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Single Axis Tracker- Factors Affecting Gain

Solar trackers have seen a tremendous growth in the last few years as costs came down. However, the growth for tracker stayed flat in Indian solar market in 2017-18 in anticipation of fall in module price. Also, developers are still conservative in terms of using a PV tracker in place of a fixed tilt system. One of the reason for this reservation is the difference between tracker gain estimated by PVsyst and the actual gain observed at site. Let’s look at how onsite factors like irradiance, Sun’s position, tracker availability etc. affects tracker gain but still remains a preferential technology with respect to fixed tilt system, especially with higher modules prices.

The total solar radiation, often called as global radiation is the sum of direct, diffuse and reflected radiation. While Solar trackers help in maximizing the direct radiation component, the diffuse radiation can be maximized only when the panels are kept horizontally. That’s where a horizontal tracking system which when tracks the sun captures most of the direct radiation, the amount of diffused radiation captured goes down. So on a given day the ratio between two components of radiation decides the gain. Irradiance variation between days and seasons is one major reason for Tracker gain variation. Daily Tracker gain between predicted vs actual data is shown in figure below for one of the sites.

The change in sun’s position also causes the tracker gain to vary. The difference in average gain in different seasons for one of the sites is tabulated below. As you can observe the gain during May- August, i.e. during Summer is higher as compared to winter i.e. December-January:

Sr. No. Month-Year % Gain in Specific Yield wrt FT
1 May-16 25.34%
2 Jun-16 20.06%
3 Jul-16 23.90%
4 Aug-16 21.45%
5 Sep-16 19.85%
6 Oct-16 16.63%
7 Nov-16 8.80%
8 Dec-16 12.38%
9 Jan-17 13.65%
10 Feb-17 19.77%
11 Mar-17 20.57%
12 Apr-17 26.80%
13 May-17 22.21%
14 Jun-17 23.34%

Another reason which causes the gain to vary significantly between days is the timing of certain events like Grid Outage, Clouds. If the grid outage happens at a time when tracker gives maximum gain like in the morning or in evening, the tracker gain with respect to fixed tilt would be much lower for that day.

Fig. 4 Power Distribution Chart

In the above Power Distribution Chart, tracker generates maximum gain between the time intervals of 6:00 AM to 10:00 AM and 14:00 to 18:00 PM. However, if the grid outage occurs before 10:00 AM or after 14:00 PM in the evening, the overall tracker gain will be affected. One such example of the same is shown below, where even with higher plant downtime the tarcker gain is higher on a partciular day compared to the other day

Date GHI (Wh/m2) Actual S.Y. Gain wrt FT Gross generation considering grid out & load shedding (kWh) Plant Downtime (Min)
02-June 5788.78 25.31% 28219 695
13-June 6250.27 31.4% 31267 10
21-June 5045.92 16.8% 25353 10
25-June 5255.56 16.7% 25219 5

Other reasons like backtracking, location of installation, proximity to equator, pitch also impacts the overall generation. In conclusion, solar tracking gain is an amalgamation of various factors like season, timing of grid outage or clouds, backtracking, efficiency of modules, Sun’s Position, etc.

Day to day gain is not a right way of analysing the gain of solar tracker. Overall gain captured over a year is the right parameter, and the differences between actual vs PV syst gain are not that high, making Solar Tracker the preferred choice to improve gains of the plant.

With over 481 MWp of tracker portfolio in India and Thailand, Mahindra Susten Solar tracker MSAT100 can help reap the benefits of the tracker technology. With gains ranging from 18% to 22% over fixed tilt MSAT 100 continues to develop as a viable alternative to fixed tilt for PV plants.