Energy Modelling in PVFARM

First, you must upload the meteo data file. The SolarAnywhere format is currently supported.

This file should contain Horizontal irradiance, Diffuse irradiance, Direct irradiance, Temperature, Humidity, and Wind speed for a typical year.

The time zone and geographic coordinates in which this meteo data was received are also read from this file. The correct time zone and geographic coordinates are very important for Energy calculations.

Energy calculations are performed in real-time. When changing a parameter in the Energy panel or Layout, Energy will be automatically recalculated.

PVFARM calculates how much energy will be produced by the created Layout for a typical year under the meteorological conditions contained in the meteo file.

Based on the data in the meteo file about solar irradiation incident on the horizontal surface of the earth,

it will be calculated how much solar irradiation will incident on a tilted fixed surface (for fixed-tilt) or rotating surface (for trackers) PV modules.

To do this, for each position of the sun (sun height and azimuth) and tracker (rotation angle), the incidence angle of solar irradiation on the PV module is calculated. Taking this angle into account, the value of the direct and diffusion components on the surface of the module is calculated. It also takes into account the reflected radiation from the earth's surface and incident radiation on the front surface of the module.

You can enable Shading to calculate the Energy losses due to the shading of trackers by each other.

It is important to place the trackers on a surface before making calculations. It makes sense to disable the calculation of the shading of trackers by the earth's surface. This calculation takes a lot of time, and the shading of the trackers by the surface of the earth on which the excavation work is carried out is small.

To calculate shading, an approach called Ray tracing is used. By this approach, the tracker surface is described by a mesh. For each cell of this mesh, a ray to the sun is built. If there is an obstacle in the path of the ray (for example neighboring trackers), then the cell is considered shaded. If there are no obstacles, it is considered not shaded. Based on the number of shaded and unshaded cells on the tracker, the shading factor for the tracker is calculated. This calculation process is performed for different values of sun height and sun azimuth. The result is a shading table for the tracker. This shading table is then used to calculate the radiation loss due to shading.

You can take into account the impact on Energy production of solar irradiation reflected from the earth hitting the back side of Bifacial modules (”bifaciality factor” must be specified for the module).

You can take into account the Accumulation of dirt and its effect on the system's performance. To do this, you need to set the percentage of energy loss due to soling.

You can take into account the decrease of the irradiance reaching the PV cells's surface, concerning irradiance under normal incidence. This decrease is due to reflections on the glass cover, which increases with the incidence angle.

PVFARM uses Fresnel's law to take this effect into account. Fresnel's Law describes transmission and reflections at the interface of two transparent materials of different refraction indexes.

PV module converts solar irradiation incident on its surface into electrical energy. In PVFARM, this process is modeled as follows:

1. At Standard Test Conditions (Solar irradiation: G0 = 1000 W/m², Cell temperature Tcell = 25 C, Air Mass: AM = 1.5) the dependence of current on voltage (IV curve) is built based on data from the datasheet

   

   1. Vmp - Voltage at maximum power
   2. Imp - Current at maximum power
   3. Voc - Open Circuit Voltage
   4. Isc - Short Circuit Current

   

2. To take into account the influence of irradiance on the current, the following equation is used:

   I(G) = I(G0)*G/G0

   

3. To take into account the influence of temperature on the dependence of current on voltage, data from the datasheet is used:

   1. Temperature Coefficient of Pmax

   2. Temperature Coefficient of Voc

   3. Temperature Coefficient of Isc

      

4. Based on the IV curve, the dependence of power on voltage is built and the current and voltage at which the power output by the solar module will be maximum is determined.

   

PV module temperature (Tcell) is determined based on the ambient temperature (Tamb) and solar irradiation

Tcell = Tamb + ModuleAbsorption * G * (1 - Pmax / (ModuleArea*G0)) / (HeatTransfer + ConvectiveHeatTransfer * WindSpeed)

Temperature loss is the difference in the produced energy at the ambient temperature from the meteo file and the PV module temperature equal to 25 degrees Celcius.

For calculation, the user sets the parameters:

• Module absorption coefficient of solar irradiance (default is 0.9, it is not recommended to change).
• Constant heat transfer component - takes into account the heat exchange of modules with the surrounding air due to natural convective currents of the air (not wind).
• Convective heat transfer component - takes into account the heat exchange of modules with the surrounding air due to the wind blowing the surface of the module

The user can enable Spectral correction accounting. The spectral correction takes into account changes in the solar module's energy production when the solar spectrum changes (due to its change in water content in the atmosphere and Air Mass compared to STC).

In PV FARM, the calculation of spectral correction is carried out based on the Lee and Panchula model.

Using the Module quality loss parameter, the user can take into account differences in the real module's performance, according to the manufacturer's specifications.

Using the Module quality loss parameter, you can simulate the degradation of a solar panel due to aging.

If you need to calculate how much energy will be produced in the second year, taking into account the degradation of the module in the first year, you need to set

module quality loss = 1st year power degradation of the PV module from the datasheet

If you need to calculate how much energy will be produced in the N year, taking into account the degradation of the module, you need to set

module quality loss = 1st year power degradation + annual power degradation * (N - 1)

The user can specify module and string mismatch loss.

This is loss due to a decrease in the output power of the PV array due to a mismatch of the current-voltage characteristics of the PV modules and strings of modules, due to different shading, different orientation, deviation of the module parameters from each other, etc.

Note that due to shading you get not only the direct loss of solar irradiations reaching the surface of the PV module (which was taken into account earlier). But you also get mismatch losses, since each module is shaded differently and the total power of series-connected modules will be less than the sum of their powers due to mismatch losses. You can take these energy losses due to shading into account here.

PVFARM can take into account the impact of DC ohmic losses on power generation.

DC ohmic losses calculated under standard conditions (T = 25 C and G = 1000 W/m²) will differ from losses in real conditions. For example, with the value of current in the wires under standard conditions, we can get DC ohmic losses 1.5%. But such conditions are not always during the year (the rest of the time the solar irradiation will be less than 1000 W/m² and therefore the current will also be less). Accordingly, if using the energy model you would for example get an energy loss of 1.35% for a typical year.

PVFARM calculates inverter losses due to over and under input voltage, clipping of input DC power on the inverter when it exceeds the maximum AC power of the inverter, and losses due to the efficiency of the inverter.

Inverter loss due to over and under input voltage is a loss because the voltage of the PV array has gone beyond the operating voltage range of the inverter due to changes in solar irradiation and temperature.

Inverter power clipping will show you how much energy you will lose at the selected ILR in meteorological conditions from the meteo file.

Losses since the Efficiency of the inverter is less than 100% and changes in the Efficiency of the inverter depend on the input DC power (Inverter loss during Efficiently).

As a result of modeling energy production in PVFARM, you get:

1. Key metrics

   1. Annual yield - how much energy will be generated by your layout in a typical year
   2. Daily yield - how much energy is produced per day on average
   3. Performance ratio - energy production efficiency of your layout
   4. Specific annual yield - how much energy each DC watt of your layout produces

   

2. Loss diagram

   

3. Chart changes over time in energy produced and energy lost at each of the above stages.