Five Basics of Cleaning and Inspection to Increase Solar Power Generation

Table of Contents

• Cleaning and inspections to increase power generation should begin with identifying the cause

• Basic 1: Before cleaning, check power generation data by time of day and by equipment unit

• Basic 2: Safely remove dirt and deposits from panel surfaces

• Basic 3: Inspect for shadows from weeds, trees, and structures

• Basic 4: Check for abnormalities in connections, cables, and power conversion equipment

• Basic 5: Organize drainage, terrain, and inspection records to prevent recurrence

• Operational practices to link cleaning and inspections to improved power generation

• Summary

Cleaning and inspections to increase power output begin by identifying the cause

When aiming to increase solar power output, the first thing that comes to mind at many sites is cleaning the panels. If dirt adheres to the panel surface, sunlight has difficulty reaching the cells, leading to reduced power generation. Therefore, cleaning is an important measure. However, if you perform only cleaning without confirming the causes of low power generation, improvements may not be as great as expected. This is because the causes of reduced power generation can be multiple and overlapping—not only dirt, but also shadows from weeds or trees, faults at connection points, cable damage, inverter shutdowns, temperature increases, poor drainage, insufficient inspection records, and so on.

For practitioners searching for "how to increase power generation," the important point is to regard increasing generation as moving closer to a state in which you do not lose electricity that should otherwise be generated. In photovoltaic power generation, you cannot increase the solar irradiance at the site itself. You cannot increase the number of sunny days or change the seasonal solar altitude. However, you can move closer to a state in which the incident solar radiation is converted into electricity with as little waste as possible. To achieve that, it is important not to treat cleaning and inspection as separate tasks, but to handle them as a continuous process of finding and improving generation losses.

A common mistake when power generation is low is deciding the cause based only on the site’s appearance. Cleaning panels because they are dirty, removing weeds because grass has grown, or suspecting equipment degradation because the equipment looks old are judgments that are sometimes necessary. However, if the main cause of the power drop lies elsewhere, those actions will not lead to sufficient improvement. For example, even if you clean the panels, generation is unlikely to recover if shadows remain in the morning and evening, and even if you remove weeds, daytime generation will not increase if the power conversion equipment continues to experience brief shutdowns.

In cleaning and inspections to increase power generation, first check the generation data to identify during which time periods, on which equipment, and in what ways output is declining. Based on that, go on site and inspect for dirt, shading, connections, equipment condition, drainage, and inspection routes. After taking measures, compare how power generation has changed and record the results so they can be applied to the next inspection. By establishing this workflow, cleaning and inspections become practical tasks that directly lead to improved power generation rather than mere maintenance.

Basic 1: Check power generation data by time period and by equipment before cleaning

Before starting cleaning or on-site inspections, first check the power generation data. If you only look at monthly or annual generation, you cannot tell when or where generation losses are occurring. Even if nothing looks abnormal on a monthly basis, there may be drops in output during certain hours of clear days, or prolonged low output affecting only specific rows, specific strings, or areas connected to particular power conversion equipment. To prioritize cleaning, it is important to first narrow down the time periods and areas of decline using the data.

If morning generation is low, shadows from trees on the east side, slopes, surrounding structures, or adjacent equipment may be involved. If generation is low in the evening, check for shadows on the west side and the surrounding topography. If the midday peak does not rise, candidates include dirt on the panel surface, temperature rise, power conversion equipment limitations, output curtailment, or equipment shutdowns. If the generation curve suddenly drops during a sunny day, it is necessary to cross-check shutdown history and alarm history with the timestamps.

When comparing on an equipment-unit basis, compare equipment under the same conditions. If you simply compare equipment with different orientation, tilt, number of panels, shading conditions, or connection configurations, you may mistake normal differences for abnormalities. If, compared with adjacent rows or equipment with the same orientation, a particular area is consistently lower, suspect localized soiling, partial shading, connection faults, cable damage, or abnormalities on the power conversion equipment. Do not judge based only on the plant-wide figures; detecting small differences is the quickest way to improve power generation.

When examining power generation data, consider weather and seasonal differences. On cloudy or rainy days, power output fluctuates greatly due to cloud movement, making it difficult to distinguish from equipment faults. It is effective to use the generation curve on clear days as a reference and compare days with similar solar irradiance conditions. In winter the sun’s altitude is lower and shadows tend to be longer, while in summer solar irradiance is stronger but output declines due to temperature rises are more likely. When checking data, it is important to separate these natural variations from generation losses that can be improved on-site.

If you check the data before cleaning, you can prioritize locations that have a large impact on power generation. Even if dirt is conspicuous in some places, if a drop in power generation cannot be confirmed, you can decide to prioritize investigating other causes rather than cleaning immediately. Conversely, if a particular piece of equipment shows low output even on sunny days and dirt or deposits are concentrated in that area, cleaning should be given higher priority. Checking the data is the fundamental first step to enhance the effectiveness of cleaning and inspection.

Basic 2: Safely remove dirt and deposits from panel surfaces

Soiling and deposits on the panel surface are common factors that reduce solar power generation. Because solar panels generate electricity by receiving sunlight on their surface, when dirt adheres the amount of light reaching the cells is reduced. The way panels become soiled varies with site conditions, including dust, pollen, yellow sand (Asian dust), bird droppings, fallen leaves, sap, dust from nearby construction, road-derived dust, and contamination containing salt that easily adheres in coastal areas. Even thin soiling can affect power output if it spreads over a wide area, and localized deposits like bird droppings or fallen leaves can act as strong shadows even over a small area.

Particular attention should be paid to the band-like dirt that remains along the bottom edge of panels and around the frame. It is often assumed that rain will wash it away naturally, but in reality the flow of rainwater can collect dirt at the lower edge and leave it there. Panels with a shallow tilt drain poorly and are more prone to dirt accumulation. Even dirt that is not noticeable from a distance can affect power generation if it covers part of a cell. During inspections, it is necessary to carefully check not only the overall coloration of the panel but also the bottom edge, corners, and areas around the frame.

When cleaning, prioritize areas that have the greatest impact on power output. Instead of cleaning all panels at the same frequency, concentrate on installations where a drop in power output has been confirmed, rows with concentrated soiling, areas where soiling is particularly noticeable along the lower edge, and locations with heavy bird damage or leaf accumulation. Keeping pre- and post-cleaning photographs and power output data makes it easier to determine how much the soiling at that site affected power output.

What's important in cleaning is not to damage the equipment. Even if you want to increase power generation, you should avoid vigorously scrubbing with hard tools, performing sudden work during times when panels are at high temperatures, or skipping safety checks for electrical equipment. Cleaning is not a cosmetic task; it is maintenance to restore the panels' light-receiving condition and to keep the equipment in stable service for a long time. Before starting work, check the safety of the surroundings, the condition underfoot, and precautions related to energized equipment, and avoid attempting tasks that are unsafe or beyond your capability.

After removing the dirt, also check why that spot tends to get dirty. Check whether dust from unpaved walkways is easily kicked up, whether leaves or sap from nearby trees are likely to fall, whether there are structures that attract birds, or whether the panel tilt impedes rainwater runoff. If you record locations where soiling repeatedly occurs, it will be easier to prioritize the next inspection and to prevent a decline in power generation at an early stage.

Basic 3: Inspect shadows of weeds, trees, and structures

As important as cleaning is, inspecting for shading is also crucial. Because solar panels generate electricity from sunlight, even a shadow over part of a panel can reduce power output. Shadows can be caused by a variety of things, such as weeds, trees, fences, utility poles, nearby buildings, mounting racks, adjacent rows of panels, and monitoring equipment. Since shadows move with the time of day and the seasons, not seeing a shadow at the time of inspection does not necessarily mean there is no problem.

Weeds are a common cause of on-site power generation losses. Even if there is no problem in winter or immediately after installation, they can grow rapidly from spring to summer and cast shadows on the lower edge of panels and the front row. Even if the vegetation does not touch the panels, shadows lengthen at the low sun angles of morning and evening. Furthermore, when weeds become overgrown, airflow is reduced, inspection walkways are blocked, and it becomes more difficult to check around equipment. Because it affects not only power output but also maintainability and safety, weed management is as important as cleaning.

Shading from trees is a factor that tends to become problematic during long-term operation. Even trees that had little effect at the time of installation can grow over several years and reduce power generation. In particular, trees located to the south, east, and west cast shadows on the panels depending on the time of day. At power plants near forests or slopes, the elevation of the terrain combined with the height of trees can create long shadows in winter. If power generation is low only in winter, or if there are large drops in the morning and evening, it is necessary to check both the trees and the terrain.

When inspecting shadows, it is important to time the inspection to the periods when power generation data shows a drop. If output is low in the morning, check the on-site conditions in the morning; if it is low in the evening, inspect the evening shadows. Even if there is no problem at noon, significant shadows can appear in the morning and evening. Also, even if there is no problem in summer, shadows can lengthen in seasons with a lower solar altitude. Shadow inspections should be carried out based on changes over time and season, not as a one-time visual check.

Be aware of shadows cast by nearby structures and added equipment. Installing new equipment inside the power plant, or erecting fences, signs, or monitoring poles, can create shadows at certain times of day. To increase power output, it is important not only to reduce existing shadows but also to operate in a way that avoids creating new ones. When you find a shadow, record the time it occurs, its source, the equipment affected, and photographs; these records can be used to guide decisions on weeding, branch trimming, or layout adjustments.

Basic 4: Check for abnormalities in connection points, cables, and conversion devices

When cleaning and inspecting to increase power output, you need to check not only panel surfaces and shading but also the electrical paths that extract the power. Even if solar panels are receiving sunlight normally, faults in connections, cables, or conversion equipment can prevent the generated electricity from being fully extracted. String-level generation differences, loose terminals, poor contacts, damage to cable sheathing, ingress of moisture, animal damage, shutdown of conversion equipment, and output curtailment are all significant causes of reduced power generation.

When checking for abnormalities at the string level, compare units under the same conditions. If you simply compare systems with different numbers of panels, orientations, tilts, shading conditions, or connection configurations, you may mistakenly interpret normal differences as abnormalities. Check whether any are consistently lower compared with adjacent rows or installations with the same orientation. If only a specific string is low, possible causes include soiling, partial shading, poor connections, cable damage, or equipment-side issues.

Suspected problems with connections or cables occur when only specific equipment has low power generation, when abnormalities tend to appear after rain, when power generation suddenly drops, or when output fluctuates unstably. In areas with heavy weeds, it becomes difficult to check the condition of the cables. In places with poor drainage, moisture and standing water can affect the connections. At sites where animals can easily enter, cable damage may also occur. If power generation does not recover through cleaning or weed removal alone, electrical pathway abnormalities should also be suspected.

For conversion equipment, check the operating status, shutdown history, alarm history, and whether output curtailment occurred. Even a short stoppage can cause large losses if it happens during daytime when generation is high. If the generation curve on a sunny day is flattening out, check for output curtailment, equipment capacity limits, temperature rise, measurement anomalies, and so on. Do not judge based only on the generation curve; it is important to view equipment records together with on‑site conditions.

When checking electrical equipment, safety must be the top priority. Even if you want to increase power generation, on-site personnel should avoid forcibly touching connection points or the insides of equipment to make judgments. Document the equipment showing anomalies, the time they occurred, changes in power output, on-site photos, and the surrounding environment, and, when necessary, arrange for a professional inspection. The basic rule for inspections is not to proceed with hazardous work based on on-site decisions, but to clearly identify the locations suspected of being abnormal and the rationale for those suspicions.

Basic 5: Organize Drainage, Topography, and Inspection Records to Prevent Recurrence

To maintain the long-term effectiveness of cleaning and inspections, it is important to address drainage, terrain, and inspection records. Even if panels are cleaned, if conditions that allow soil or water to accumulate in the same spot remain, the dirt will recur. Even if weeds are removed, grass will regrow more readily in areas where water tends to pool. Even if connections are repaired, if the causes of moisture or cable exposure remain, faults may occur again. To increase power generation, it is essential not only to remove immediate abnormalities but also to identify the factors that cause recurrence.

Areas where water tends to accumulate, places where sediment flows in, muddy walkways, slope failures, scouring around mounting structures, and locations where cables are easily exposed cause a decrease in power generation, either directly or indirectly. Poor drainage and changes in terrain may at first glance seem unrelated to power output, but they lead to soiling, weeds, connection faults, and reduced inspectability. If the same problem recurs in the same location even after cleaning or weeding, drainage or terrain issues should be suspected.

When checking terrain and drainage, on-site inspections after rain as well as during fine weather are effective. Identify where water flows in, where it accumulates, and where it drains away. Recording puddles, sediment deposits, vegetation overgrowth, pathway settlement, and slope changes helps pinpoint locations prone to recurrence. If drainage problems are left unaddressed, soiling and weeds will recur, resulting in the same power generation losses happening repeatedly.

Inspection records are also essential for preventing recurrence. If you record the locations of equipment with low power output, rows that tend to get dirty, places where shadows occur, spots where water accumulates, locations where connection failures have occurred, areas that were repaired, and the areas where cleaning or weeding was carried out, it will be clear which places should be checked at the next inspection. If records are insufficient, even if the same problem repeats you will not be able to learn its cause and will have to check everything from scratch each time.

After implementing measures, verify how power generation has changed. After carrying out cleaning, weeding, repairs, equipment inspections, and drainage checks, record the power generation before and after the work, on-site photos, the scope of the work, and the weather conditions. Give priority to measures that had a large effect in future efforts, and if an effect is not clearly visible, consider other possible causes. This repeated process is the basic principle for ensuring that improvements in power generation do not end up as one-off actions.

Operations to Link Cleaning and Inspections to Improved Power Generation

To translate cleaning and inspections into improved power generation, the work should not be treated as one-off tasks but integrated into regular operations. Solar power plants are outdoor facilities, and their condition changes with the seasons, weather, surrounding environment, and aging of equipment. Even after cleaning, dirt will return; even after weeding, grass will regrow; trees will grow; and equipment and wiring will change over long-term operation. Therefore, to steadily increase power generation, cleaning and inspections must be designed as continuous management.

First, the important thing is to establish criteria for checking power generation. Decide how frequently to review generation data, at what level of decline to carry out an on-site inspection, and down to which equipment unit comparisons should be made; doing so speeds up anomaly detection. Relying solely on the intuition of staff leads to oversights and inconsistent judgments. Standardizing sunny-day generation curves, comparisons with equipment under the same conditions, checks of shutdown history, and the recording of on-site photographs will stabilize the accuracy of improvements.

Next, clarify the prioritization of countermeasures. If you try to address all issues at once, the workload becomes large and measures that have a major impact on power generation may be postponed. Prioritize inspecting equipment that shows a clear decline in power generation data, shadows with long impact durations, recurring soiling or poor drainage, and equipment that experiences frequent short stops. In improving power generation, it is more important to take the right actions on locations with large generation losses than to simply increase the amount of work.

When multiple people are responsible for management, there also needs to be a system to share the exact same location. In large power plants, rows and equipment that look similar are often lined up, so a photo alone may not make the location clear. By recording equipment numbers, location information, photos, and work history together, on-site staff, managers, inspectors, and maintenance personnel can more easily confirm they are looking at the same place. Cleaning and inspections should be considered to include creating mechanisms that use on-site observations to drive the next improvements.

Also, it is important not only to respond after power generation declines, but to identify conditions that are likely to cause drops in advance. By recording rows that easily accumulate dirt, times of day when shadows are likely to occur, locations where water pools, walkways that tend to deteriorate, and equipment that is prone to abnormalities, you can check them before power generation falls significantly. Continuing basic cleaning and inspections will lead to early detection of declines in power generation and help prevent recurrence.

Summary

When cleaning and inspecting to increase solar power output, it is important not only to clean the panels but also to identify the causes of generation losses in order. In solar power generation you cannot increase the amount of solar irradiance on site. However, you can improve output by bringing the system closer to a state that converts the received sunlight into electricity without waste. To do that, it is necessary to check, in sequence, the power generation data, dirt on the panel surfaces, shadows from weeds and trees, connections and cables, conversion equipment, drainage and terrain, and inspection records.

When you feel power output is low, don't immediately carry out cleaning or repairs; first separate and review the data. Identify when it is low, which equipment is underperforming, and whether there is a difference compared with equipment under the same conditions. Then, when you inspect the site, it will become clear where to clean, what area to weed, which connections to check, what devices to confirm, and which drainage or access routes to reconsider. To improve the effectiveness of cleaning and inspections, it is important to make judgments by linking data with onsite conditions rather than relying on intuition.

Also, cleaning and inspections are not tasks that can be completed in a single operation. Even if you clean, dirt will return; even if you remove weeds, grass will regrow; trees will grow; and equipment and wiring will change condition with age. By comparing power generation before and after countermeasures, retaining on-site photographs and work histories, and using them for the next inspection, the accuracy of improvements increases. To stably increase power generation, it is essential not only to eliminate the causes but also to create a site environment and management system that make the same causes less likely to occur.

Especially at large power plants, a system for accurately sharing problem locations is important. If you record soiling-prone rows, shadowed areas, spots where water accumulates, anomalous strings, repair locations, the scope of cleaning, and inspection photos together with location information, stakeholders can more easily identify the same spot. By combining generation data with on-site location information, it becomes easier to explain the priority of cleaning, weeding, and repairs, and to streamline recurrence checks on subsequent visits.

If you want to continue cleaning and inspections that increase solar power generation based on field data, using LRTK can also be effective. LRTK, an iPhone-mounted high-precision GNSS positioning device, is useful for recording inspection locations within a solar power plant, spots prone to soiling, areas where shadows occur, locations with poor drainage, faulty equipment, repair locations, cleaning coverage, and on-site photos along with highly accurate location information. By keeping the results of cleaning and inspections with location data, it becomes easier to pursue power generation improvements based on field data rather than on intuition.