It is the modern day Gold Rush. Everyone wants to win a solar project. They bid aggressively. The only way to win this bidding war is with low costs. “Cost is king and everything else be dammed!” Once the bid has been won, almost always at very low bids, the pressure is on everyone to deliver.
Aggressive bidding by developers to win projects has meant that very low project costs are inevitable and they are then thrust on to the suppliers. Technology selection of Modules and Inverters is much easier to do as compared to BOS, specially Structures.
Currently MMS designs are done using wind loads derived using IS 875-III:1987/2015/ ASCE7-05/10 / EURO wind codes and structures are designed as per IS 800:1984/2007 / IS 801:1975. Very often, MMS vendors DO NOT take into account the “eccentric” moment induced in the structure due to flow of wind. This is because this particular clause appears as a footnote and is often missed. Very thin, cold formed members are designed using IS 800 and IS 801 only. It is well-known a lot of members design in tracker MMS is governed by torsion considerations, and using IS 800/IS 801 LRFD misses the torsion design entirely.
This leads to the structures being extremely under-designed as Solar PV MMS designs are predominantly governed by torsional instabilities-both wind induced and strength deformations and need to be designed by using the AISC 360-10 / AISI S100-96/16 codes.
Additionally, the existing codes do not help with the dynamic effects and aero-elastic instabilities – which in real life situations leads to the imposition of much higher loads than the calculated static loads on the structure. The memory of a recent thunderstorm’s devastating effect on a fixed tilt solar plant in North India would be fresh in the industry’s mind.
Wind tunnel testing at a reputed company with a scaled model of MMS is essential to deal with these kinds of uncertainties. It’s worth noting here how historically improper MMS have faced partial or full failures as a result of ignoring realistic wind influences. Wind loads and pressures on a structure can only be derived from an actual BOUNDARY LAYER WIND TUNNEL and not a theoretical calculation or any other type of Wind Tunnel.
Incorrect assumptions in surveying and levelling add more to the delays and project cost. Inadequate knowledge and testing of soil strengths add to hindrances in execution.
Let’s look at Solar Trackers in particular.
The General view is that Solar Trackers are a relatively simple technology to implement - make a pivot, get a screw jack or gear, fit a motor, get a controller to move it and sort of copy an existing MMS design – and a single axis tracker is launched!
Margins seem nice, business is assured, so why not make one.
Unfortunately, it is not that simple!
The fact is that ALL the leading Tracker brands across the world, including in India, are PURE PLAY Tracker technology companies. All these companies have a very strong technology and product development ETHOS.
With all new technologies, there are always a bunch of ‘cheaper’ and ‘me too’ options available in the first couple of years. These companies sell a lot, but their offerings break down a lot. After the dust has settled, the best engineered technologies remain. This is a classic TECHNOLOGY PRODUCT Cycle.
The success of a Tracker solution depends on its (a) Mechanical components and (b) Electronic control components.
The Mechanical components mainly comprises of the bearings, the MMS and the fasteners.
It is assumed that bearings will last for more than 50 years, incurring no O&M costs – but does test data validate this assumption?
The electronic component is rarely assessed. However, the gain delivered by the tracker by efficiently tracking, stowing, shadow handling and backtracking depends entirely on the electronics and the algorithms.
The decision, more often than not, is based solely on MMS Weight and therefore total cost ONLY.
For example, Supplier X quotes MMS weight of 50 tons. Another established supplier Y provides 60 ton MMS. Now, Y has already installed plants, has a solid track record and has a bankable tracker solution.
So what does X know that Y does not, which allows a >15% reduction in MMS weight from supplier X? NOTHING!
The truth is - It is not possible to reduce the weight of the MMS beyond a certain point without compromising on the design integrity
Add to this an equally important factor in selecting a tracker – not related to Technology and design – but to Delivery time and installation effort. Installation time required at site and O&M costs also need to be considered in depth, but are often ignored.
Both these have a direct impact on the ‘GO LIVE’ date of the project. Even a delay of a month means significant losses in generation income. More often than not, even though a ‘cheap’ technology is selected, the saving in CAPEX gets wiped out in construction delays (and related generation loss).
So, what needs to be addressed before selecting a Tracker supplier is:
Is the technology reliable?
Is the technology durable?
And since the above points are subjective, based on very preliminary assessments, some tangible indicators for buyers could be -
Does the company have an IE bankability report?
Does the company have a proven track record?
Credit: Nimish Prabhukhanolkar (B.Tech/M.Tech IIT Bombay), Partner/Founder at AGAMI ENGINEERING