02-08-2018 | | By Rob Coppinger
A silicon carbide inverter could halve the system cost of a photovoltaic facility and enable solar power to be consistently delivered to a growing number of homes and businesses through the power grid.
Solar power arrives as a direct current (DC) and must be converted to alternating current (AC) for the electrical grids that supply society. This requires an inverter to convert the DC into AC, adding cost and energy losses to any system. Another challenge is the variability of solar power, due to changing light levels during the day, and the lack of light at night. The solution to the variability is batteries and they can store the photovoltaic cells’ DC power.
“The basic idea is one inverter that has both PV [photovoltaics] and storage utilising the same hardware. There is no additional hardware needed for storage,” said UT electrical and computer engineering professor Alex Huang. He is the principal investigator for the work. A typical solar cell system locates the storage separately to the photovoltaics’ power generation. Huang’s team has designed the all-in-one system, but it has not been built yet. The second part of Huang’s project is focusing on how large the storage, the battery, would have to be; large or small. This will also contribute to the overall system cost.
Dr. Alex Huang is a professor in the Department of Electrical and Computer Engineering at The University of Texas at Austin.
Called M4, Huang’s inverter uses a high frequency transformer which operates at 50-100 kilohertz. An inverter converts DC to AC with electromagnetic switches that flick on and off at high speed, typically about 50-60 hertz, to repeatedly reverse the current direction, to turn DC into AC. One reason why the switching occurs at 50-60 hertz, or times per second, is that at higher frequencies, silicon, the semiconductor used for inverters, would generate a lot of heat; wasting energy.
The M4’s 100 kilohertz switching would be too great for silicon and so silicon carbide is used instead. Silicon carbide, even at 100 kilohertz, generates little heat, making it more efficient. Huang said that with M4 the inverter is also more compact and, “not bulky,” like a normal, lower frequency, inverter. The overall system would not use additional transformers either, another cost reduction.
The M4 would control the flow of electricity between three paths. They are, from the photovoltaics to the grid, from the photovoltaics to the DC battery, and from the battery to the grid. In normal operation the solar energy would go directly to the DC battery from the photovoltaic cells for a managed distribution, unless the grid had high demand for immediate power supply.
The US government’s department of energy (DOE) has awarded Huang’s team USD3 million for the inverter work. Huang’s team is working with the Electric Reliability Council of Texas, Toshiba International, silicon carbide specialist Wolfspeed, simulation provider Opal-RT and the Argonne National Laboratory. The DOE wants to cut the cost of a solar system by half by 2030. Another eight projects are being funded for solar power electronics with USD17 million.
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