144 research outputs found
The magnetic properties of the hollow cylindrical ideal remanence magnet
We consider the magnetic properties of the hollow cylindrical ideal remanence
magnet. This magnet is the cylindrical permanent magnet that generates a
uniform field in the cylinder bore, using the least amount of magnetic energy
to do so. The remanence distribution of this magnet is derived and the
generated field is compared to that of a Halbach cylinder of equal dimensions.
The ideal remanence magnet is shown in most cases to generate a significantly
lower field than the equivalent Halbach cylinder, although the field is
generated with higher efficiency. The most efficient Halbach cylinder is shown
to generate a field exactly twice as large as the equivalent ideal remanence
magnet.Comment: 5 pages, 3 figure
The maximum theoretical performance of unconcentrated solar photovoltaic and thermoelectric generator systems
The maximum efficiency for photovoltaic (PV) and thermoelectric generator
(TEG) systems without concentration is investigated. Both a combined system
where the TEG is mounted directly on the back of the PV and a tandem system
where the incoming sunlight is split, and the short wavelength radiation is
sent to the PV and the long wavelength to the TEG, are considered. An
analytical model based on the Shockley-Queisser efficiency limit for PVs and
the TEG figure of merit parameter is presented. It is shown that for
non-concentrated sunlight, even if the TEG operates at the Carnot efficiency
and the PV performance is assumed independent of temperature, the maximum
increase in efficiency is 4.5 percentage points (pp.) for the combined case and
1.8 pp. for the tandem case compared to a stand alone PV. For a more realistic
case with a temperature dependent PV and a realistic TEG, the gain in
performance is much lower. For the combined PV and TEG system it is shown that
a minimum value is needed in order for the system to be more efficient
than a stand alone PV system.Comment: 6 pages, 5 figure
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