While the sun comes up and the sun goes down, wherever in the world you install your solar system you will not be able to achieve optimal harnessing of the available irradiation without tracking the sun’s daily movement. In an era where efficiency and output are imperative, solar trackers were always the natural evolution to this challenge and are now widely deployed.
A solar tracker system could increase the energy production of solar farms by between 15-30%1 and includes the safety feature of travelling to a horizontal position to protect against an oncoming storm. Chasing the sun and weathering the storm - it seems like a winning combination! But is it too good to be true? In this article we analyse the benefits of tracker systems and the impact they have on a solar project's insurance premium.
When designing a solar photovoltaic (PV) power plant, developers are faced with a choice of three main types of racking systems:
Each has its own distinct advantages and disadvantages, and ultimately the best option for a PV plant will require a full analysis of the site location, conditions, topography and overall project design. These systems initially met with resistance in the early 2000s due to the associated maintenance requirements and higher costs; however, since then these racking systems have steadily grown in popularity amongst developers. The global solar PV tracker market is poised to grow by 102.11 GW during 2020-2024, progressing at a compound annual growth rate of 39% during the forecast period2. Single-axis trackers are dominating the solar market and this trend is expected to continue to nearly 90% of ground-mounted shipments in 20213.
It has been observed in recent years that many solar park developers are focusing on the development and construction of lower cost projects in order to sell them under Build Sell Operate (BSO) and other similar financial/profit models. From an economic perspective, whilst the cost of trackers might typically add upfront costs of 5-10%4 on large utility scale projects, they are also able to produce more power during peak demand hours as they track the sun throughout the day, resulting in the lowest available levelled cost of electricity. In addition, developers can generally expect an increase in the investment rate of return of the project. The attraction is understandable, especially when measured against the rapidly decreasing rewards of fixed and variable solar PPAs (Power Purchase Agreements) and rapidly increasing costs of insurance. The ability to increase power production becomes critical in assisting project owners and operators to achieve an enhanced Return on Investment.
However, this should not be a ‘one size fits all’ approach. In all circumstances, the design which has been made to operate efficiently in the chosen location should be paramount (for instance, the hurricane version of a tracker which has been designed by the manufacturer to allow fitting in a higher risk location). This is instead of the alternative, which is attempting to install a lower cost version with a design not specific to the potential exposures of the location, leaving any location inappropriate or under design risk with insurers. The last 18 months has shown that such projects are facing substantial challenges in securing a level of insurance cover with a commercially acceptable deductible and premium.
Furthermore, from an insurer perspective, trackers bring the risk of moving parts, resulting in greater risk of mechanical and electrical breakdown. When there is a failure of the tracker, tracker arms or lack of power, either during construction prior to energisation or if there is a failure during the operational phase, the inability of the tracker to return to a safe position will create a substantial value/risk exposure. Consequently, the plant will likely suffer from loss of revenue; since trackers tend to have a longer lead time, insurers will argue that they are exposed to higher revenue losses.
Alongside the developing tracker technology, solar photovoltaic technology is continually evolving. PV string DC voltage are getting close to a thousand volts DC, combined with much smaller string inverters that are more efficient (with less heat loss) having built-in dispatching software, electrical and temperature protection systems. But what happens when this is combined with poor tracker design? Unfortunately, not all trackers are designed equally. There are known poor tracker designs; in the long term, as the insurance industry suffers from losses from certain just-in-time design and installations, project owners may find that they are unable to procure the required insurance coverages at commercially acceptable premiums and terms. As we have noted in this report, the insurance market is not about to rapidly return to soft trading conditions and limitations on capacity are forcing some projects to retrofit improved design standards at additional cost to maintain a higher level of insurability.
Perhaps a redeeming feature is the protection that trackers claim to offer against extreme weather, particularly windstorm, flood and hail. “It is a fact that wind is the most common cause of damage for photovoltaics systems in general,” says Thorsten Kray, of IFI Aachen5. It was generally thought that the safety feature of a tracker travelling to a horizontal position to protect against an oncoming storm was a good idea. The panels would present the minimum aspect to the wind putting the least load on the structure, preventing the panels from being damaged by flying debris.
However, it is being widely argued that trackers are more prone to windstorm damage due to their structure and default storage positions, especially if the mechanism or power supply fails during movement, leaving entire arrays exposed to wind borne damage. The stow safety position might be an angle just off horizontal, in which case the wind attacks from all angles, pushing down on the panels which increases the pressure on the support legs and also from behind, which has the effect of lifting the panel and applying pressure in the opposite direction. As a result, the tracker structure must be strong enough to maintain control of the panels throughout the storm and high wind speeds. While leading manufacturers in the renewables industry have designed trackers capable of withstanding certain maximum wind speeds, if these potential speeds are higher than those specified, a tracking system is no longer a viable option. While long term site-specific historical data is not always available, design standards to 1 in 20 or 1 in 50 years may be inherently flawed.
When using the horizontal stow safety position, not only are the panels more exposed to hail damage, but wind will pass over and underneath the structure, causing oscillation in the tracker arms and consequently in the panels, potentially resulting in microcracking (discussed in a separate article in this publication). It might not be obvious at first, but the unseen damage can be extremely costly; in many cases, the cost of testing the capacity of the cells is similar, if not more expensive, than the replacement cost. This has led (amongst other reasons) to many insurers recently imposing a microcracking exclusion to all new and/or renewing policies. Following some recent high-profile hail losses, some insurers are seeking to tighten this exclusion further, with an outright exclusion of microcracking caused by hail. It is a further concern that while trackers will be returned to a safe position, often automatically following anemometer wind readings, when there is a hailstorm, it frequently occurs with relatively low wind speeds; moving the trackers to a safe position requires a manual override.
In summary, it appears that large scale PV plant operators will always adopt tracking structures, as there is more control and a larger return on desired production; however, the downside is a greater exposure and higher Probable Maximum Loss (PML) through the design criteria and the mechanical tracker systems ability to adapt to protect exposure to Natural Catastrophe (Nat Cat) events. Better metrological prediction software and more positive action tracking systems are coming on stream to help mitigate this risk so that we can keep following the sun but weather the storm better.
Melanie Carter is an Account Director, Renewable Energy GB, Willis Towers Watson. Melanie.Carter@willistowerswatson.com
1 Compared to fixed tilt arrays of the same size https://www.kiewit.com/plant-insider/current-issue/fixed-tilt-vs-axis-tracker-solar-panels 2 https://www.businesswire.com/news/home/20200218005428/en/Global-Solar-PV-Tracker-Market-2020-2024-Evolving-Opportunities-with-Array-Technologies-Inc.-and-Convert-Italia-SpA.-Technavio#:~:text=The%20solar%20%23PVtracker%20market%20is,%23marketresearch%20report%20by%20%40Technavio. 3 https://www.solarpowerworldonline.com/2018/02/fixed-tilt-vs-tracker-one-size-fits-approach-can-limit-solar-production/ 4 https://www.greenworldinvestor.com/2017/08/23/tracking-the-sun-all-you-wanted-to-know-about-solar-trackers/ 5 https://www.pv-magazine-australia.com/2019/09/07/long-read-pt-1-tracking-in-the-wind/
