The Department of Energy’s National Renewable Energy Laboratory announced a new high of 31.1 percent conversion efficiency for a two-junction solar cell under one sun of illumination, which beats the previous record of 30.8 percent efficiency from Alta Devices, and is part of a program focused on lowering the cost of solar power.
NREL made the announcement last week at the 39th IEEE Photovoltaic Specialists Conference in Tampa, Fla. The work was done at NREL as part of the DOE’s Foundation Program to Advance Cell Efficiency (F-PACE), a project that aims to lower the cost of solar energy to a point at which it is competitive with other sources including fossil fuels.
The F-PACE project aims to produce a 48 percent efficient concentrator cell and NREL scientists believe last week’s announcement has brought them closer to that goal, so the new record may not last long as scientists work on constantly improving efficiency.
The tandem solar cell is made of a gallium indium phosphide cell laid on top of a gallium arsenide cell. It was grown inverted, like the inverted metamorphic multi-junction solar cell, also developed by NREL, and flipped during processing. The front of the cell is covered with a two layer anti-reflection coating and on the back there is a highly reflective gold contact layer, which reflects photons back into the cell and helps improve its efficiency.
The world PV market is dominated by silicon solar cells but researchers see opportunities for new materials. Utilities are beginning to show interest in high-efficiency concentrator cells bolstered by lenses that magnify the power of the sun, because the modules have demonstrated efficiencies well over 30 percent. NREL says if costs can be reduced and growth rate increased, the low concentration one-sun cells may also be viable commercially, because the same cell should work well when lenses are added to multiply the sun’s power.
New materials can make the difference in growing the market by reducing costs while improving efficiency, reliability and performance – which will offer better margins for utilities selling electricity under power purchase agreements, Lux Research says. Devices with wide bandgap semiconductors like Silicon carbide (SiC) and Gallium nitride (GaN) will be key to solar inverters as the residential and commercial market for microinverters and small string inverters grows 7 percent to $1.4 Billion in 2020, the research firm says in a report.
Until now, inverters have been appreciated for their ability to lower costs in a solar market faced with over supply and price pressure, but Lux analysts say the holy grail for solar inverters is the implementation of wide bandgap semiconductors like SiC and GaN, which can perform so well as to justify charging a premium while still lowering the cost of the solar power generated.
Solar installations are booming worldwide as solar electricity becomes cheaper than electricity from fossil fuels and it has already happened in 105 countries, says Energy Manager Today guest columnist Giorgio Cellere, R&D manager with Applied Materials, in a post last October. This is the tipping point where economics takes over from altruism and solar PV becomes a serious part of the global energy mix. He says the steady drop in cost-per-watt is great news for the end user and is enabled by simultaneous increases in cell efficiency and lower manufacturing costs.