The simulation involves about
fifty variables, which are all accumulated in monthly
values.
When starting,
the early parameter definition parts in the program have already
verified the consistency of all input parameters.
If Near
shadings are defined for the simulation, the "Shading factor tables" are computed (if not
already done).
The
diffuse attenuation factor should be calculated, by
integrating
simultaneously the shading factor due to horizon, the near
shadings factor according to the table, and the IAM attenuation
factors over the visible part of the sky hemisphere.
The same thing
holds for the
albedo attenuation factor.
As these
factors (integrals) don't depend on the sun's position, they are
constant over the year.
Then the hourly simulation performs the
following steps, for each hour:
Incident
"effective" energy calculation
| - |
Reading one hour data on the
Meteo file (Horizontal
global irradiance, temperature, eventually diffuse irradiance and wind
velocity). |
| - |
Performs the transposition (global,
diffuse, albedo irradiances) in the collector plane, using either
Hay or according to your user's preference. |
|
|
This is done using solar angles
at the middle of the time interval, taken from the meteo file
(with possible
time shift if defined in your meteo data). |
| - |
If horizon is defined,
applies the horizon correction on
the beam component (ON/OFF), |
| - |
If near shadings defined,
applies the shading factor on the
beam component (from the Shading factor table, or
recalculated) => evaluation of the "Linear" shading loss (loss due to the
irradiance deficit). |
| - |
Applies the IAM factor on the beam
component. |
| -
|
Applies the diffuse and albedo
attenuation factors (previously computed) on Diffuse and
Albedo parts. |
| - |
If soiling defined, applied the
soiling factor to all
components (global, diffuse, Albedo). |
This leads to
the so-called "Effective incident
energy", i.e. the irradiance effectively reaching the PV
cell surface after optical corrections.
Other
secondary variables
(essentially ratios of the above energy quantities) are available
for displays:
=>
Bm/Gl, Diff/Gl, DifS/Gl, Alb/Gl, Ftransp, FIAMBm, FIAMGl, FShdBm,
FShdGl, FIAMShd.
Array MPP
"virtual" energy EArrMPP and effectively used
energy EArray
For each
sub-array (i.e. each orientation independently), the
simulation calculates:
| - |
The array temperature
TArray (energy balance between absorbed and heat loss
energy), |
It applies the
one-diode model for the module, and evaluates:
| - |
The MPP operating point of the
array, calculated by the one-diode model if the system was running
at STC efficiency (1000
W/m² and 25°C). |
| - |
The irradiance loss, i.e. the loss due to the
low-light performances of the module. |
| - |
The temperature loss due to the cell's
temperature TArray. |
| - |
The spectral loss if defined (amorphous
modules or Sandia model). |
| - |
The electrical mismatch loss due to shadings
|
| - |
The module quality loss. |
| - |
Eventually the LID loss if defined. |
This results in
the MPP virtually
available energy EArrMPP.
This is not
necessarily the true Array output energy:
| - |
The operating point may be
displaced by the rest of the system (inverter in overpower or
other limit conditions, direct coupling on the battery, etc),
resulting in a MPPLoss. |
| - |
The energy may be unuseable if
the battery or water tank is full: this will lead to EUnused loss. |
The energy
really used by the system is called EArray.
For
sub-array with mixed
orientations, the whole meteo calculation is repeated for
the second field orientation, output meteo variables are
accumulated as averages between the two orientations, weighted by
the field area ratio.
Then both array
characteristics are electrically combined (on a same inverter
input), in order to search the real maximum power point. The loss
with respect to a common orientation is accounted as "MixLoss". It is usually negligible or very
close to 0, as the mismatch when combining two different sub-arrays
in voltage is very low.
System
energy
The next simulation stages are system dependent
:
- Grid
connected system,
- Stand-alone
system,
- Pumping
system,
- DC-grid
system.
| NB.
|
All energies are calculated here
as average
power during one hour. They are expressed in [kWh/h] or
[MJ/h], that is in a power equivalent unit. Therefore with hourly steps Power and Energy
hold the same numerical values. Although most calculations are
indeed related on power quantities, we will express them as
energies for simplification. |
