Inadequate longevity of solar String Inverters

The above data concern solar 'String Inverter' survival times in the field. They are not overly encouraging with 1-in-5 requiring replacement after as little as SIX YEARS for those installed outdoors. These data regroup all manner of makes and models and installations, but nonetheless they represent the largest available study set concerning extended DC/AC string inverter survival times (n= 2,150). Notably, inverter-related issues prior to replacement remain the number one cause of field-based “call-out service tickets” at up to 81% of all interventions ((3) Micro-inverter redundancy and avoidance of ‘Single Point of Failure’ can assure continuity of power production at utility-scale solar. | LinkedIn). The associated production outages are linked to: i) costly service interventions in the field; and ii) sometimes significant lead times for product replacement. The latter figure is further negatively impacted by an alarmingly-high level of inverter manufacturer disappearances within the installed base.

The Bern University of Applied Sciences study (as per above Figure) noted that: “For string inverters, a malfunction often equals the end of the device’s life. And operators frequently need to replace all of the inverters in a project before the period of feed-in tariff guarantees expires”.

At utility scale, it is a common event to replace one or more string inverters even during the first year of operations. Early in the life-cycle of solar installations, these replacements are covered by manufacturer warrantees. However, the question arises:

How many times must I replace some or all of my string inverters during a projected installation lifespan of 20 to 30 years or longer?

And, how will this impact Project Profitability?

Financiers of these projects have not always been fully informed on this front. These replacement costs negatively impact project viability at both P50 or P90 (US- or EU- norms respectively for the likelihood of meeting projected energy production, and by default, cashflow predictions based upon historical climate data for the region in question).

“Solar Operating Systems Resilience" is an emergent property of the percentage of the total number of panels being managed individually”.?This emergent 'operational resilience' can tolerate multiple outages of both inverters and solar panels without the need for energy production shutdowns.?

LanneSolaire perceives a near-term future (less than 10 years hence) where individual solar panels in all solar installations will have their performance remotely monitored via the Internet of Things (IoT). Under such a scenario, String and Central Inverters may become a thing of the past. This trend is increasingly in evidence in Domestic and Commercial & Industrial rooftops settings in association with intelligent Junction Boxes, DC/DC optimizers, Micro-Inverters and Multi-Module Micro-Inverter.?The speed of this transition over time will be linked to the affordability of these technologies.

IoT connectivity alone or the use of DC/DC optimizers cannot deliver operational resilience. This only becomes possible once individual solar panels are: i) wired in parallel, ii) managed individually, and iii) able to operate independently of otherwise uniform string voltages. When solar panels are wired 'In Series', the poorest performing solar panel in that string negatively impacts the performance of all other solar panels in the string. This applies to very subtle underperformance or catastrophic failure(s) whereby production is dependent upon the lowest common denominator. Installations featuring large numbers of higher-powered solar panels stand the most to lose.

Modification of a systems architecture to 'In parallel' is more expensive, but works to enhance energy production. Replacement of individual modules or inverters can be undertaken knowingly and when seen as capable of delivering DESIRABLE COST BENEFIT over whatever time period, be that defective units detected remotely at installation or at any time in the future.

Importantly, technological advances in power ratings of solar panels decades after commissioning can be accomodated seamlessly.

Today, ‘In Series’ configurations are the norm across the bulk of solar industry, be they one or many small, intermediate, or utility-scale installations. Progressively, more and more solar installations will become part of what is termed ‘Distributed Energy Generation’ . The latter will be found across disparate geographies and substrate types and comprised of many millions of solar panels, storage facilities and tracking devices – all of which increase an investor's risk exposure to systems underperformance.

Underperformance can compromise one’s Payback Period &/or one’s ability to maximise investment returns.?It needs to be managed knowingly through informed decision making.

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