EBSILON®Professional Online Documentation
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Line Connection |
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Link to receiver |
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2 |
Limit input |
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3 |
Electric consumption |
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General User Input Values Physics Used Structure of the Heliostat Field Data File Displays Example
The heliostat field is used to concentrate the incoming solar irradiance onto the receiver aperture area. This is realized by a large number of individually tracked heliostats. The output of the heliostat field is a flux density distribution on a defined aperture surface. This aperture surface can be used as an interface between the optical concentrator and the solar receiver. Each heliostat has an individual efficiency that can be defined as the ratio of reflected irradiance hitting the receiver to the irradiance accepted by the heliostats mirror surface. The location of the heliostat inside the field determines its cosine angle and the distance to the aperture plane. Both quantities determine its efficiency. Ray-tracing tools are usually used to determine these efficiencies in dependence of the actual sun position and thus the overall solar field performance.
The EBSILON®Professional implementation is based on such an integral formulation. As a second simplification EBSILON®Professional assumes a homogeneous flux distribution on the aperture area which is usually sufficient for thermodynamic analysis on system level. The incident power on the receiver aperture area is calculated as.
(1)
with the average field reflectivity rrefl, the heliostat field aperture area Arefl, and the solar field optical efficiency hfield which depends on the sun azimuth gS and the sun’s elevation aS. If available, the user may include a wind correction term 
.
Actual field cleanliness is expressed by parameter REFL (relative to design reflectivity included in the heliostat field matrix). The user has to provide the field efficiency matrix for the configuration to be simulated. Any heliostat field design tool like HFLCAL can be used to generate the field performance data. An ASCII file format is defined that holds all values required to describe the heliostat field including the efficiency matrix.
There are several options to limit the power the heliostat field delivers to the receiver. This can be done by a focus factor 
that is automatically reduced by Ebsilon if a certain limit is exceeded in the fluid that is passing through the receiver. As a limit, the user may choose between a maximum outlet state of the receiver (temperature, enthalpy, steam fraction), a maximum mass flow, or a maximum power. The limits may be provided either by a parameter or by a logic line from outside of the heliostat field component.
It is recommended to read the data from a file to reduce misfits of efficiency matrix and related parameters. Some parameters used during the heliostat field design can be stored by Ebsilon for information of the user. These are not used in the calculations but are automatically read by Ebsilon from the file (if they are specified there).
There are only some parameters in the heliostat field model that can be changed by the user. This is the effective reflectivity of the system and the definition of irradiance, sun angles, and wind parameters. All other parameters are read from the heliostat field data file and printed for information in the specifications tab.
Adaptation polynomial (ADAPT) or a kernel expression (EADAPT) of ETAMAT
In this component it is possible to use an adaptation polynomial or a Kernel expression instead of or in addition to the efficiency matrix as well. The following parameters can be used in the adaptation polynomial and in the Kernel expression respectively:
Sample files under Examples\Components :
• Component_121_ADAPT.ebs shows the application of an adaptation polynomial using the internal parameters RSHEIGHT and RSAZIM
• Component_121_ADAPT_IND.ebs shows the application of an adaptation polynomial with access to the solar altitude and azimuth via value indicators on the logic outlet of the
sun and corresponding reference indices
• Component_121_EADAPT.ebs shows the application of a Kernel expression using the internal parameters RSHEIGHT and RSAZIM
| FIELDSET | Heliostat field type name |
| AREFL | Total reflective area of the heliostat field (restricted specification value) |
| NHEL | Total number of heliostats (restricted specification value) |
| AMIR | Heliostat reflective surface |
| REFL | Effective reflectivity of the field (contains also soiling) |
| FDETEFF |
Method to calculate additional efficiencies
Like in Parent Profile (Sub profile option only) Expression =0: Use MXFIELDEFF and do not calculate RETACOS, RETABAS, RETAATM, RETAINT (even if matrices are provided) =1: Use MXCOSEFF, MXSHDEFF, MXATMEFF, MXINTEFF (Calculate the values (RETACOS, RETABAS, RETAATM, RETAINT) if the =2: Use MXFIELDEFF, but calculate RETACOS, RETABAS, RETAATM, RETAINT . ( In case of an inconsistency with the overall |
| PATRACK | Specific track consumption (time averaged value for periods where heliostat field is in operation) |
| MINTRACK | Minimum DNI for activation of tracking system |
These specification values for power limitation are used if definition by specification value is chosen in FLIMITS (=0). Otherwise (FLIMITS=1) the corresponding values are read from line "2".
| FLIMIT |
Flag to specify a Method for limitation of power =0: Focus state predefined (FOCUS) |
| FLIMITS |
Method for definition of limiting value
Like in Parent Profile (Sub profile option only) =1: Given from logic line "2"
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| FOCUS | Focus state of the collector (0=not focused, 1=focused, linear in between, used if FLIMIT=0) |
| M2MAX | Maximum mass flow (used if FLIMIT=1) |
| QMAX | Maximum thermal power of field (used if FLIMIT=2) |
| T2MAX | Maximum outlet temperature (used if FLIMIT=3 ) |
| H2MAX | Maximum outlet specific enthalpy (used if FLIMIT=4) |
| X2MAX | Maximum outlet steam fraction (used if FLIMIT=5) |
| FWIND |
Method for calculation of wind effects
Like in Parent Profile (Sub profile option only) =1: Adaptation function EWIND |
| CORWIND | Factor to describe wind impact on optical performance (1=no impact or impact defined by EWIND) |
| EWIND | for FWIND=1 adaptation function wind impact: Result: 0..., default is 0. |
| VMAX | Maximum tolerated wind speed |
| FATM |
Method for calculation of atmospheric attenuation correction
Like in Parent Profile (Sub profile option only) =0: Given by constant factor CORATM |
| CORATM | Correction factor for atmospheric attenuation |
| EATM | Aadaptation function for atmospheric attenuation |
| FSDNI |
Definition of direct normal irradiance
Like in Parent Profile (Sub profile option only) =1: Taken from SUN component with index ISUN |
| DNI | Incident power on receiver aperture AREC |
| FSSUN |
Definition of sun position
Like in Parent Profile (Sub profile option only) =0: Given by parameters |
| SHEIGHT | Sun height angle (angle between sun center and horizon) |
| SAZIM | Sun azimuth angle (north=0°, positive in east direction) |
| FSWIND |
Definition of wind speed and wind direction =0: Given by parameters VWIND and AWIND |
| VWIND | Wind speed (>0, this value is used if FSWIND=0) |
| AWIND | Wind direction (from south to north=0°, positive in east direction, values in the range of 0..360°, this value is used if FSWIND=0) |
FADAPT |
Flag for adaptation polynomial ADAPT/ adaptation function EADAPT Like in Parent Profile (Sub profile option only) =0: Not used and not evaluated
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| EADAPT | Adaption polynomial for ETAMAT (Input) |
| ISUN | Index of reference solar data component |
These parameters are read from the heliostat field file and stored in the heliostat field component. Via the link between component 120 and 121 these data are made available in the solar tower receiver component 120. The user is not able to change these data within EBSILON since a given heliostat field efficiency matrix is only valid for the underlying geometry. Nevertheless, the user is free to edit the heliostat field data file manually and load the modified version into Ebsilon.
| AREC | Receiver aperture area |
| QINCDES | Design intercept power in receiver aperture |
| RECELEV | Height of receiver above ground (provided for user defined modeling) |
| FRECFORM |
Form of the receiver (provided for user defined modeling)
Like in Parent Profile (Sub profile option only) =1: Circular |
| RECDIAM |
Receiver diameter (provided for user defined modeling)
(provided for user defined modeling) |
| RECHEI |
Receiver height (provided for user defined modeling)
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| RECTILT |
Receiver tilt angle (provided for user defined modeling)
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| RECVIEW |
Receiver view angle (provided for user defined modeling)
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The values are given as information only and do not have any impact on the calculation within Ebsilon.
| HELBEAM | Beam quality EXPLAIN |
| HELFOC | Focal length (-1: individual slant range) |
| HELDENS | Field density (reflective area AREFL / land area) |
| HELMUL | Multiaiming (T=with / F= without) |
| LATIDES | Design latitude |
| HEIGDES | Height above sea |
| DATETIMEDES | Design point date DD.MM[.YYYY], year is optional |
| DNIDES | Design DNI |
| REFLDES | Design mirror reflectivity |
Generally, all inputs that are visible are required. But, often default values are provided.
For more information on colour of the input fields and their descriptions see Edit Component\Specification values
For more information on design vs. off-design and nominal values see General\Accept Nominal values
| QSOLAR | Useable solar irradiance = DNI*AREFL |
| RQINC | Incident power on receiver aperture AREC |
| ETAFIELD | Effective field efficiency = ETAMAT*REFL*RFOCUS*ETAWIND |
| ETAMAT | Efficiency of the fully tracked and clean field obtained from matrix MXFIELDEFF |
| RSHEIGHT | Sun height angle used in calculation (angle between sun center and horizon) |
| RSAZIM | Sun azimuth angle used in calculation (north=0, positive in east direction) |
| RDNI | DNI used in calculation |
| RVWIND | Wind speed used in calculation |
| RAWIND | Wind direction used in calculation |
| ETAWIND | Factor for wind impact |
| RCORATM | Correction term for atmospheric attenuation relative to design point |
| RETACOS | Cosine efficiency (if matrix MATCOS is available) |
| RETABAS | Blocking & shading efficiency (if matrix MATBAS is available) |
| RETAATM | Atmospheric efficiency (if matrix MATATM is available) |
| RETAINT | Intercept efficiency (if matrix MATINT is available) |
| RFOCUS | Used value for FOCUS |
| RADAPT | Result of ADAPT / EADAPT |
The useable solar power is calculated by
| QSOLAR = AREFL * RDNI |
Due to optical losses only a fraction of this power is useable in the receiver,
| QINC = QSOLAR * RFOCUS * REFL * ETAMAT * ETAWIND = QSOLAR * ETAFIELD |
The heliostat field efficiency ETAMAT of the fully tracked (RFOUCS=1) and clean (REFL=1) field is determined from the two-dimensional field efficiency matrix MXFIELDEFF by linear interpolation between the nodes. The nodes are
Please note, that the interpolation routine uses constant values in case of extrapolation. In order to avoid unphysical efficiency value make sure that the matrix values are bounded by zeros.
Due to the strong variations in effective solar irradiation over the day and over the year solar fields are over-dimensioned. Some fraction of the year they are able to produce more heat than can be used by the storage and power block. In this case, a part of the heliostat field is taken out of the focus to reduce the incoming power. For the power limitation the values in the connected receiver model are evaluated. The user has several possibilities to cover this effect via flag FLIMIT:
The limiting values FOCUS (use line value enthalpy), T2MAX, H2MAX, X2MAX, M2MAX, and QMAX can be provided by the specifications values (FLIMITS=0) or via logic line "2".
Under wind loads the heliostats are deformed which reduces the optical efficiency of the field. This effect is represented by the factor ETAWIND. There is no model or standard formulation for the wind effect included so far since data on this effect are sparse. The user has two possibilities:
For both cases a maximum tolerated wind speed for operation can be defined by parameter VMAX. If RVWIND>VMAX ETAWIND is set to 0 and thus the whole field is taken out of focus.
Tracking of the heliostat fields requires electricity. By parameter PATRACK the user can specify an average value for the specific power. This value is multiplied by the reflective area AREFL to finally yield the electric consumption. In case the direct solar irradiance is below 100 W/m2 the value is set to zero since the field is not in operation.
The field efficiency matrix for the configuration to be simulated cannot be calculated by Ebsilon itself, but has to be provided by the user. Any heliostat field design tool can be used to generate the field performance data. For out tests, the program HFLCAL from the DLR was used. For more information, please contact
Deutsches Zentrum for Luft- und Raumfahrt (DLR)
Institut for Solarforschung
Abteilung Punktfokussierende Systeme
Herr Peter Schwarzbözl
Linder Höhe
51147 Köln
Germany
E-Mail: peter.schwarzboezl@dlr.de
The structure of the heliostat field data file is based on the structure of typical Windows init-files. Each line begins with a predefined identifier KEYWORD (no blanks allowed), followed by "=", and the value to be read. The keyword is type in capital letters and is identical to the variable name in the Ebsilon heliostat field component. Values are read as a string where the string begins after the "=" and ends before the semicolon or the line break. Blanks at the beginning and end of the string are ignored during reading. All text behind the semicolon is treated as a comment and not read. the values have to be provided in the pre-defined units.
; Individual comments from the generating tool AREFL=120000 ; Heliostat field reflective area AREC=155.3 ; Receiver aperture area ; Second comment from the generating tool QINCDES=12000000; Design incident power on receiver ....
The order of the entries is arbitrary. The only exception is the definition of the efficiency matrix that is started with the keyword MATEFF and continued by the matrix values beginning in the following line. The first row of the matrix contains the sun azimuth angle (deg), the first column contains the sun elevation (deg). Values are comma separated with a line break at the end of each row. The syntax thus reads:
MATEFF=(8,8) ; Rows (elevation in deg) and columns (azim in deg) of the efficiency matrix , -165 , -135 , -105 , -75 , -45 , -15 , 15 , 45 LineBreak
5 , 0.2229 , 0.2303 , 0.2485 , 0.2691 , 0.2913 , 0.3063 , 0.3053 , 0.2925 LineBreak
15 , 0.3459 , 0.3612 , 0.3982 , 0.4377 , 0.4743 , 0.4965 , 0.4963 , 0.4757 LineBreak
25 , 0.4167 , 0.4344 , 0.4742 , 0.5206 , 0.5591 , 0.5830 , 0.5831 , 0.5606 LineBreak
35 , 0.4694 , 0.4865 , 0.5227 , 0.5642 , 0.5989 , 0.6209 , 0.6212 , 0.6000 LineBreak
45 , 0.5072 , 0.5226 , 0.5529 , 0.5878 , 0.6182 , 0.6359 , 0.6363 , 0.6190 LineBreak
60 , 0.5535 , 0.5645 , 0.5856 , 0.6097 , 0.6311 , 0.6431 , 0.6433 , 0.6314 LineBreak
75 , 0.5936 , 0.5996 , 0.6100 , 0.6222 , 0.6328 , 0.6390 , 0.6388 , 0.6330 LineBreak
90 , 0.6223 , 0.6223 , 0.6223 , 0.6223 , 0.6223 , 0.6223 , 0.6223 , 0.6223 LineBreak
The efficiency matrix is required for the performance calculation. In addition, more matrices describing the composition of the efficiency from different optical effects can be read and interpolated in EBSILON. The format is defined in the same way with the keywords:
The single effect efficiencies are only calculated in case the corresponding matrix is provided. They are displayed in the result values RETACOS, RETABAS, RETAATM and RETAINT. Then, the overall efficiency is the product of the four single efficiencies
ETAMAT = RETACOS * RETABAS * RETAATM * RETAINT
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Display Option 1 |
Click here >> Component 121 Demo << to load an example.
