From Silicon to Gallium: Application Prospects of GaN in Photovoltaic and Energy Storage

1. High-Frequency Technology Route of PV-Storage Converters

The core circuit of photovoltaic (PV) energy storage is essentially a power electronic converter. Its basic function can be understood as follows: the continuous energy flow at the input is chopped into energy packets through high-frequency switching, then recombined into the required continuous energy flow at the output via the energy storage and buffering effects of inductors and capacitors.

An inductor stores energy when the switch is turned on and releases energy to the load when the switch is turned off, thereby smoothing current ripple. A capacitor stores energy when the switch is turned off and releases energy to the load when the switch is turned on, thereby smoothing voltage ripple.

The key point is: The higher the switching frequency, the less energy needs to be buffered and stored by inductors and capacitors in each switching cycle. Taking the Buck converter as an example, the relationship between the peak-to-peak inductor current ripple ΔIL and the switching frequency is expressed as follows:

Where D is the duty ratio and f is the switching frequency. With fixed input/output voltage and ripple requirements, increasing the frequency f allows the inductance L to be reduced proportionally to maintain constant current ripple. Inductance L is proportional to the square of the number of turns N². When L is reduced to 1/k, the number of turns can be reduced to 1/√k of the original, resulting in lower total copper wire length and copper usage.

Similarly, the relationship between the voltage ripple of the output capacitor and the switching frequency is expressed as follows:

With fixed current and voltage ripple requirements, increasing the frequency f allows the capacitance C to be reduced proportionally. The energy stored in the capacitor, 1/2·CV², decreases accordingly, enabling the use of smaller-volume capacitors.

Challenges of High-Frequency Operation to Device Performance

High-frequency operation is not without cost. From the perspective of power semiconductor devices themselves, increasing the switching frequency is mainly limited by device parasitic parameters — this is why conventional silicon-based devices only operate at around 20 kHz.

Gate Charge (Qg) Limits Switching Speed

The switching speed of a device is restricted by the charging and discharging capability of the gate drive circuit to the gate capacitance Cg. The gate charge Qg=∫igdt determines the total charge required for the device to transition from the off-state to fully on-state. A higher Qg implies longer driving time and larger driving power, limiting the minimum achievable switching period. Longer turn-on and turn-off durations in conventional hard-switching topologies lead to higher single switching loss, making total loss unbearable at high frequencies.

Dissipation of Energy Stored in Output Capacitance (Coss)

During each switching cycle, the energy stored in the output capacitance Coss, 1/2·Coss·V², is dissipated through the channel when the device turns on. This loss is also proportional to the switching frequency. Meanwhile, in soft-switching topologies typified by LLC converters, Coss determines the minimum dead time, which greatly affects circulating current loss and the gain range of the overall circuit.

Additional Losses Caused by Reverse Recovery Charge (Qrr)

In inverter bridge topologies, the reverse recovery process of the body diode requires charging the reverse recovery charge Qrr, generating large current spikes and extra losses. This forces the system to use longer dead time to improve safety margins, thereby limiting the system switching frequency.

These device-level constraints define the frequency ceiling of conventional silicon-based solutions. To break through this ceiling, a new generation of power semiconductor materials with lower switching loss, smaller parasitic parameters, and zero reverse recovery must be adopted. This is the fundamental reason why wide-bandgap devices — first SiC, then GaN — have entered industrial focus.

High-Frequency Practice in the PV-Storage Industry

For the PV-storage industry, improving system power density and reducing cost by adopting advanced power semiconductor devices is already an ongoing trend.

On the PV boost side, replacing Si IGBTs with high-voltage SiC MOSFETs and raising the switching frequency from 20 kHz to 60 kHz reduces system cost by 40% and greatly improves overall power density. For PCS applications, high-voltage high-power SiC modules are gradually replacing conventional IGBT modules.

Inovance’s InoLynx integrated AC/DC PCS using SiC modules achieves a 29% higher energy density than the previous generation, with a peak efficiency of 99.3%. It also raises full-load efficiency across the full operating range by 0.5% to 98.5%, and improves full-load charge-discharge cycle efficiency by 1%.

The large-scale commercialization of SiC has proven that wide-bandgap devices enable higher efficiency at high frequencies. The benefits of reduced magnetic components and lower thermal dissipation requirements have been fully validated by the market.

2. Application Potential of GaN in PV-Storage Systems

GaN is a wide-bandgap material (bandgap 3.4 eV, much higher than silicon’s 1.1 eV), with high electron mobility and a two-dimensional electron gas (2DEG) conduction channel. As a unipolar device, GaN has no parasitic body diode found in Si MOSFETs.

In terms of switching speed, GaN devices typically achieve 100–150 V/ns, while SiC devices are generally only 40–50 V/ns. This indicates that GaN can increase the system switching frequency by 2–3 times compared with SiC. The switching frequency of PV boost circuits can be further raised to 100–150 kHz, further reducing system cost.

Actual circuit loss analysis shows that the switching crossover loss of GaN devices is drastically reduced compared with SiC, and reverse recovery loss is reduced to zero. Thanks to smaller Coss, dead-time loss is also reduced.

Industrial Practices of GaN in PV-Storage

Given this promising application prospect, cutting-edge manufacturers and leading international power device vendors have launched PV-storage solutions using high-performance GaN devices.

Enphase Energy IQ9N-3P™ Microinverter

Enphase Energy began shipping its new-generation IQ9N-3P™ commercial microinverter in the United States in late 2025. As Enphase’s first GaN-based product, it supports continuous DC current of 16 A, peak output power of 427 VA, and is compatible with PV modules up to 600 W. Compared with the IQ8 series, it is 25% lighter and 35% smaller.

TI GaN-Based PV MPPT Reference Design

Texas Instruments (TI) updated its PV MPPT reference design using integrated driver half-bridge GaN devices. The original design used Si MOSFETs, two-phase interleaved Buck, at 180 kHz. After adopting GaN, the topology is simplified to single-phase Buck with frequency increased to 250 kHz. PCB area is reduced by 37%, BOM cost lowered by 37%, and peak efficiency improved by 1.2%–1.7% (reaching 98.5%).

Statistical results of different BOM cost versions clearly show that topology simplification and frequency increase using GaN lead to a significant reduction in the cost of system passive components. This directly demonstrates the enormous potential of GaN in PV-storage systems.

Unique Bidirectional Conduction of GaN HEMT

In addition to excellent switching performance in conventional topologies, the planar structure gives GaN HEMTs a unique capability: bidirectional conduction.

The drain (D) and source (S) of a GaN HEMT are physically symmetrical, allowing bidirectional current flow in the on-state. Based on this characteristic, Infineon and Navitas have respectively launched 650 V GaN BDS (Bidirectional Switch) devices. With a symmetric gate design, a single BDS device can replace a back-to-back transistor pair.

The launch of this device makes single-stage AC/DC topologies highly competitive for microinverters and PCS, because such topologies eliminate the need for bus capacitors and feature a simpler structure.

TI demonstrated a 600 W microinverter PCS using a single-stage AC/DC topology. Its front-end half-bridge uses two pairs of back-to-back GaN devices. Unlike conventional microinverters with an MPPT + inverter structure, this solution directly implements power tracking and inverting/rectifying functions through a single-stage DAB.

The scheme achieves a peak efficiency of 96.1%. If BDS GaN devices are used, conduction loss will be significantly reduced, further improving system efficiency.