Layout
Modules per String
The number of modules connected in series in a single string. Solar Advisor assumes that all strings in the array have the same number of modules connected in series. Press the Enter or Tab key after changing a value to update variables that depend on these values.
Note. When the module type on the Module page is an array from the Sandia database (indicated by the word "array" in its name), the Modules per String variable represents the number of arrays rather than number of modules.
Strings in Parallel
The number of module strings connected in parallel. Press the Enter or Tab key after changing a value to update variables that depend on these values.
Total Modules
The number of modules in the array, equal to the product of the number of modules per string and the number of strings.
Total Area (m2)
The array's total area, not including space between modules, equal to the product of the module area from the Module page and the number of modules
Array Power at reference conditions (Wdc)
The maximum DC power output of the array, equal to the product of the module's maximum power at reference conditions as specified on the Module page and the number of modules in the array.
Voc, string at 1000 W/m2 Tc=25'C (Vdc)
The open circuit DC voltage of each string of modules, equal to the product of the number of modules per string and the module's open circuit voltage at 1,000 W/m2 incident radiation and 25 ºC cell temperature. Solar Advisor displays an open circuit voltage of zero for the simple efficiency module performance model because the model does not include voltage ratings.
Vmp, string at reference conditions (Vdc)
The maximum power point DC voltage of each string of modules, equal to the product of the module's maximum power point voltage at reference conditions as specified on the Module page and the number of modules per string. Solar Advisor displays a maximum power point voltage of zero for the simple efficiency module performance model because the model does not include voltage ratings.
Vdco, dc-inverter (Vdc)
The inverter's rated input DC voltage displayed on the Inverter page. Solar Advisor displays an inverter voltage of zero for the single-point efficiency inverter performance model because the model does not include voltage ratings.
Number of Inverters
The total number of inverters in the system.
Total Inverter Capacity (kWac)
The total inverter capacity in AC kilowaatts, equal to the product of the inverter's nominal AC power rating on the Inverter page and the number of inverters.
System Derates
Pre-Inverter Derate
Applies to the array DC power output in the hourly simulation. A derate factor of 100% is equivalent to no derating. A derate factor of 75% would reduce the calculated array DC output by 25%.
Post-Inverter Derate
Applies to the inverter AC power output in the hourly simulation. A derate factor of 100% is equivalent to no derating. A derate factor of 75% would reduce the calculated inverter AC output by 25%.
Total Derate Factor
The product of the pre- and post-inverter derate factors. This value is useful for comparing to hand-calculated performance estimates, but is not used by Solar Advisor.
Tracking and Orientation
Fixed
The array is fixed at the tilt and azimuth angles defined by the Tilt and Azimuth variables.
1 Axis
The array is fixed at the angle from the horizontal defined by the Tilt variable and rotates about the tilted axis from east in the morning to west in the evening to track the daily movement of the sun across the sky.
2 Axis
The array rotates from east in the morning to west in the evening to track the daily movement of the sun across the sky, and north-south to track the sun's seasonal movement throughout the year.
Azimuth Axis
The array rotates in a horizontal plane to track the daily movement of the sun.
Tilt (degrees)
Applies only to fixed arrays and arrays with one-axis tracking. The array's tilt angle in degrees from horizontal, where zero degrees is horizontal, and 90 degrees is vertical. As a rule of thumb, system designers often use the location's latitude (shown on the Climate page) as the optimal array tilt angle. The actual tilt angle will vary based on project requirements.
Force Tilt = Latitude
Populates the array tilt value with the latitude value stored in the weather file and displayed on the Climate page.
Azimuth (degrees)
Applies only to fixed arrays with no tracking. The array's east-west orientation in degrees. An azimuth value of zero is facing the equator in both the northern and southern hemispheres. Positive 90 degrees is facing due west and negative 90 degrees is facing due east in both hemispheres. As a rule of thumb, system designers often use an array azimuth of zero, or facing the equator.
Ground Reflectance
The ground reflectance value for hours when the weather data indicate that there is no snow on the ground. A value of zero means that the ground is completely non-reflective, and a value of 1 means that it is completely reflective. A typical value for grassy ground is 0.2.
Ground Reflectance with Snow
The ground reflectance value for hours when the weather data indicate that there is snow on the ground. A value of zero means that the ground is completely non-reflective, and a value of 1 means that it is completely reflective. A typical value for snowy ground is 0.6.
Radiation Model
Note. The radiation model and tilt radiation type options are for advanced users. Use the default Total and Beam and Perez Model options unless you have a reason to change them.
The radiation model options determine how Solar Advisor uses the global horizontal radiation, direct normal radiation, and diffuse horizontal radiation data in the weather file in radiation calculations.
Beam and Diffuse
This option tells Solar Advisor to use the direct normal radiation (beam) and diffuse horizontal radiation data, and to ignore the global horizontal radiation data. Solar Advisor calculates the global horizontal radiation as the sum of the direct normal and diffuse horizontal radiation.
Total and Beam
This option tells Solar Advisor to use the global horizontal radiation (total) and direct normal radiation (beam) data, and to ignore the diffuse horizontal radiation.
Tilt Radiation Type
Note. The radiation model and tilt radiation type options are for advanced users. Use the default Total and Beam and Perez Model options unless you have a reason to change them.
Solar Advisor allows you to choose the method it uses to convert global horizontal solar radiation data to global solar radiation incident on the array. Each method uses information about the global horizontal solar radiation and either the direct normal or diffuse solar radiation, and about the sun's position and orientation of the array. The four methods differ in how they estimate the diffuse radiation incident on the array.
The isotropic sky model tends to under-predict the global radiation on a tilted surface, and is included as an option for analysis wanting to compare Solar Advisor results with those from other models using this approach. The remaining three methods provide comparable estimates of the incident global radiation.
Isotropic Sky Model
Assumes that diffuse radiation is uniformly distributed across the sky, called isotropic diffuse radiation.
Hay and Davies Model
Accounts for the increased intensity of diffuse radiation in the area around the sun, called circumsolar diffuse radiation, in addition to isotropic diffuse radiation.
Reindl Model
Accounts for the effect of horizon brightening, in addition to circumsolar diffuse radiation.
Perez Model
Accounts for horizon brightening, circumsolar and isotropic diffuse radiation using a more complex computational method than the Reindl and Hay and Davies methods.
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