  Thermophotovoltaic systems in principle enable utilization of heat that is
usually regarded as wasted energy. However, the wavelength selectivity of the
thermal emitter required for high efficiencies is rather difficult to control
with conventional designs. Here, we design a thermophotovoltaic system
comprising silicon rods as thermal emitter with a relatively narrow emission
spectrum and a photovoltaic cell with a band gap corresponding to 1.76 $\mu$m,
and verify efficient power generation. By accurately measuring the heat flux
that enters the emitter, the emitter temperature, and the electrical output
power of the photovoltaic cell, we find that the actual system efficiency
(ratio of ingoing heat flux to output power) is 11.2% at an emitter temperature
of 1338 K, and that the output power density footprint is 0.368 W/cm2. The
obtained efficiency is relatively high, i.e., 1.65 times that of the previously
reported record value (6.8%). Further efficiency improvements in the future may
lead to development of distributed energy supplies using combustion heat.
