Drone surveillance of solar assets: Strengths and Weaknesses

Drones or Unmanned Aerial Vehicles (UAV's) provide an invaluable adjunct to current management practices employed for the operational supervision of solar assets of varying size. This includes applications during development, construction, commissioning and extended operations designed to help improve the efficiency of power generation and project duration and profitability. However, if solar energy is to play a more important contribution into national grids globally, it must progress beyond biennial or occasional drone inspections of its critical infrastructure elements. Performance monitoring by the Internet of Things (IoT) of individual solar panels will become a reality eventually. In the interim, where lie the respective strengths and weaknesses of drone surveillance?

Drone inspections employ what is termed Orthomosaic RGB (Red Green Blue) Thermal Composite Images based upon IR (infra-red) light detection using air-borne optics and Charge-Coupled Device imagery. As the efficiency of converting solar irradiation into electricity abates over time, solar cells produce increasing amounts of undesirable heat, i.e., instead of electricity. These are colloquially referred to as 'Hot-Spots'. The objective of these aerial inspections is the elimination of severely underperforming panels and those that have undergone catastrophic failure. The earlier panel manufacturer guarantees can be activated, energy production and project revenues can be maximised by effective project Operations and Management (O&M).

Drone-based inspections are almost of uncontested value-add during the Pre-Commissioning phase. They allow for progress monitoring in the form of visual counts of trenches, cables, racking, modules numbers over time, missing elements, supervision of EPC (Engineering, Procurement & Construction) works, verification of progress, EPC/OEM (Original Equipment Manufacturer) warranty claims and Milestone delivery. When it comes to Project Commissioning, site acceptance tests can be underwritten by hard evidence of project delivery coupled with measures of baseline zero energy production measures. During Operations, comprehensive site inspections are easily facilitated following adverse weather (high winds, hail, flooding, lightning, snow) and other phenomena, such as, bird soiling, dust, salt spray, pollen, and recent vegetation growth giving rise to shade.

Panel manufacturers guarantees can be activated once the annual degradation rate exceeds 0.4% to 0.45%. Drone inspections are incapable of such measurements or the necessary detection sensitivity. Their lack of sensitivity is dictated by Sir Isaac Newton's Inverse Square Law as applies equally to all sources of light (infra-red included), gravitational force, radiation, electrical field and sound. As distance increases, the sensitivity of detection falls away at a rate inverse to the distance from source squared. Flat-bed scanners as used for electrical luminescence to do away with constraint, but the technology cannot be deployed at scale. Electronic detection does not suffer this fate. The latter allows for very accurate measurement of multiple electrical parameters coupled with both sensitivity and dynamic range.

Most importantly, drone surveillance of solar infrastructure is a vast improvement upon zero monitoring of individual solar panel performance. Manufacturer guarantees of 25 to 30 years encourage user confidence by do not necessarily translate to 25 to 30 years of uninterrupted performance. Until such performance is monitored continuously in real time, promises of long-duration and reliable electricity generation are simply empty. Unfortunately, underperformance as detected by drone surveillance can persist sometimes for many months or years prior its detection and subsequent elimination.

If underperformance is left to persist, serious shortfalls in power generation and project revenues can result. These negatively impact the confidence of investors and credit providers active in the solar industry. It exposes them to undue risk that could and should have been addressed during the project design phase. Drone height and any variation in distance to target further compromises the usefulness of data derived IR imagery. We need to move beyond a priori assessment of "too far gone to possibly be performing well" and work to more accurately and more rapidly activate panel manufacturer guarantees.

Short-comings negatively influencing data acquisition:

• Inability to detect changes in panel orientation, as seen on unstable substrates
• No reliable means to predict imminent panel failure?
• Soiling and low ambient light produce low infra-red signals
• Time of day and weather conditions dramatically influence results
• Distance to target must be kept constant?
• Lack of automated image annotation tied back to real electrical performance data
• Infrequency and insensitivity of drone inspections

CONCLUSION:

The is the last of fifteen 'LinkedIn articles' highlighting current inadequacies as concerns Operations and Management of solar energy production and the need for improvement. This situation is further exacerbated by the increasing cost NOT of solar panels, but rather the associated infrastructure of energy storage and solar tracking. The latter serve to significantly increase investor and lender risk. The past decade has witnessed a positive trend away from central to string inverters monitoring. These are responsible for DC to AC power conversion of many hundreds and sometimes many thousands of panels linked 'In Series'. This trend needs to continue in the sense of higher granularity, as it currently occludes resolution of performance attributes at the level of individual solar panels. Regrettably, this lack of high granularity resolution currently applies to vast majority of all solar panel deployment internationally. "Least cost design" pervades the solar industry and seriously limits systems durability and reliability anywhere near that delivered by our competition (nuclear, wind, geothermal, combined-cycle coal or gas, and hydroelectric power generation).

The next stage in the evolution towards higher granularity panel performance monitoring is the universal deployment of standardised O&M practices featuring real-time data accessed via the Internet of Things at the level of each and every solar panel whether it is, for example:?

• standing alone and coupled to a low volume water pump in Morocco
• situated within an off-grid PV system servicing a small village in Kenya
• one of many panels located on top of some 600,000 domestic dwellings in France, or
• part of a mega solar farm in Saudi Arabia or China.

A decade ago saw several solar giants disappear due to excessive levels of debt. High levels of commercial growth alone cannot suffice. The solar industry is faced with burgeoning levels debt needing to be serviced and an ever-growing requirement for still further debt &/or equity investment. Thus, a healthy future for the solar sector will depend upon avoiding faults of the past (excessive debt) and focusing on:

“Enhanced reliability, durability and energy output to increase financial returns at the lowest possible investor risk"

Effective O&M at the level of the units of energy production (individual solar panels) is an essential prerequisite for such.

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