Energize RE: Renewable Energy Supplement - June 2015 - Page 45

Utility RE Systems

How to increase PV plant output and effi ciency with solar trackersby Robert Timmis, Exosun

Maximising return on investment is the primary goal for utility-scale solar plant owners and developers. Achieving this objective requires a combination of careful planning, smart design and strong components selection. While optimising balance of systems for these plants is a major concern, the focus typically centers on inverters, mounting and racking solutions for fi xed-tilt systems. An often overlooked contributor with major ROI acceleration potential is solar tracker technology. Through project case studies carried out in South Africa, this article explains the benefi ts of solar trackers compared to fi xed-tilt systems and how to further optimise PV plants using this method.

Solar trackers are motorised structures that orient photovoltaic panels toward the sun, from East to West, in order to collect more direct sunlight throughout the day and consequently to increase solar plant output. Trackers maintain an optimal sun angle on the panels significantly longer than a fixed-tilt system, yet they only move 30 minutes a day.

Performance comparison between trackers and fixed-tilt installations

The below case study compares the energy and financial performance of two technologies for a 10 MWp PV plant located near the city of Springbok, in South Africa, using horizontal single-axis trackers and a fixed-tilt installation.

System characteristics

Tables 1, 2, 3 and 4 describe the main character ist ics of the plant, the two technological solutions and the estimated losses used for the calculations. The same hypothesis on losses and the same layout are considered for both systems.

Modelling assumptions

For the chosen site (GPS Coordinates: -29.7°N; 17.9°W), meteorological data were calculated by interpolation with Meteonorm 7 software. This data was the only necessary input to the proprietary production simulation software, based on accurate calculations with a 15 min time-step. Moreover, no distant mask was considered for the simulation.

Analysis: output comparison

Fig. 2 shows the annual output for the two technologies during the first year. In both configurations, the same ground coverage ratio (GCR) and number of grid-tied inverters are considered. The GCR is the ratio between the PV modules’ area and the total ground area, defining the east-west distance between the tables.

The tracker enables production of 23,3% more

energy output per year. While fixed-tilt systems may offer a slight advantage in May, June and July, the tracker-equipped plant experiences a considerable output gain during the spring and summer months, with a 58% increase in December alone. This boost in output easily offsets any production losses during other times of the year.

Another advantage of the tracker system is its period of production and the shape of

its homogeneous daily power production curve. As indicated on Fig. 3, the production is stable throughout the day. The maximum output remains consistent during 80% of the day, contrary to the classic gaussian-shaped curve of a fixed-tilt installation which includes a power peak at midday. The tracker also allows to capture more sunlight when the sun is low in the sky, thus producing power earlier in the morning and later in the evening. This results in 58% more energy output.

Fig. 1: Functioning of a solar tracker.

Location Capacity [kWp] Module type No. of modules Inverters AC/DC ratio

Spr ingbok, AZ

12 000Jinko Solar

JKM300WM – 7233 333

SMA - Sunny Central SC500CP-10

1

Table 1: PV plant data.

Azimuth GCR [%] Tilt [°]Modules per

stringNo. Strings

0° 30% 30° 20 1667

Table 2: Fixed-tilt data.

Axis Azimuth GCR [%] Modules per string No. tables (Strings)

0° 30% 20 1667

Table 3: Exotrack HZ horizontal single-axis tracker data.

Energize RE: Renewable Energy Supplement - June 2015 - Page 46

Utility RE Systems

Soiling 3%

Mismatch 2%

Non-ideal inverter MPPT 1%

Availability 1%

DC & AC wiring 1% & 0,5%

Auxiliary equipments 0,5%

Motorisation 0,2%

Transformer 1%

Table 4: Estimated losses.

What’s the impact on the project revenue?

When taking into consideration a power purchase agreement of $0,10 per kWh, the gain in energy output with solar trackers allows to increase revenue by $430 000 over one year, and $8,6-million over 20 years, in comparison with fixed-tilt systems.

Optimisation of tracker-equipped PV plants

After demonstrating that solar trackers considerably increase output and the revenue of a PV plant, we will now focus on how to configure a tracker-equipped plant in the best possible way in order to reduce Capex expenditures and further boost output.

Case study: Considering the GCR and tracker orientation

Each solar plant is sized and equipped according to site constraints (irregular side boundaries, land slopes, etc.). In order to ensure an efficient implementation of the PV array, the orientation of the solar trackers and the GCR should be considered.

The GCR is the amount of land covered by PV panels versus not covered by panels. The higher the GCR percentage, the closer the panels are together, thereby increasing panel on panel shading. Unlike fixed-tilt structures, trackers can position tables to avoid shading on neighbouring panels. Orientation along the North-South axis should also be taken into consideration.

Consider the site located near Springbok, in South Africa, (Global Horizontal Irradiance: 2278 kWh/m²) in order to study the influence of the GCR and orientation parameters on the output of this tracker-equipped plant.

The system output decreases linearly while the GCR is increasing, whatever the orientation. Between 30% and 50% GCR, the output gap reaches 130 kWh/kWp, which represents a 5% drop. The lower the GCR, the higher the

Fig. 2: Annual yield comparison between a fixed-tilt installation (in grey) and the Exotrack HZ solar tracker (in orange).

Fig. 3: Daily output comparison between employing trackers (in orange) and a fixed-tilt system (in grey) on 11 December.

Orientation 0° Orientation 20° Orientation 20°

Power 2 MWp 2 MWp 2,3 MWp (+16%)

Motors 12 10 (-16%) 12

Trenches and DC cablesComplicated infrastructure

100 m shorter (-31%) 60 m shorter (-19%)

Specific production losses N/A <1% <1%

Table 5: Example of an optimised 2 MWp layout with a single-axis tracker.

Energize RE: Renewable Energy Supplement - June 2015 - Page 47

Utility RE Systems

Fig. 4: Influence of the GCR and tracker orientation on the plant output.

output, and the higher the GCR, the higher the capacity.

The orientation parameter has less influence on the specific production. Between 0° and 10°, the output difference is about -0,3% and from 0° to 30° the difference reaches -2,5%. Consequently, we can conclude that the GCR has more influence on the plant output than the tracker orientation. The tables can be slightly rotated from the South to decrease the GCR and improve the implementation.

Case study: how does tracker orientation affect CAPEX and output?

The best solar plant layouts are the result of a perfect balance between upfront costs, plant configuration and energy yield.

Table 5 indicates three different tracker implementation options on a 2 MWp plant. The first configuration is based on a tracker implementation option on a north-south Axis. The second and third one include a tracker layout on a south-east axis with a 20° orientation, with very limited production losses. Option one and two provide a 2 MWp power capacity, option three has a capacity of 2,3 MWp, with considerable differences in constructability and overall costs.

When comparing options one and two, we can notice that with a 20° configuration, the DC trench constructions are much easier, since all the drive motors of the trackers are located on the same virtual line. The total DC trench is 100 m shorter and only ten motors are needed against twelve for option 1. Option 3 shows that whilst achieving higher power capacity, the number of drive motors remains the same as for option 1, and allows to win only 40 m of DC trench length, in comparison to option two, where 100 ms can be gained.

Trackers, the right choice for a PV project

Partnering with a tracker supplier that can consistently increase system yield without compromising long-term reliability is essential. Third-party certifications from reputable organizations offer more insight into the durability and safety of a given tracker and should not be overlooked. With the right LCOE friendly tracker technology, accompanied by an optimised plant and smar t t racker implementat ion, project developers and plant owners can considerably increase their revenues and accelerate their ROI.

The Exotrack HZ horizontal single-axis tracker, increases plant production up to 25%

in comparison to fixed-tilt systems and is a revenue booster for any solar project. UL 3703 compliant, the tracker has been designed for fast and simple installation, as well as for minimal preventive operation and maintenance actions. Its unique centralised control-command system can monitor up to

8 MWp of trackers. In addition, the intelligent patented tracking process, allows to generate up to 5% higher yield compared to other single-axis tracker technology.

Contact Robert Timmis,Exosun, Tel 021 526-0468, r.timmis@exosun.net

Equation 1: Calculation of revenue increase over 20 years using a tracker.