy.