Glossary and Definitions
Array
The set of all strings (which must all be of the same length) connected in parallel to a single bipolar input of an inverter.
Axis
The line about which something rotates, in this case the axle, modules and associated mounting structure in Trackers.
Axis Tilt
Angle of inclination of a Tracker Axis from the horizontal. This applies to both “horizontal axis” trackers, where the axis may not in fact be horizontal owing to underlying terrain slope, and Tilted Axis trackers. Axis Tilt is positive if the axis is higher at the end further from the equator, regardless of hemisphere. For horizontal axis trackers, the Axis Tilt is dependent on the System Plane Azimuth and Zenith, and the System Rotation
Azimuth
Nominal orientation of fixed tilt or tracking arrays.
For Fixed-Tilt arrays, this is the direction of a normal to the primary active face of the modules projected onto a horizontal plane measured clockwise from true north, if positioned on a flat, horizontal surface. Fixed-Tilt rows appear normal to the Azimuth Angle when viewed from directly above.
If a rack is positioned on uneven terrain such that one end is higher than the other, the actual azimuth of the modules on that rack will differ from this value - see Effective Azimuth. For Tracker arrays, this is the direction of the Axis.
Default Azimuth value is 180° (i.e. south-facing) in the northern hemisphere, 0° (i.e. north-facing) in the southern hemisphere for both fixed-tilt and tracker arrays.
Bay
Set of modules along a tracker axis which are positioned adjacent to each other (or as close as the mounting brackets allow). Typically, a Bay falls between Drive- or Support Gaps. For simplicity, Bays are not currently modelled in SolarFarmer.
Drive Gap
The gap between adjacent bays on a tracker at the point where the tracker is driven (either directly, or via a link to a central drive). For simplicity, Drive Gaps are not currently modelled in SolarFarmer.
Effect
SolarFarmer uses the word “Effect” to refer to a factor that either increases or decreases the amount of irradiance, power or any other relevant quantity.
- A positive value for an Effect indicates that the effect resulted in more irradiance or power in the calculation (for example the “Tilt Effect” will normally be positive, as tilting the modules to reduce the average incidence angle results in higher irradiance at the modules).
- A negative value for an Effect indicates that the Effect resulted in less irradiance or power in the calculation (for example the “Soiling Effect”).
- Some effects will almost always have the same sign, others may be negative under some circumstances and positive under others (e.g. “Spectral Effect”).
The sole exception to this is in the Transformer inputs, where “No-Load Loss” and “Full-Load Loss” are used to describe these inputs, to conform with terminology in standard transformer specifications.
Effects are specified in percent, and an Effect of 0% means that the Effect causes no change.
An Effect of +3% would be equivalent to multiplying the relevant quantity by 1.03; an Effect of -1.5%
would be equivalent to multiplying the relevant quantity by 0.985.
Effective Tilt
The Effective Tilt of a module is the angle between the vertical and a normal to the face of that module considering any end-to-end slope on a fixed-tilt Rack or any Axis Tilt and Rotation on a Tracker.
Effective Azimuth
The Effective Azimuth of a module is the angle between a normal to the face of that module projected onto the horizontal and measured from true north, considering any end-to-end slope on a fixed-tilt Rack or any Axis Tilt and Rotation on a Tracker.
Frame
Part of tracker or rack that surrounds and protrudes beyond the edges of the modules in a single Rack or Tracker. Frames cause shading.
Ground Coverage Ratio (GCR)
The ratio of the rack height to the pitch.
Horizontal-Axis Tracker
A single-axis tracker where the axis is nominally horizontal. In practice, the axis may not be horizontal, owing to underlying terrain slope. Typically, a Tracker System manufacturer will specify the maximum Axis Tilt angle. Unlike fixed-tilt racking systems, Horizontal Axis Trackers are installed in rows oriented close to north-south.
Layout
All Layout Regions in a Plant, as defined in the SolarFarmer model.
Layout Region
Area inside a single, closed boundary in the map. Racks and Trackers can only be positioned within a Layout Region, but other items like Inverters and Transformers can be positioned outside.
Module
A single physical PV module, including all cells, wiring, diodes etc, in suitably transparent protective encapsulation.
Pitch
A way of specifying the spacing of adjacent Rows in a Layout Region, the Pitch is the absolute distance between centre lines of the Rows projected onto a horizontal plane (i.e. the distance between centre lines as seen from above).
Plant
Entire PV installation including all arrays, wiring, inverters and transformers up to the network connection point.
Plant Array
All Arrays making up the plant.
Rack
The available Rack Templates in the Rack System are used to create Racks within the Layout Regions of fixed-tilt Layouts.
Rack System
A fixed-tilt Layout will typically be composed of Racks that are similar in design and share many common dimensions, but vary in length; there may be two, three or more different length Racks based on the same Rack System in the layout, to enable the most efficient use of available space, and/or reduce wind loading at the edges of the Layout.
Rack Template
A Rack System must have at least one Rack Template based on the system. A Rack Template specifies the dimensions of an available rack length option within the system that are not common with other members of the system. Once a Rack Template has been defined, Racks with the specified dimensions can be placed in the Layout. In rooftop Layouts, modules are often mounted individually to allow efficient use of complex spaces divided by obstacles such as AC units and parapets, in which case the Rack size would effectively be 1 x 1.
Row
Line of Racks or Trackers in a Layout Region, potentially including gaps. Potential positions for these rows (Row Lines) are shown as dotted lines in the Layout Regions in SolarFarmer.
Row Line
Dotted line in Layout view showing each potential Row position in the Layout Regions.
String
A set of PV modules connected in series (i.e. the positive terminal of one module is connected to the negative terminal of the next, repeated all the way along the string)
Submodule
A group of cells and wiring within a PV module connected in parallel with a single bypass diode. There are normally three of these per module. A string of modules is modelled electrically like a string of submodules.
Substring
A Substring is a set of series-connected cells connected across a bypass diode within a Module.
Support Gap
The gap between adjacent bays on a tracker at the point where the tracker axis is supported. For simplicity, Support Gaps are not currently modelled in SolarFarmer.
System Plane
Within a Layout Region, the Axes of horizontal trackers are confined to lie within a single plane, the System Plane. The plane is defined by the System Plane Azimuth and System Plane Zenith, and the vertical offset of the plane.
System Plane Azimuth
The clockwise angle from true north of the projection of the upwards-pointing normal to the System Plane on a horizontal plane.
System Plane Zenith
The angle between the vertical and the upwards-pointing normal to the System Plane.
System Rotation Angle
The System Rotation Angle describes the angle between the true north-south axis at the site, and the centre lines of horizontal axis trackers at the site. A positive angle indicates a clockwise rotation, regardless of the hemisphere in which the site is located. System rotation angle is confined to be between -90o and +90o.
Tilt
For fixed-tilt racks, the Tilt is the nominal angle between the vertical and a normal to the plane of the modules mounted on the rack, when the rack is placed on flat, horizontal terrain.
A positive tilt angle indicates that the racks are inclined such that a projection of the normal to the plane of the modules on rack onto the horizontal plane points toward the equator (in both hemispheres), i.e. the typical tilt used to increase the irradiance falling on the modules.
If a rack is positioned on uneven terrain such that one end is higher than the other, then this will not be the actual angle between the normal to the face of the rack and the vertical – see Effective Tilt.
For horizontal-axis trackers, see Axis Tilt.
Tracker
The available Tracker Templates in the Tracker System are used to create Trackers within the Layout Regions of tracking Layouts.
Tracker Rotation Angle
Angle of rotation of Tracker from the middle position (normal to active face of modules on Tracker points vertically upward – in this position the Rotation angle is 0). SolarFarmer uses a negative rotation angle to indicate that the active faces of modules on the Tracker are oriented to point to the East, regardless of hemisphere, and a positive rotation angle to indicate an orientation to the west. Thus, the rotation angle will normally progress from negative in the morning to positive in the evening.
Tracker System
A Layout will typically be composed of Trackers that are similar in design and share many common dimensions and properties, but vary in length; there may be two, three or more different length Trackers based on the same Tracker System in the layout, to enable the most efficient used of available space.
Tracker Template
A Tracker System must contain at least one Tracker Template based on the System. A Tracker Template specifies the dimensions of an available Tracker within the system that are not common with other members of the system – those quantities that define the length of the Tracker. Once a Tracker Template has been defined, Trackers with the specified dimensions can be placed in the Layout.