Geometrical Optimisation of Receivers for Concentrating Solar Thermal Systems
Date
2018
Authors
Asselineau, Charles-Alexis
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Abstract
In concentrated solar thermal technologies, the receiver converts
concentrated solar radiation into high-temperature heat. Solar
receivers are commonly simulated with a stochastic integration
method: Monte-Carlo ray-tracing. The optimisation of the geometry
of receivers is challenging when using existing optimisation
methods for two reasons: each receiver evaluation using
Monte-Carlo ray-tracing requires significant computational effort
and the outcome of a simulation involves uncertainty.
A series of novel optimisation techniques are proposed to enable
gradient-free, stochastic and multi-objective optimisation
adapted to such problems. These techniques address the
computational load difficulty and the challenge of conducting
stochastic optimisation based on uncertain evaluations by
introducing the concepts of “Progressive Monte-Carlo Evaluation
(PMCE)”, “Intermediate Ray Emission Source (IRES)” and
adaptive view-factor calculation. A new “Multi-Objective and
Evolutionary PMCE Optimisation (MOEPMCE-O)” method is then
built around PMCE to enable multi-objective geometrical
optimisation of receivers.
PMCE is shown to be able to reduce the computational time of a
random search optimisation by more than 90% and is used in the
geometrical design of a new receiver for the Australian National
University SG4 dish concentrator that achieved 97.1% (±2.2%) of
thermal efficiency during on-sun testing. MOE-PMCE-O is applied
to a multi-objective tower receiver problem where liquid sodium
is used as the receiver heat-carrier in a surround configuration
heliostat field. A series of useful geometrical concepts emerge
from the results, with geometrical features able to maintain high
efficiency while keeping acceptable incident peak flux values
with a moderate receiver total mass.
Finally, a more fundamental look at the impact of the interaction
of concentrating optics on the exergy of radiation available at
the receiver location highlights the major role played by
concentrator surface slope error in lowering the exergy in
concentrated solar thermal systems and quantifies the exergy loss
associated with non-ideal match between flux and surface
temperature in receivers.
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Keywords
concentrated solar thermal, stochastic optimisation AND stochastic optimization, solar energy, simulation optimisation AND simulation optimization, solar thermal receivers, concentrating optics
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Thesis (PhD)
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