The result was an STPV that was closer
to achieving the Landsberg limit and increasing the chances of
making a single junction photovoltaic cells, thereby further
increasing the efficiency of the system.
Such STPVs would be more compact and
could also be combined with a thermal energy storage unit to
generate electricity 24/7. This would be a much easier system to
build up and use when compared to plans of
putting mirrors in space to access solar energy at night to
transition to a carbon-free electric grid.
According to estimates by the Solar
Energy Technologies Office at the U.S. Department of Energy, solar
energy could account for as much as 45 percent of the U.S.
electric supply by 2050. A system of nonreciprocal STPVs could
drastically increase this number, and the severe limitation
associated with solar energy would go away.
The research findings were published
last month in the journal
Physical Review Applied.
Abstract
Traditional solar thermophotovoltaics
(STPVs) rely on an intermediate layer to tailor sunlight for
better efficiencies. However, the thermodynamic efficiency limit
of STPVs, which has long been understood to be the blackbody limit
(85.4%), is still far lower than the Landsberg limit (93.3%), the
ultimate efficiency limit for solar energy harvesting. In this
work, we show that the efficiency deficit is caused by the
inevitable back emission of the intermediate layer towards the sun
resulting from the reciprocity of the system. We hereby propose
nonreciprocal solar theromophotovoltaics (NSTPV) that utilize an
intermediate layer with nonreciprocal radiative properties. Such a
nonreciprocal intermediate layer can substantially suppress its
back emission to the sun and funnel more photon flux towards the
cell. We show that, with such improvement, the NSTPV system can
reach the Landsberg limit, and practical NSTPV systems with
single-junction photovoltaic cells can also experience a
significant efficiency boost.
