// Calculate manages calculations that need to be run for each time step
public void Calculate
(
double PanelTilt // The angle between the surface tilt of the module and the ground [radians]
, double Clearance // Array ground clearance [m]
, double HDif // Diffuse horizontal irradiance [W/m2]
, double TDifRef // Front reflected diffuse irradiance [W/m2]
, double HGlo // Horizontal global irradiance [W/m2]
, double[] frontGroundGHI // Global irradiance for each of the ground segments to front of the row [W/m2]
, double[] rearGroundGHI // Global irradiance for each of the ground segments to rear of the row [W/m2]
, double aveGroundGHI // Average global irradiance on ground segment to the rear of row [W/m2]
, int month // Current month, used for getting albedo value [#]
, double backSH // Fraction of the back surface of the PV array that is unshaded [#]
, double TDir // Back tilted beam irradiance [W/m2]
, DateTime ts // Time stamp analyzed, used for printing .csv files
)
{
// For tracking systems, panel tilt and ground clearance will change at each time step
itsPanelTilt = PanelTilt;
itsClearance = Clearance / itsArrayBW; // Convert to panel slope lengths
int numGroundSegs = Util.NUM_GROUND_SEGS;
double h = Math.Sin(itsPanelTilt); // Vertical height of sloped PV panel [panel slope lengths]
double b = Math.Cos(itsPanelTilt); // Horizontal distance from front of panel to back of panel [panel slope lengths]
// Calculate x, y coordinates of bottom and top edges of PV row behind the current PV row so that portions of sky and ground viewed by
// the PV cell may be determined. Coordinates are relative to (0,0) being the ground point below the lower front edge of current PV row.
// The row behind the current row is in the positive x direction.
double bottomX = itsPitch; // x value for point on bottom edge of PV panel behind current row
double bottomY = itsClearance; // y value for point on bottom edge of PV panel behind current row
double topX = bottomX + b; // x value for point on top edge of PV panel behind current row
double topY = bottomY + h; // y value for point on top edge of PV panel behind current row
// Get albedo value for the month
Albedo = itsMonthlyAlbedo[month];
// Accumulate diffuse, reflected, and beam irradiance components for each cell row over its field of view of PI radians
for (int i = 0; i < numCellRows; i++)
{
double cellX = b * (i + 0.5) / numCellRows; // x value for location of cell
double cellY = itsClearance + h * (i + 0.5) / numCellRows; // y value for location of cell
double elevUp = 0.0; // Elevation angle from PV cell to top of PV panel
double elevDown = 0.0; // Elevation angle from PV cell to bottom of PV panel
if (itsRowType == RowType.INTERIOR)
{
elevUp = Math.Atan((topY - cellY) / (topX - cellX));
elevDown = Math.Atan((cellY - bottomY) / (bottomX - cellX));
}
int stopSky = Convert.ToInt32((itsPanelTilt - elevUp) * Util.RTOD); // Last whole degree in arc range that sees sky; first is 0 [degrees]
int startGround = Convert.ToInt32((itsPanelTilt + elevDown) * Util.RTOD); // First whole degree in arc range that sees ground; last is 180 [degrees]
// Compute sky diffuse component
backDif[i] = RadiationProc.GetViewFactor(0, stopSky * Util.DTOR) * HDif;
// Compute front surface reflected component
if (itsRowType == RowType.INTERIOR)
{
backFroRef[i] = RadiationProc.GetViewFactor(stopSky * Util.DTOR, startGround * Util.DTOR) * TDifRef;
}
backGroRef[i] = 0;
// Add ground reflected component
for (int j = startGround; j < 180; j++)
{
// Get start and ending elevations for this (j, j + 1) pair
double startElevDown = elevDown + (j - startGround) * Util.DTOR;
double stopElevDown = elevDown + (j + 1 - startGround) * Util.DTOR;
// Projection onto ground in positive x direction
double projX2 = cellX + cellY / Math.Tan(startElevDown);
double projX1 = cellX + cellY / Math.Tan(stopElevDown);
// Initialize and get actualGroundGHI value
double actualGroundGHI = 0;
if (Math.Abs(projX1 - projX2) > 0.99 * itsPitch)
{
if (itsRowType == RowType.SINGLE)
{
// Use measured GHI if projection approximates or exceeds the pitch
actualGroundGHI = HGlo;
}
else
{
// Use average GHI if projection approximates or exceeds the pitch
actualGroundGHI = aveGroundGHI;
}
}
else
{
// Normalize projections and multiply by n
projX1 = numGroundSegs * projX1 / itsPitch;
projX2 = numGroundSegs * projX2 / itsPitch;
if (itsRowType == RowType.SINGLE && ((Math.Abs(projX1) > numGroundSegs - 1) || (Math.Abs(projX2) > numGroundSegs - 1)))
{
// Use measured GHI if projection exceeds the pitch
actualGroundGHI = HGlo;
}
else
{
while (projX1 < -numGroundSegs || projX2 < -numGroundSegs)
{
projX1 += numGroundSegs;
projX2 += numGroundSegs;
}
while (projX1 >= numGroundSegs || projX2 >= numGroundSegs)
{
projX1 -= numGroundSegs;
projX2 -= numGroundSegs;
}
// Determine indices (truncate values) for use with groundGHI arrays
int index1 = Convert.ToInt32(Math.Floor(projX1 + numGroundSegs) - numGroundSegs);
int index2 = Convert.ToInt32(Math.Floor(projX2 + numGroundSegs) - numGroundSegs);
if (index1 == index2)
{
// Use single value if projection falls within a single segment of ground
if (index1 < 0)
{
actualGroundGHI = frontGroundGHI[index1 + numGroundSegs];
}
else
{
actualGroundGHI = rearGroundGHI[index1];
}
}
else
{
// Sum the irradiances on the ground if the projection falls across multiple segments
for (int k = index1; k <= index2; k++)
{
if (k == index1)
{
if (k < 0)
{
actualGroundGHI += frontGroundGHI[k + numGroundSegs] * (k + 1.0 - projX1);
}
else
{
actualGroundGHI += rearGroundGHI[k] * (k + 1.0 - projX1);
}
}
else if (k == index2)
{
if (k < 0)
{
actualGroundGHI += frontGroundGHI[k + numGroundSegs] * (projX2 - k);
}
else
{
actualGroundGHI += rearGroundGHI[k] * (projX2 - k);
}
}
else
{
if (k < 0)
{
actualGroundGHI += frontGroundGHI[k + numGroundSegs];
}
else
{
actualGroundGHI += rearGroundGHI[k];
}
}
}
// Get irradiance on ground in the 1 degree field of view
actualGroundGHI /= projX2 - projX1;
}
}
}
backGroRef[i] += RadiationProc.GetViewFactor(j * Util.DTOR, (j + 1) * Util.DTOR) * actualGroundGHI * Albedo;
}
double cellShade = 0.0;
if (itsRowType == RowType.INTERIOR)
{
// Cell is fully shaded if >= 1, fully unshaded if <= 0, otherwise fractionally shaded
cellShade = (1.0 - backSH) * numCellRows - i;
cellShade = Math.Min(cellShade, 1.0);
cellShade = Math.Max(cellShade, 0.0);
}
// Compute beam component, corrected for back shading
backDir[i] = TDir * (1.0 - cellShade);
// Correct each component for AOI and structure shading losses
backDif[i] = backDif[i] * IAMDif * (1.0 - structLossFactor);
backFroRef[i] = backFroRef[i] * IAMRef * (1.0 - structLossFactor);
backGroRef[i] = backGroRef[i] * IAMRef * (1.0 - structLossFactor);
backDir[i] = backDir[i] * IAMDir * (1.0 - structLossFactor);
// Sum all components to get global back irradiance
backGlo[i] = backDif[i] + backFroRef[i] + backGroRef[i] + backDir[i];
}
BDif = 0;
BFroRef = 0;
BGroRef = 0;
BDir = 0;
double maxGlo = backGlo[0];
double minGlo = backGlo[0];
for (int i = 0; i < numCellRows; i++)
{
// Calculate mean irradiance components
BDif += backDif[i] / numCellRows;
BFroRef += backFroRef[i] / numCellRows;
BGroRef += backGroRef[i] / numCellRows;
BDir += backDir[i] / numCellRows;
// Find the max and min global irradiance values
maxGlo = Math.Max(maxGlo, backGlo[i]);
minGlo = Math.Min(minGlo, backGlo[i]);
}
BGlo = BDif + BFroRef + BGroRef + BDir;
// Calculate the homogeneity of values as the range normalized by the sum
IrrInhomogeneity = (BGlo > 0) ? (maxGlo - minGlo) / BGlo : 0;
// Option to print details of the model in .csv files. Only recommended for single day simulations.
// PrintModel(ts);
}
double CalcSkyViewDirection
(
double x // Horizontal dimension in the row-to-row ground area
, RowType rowType // The position of the row being calculated relative to others [unitless]
, double direction // The direction in which to move along the x-axis [-1, 0, 1]
)
{
double h = Math.Sin(itsPanelTilt); // Vertical height of sloped PV panel [panel slope lengths]
double b = Math.Cos(itsPanelTilt); // Horizontal distance from front of panel to back of panel [panel slope lengths]
double offset = direction; // Initialize offset to begin at first unit of given direction
double skyPatch = 0; // View factor for view of sky in single row-to-row area
double skySum = 0; // View factor for all sky views in given direction
double angA = 0;
double angB = 0;
double angC = 0;
double angD = 0;
double beta1 = 0; // Start of ground's field of view that sees the sky segment
double beta2 = 0; // End of ground's field of view that sees the sky segment
// Sum sky view factors until sky view factor contributes <= 1% of sum
// Only loop the calculation for rows extending forward or backward, so break loop when direction = 0.
do
{
// Set back limiting angle to 0 since there is no row behind.
if (rowType == RowType.LAST)
{
beta1 = 0;
}
else
{
// Angle from ground point to top of panel P
angA = Math.Atan2(h + itsClearance, (offset + 1) * itsPitch + b - x);
// Angle from ground point to bottom of panel P
angB = Math.Atan2(itsClearance, (offset + 1) * itsPitch - x);
beta1 = Math.Max(angA, angB);
}
// Set front limiting angle to PI since there is no row ahead.
if (rowType == RowType.FIRST)
{
beta2 = Math.PI;
}
else
{
// Angle from ground point to top of panel Q
angC = Math.Atan2(h + itsClearance, offset * itsPitch + b - x);
// Angle from ground point to bottom of panel Q
angD = Math.Atan2(itsClearance, offset * itsPitch - x);
beta2 = Math.Min(angC, angD);
}
// If there is an opening in the sky through which the sun is seen, calculate view factor of sky patch
skyPatch = (beta2 > beta1) ? RadiationProc.GetViewFactor(beta1, beta2) : 0;
skySum += skyPatch;
offset += direction;
} while (offset != 0 && skyPatch > (0.01 * skySum));
return(skySum);
}
