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@PHDTHESIS{Wolfertstetter:706465,
author = {Wolfertstetter, Fabian Anselm},
othercontributors = {Pitz-Paal, Robert and Wiedensohler, Alfred},
title = {{A}uswirkungen von {V}erschmutzung auf konzentrierende
solarthermische {K}raftwerke},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
reportid = {RWTH-2017-08665},
pages = {1 Online-Ressource (205 Seiten) : Illustrationen,
Diagramme},
year = {2016},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2017; Dissertation, RWTH Aachen University, 2016},
abstract = {The soiling of solar mirrors compromises significantly the
efficiency of concentrating solar power (CSP)-plants. It
causes a partial loss of incoming radiation when being
reflected at the mirror surfaces of the solar field. This
reduces the output of the power plant or causes increased
cleaning costs. Many potential CSP-sites lackinformation on
soiling. In this thesis measurement methods are presented to
quantify the effect of soiling. The collected data is
applied in a financial yield analysis study and a
statistical analysis concerning the meteorological causes of
soiling.A novel measurement device called Tracking
Cleanliness Sensor (TraCS) is presented. It is an accessory
to an existing irradiance measurement station with a solar
tracker. It consists of a second pyrheliometer that is
installed to measure the direct normal irradiance (DNI) as
reflected by a sample mirror. Comparing the reflected to the
directly measured DNI is a measurement for the reflectivity
of the sample mirror. The parameter cleanliness is
calculated by comparing the reflectivity of a soiled mirror
to its reflectivity in the clean state. In a next step, the
soiling-rate is calculated. The soiling-rate is defined as
the daily loss of cleanliness with time. TraCS is a low cost
instrument that requires little additional maintenance.
Further advantages compared to currently employed
measurement methods are its high time resolution, the use of
the current sun spectrum and the measurement of alarge
mirror surface area of 30 cm2. A soiling-rate dataset of 1,
5 years measured at Plataforma Solar de Almería (PSA) in
Spain in daily time resolution is presented and analyzed.
The mean soiling-rate is - 0, 0052 /Tag.The dataset is
applied in a yield analysis study for two types of power
plants at two different sites. The focus lies on the exact
reproduction of cleaning activities and costs. Adjustment of
cleaning activities to a daily measurement of the
soiling-rate can increase the profit of a power plant
project over its lifetime. Candidate cleaning strategies are
compared to a constant cleaning activity with one vehicle
(reference). The increase in profit ranges up to 2, 6 $\%.$
In existing yield analysis software packages the mean
cleanliness of the solar field $(Cl_Feld)$ is assumed as
constant. Setting $Cl_Feld$ equal to the yearly mean value
of $Cl_Feld$ resulting from thereference strategy and
calculating the yearly monetary yield results in a 0, 58
$\%$ higher profit than that resulting from a time resolved
$Cl_Feld.$ The assumption of a constant $Cl_Feld$
overestimates the project’s revenues in this case because
the different weighting of daily DNI-sums by $Cl_Feld$ is
not accounted for. Time resolved soiling-rate measurements
therefore are an important pre-requisite for the correct
estimation of yield analysis studies and optimization of
cleaning activities.In a next step, the soiling-rate dataset
is compared to the simultaneously measured weather
parameters airborne particle mass concentration, diffuse
irradiance, dew, wind speed, wind direction, relative
humidity and combinations of the latter. It follows, that
the particle mass concentration for particles up to 10 m
(PM10)correlate best with the soiling rate. The adhesion of
particles of this size class to the mirror surface is
potentiated by the occurrence of dew. On days where
particles impact mainly perpendicular to the mirror surface,
the correlation coefficients between PM10 and the
soiling-rate are higher for many subperiods of two to four
months. The slopes of linear fits between soiling-rate and
the investigated weather parameters vary with time. This can
be explained by alternating properties of the adhered
particles. For the definition a general model, further
measurement parameters have to be included. The novel
instrument TraCS enables measurements of time-resolved
soiling datasets.These are necessary for a refinement of
yield analysis and the development of improved cleaning
strategies as shown here. The influence of several weather
parameters on the soiling-rate has been identified.},
cin = {412910},
ddc = {620},
cid = {$I:(DE-82)412910_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2017-08665},
url = {https://publications.rwth-aachen.de/record/706465},
}
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