40% efficient sunlight to electricity conversion

Abstract

Increasing sunlight conversion efficiency is a key driver for on-going solar electricity cost reduction. For photovoltaic conversion, the approach most successful in increasing conversion efficiency is to split sunlight into spectral bands and direct each band to a dedicated solar cell of an appropriate energy bandgap to convert this band efficiently. In this work, we demonstrate conversion of sunlight to electricity in a solar collector with an efficiency value above 40% for the first time, using a small 287-cm 2 aperture area test stand, notably equipped with commercial concentrator solar cells. We use optical bandpass filtering to capture energy that is normally wasted by commercial GaInP/GaInAs/Ge triple junction cells and convert this normally wasted energy using a separate Si cell with higher efficiency than physically possible in the original device. The 287-cm 2 aperture area sunlight-concentrating converter demonstrating this independently confirmed efficiency is a prototype for a large photovoltaic power tower system, where sunlight is reflected from a field of sun-tracking heliostats to a dense photovoltaic array mounted on a central tower. In such systems, improved efficiency not only reduces costs by increasing energy output for a given investment in heliostats and towers but also reduces unwanted heat generation at the central tower.

Solar cell efficiency tables (version 48)

“…A final new result in Table is a new efficiency level of 40.6% for a concentrator submodule of 287 cm 2 aperture area, measured in outdoor testing by NREL for a 287 cm 2 split‐spectrum concentrator submodule fabricated by UNSW using commercial GaInP/GaInAs/Ge and Si cells manufactured by Spectrolab and SunPower, respectively .…”

A review of concentrator silicon solar cells

“…Gee et al made a two-junction GaAs/Si tandem cell with the efficiency of 31% under 347 suns [119], DiNetta et al made a two-junction Al x Ga 1-x As/Si tandem cell with the efficiency of 29.2% under 100 suns [120]. Green et al built a power tower concentrating system, they used a bandpass filter to split the concentrated sunlight into two parts, a three-junction GaInP/ GaInAs/Ge cell was used to absorb the reflected light, a Si back contact cell made by Sunpower company was used to absorb the transmitted light, the concentration ratio was 365 suns and the total efficiency reached 40.4%, which was the highest efficiency of the concentration systems of this kind [121]. Barnett et al proposed a six-junction tandem cell, which was consisted of a sub-cell with the bandgap of 2.4 eV, a GaInP sub-cell, a GaAs sub-cell, a Si sub-cell, a sub-cell with the bandgap of 0.95 eV and a sub-cell with the bandgap of 0.7 eV from top to down [95], they calculated the overall system efficiency and found that it could reach 53.5% under 20 suns.…”

“…The VMJ cell has the smallest series resistance among all cells, its costs is low, its highest efficiency is 19.48% under very high concentration (1200 suns) [24] and will increase after optimizing the manufacturing process and device parameters. The silicon based multijunction cell is considered to be a possible "ultimate photovoltaic solution" [126], its highest efficiency is larger than 40% under high concentration (365 suns) although its costs is high [121].…”

The potential and design principle for next‐generation spectrum‐splitting photovoltaics: Targeting 50% efficiency through built‐in filters and generalization of concept

“…For the second power loss mechanism, the previous band‐pass filter directs out light from 880 to 1030 nm (1.41 to 1.206 eV) only (Figure ), suggesting that the Ge cell is still generating more photocurrent than the top two cells hence still dissipating some power. In fact, the wavelength range for the directed light can be extended further to ~1190 nm (1.04 eV) where the Ge cell can generate just matched photocurrent, unless it has significant defects resulting in too much bend in its I‐V curve before reaching its maximum power point voltage.…”

“…It uses not only built‐in filters to minimize luminescent coupling related losses and divide sunlight more appropriately, but also two cell stacks to better harness the entire solar spectrum and reduce some mismatch issues. The method is readily accessible to the industry in that a recent landmark result was demonstrated by commercial cells and the proposed Bragg‐type filters for the next‐generation version can be feasibly built into cells by industrial facilities.…”