Silicon Carbide Is Changing the Game of Solar Energy
There's plenty of buzz about SiC for electric vehicles. How is the wide-bandgap semiconductor pushing innovations in solar power, though?
In 2013, Lux Research released a report estimating that the market for solar inverter discrete devices would spike to $1.4 billion in 2020. How has this estimate panned out with an increased interest in silicon carbide (SiC) and gallium nitride (GaN) for renewable energy applications, specifically solar power?
What Is Silicon Carbide's Role in Solar Energy?
The US government has a department dedicated solely to researching and developing SiC in devices like inverters, which transfers energy from photovoltaic rays (PV) to an electric grid, heat exchangers in concentrating solar power, and electric vehicles.
An inverter from Oak Ridge National Laboratory with SiC MOSFETs and diodes acting as switches. Image used courtesy of SETO and Oak Ridge National Laboratory
The Solar Energy Technologies office (SETO) states that it supports projects focusing "on making inverters and converters that last longer, work more efficiently, and reduce costs" while "others are furthering grid integration by designing devices that can connect with energy storage or load-management devices, detect and respond to abnormal current, or rapidly restore power after an outage." These efforts depend on the high performance of SiC.
Inverters as a Target SiC Component for Solar Power
Inverters are the critical center points that connect solar panels to the power grid. They do this by converting the DC harvested by solar arrays into the AC employed by most power transmission lines. This is illustrated in the image below.
The job of the inverter in solar power utilization. Image used courtesy of UnitedSiC
The inverter that occupies the center-right portion of the illustration is best served through the employment of silicon carbide (SiC) semiconductors.
SiC for Solar Power Around the Industry
A number of prominent manufacturers are tapping into SiC for devices compatible with solar energy applications.
One of the most recent is ON Semiconductor, which offers a variety of SiC MOSFETS that handle 900 V and 1200 V. In particular, the two new devices can handle 118 A and 103 A, respectively.
On-resistance vs. gate-to-source voltage of NTH4L040N120SC1. Image used courtesy of ON Semiconductor
The new devices feature gate charges (QG) as low as 220 nC. The gate charge is the amount of charge in coulombs that the switching source needs to insert into the unit’s gate to overcome its inherent capacitance and turn it on. This is an important factor. The higher charge takes more time to accumulate, slowing down the acceptable switching speed. It also wastes power.
ON Semiconductor has explained that these characteristics make the two new SiC MOSFET families a useful option for solar power inverters, on-board EV chargers, EV charging stations, uninterruptible power supplies, and server power supplies.
Last month, Infineon also announced new CoolSiC MOSFETs. These 650 V devices, which are rated from 27 mΩ to 107 mΩ, have stated usefulness in telecom, industrial, EV, and solar power applications, among others.
UnitedSiC is another company famously known for their SiC devices. It offers the UF3C family of 650 V and 1200 V SiC FETs, which, like Infineon's 650 V CoolSic MOSFET, offer RDS(on) as low as 27 mΩ. This is an important property because it represents the amount of resistance that exists between the device’s drain and source when it is conducting.
Simple schematic of UF3C065030B3. Image used courtesy of UnitedSiC
Since power is equal to I2R, and these units can carry in the range of 85 A, that would mean, even at 0.027 Ω, the units offer 200 W of power.
For solar power inverters, heat kills! So, a low RDS(on) is a vital factor affecting inverter longevity.
SiC Devices for Renewable Energy In the Wild
Several companies and research institutions are getting elbow-deep in SiC development for solar power development.
One of these institutions includes "Solar Team Twente," a Dutch solar car team from the University of Twente and Saxion Hogeschool. Solar Team Twente has opted for the aforementioned UF3C SiC devices from UnitedSiC for its solar racing car. This vehicle, powered only by solar energy, participated in a 3,000 km competition held in Australia.
The solar car, called "RED E" competed in the Bridgestone World Solar Challenge. Image used courtesy of UnitedSiC
Anup Bhalla, VP of Engineering at UnitedSiC commented on their device's implementation into the solar-powered vehicle, explaining "UnitedSiC FAST Series SiC FETs will offer the designers significant system benefits from the device’s increased switching frequencies, such as increased efficiency and reduction in the size and cost of passive components.”
Mobile Solar Energy-Harvesting System
Japanese researchers at the University of Shiga Prefecture conducted a study where they assessed the effectiveness of SiC devices in sub-200 watt applications. The goal? To create a PV power generation system for mobile devices. The researchers employed a maximum power point tracking (MPPT) circuit, which continually adjusted the load conditions in relation to the sun’s strength and the energy thus available.
Schematic of the photovoltaic inverter system and photographs of inverter battery unit. Image used courtesy of Science Direct
Using four SCT3060AL SiC FETs from ROHM Semiconductor, the device's inverter was able to switch at 200 kHz, enabling a volume and weight reduction of a full 35%. Unsurprisingly, the researchers concluded, "The SiC-based inverter exhibited a peak direct current (DC)-alternating current (AC) conversion efficiency higher than that of conventional Si inverters."
Do you work with solar power systems? Where do you see the future of SiC or GaN in that field? Share your perspective in the comments below.