6 ways to select solar trackers

Guidelines for selection of solar trackers for large scale solar power plants
  Single Axis E-W Horizontal Solar trackers are capable of enhancing the power generated from PV panels by 16-24 per cent over fixed tilt systems depending on the site. Although this technology has been in existence for more than 5 years now, its application to large scale utility plants in India has just begun picking up. A number of tracker suppliers with different tracking technologies are present in the Indian market. This has created a need for developers to evaluate the right technology keeping in mind factors such as, ease of installation, maintenance, availability of spares, reliability and lifecycle costs of the technology. This article will lay down a set of guidelines that will simplify and help evaluate various tracker technologies.
Think beyond the offer price Tracker products at macro level may seem similar and suppliers can take attention away from minute technical details by making the upfront CAPEX cost very attractive. It is natural to base the purchase decision purely on the offer price in such cases. But the devil is in the detail; selection of a poor tracker can significantly undermine the benefits of using them and cause significant installation, maintenance and reliability issues.
Here are a few decision metrics along with their influence on the above issues:Type of tracker: The first decision to be taken is exercising the choice between a single axis (SAT) or a dual axis tracker (DAT). ASAT moves only in the East-West direction vertically, whereas a DAT can rotate horizontally as well resulting in greater energy generation. But, the ratio of additional power to additional investment made in upgrading from a fixed system to a SAT mechanism is roughly 2 to 2.5 against a ratio of only 1.2 – 1.25 in using DAT. Also, maintenance costs incurred on the latter is much more than the former due to greater complexity besides additional land. Hence, at present, it makes economic sense to use SAT.
Tracker configuration: Next decision is to finalise the configuration. There are two main configurations available in the market namely Building Block (BB) and Independent Row (IR). A BB essentially connects a single driving motor to multiple rows of modules. An IR type has one motor per row. IR tracker provides at least five main advantages over the BB type tracker:Site levelling cost incurred during installation of IR tracker is less compared to BB as the disjoint rows take care of undulations over a large area. Selection of BB in an undulated site could significantly increase the installation costs – estimation is up to 2 lakhs per MW.IRs with assigned trackers enable customised fine tuning thereby ensuring maximum energy efficiency of modules. Effect of failure of tracker is restricted only to that particular row in an IR tracker. Hence, power loss due to downtime is localised and minimised. Thus, IR has enhanced system reliability.Module cleaning and other maintenance activities are easier in IR system due to greater manoeuvrability.Better land utilisation and thus minimising area per MWp when using an IR configuration.
Ease of installation: Another important consideration is the ease of installation both structural and electrical. The tracker design should be simple enough to the extent that it doesn’t add any additional time or need any special training for installation. On the electrical front, absence of inbuilt power source for trackers could significantly increase site cabling requirements. Here too, there are two types of tracker systems available: Type 1 – Externally powered with input from the inverter room.Type 2 – Self powered with dedicated PV modules and energy storage module for each tracker or combination of trackers.
Type 2 Trackers will not only ease the need for cabling at site but will also not need additional Auxiliary supply. The cost savings will be Rs 1 lakhs per MWp due to reduced auxiliary cable supply and installation besides reducing the hassles involved in cable handling. It also saves Rs 0.3 lakhs per MWp on account of no auxiliary consumption every year. Additionally, it is also important to see if the trackers are supplied with integrated and localised batteries for power backup. If this is not the case, then the user has to spend close to Rs1.25 lakhs per MW on UPS, battery and cables.

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