When the surface of the module is directly facing the sun, the solar module generates maximum power. For fixed modules facing the equator, this usually occurs at noon. The high performance of solar tracking arrays comes from the ability to maintain the optimal angle for a long time. The most common type in Australia is the North-South Axis Tracker, which tracks the Sun from east to west, hence the name because its axis runs in a north-south direction.
The theoretical best way to locate a north-south axis tracker is to align the axes with true north and true south. However, this is not always feasible due to physical limitations such as limited land area and non-uniform land boundaries. Moving the array axis away from the north can sacrifice system performance for ease of installation or by increasing array capacity within the project area. But how many generations are lost when the array axis is no longer pointing toward True North? When it is far from the equator, does the tracker system lose production?
This article explores the effects of direction and latitude on sun tracking performance. Tracking systems with different latitudes and orientations were modeled in PVSyst and their performance was compared to the optimal layout.
This article only examines north-south axis trace arrays.
Figure 1: North-south tracking array oriented at different azimuths
Solar tracking performance model parameters
The system's performance in terms of orientation and latitude is modeled in PVSyst (version 7.0). A north-south axis tracker is modeled with 90 modules with a total power of 30.15 kWp. The array is matched to a 27kVA inverter. If you are not familiar with PVsyst, you can learn online here through our PVsyst short courses.
The following parameters remain unchanged in all scenes to avoid differences:
- PV Module Model: Trina TSM-335DD14A(II)
- Inverter model: Fronius ECO 27.0-3-S
- Albedo effect: 0.2 (typical ground mounting).
- Use a sunny model (i.e. no cloudy days are simulated).
- Altitude: 0 meters
- IAM loss when the global default ASHRAE parameterization, B o = 0.05.
- There are no horizon shadows/far-field shadows.
- Power factor: unified.
- Backtracking is disabled (simulation is performed on a single tracker).
- The minimum and maximum field temperatures are designed to remain constant.
- Loss parameters such as heat loss, module mass loss, LID, module mismatch, pollution, AC and DC ohm loss remain constant.
- System unavailability is not modeled.
- Aging is not taken into account.
- Meteonorm (built into PVSyst) is used to generate synthetic weather data.
Survey results/analysis
Simulations were completed for a single north-south axis tracker with axis azimuths ranging from 345° to 15° at latitudes ranging from 0° to -30°. The following figure compares the specific energy generation, performance ratio, and temperature loss of the solar tracking array at different latitudes and directions.
Figure 2: Specific yields of PV trackers from NW to NE at different latitudes
The effect of direction on sun tracking performance
Figure 2 illustrates the specific yield of the system at different latitudes, where the tracker axis faces a direction ranging from -15° W (i.e., 345°) to 15° E. The specific yield is plotted as this value can be used to give an indication of energy yield for any given system size.
It can be observed that when the axis of the north-south axis tracker is aligned with true north, the best performance is indeed experienced at all latitudes. At all modeled latitudes, when the axis is far from true north, the loss of a particular yield is in the range of 27-31 kWh/kWp/yr. It was also observed that the system performed slightly better when the axis was slightly west-north, i.e., the axis was oriented from -15° to -0°, and the module experienced a slight northeast-southwest orientation, rather than the axis being slightly east-aligned with the north. This may be because in the case of the west-facing (east-facing) axis, the module is cooler when it is in the best position.
Latitude effect
Surprisingly, comparing energy production at different latitudes, we can observe that lower latitudes (far from the equator) tend to perform better. The 0° axis directional yield comparison showed a slight increase of 1.3% between 0° and -10° latitudes, a 6.5% increase in -10° and -20° latitudes, and then a 2% increase between -20° and -30° latitudes. The specific yield difference between 0° and -30° latitudes is a staggering 267kWh/kWp/yr.
The increase in energy production relative to latitude may be due to the fact that despite the reduced amount of radiation, the temperature loss at latitudes far from the equator is reduced by about 3%, which improves the overall performance of the system.
Figure 3: The effect of latitude on tracking the performance ratio and temperature loss of a PV array
Figure 3 depicts the temperature loss changes observed as the modeling system moves away from the equator toward the lower latitudes of the southern hemisphere. The temperature loss between latitudes 0°, -10°, and -20° remains approximately the same. The temperature loss suddenly drops by about 3% only at -30°. This also explains the increase in the performance ratio, i.e. if the system works with its nameplate efficiency, the ratio of energy that the system will effectively produce to the output of the system.
The reduction in temperature loss may be due to the fact that the modeled system is no longer in a tropical climate zone and has entered a temperate climate zone. In the latitude range of 0° to -20°, the performance ratio appears to be similar. At -30° latitude, we see an improvement in performance ratios of about 1.5%. While one would suspect that the performance of the system would decrease as the amount of irradiation decreases, it appears that as the amount of irradiation decreases, the system will operate at lower temperatures, improving the overall efficiency and performance of the system.
conclusion
Based on our PVSyst model, we confirmed that the north-south axis tracking system performs best when the tracker axis (as the name suggests) is fully oriented along the north-south axis. However, if there are physical limitations on the project site, such as azimuth issues or site boundaries, a north-south axis tracking system can be installed to deviate from true north by up to 15° without causing significant power generation losses. Based on our analysis, we estimate that the north-south axis tracking system at a 15° angle to the north has a specific production loss of approximately 30 kWh/kWp/yr.
In addition, installing a tracking system at lower latitudes appears to be more favorable to the overall LCOE of the project than a system installed on the equator, as it operates more efficiently, increasing by about 267 kWh/kWp/yr over production, possibly due to more favorable climate and modeling assumptions. Compiled by Chen Yunyun