8 Inspection Procedures to Increase Power Generation｜On-site Inspection Flow

Table of Contents

• Inspections to increase power generation begin before arriving on site

• Step 1：Check the time periods with decreased generation in the power generation data

• Step 2：Narrow down the abnormal range by comparing with installations under the same conditions

• Step 3：Isolate weather, solar irradiance conditions, and seasonal variations

• Step 4：Check the panel surface for dirt and deposits

• Step 5：Check for shadows from weeds, trees, and structures

• Step 6：Check strings, connection points, and cables for abnormalities

• Step 7：Check for shutdowns, curtailment, and the temperature environment of the power conversion equipment

• Step 8：Check drainage, terrain, inspection access routes, and records

• Process to translate inspection results into power generation improvements

• Summary

Inspections to increase power generation begin before arriving on site

When you want to increase the power output of a solar power system, the first thing you should do is not to immediately clean or repair the spots that catch your eye on site. The causes of low output are not necessarily a single issue; multiple factors may overlap, such as dirt on panel surfaces, shading from weeds or trees, faults in connections, cable damage, stoppage of conversion equipment, output curtailment, temperature rise, poor drainage, and lack of inspection records. Therefore, inspections aimed at increasing power output should start with checking the data before going to the site.

For practitioners who search "how to increase power generation", what matters is to regard the idea of increasing generation as an effort to reduce generation losses. In solar power generation, you cannot increase the solar irradiance itself at the site. However, you can move closer to a state in which the received sunlight is converted into electricity with as little waste as possible. In other words, improving power generation means finding where the electricity that should have been generated is being lost, and reducing those causes one by one.

A common pitfall during on-site inspections is deciding the cause based solely on appearance. Cleaning panels because they look dirty, removing weeds because vegetation has grown, or assuming deterioration because equipment looks old—such judgments are sometimes necessary. However, the actual main cause of reduced power output may be equipment shutdowns or connection faults, or shadows that occur only in the morning and evening. If you do not verify whether visible abnormalities align with the drop in power output, you may end up prioritizing measures that have little effect.

Clearly defining inspection procedures can greatly improve the efficiency of on-site checks. First, use data to narrow down the time periods and equipment with reduced performance. Next, separate out the effects of weather and seasonal variations, and on site check for dirt, shading, connection points, devices, drainage, and inspection routes. Based on that, address causes in order of their impact on power generation. Inspections are not only for finding abnormalities but also for verifying whether power generation has improved after countermeasures and for recording information to inform future inspections.

Step 1: Check the time periods showing a decline in the power generation data

In inspections aimed at increasing power output, the first step is to check the generation data by time of day. Looking only at monthly or annual power output does not reveal when generation losses are occurring. Likewise, even if overall output is low, the suspected causes differ depending on whether it is low only in the morning, the midday peak fails to develop, it drops only in the evening, or there are sudden dips during the day. To improve the accuracy of inspections, it is important to identify the time periods of the decline before visiting the site.

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

For time-of-day checks, it is useful to look at the generation curve on clear days as much as possible. On cloudy or rainy days, power output can fluctuate greatly with cloud movement, making it difficult to distinguish from equipment faults. With the generation curve on clear days, features such as shading, shutdowns, output curtailment, and string-level anomalies become easier to see. If similar dips occur at the same time every day, suspect site conditions or equipment-related causes rather than the weather.

As a procedure for on-site checks, it is ideal to inspect at the times when power generation is low. If generation is low in the morning, check the on-site conditions in the morning; if it is low in the evening, check the shadows in the evening. Visiting the site only at noon can cause you to miss the morning and evening shadows. By narrowing down the time periods using power generation data before going to the site, you can clarify which places and times to inspect even at large power plants.

Step 2: Narrow down the abnormal range by comparing with equipment under the same conditions

After confirming the time period, next compare on an equipment-by-equipment basis. If you only look at the power plant's total generation, some anomalies can be masked by the average. Even if it doesn't appear to be a major problem overall, output may be reduced only for a specific row, a specific string, or the area connected to a specific converter/inverter. Detecting these partial power losses early is important in inspections aimed at increasing generation.

When making comparisons, compare installations under the same conditions. If you simply compare installations with different orientation, tilt, number of panels, shading conditions, or connection configurations, you risk mistaking normal differences for abnormalities. If, compared with adjacent rows or installations with the same orientation, a particular area is consistently lower, localized soiling, partial shading, connection faults, cable damage, or equipment-side malfunctions may be suspected.

Differences in power output are easily overlooked when they are small. However, even a small difference can lead to a large generation loss if it continues over a long period. Especially on sunny days, when a clear difference appears compared with equipment under the same conditions, it is more likely that on-site factors rather than the weather are responsible. During inspections, do not be satisfied with the overall figures for the plant alone; compare with equipment under the same conditions to narrow down the range of anomalies.

When you narrow down the anomaly range, make sure you can accurately pinpoint that area on site. At locations where equipment numbers or row numbers are hard to read, even if a drop is detected in the data it can take time to locate the corresponding spot in the field. Organize the positions to be checked before inspection and prepare them so they can be cross‑referenced with on‑site photos and drawings; this will make the work smoother. For improving power output, it is important not only to detect anomalies but also to be able to reliably reach them on site.

Step 3: Separate weather, solar radiation conditions, and seasonal differences

When you notice low power generation, separate out weather, solar irradiance, and seasonal differences before suspecting equipment failure. Solar power generation is greatly affected by the amount of sunlight, so output will fall during periods with many cloudy or rainy days even if there is no problem with the equipment. If you compare only monthly generation with the same month of the previous year or with the previous month and immediately conclude that there is an equipment fault, the actual cause may have been differences in the weather.

On the other hand, you must avoid overlooking real anomalies by attributing them to the weather. If the entire plant is similarly reduced in line with regional weather, the impact of solar irradiance conditions is likely significant. However, if only part of the plant is underperforming while other equipment in the same plant is operating normally, or if there is a clear difference compared with equipment under similar conditions, weather alone cannot explain it. In that case, check for soiling, shading, poor connections, equipment shutdowns, and output curtailment.

Seasonal differences are also important. In winter, the sun’s elevation is lower, and shadows from surrounding trees and terrain tend to stretch longer. In summer, although solar radiation is stronger, panel temperatures and ambient temperatures around equipment rise, which can make it harder for output to increase. During periods with heavy rainfall, monthly power generation tends to be lower, and after strong winds or heavy rain attention should be paid to fallen leaves, sediment, deposits, poor drainage, and the condition around cables.

Before on-site checks, instead of looking only at days with low generation, compare sunny days with each other and days with similar weather. Using the generation curve from a sunny day as a baseline makes features such as shading, shutdowns, curtailment, and string faults easier to spot. By separating weather-related causes from equipment-related causes, you can reduce unnecessary inspections and measures and focus on generation losses that can actually be improved.

Step 4: Check the panel surface for dirt and deposits

After checking the data and weather conditions, inspect the panel surface on site for dirt and deposits. Because solar panels generate electricity by receiving solar radiation on their surface, when dirt adheres the light reaching the cells is reduced. Soil dust, pollen, yellow sand, bird droppings, fallen leaves, sap, dust from nearby construction, road-borne dust, and salt-containing grime that tends to adhere in coastal areas are examples of how soiling can vary with the site environment.

Particularly noteworthy are the band-like stains that remain at the lower edge of the panels and around the frames. People tend to assume that rain will wash them away naturally, but in reality the flow of rainwater can gather the dirt at the bottom edge and leave it there. On panels with a shallow tilt, water does not drain easily and dirt tends to accumulate. Even dirt that is not noticeable from a distance can affect power generation if it covers part of a cell.

Localized deposits such as bird droppings or fallen leaves should not be overlooked. Unlike dirt that spreads thinly over the entire surface, these heavily cover specific spots and act as partial shading, reducing power generation. If only some installations show low power output, concentrate your inspection on the panel surfaces around those installations. Rows near trees, areas around structures where birds are likely to perch, rows that are prone to being downwind, and locations close to unpaved access ways are more likely to accumulate dirt and deposits.

When performing cleaning, prioritize locations that have the greatest impact on power generation. Instead of cleaning all panels at the same frequency, concentrate on equipment where a drop in generation has been confirmed, rows with concentrated soiling, areas where soiling along the lower edge is noticeable, and places with heavy bird damage or fallen leaves. Keeping before-and-after photos and comparing power generation will make it easier to determine how much the soiling at the site affected output.

When cleaning, assume that the equipment must not be damaged. Avoid vigorously scrubbing with hard tools, performing sudden work during periods when panels are at high temperature, or working without first confirming the electrical safety of the equipment. As part of the inspection procedure, it is important to record not only whether dirt is present but also the type of dirt, its extent, and the likely causes.

Step 5: Check for shadows from weeds, trees, and structures

When conducting on-site inspections to increase power generation, checking for shadows is essential. Because solar panels generate electricity from sunlight, even a shadow covering part of a panel can reduce its output. Causes of shadows include weeds, trees, fences, utility poles, nearby buildings, mounting structures, adjacent rows of panels, monitoring equipment, and various other factors. Shadows shift with the time of day and season, so the absence of visible shadows at the time of inspection does not necessarily mean there is no problem.

Weeds are a common cause of power generation losses at sites. 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 rows. Even if the vegetation does not touch the panels, the low solar altitude in the morning and evening causes long shadows. Furthermore, when weeds become overgrown they reduce ventilation, block inspection walkways, and make it difficult to check around equipment. Because they affect not only power output but also maintainability and safety, weed management is important.

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

When checking for shadows, it is important to align the inspection with the time periods when power generation data shows a decrease. If output is low in the morning, check the site conditions in the morning; if it is low in the evening, inspect for evening shadows. Even if there are no issues at noon, large shadows can appear in the morning and evening. When you find a shadow, record the time it occurs, the source, the equipment affected by the shadow, and take photographs. Weeding and pruning should be prioritized, starting with the areas that have the greatest impact on power generation.

Step 6: Inspect strings, connection points, and cables for abnormalities

After checking the panel surfaces and any shading, also inspect the paths that carry the electricity. Even if the solar panels are receiving sunlight normally, faults in the strings, connections, or cables can prevent you from fully extracting the generated electricity. Differences in output between strings, loose terminals, poor contacts, damaged cable sheathing, moisture ingress, animal damage, damage during mowing operations, and deterioration due to aging are important causes of reduced power generation.

When checking for anomalies at the string level, compare strings under the same conditions. Simply comparing strings that differ in panel count, orientation, tilt, shading conditions, or connection configuration can lead to mistaking normal differences for anomalies. Check whether any strings are consistently lower than 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 problems.

Pay attention to how the anomaly appears. If it is consistently lower than the surroundings even on clear days, dirt or connection problems may be suspected. If it is lower only in the morning and evening, check for shading effects. If anomalies tend to appear after rain, moisture ingress or the condition of the connection points may be involved. If it becomes unstable during periods of high temperature, poor contact or the temperature environment around the equipment are also possible causes.

When inspecting electrical equipment, safety is the top priority. Even if the goal is to increase power generation, on-site personnel should avoid forcibly handling connection points or the interior of equipment to make a judgment. Record the equipment showing abnormalities, the time they occurred, changes in power generation, on-site photos, and the surrounding environment, and, when necessary, escalate to specialized inspections. At the stage of identifying the cause, it is important to clearly specify where and what kind of abnormality is suspected.

Faults in connection points and cables can be related to the surrounding environment. In areas with heavy weed growth, it becomes difficult to inspect the condition of cables. In locations with poor drainage, moisture and puddles can affect the connection points. On sites that are easily accessed by animals, cable damage can also occur. For improving power generation, it is essential not only to carry out repairs but also to check site conditions that could lead to recurrence.

Step 7: Verify shutdown, suppression, and temperature conditions of the conversion equipment

The causes of low power generation are not limited to the panels and wiring. If the equipment that converts the generated electricity is stopped or its output is being limited, power generation will not increase even when solar irradiance is sufficient. In inspection procedures, check the operating status of the conversion equipment, shutdown history, alarm history, and whether output curtailment is in effect.

When reviewing downtime history, check which equipment stopped, when it stopped, and for how long. Even brief downtime can cause large losses if it occurs during the daytime when generation is high. If equipment repeatedly stops and restarts during the day, it may not stand out in the monthly totals but can still mean lost generation. Whether only a specific device stops or multiple devices stop simultaneously will change which causes you should suspect.

If output curtailment is occurring, power generation can plateau even on sunny days. If the top of the generation curve appears flat, check the operating data and history. However, a flat curve does not necessarily indicate output curtailment. Similar shapes can result from equipment capacity limits, temperature rise, soiling, shading, or measurement anomalies. Do not judge based solely on the generation curve; it is important to verify equipment records together with on-site conditions.

Also check the temperature environment. For solar power generation, the stronger the sunlight the easier it is to generate electricity, but when temperatures rise the output may not increase as much. If, on a clear summer day, the amount of generation does not increase as expected, check not only the solar irradiance but also the effects of panel temperature and the temperature around the equipment. If weeds are growing under the panels, if there is grass or obstacles around the equipment, or if dust and deposits make heat dissipation difficult, these can affect the increase in generated power.

It is also important not to confuse equipment-side faults with panel-side problems. Even if a panel appears dirty, the primary cause may actually be equipment shutdowns or output curtailment. Correlate the time of the generation drop with equipment logs, and choose countermeasures based on evidence rather than speculation—this will lead to improvements after inspection.

Step 8: Check drainage, topography, inspection routes, and records

Finally, the items you should check are drainage, terrain, inspection access routes, and inspection records. Even when looking only at panels and equipment, you may not be able to determine the root cause of reduced power generation. Areas where water tends to pool, places where sediment flows in, paths prone to becoming muddy, slope failures, scour around the mounting structures, and spots where cables are likely to be exposed can directly or indirectly cause decreases in power generation.

In locations where puddles remain after rain, weeds are more likely to grow. When weeds grow they create shading, reduce ventilation, and make inspections more difficult. Muddy walkways can slow work and lower the frequency of cleaning and weeding. Where sediment flows in, it can accumulate under panels and around cables, causing soiling and damage. If cleaning and weeding repeatedly fail to solve the problem in the same locations, suspect drainage or terrain issues.

When checking topography and drainage, on-site inspections after rain are effective as well as inspections in clear weather. Determine where water flows in, where it accumulates, and where it drains to. Recording puddles, sediment buildup, vegetation overgrowth, pathway subsidence, and changes in slopes will reveal locations prone to recurrence. If poor drainage is left unaddressed, dirt and weeds will continue to recur, resulting in the same power generation losses occurring repeatedly.

Inspection routes are also important. Locations that are difficult to inspect tend to delay the discovery of abnormalities. If grass has overgrown so you cannot pass, if it is too muddy to get close, if equipment numbers are hard to read, or if it is difficult to share the location of an abnormality, on-site response will take longer. Even if you identify equipment with low power output from the data, if it takes time to reach the relevant location on site, improvements will be delayed.

Also be sure to check the inspection records. If you can confirm whether dirt has appeared at the same location in the past, whether weeds have grown in the same row, or whether the same equipment has experienced stoppages, you can narrow down the cause more quickly. If the records are insufficient, begin recording from this inspection photos, the date and time, the equipment number, the location, the details of the abnormality, and the response status so they can be used for the next inspection.

Process for Converting Inspection Results into Power Generation Improvements

To turn inspection results into improvements in power generation, it is important to translate the confirmed information into prioritized countermeasures. Identify equipment showing reduced output from the generation data, separate out weather and seasonal effects, and after checking on site for soiling, shading, connections, equipment, and drainage, the next step is to decide on measures in order of their impact on generation. Treating all issues with the same priority can increase the workload and cause high-impact improvements to be delayed.

For example, if only a specific column shows low output even on sunny days and dirt or bird droppings are concentrated on the lower edge of that column, cleaning should be given a high priority. If generation is low only in the morning and shadows from trees or grass on the east side can be seen, prioritize measures against shading. If only a particular string is low and no dirt or shading is apparent, proceed to check the connections, cables, and the equipment side. If the same location shows anomalies after rain, review drainage, moisture, and the environment around the cables.

After measures are taken, confirm how power generation has changed. After performing cleaning, weeding, repairs, equipment checks, and drainage checks, record the pre- and post-work power generation, on-site photographs, work scope, and weather conditions. It is difficult to completely eliminate the effects of weather, but by comparing sunny days with each other or comparing with systems under the same conditions, you can identify certain trends. Prioritize measures that showed a large effect for future work, and if an effect is not apparent, suspect other causes.

It's important not to treat inspection results as a one-off. If you record locations prone to soiling, times when shadows are likely to occur, places where water pools, walkways that tend to deteriorate, and equipment that is prone to abnormalities, you can check them before power generation drops significantly. To steadily increase power generation, it is important not only to respond after output declines but also to identify conditions likely to cause declines in advance and take countermeasures.

Summary

Inspection procedures aimed at increasing power output should be carried out as a single workflow, from checking data before visiting the site, to identifying causes on-site, to verifying the effects after countermeasures. In solar power generation, the site cannot increase the amount of solar irradiance itself. However, you can improve generation by bringing the system closer to a state that converts received solar irradiance into electricity without waste. To do that, it is necessary to check, in order, power generation data, weather and irradiance conditions, soiling of panel surfaces, shading from weeds and trees, strings and connections, power conversion equipment, drainage and terrain, and inspection records.

When you feel the power output is low, it’s important not to rush into cleaning or repairs but to first break down and examine the data. Identify when the output is low, which equipment is underperforming, and whether there is a difference compared with equipment under the same conditions. With that information in hand, an on-site inspection will make it clear where cleaning is needed, which areas require weeding, which connections should be inspected, which devices need checking, and which drainage or access routes should be reconsidered. By establishing the flow for on-site checks in advance, decisions to improve power output become much easier to make.

Efforts to increase power generation are not a one-time task. Even if you clean, dirt will reaccumulate; even if you remove weeds, they will grow back; trees will continue to grow; and equipment and wiring change condition with age. By comparing power generation before and after countermeasures, keeping on-site photos and work records, and applying them to the next inspection, the accuracy of improvements increases. To raise power generation consistently, 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 dirty-prone rows, areas where shadows occur, places where water accumulates, abnormal strings, repair locations, cleaning areas, and inspection photos are recorded along with location information, stakeholders can more easily confirm the same spots. By combining power generation data with on-site location information, it becomes easier to explain priorities for cleaning, weeding, and repairs, and it also streamlines recurrence checks in subsequent inspections.

If you want to continue inspection procedures to increase power generation based on field data, using LRTK is also effective. As an iPhone-mounted high-precision GNSS positioning device, LRTK is useful for recording inspection locations within a solar power plant, locations prone to dirt, areas where shading occurs, drainage failure points, abnormal equipment, repair locations, cleaning coverage, and on-site photos together with high-precision location information. By keeping the flow of on-site checks with location information, it becomes easier to pursue power generation improvements based on field data rather than intuition.