Power Block
===========

Capacity
~~~~~~~~

**Design gross output (MWe)**
  The power cycle's design output, not accounting for parasitic losses. SAM uses this value to size system components, such as the solar field area when you use the solar multiple to specify the solar field size.

**Estimated gross to net conversion factor**
  An estimate of the ratio of the electric energy delivered to the grid to the power cycle's gross output. SAM uses the factor to calculate the system's nameplate capacity for capacity-related calculations.

**Estimated net output at design (MWe)**
  The power cycle's nominal capacity, calculated as the product of the design gross output and estimated gross to net conversion factor. SAM uses this value for capacity-related calculations, including the estimated total cost per net capacity value on the Installation costs page, capacity-based incentives on the Cash Incentives page, and the capacity factor reported in the results.

*Estimated Net Output at Design (MWe) = Design Gross Output (MWe) × Estimated Gross to Net Conversion Factor*

.. _gss-availabilitycurtailment:

System Availability
~~~~~~~~~~~~~~~~~~~

.. include:: ../includes/snip_system_availability.rst

Conversion
~~~~~~~~~~

.. note:: The generic solar system model's steam turbine model is based on the empirical parabolic trough model's power block model. For a description of how SAM uses the part-load and temperature adjustment coefficients, see :ref:`Power Block Simulation Calculations <powerblock_pbsimulationcalculations>`.

**Reference conversion efficiency**
  Total thermal to electric efficiency of the reference turbine at design. Used to calculate the design turbine thermal input and required solar field aperture area.

**Max over design operation**
  The turbine's maximum output expressed as a fraction of the design turbine thermal input. Used by the dispatch module to set the power block thermal input limits. In cases where the normalized thermal power delivered to the power block by the solar field exceeds this fraction, the field will dump excess energy.

**Minimum load**
  The turbine's minimum load expressed as a fraction of the design turbine thermal input. Used by the dispatch module to set the power block thermal input limits. In cases where the solar field, thermal storage, and/or fossil backup system are unable to produce enough energy to meet this fractional requirement, the power cycle will not produce electricity.

**Power cycle startup energy**
  Hours of equivalent full-load operation of the power cycle required to bring the system to operating temperature after a period of non-operation. Used by the dispatch module to calculate the required start-up energy.

**Boiler LHV Efficiency**
  The back-up boiler's lower heating value efficiency. Used by the power block module to calculate the quantity of gas required by the back-up boiler.

**Power cycle design ambient temperature**
  The ambient temperature at which the power cycle conversion efficiency is equal to the reference conversion efficiency. The temperature corresponds to either the wet-bulb or dry-bulb temperature, depending on the value selected by the user in the Temperature correction mode list. The temperature is used in the Temperature adjustment polynomial in the Parasitics group on the Power Block page to determine cycle conversion efficiency.

**Part load efficiency adjustment**
  Coefficients for the turbine thermal-to-electric efficiency polynomial equation. This polynomial is used to adjust the cycle conversion efficiency as the thermal load into the power cycle varies from its design-point value. The resulting value from the evaluated polynomial multiplies the reference conversion efficiency, where the polynomial is formulated as follows:

  .. image:: ../images/EQ_GSS_Feff-load.png
     :align: center
     :alt: EQ_GSS_Feff-load.png

**Temperature efficiency adjustment**
  Factors for polynomial equation adjusting power cycle efficiency based on the difference between the power cycle design temperature and ambient temperature (either wet bulb or dry bulb temperature from the weather file, depending on the option you choose for Temperature Correction Mode.) The polynomial is formulated as follows:

  .. image:: ../images/EQ_GSS_Feff-temp1.png
     :align: center
     :alt: EQ_GSS_Feff-temp1.png

  .. image:: ../images/EQ_GSS_Feff-temp2.png
     :align: center
     :alt: EQ_GSS_Feff-temp2.png

  where *T*\ :sub:`amb`\    is the wet or dry bulb temperature, depending on the **Temperature Correction Mode** selection.

The power cycle conversion efficiency |EQ_GSS_eff-cycles-pb| is calculated as the product of the Reference conversion efficiency |EQ_GSS_eff-cycle-ref-pb| and the summation of the two polynomial efficiency adjustment terms.

|EQ_GSS_eff-cycle-pb| 

**Temperature Correction Mode**
  In the dry bulb mode, SAM calculates a temperature correction factor to account for cooling tower losses based on the ambient temperature from the weather data set. In wet bulb mode, SAM calculates the wet bulb temperature from the ambient temperature and relative humidity from the weather data.

Parasitics
~~~~~~~~~~

**Fixed parasitic load (MWe/MWcap)**
  A fixed hourly loss calculated as a fraction of the power block nameplate capacity.

**Production based parasitic (MWe/MWe)**
  A variable hourly loss calculated as a fraction of the system's hourly electrical output. The total production-based parasitic is evaluated as follows:

  .. image:: ../images/EQ_GSS_Wpar-prod.png
     :align: center
     :alt: EQ_GSS_Wpar-prod.png

  where *F*\ :sub:`par,prod,ref`\    is the production based parasitic factor, Fpar,load is the load-based parasitic adjustment factor (defined below), and *F*\ :sub:`par,temp`\* is the temperature-based parasitic adjustment factor (also defined below), and *F*\ :sub:`par,DNI`\  is the solar resource-based parasitic adjustment factor (also defined below).

**Part load adjustment**
  Coefficients for a polynomial that adjusts the parasitic consumption as a function of power cycle gross power output. The result of the polynomial is denoted as *F*\ :sub:`par,load`\ in the Production based parasitic description above.

**Temperature adjustment**
  Coefficients for a polynomial that adjusts the parasitic consumption as a function of the difference between ambient temperature and the reference power cycle ambient temperature. The result of the polynomial is denoted as *F*\ :sub:`par,temp`\    in the Production based parasitic description above.

**DNI adjustment**
  Coefficients for a polynimal that adjusts the parasitic consumption as a function of the solar resource value. The result of the polynomial is denoted as F_(par,DNI) in the Production based parasitic description above.

.. |EQ_GSS_eff-cycle-pb| image:: ../images/EQ_GSS_eff-cycle-pb.png
.. |EQ_GSS_eff-cycles-pb| image:: ../images/EQ_GSS_eff-cycles-pb.png
.. |EQ_GSS_eff-cycle-ref-pb| image:: ../images/EQ_GSS_eff-cycle-ref-pb.png