5 Steps to Increase Solar Power Generation | Things to Check Before Cleaning

Table of Contents

• Identifying the causes before cleaning is important to increase solar power generation

• Step 1: Check generation data by time of day and by equipment unit

• Step 2: Isolate weather, solar irradiance conditions, and seasonal differences

• Step 3: Verify on site the types of soiling and where they occur

• Step 4: Review generation losses caused by shadows, weeds, and the surrounding environment

• Step 5: Inspect connection points, power conversion equipment, and drainage conditions to prevent recurrence

• Management methods to sustain improvements in power generation after cleaning

• Summary

Confirming the causes before cleaning is important for increasing solar power generation

When you want to increase solar power output, the first measure that comes to mind at many sites is panel cleaning. If the panel surface is dirty, it receives less sunlight and output decreases, so cleaning is certainly an important measure. However, if you perform cleaning alone without checking the reasons why output isn’t increasing, improvements may be less than expected. This is because the causes of reduced output can be more than just dirt — factors such as shading, weeds, faults in connections, stoppage of conversion equipment, output curtailment, poor drainage, and site environments that are difficult to inspect can overlap.

For operations personnel searching "how to increase power generation," what matters is not deciding whether to clean based on intuition, but isolating the causes of reduced output before cleaning. In solar power generation, you cannot increase the incident solar irradiance at the site itself. However, you can bring the system closer to a state that converts the received irradiance into electricity with as little waste as possible. In other words, practical power-generation improvement means finding the causes of lost potential generation and taking steps to reduce generation losses.

If you skip pre-cleaning checks, you may misprioritize actions on site. For example, even if the panel surfaces have a light layer of dirt, if the primary cause of reduced power generation is morning and evening shading, cleaning alone is unlikely to produce sufficient improvement. Conversely, if there are no signs of shading or equipment faults and soiling at the lower edge or bird droppings are concentrated on a specific row, cleaning is more likely to deliver improvement. To make cleaning an effective measure, you must first cross-check power generation data with on-site conditions to confirm whether soiling is truly the cause.

Also, what should be checked before cleaning is not just whether there is dirt. You should check which time periods have low power generation, whether only certain equipment is underperforming, whether it is due to weather, shading from the surroundings, whether any equipment has stopped, and whether the same dirt is recurring because of poor drainage. By establishing this workflow, it becomes easier to determine the scope, timing, and priorities for cleaning. To increase power generation, it is important to treat cleaning not as a standalone task but as part of management that includes inspection, root-cause analysis, countermeasures, and verification of effectiveness.

This article explains five steps to check before cleaning in order to increase solar power generation. To make it easy for beginners to verify on site, we organize the sequence from how to read generation data, separating out weather effects, checking for dirt, reviewing shading and weeds, to checking equipment and drainage. If you follow this process before performing cleaning, decisions about improving generation will become more practical, and the same generation losses will be less likely to recur.

Step 1: Check power generation data by time period and by facility

Before cleaning, the first thing to check is the power generation data. When you feel the generation is low, instead of immediately going to the site to look at the panel surfaces, first check on the data "when", "where", and "how" it is low. Looking only at monthly or annual generation does not reveal the time or scope of the generation loss. Even if it does not appear to be a major anomaly on a monthly basis, there may be cases where generation drops only during certain hours on sunny days, or where only specific equipment remains at a low level.

Viewing power generation by time of day makes it easier to identify the likely cause. If generation is low in the morning, 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 effects of surrounding terrain. If the midday peak does not develop, candidates include dirt on the panel surface, temperature rise, limitations of the power conversion equipment, output curtailment, or equipment shutdowns. Improvements from cleaning can be expected mainly when soiling of the light-receiving surface is related to the drop in generation. Therefore, it is important to first use the time-of-day generation curve to check for possibilities other than soiling.

Comparisons at the equipment-unit level are also indispensable. If you only look at the plant’s total power generation, some anomalies can be masked by the average. Compare installations with the same orientation, the same tilt, a similar number of panels, and the same shading conditions, and check whether certain rows or strings are consistently lower. If only a part is lower compared with installations under similar conditions, local soiling, partial shading, connection faults, cable damage, or equipment-side malfunctions may be suspected. Before cleaning, it is important to confirm that the area of decline matches the actual extent of soiling on site.

There are two types of decreases in power generation output: sudden drops and gradual declines. When output suddenly falls, equipment shutdowns, broken wiring, poor connections, or the emergence of obstructions may be involved. When it decreases gradually, accumulation of dirt, growth of weeds or trees, deterioration of site conditions due to poor drainage, or aging of equipment may be involved. To determine whether cleaning will be effective, it is important to read the pattern of this decline.

When reviewing power generation data, record the pre-work condition so you can compare before and after cleaning. If you document the cleaning date, the area cleaned, generation before cleaning, generation after cleaning, and weather conditions, you can later verify the effect of the cleaning. If generation recovers after cleaning, it becomes easy to conclude that soiling was a major factor in the generation loss at that site. Conversely, if cleaning does not lead to significant improvement, you need to check other causes such as shading, equipment, connections, temperature, and drainage.

Cleaning to increase power output is not simply something carried out because equipment is dirty. By determining which equipment is experiencing generation losses and whether those losses are related to soiling before cleaning, you clarify the priorities and effectiveness of the work. Verifying data before cleaning is the starting point for improving power generation.

Step 2: Separate weather, solar radiation conditions, and seasonal differences

Before cleaning, the next thing to check is a reduction in power generation due to weather and solar radiation conditions. Because solar power generation is strongly affected by the amount of solar irradiance, output will decline during periods with many cloudy or rainy days even if the equipment has no problems. If you judge that "power output has fallen" solely by comparing monthly output with the same month of the previous year or with the previous month, the main cause may actually be differences in weather. Before deciding whether cleaning is necessary, it is important to separate natural variability from generation losses on the equipment side.

To check for weather-related differences, it is more effective to compare sunny days with each other or days with similar weather, rather than a simple month-to-month comparison. On cloudy or rainy days, power generation can fluctuate greatly due to cloud movement, making it difficult to distinguish from equipment faults. If you select and examine generation curves from sunny days, you can more easily identify features such as shading, soiling, shutdowns, output curtailment, and string anomalies. Before cleaning, confirm whether a low-generation day was simply due to poor solar irradiance conditions or whether the decline appears even on sunny days.

Comparing equipment within the same power plant is also useful. If the entire plant is similarly low, the influence of weather or solar irradiance conditions may be significant. On the other hand, if only a portion of the plant is low, weather alone is unlikely to explain it, and you should suspect localized soiling, shading, poor connections, or equipment faults. If you manage multiple plants, comparing with other sites in the same region makes it easier to determine whether the issue is a regional weather effect or a problem specific to a particular site.

Seasonal variations also need to be taken into account. In winter the sun’s altitude is lower, and shadows from surrounding trees and terrain tend to extend farther. In summer, although solar irradiation is stronger, panel temperatures and temperatures around equipment rise, and power generation may not increase as much as expected. During periods with heavy rainfall, monthly power generation tends to be lower, and after strong winds or heavy rain, fallen leaves, sediment, deposits, and poor drainage can have an impact. The need for cleaning should be determined based on the season-specific patterns of soiling and the extent of generation decline.

The purpose of distinguishing weather and solar irradiance conditions is not to look for reasons not to clean. Rather, it is to verify whether cleaning will actually be effective at improving power output. If output was low simply because of poor weather, the improvement from cleaning will be limited. Conversely, if on sunny days only specific rows show low output, or if declines continue in areas where dirt tends to remain after rain, then cleaning and on-site inspection should be prioritized.

Recording weather conditions before cleaning makes it easier to verify the effects after cleaning. When comparing power generation before and after cleaning, you cannot make an accurate judgment if the weather differs significantly. Compare data under as similar solar irradiance conditions as possible, and also check the difference between cleaned and uncleaned equipment so that the extent of generation loss due to soiling becomes clearer. To increase power generation, it is important to understand the impact of weather and focus countermeasures on factors that can be improved on site.

Step 3: Confirm the type of soiling and where it occurred on-site

The primary check before cleaning is to identify the types of dirt and where they occur. When dirt adheres to the surface of solar panels, sunlight has difficulty reaching the cells and power generation decreases. However, dirt comes in many forms. Depending on the site environment, the types of dirt that are likely to occur differ, such as soil dust, pollen, yellow dust, bird droppings, fallen leaves, tree sap, dust from nearby construction, road-generated dust, and salt-containing deposits that readily adhere in coastal areas. Before cleaning, confirm not just whether the panels are dirty but what kind of dirt is present and where.

Particularly important to watch for are band-like deposits that remain along the lower edge of the panels and around the frame. It's often assumed that rain will naturally wash away dirt, but in reality the flow of rainwater can collect grime at the lower edge and leave it there. On panels with a gentle tilt, water does not drain well and dirt is more likely to accumulate. Even dirt that is not noticeable from a distance can affect power generation if it covers part of a cell. During on-site inspections before cleaning, you need to carefully check not only the overall coloration of the panels but also the lower edge, the corners, and the areas around the frame.

Localized deposits such as bird droppings or fallen leaves should not be overlooked. Unlike dirt that spreads thinly over the entire surface, these cover specific spots more heavily and act as partial shading. If only some installations are producing less power, focus on inspecting the panel surfaces around those installations. Rows close to trees, areas around structures where birds tend to perch, rows that are prone to being downwind, and areas near unpaved walkways are more likely to accumulate dirt and deposits.

When checking for soiling, it is important to compare it with power generation data. If locations that appear heavily soiled correspond to equipment with low power output, the priority for cleaning should be high. Conversely, if an area looks soiled but no decrease in power output is observed, it may be better to prioritize investigating other causes rather than cleaning. Because cleaning involves labor, it is practical to carry it out starting with the areas that have the greatest impact on power generation.

When choosing a cleaning method, do so on the premise of avoiding damage to the equipment. Avoid vigorously scrubbing with hard tools, performing sudden work during times when panels are at high temperature, or working without conducting safety checks as electrical equipment. Cleaning is not a task to improve appearance, but maintenance to restore the light-receiving condition while enabling the equipment to be used for a long time in a stable manner. Depending on the type of dirt, care is needed regarding how to remove it and when to carry out the work.

Furthermore, it is also important to understand the causes of recurring soiling. Check whether dust is easily raised from unpaved walkways, whether leaves or tree sap tend to fall from nearby trees, whether there are spots that attract birds, or whether the panel angle makes it difficult for rainwater to drain. Even if soiling is removed by cleaning, it will recur in the same place if the conditions that cause it do not change. To increase power generation, it is important not only to remove soiling but also to record locations prone to soiling as management targets.

Step 4: Review power generation losses due to shading, weeds, and the surrounding environment

What you should always reassess before cleaning is power loss caused by shading. If you judge low power output to be caused by dirt and clean the panels, but the real primary cause is shading, you cannot expect significant improvement. Because solar panels generate electricity from sunlight, even partial shading of a panel can reduce power output. Causes of shading vary and include weeds, trees, fences, utility poles, surrounding buildings, mounting racks, adjacent rows of panels, monitoring equipment, and similar factors.

Weeds are a common cause of power generation losses at sites. Even if they are not a problem in winter or immediately after installation, they can grow rapidly from spring to summer and cast shadows on the lower edges of panels and the front rows. Even when grass does not touch the panels, shadows lengthen at the low sun angles in the morning and evening. Furthermore, when weeds become overgrown, ventilation deteriorates, inspection walkways become blocked, and it becomes more difficult to check around equipment. If the state of the weeds is not checked before cleaning, one may overlook that shadows from grass — not dirt — were the main cause of the reduction in power generation.

Shading from trees is also a factor that can become problematic during long-term operation. Trees that had little effect at the time of installation can grow over several years and reduce power output. Trees located on the south, east, and west sides in particular cast shadows on panels at different times of day. At solar plants near forests or slopes, the height of the terrain combined with the height of trees can create long shadows in winter. If output is low only in winter, or there is a large drop in the morning and evening, shadow mitigation may need to be prioritized over cleaning.

When checking shadows, aligning the power output data with the time of the on-site inspection makes it easier to find the cause. If the power output is low in the morning, check the on-site conditions in the morning; if it’s low in the evening, inspect the evening shadows. Even if a noon check shows no issues, large shadows can appear in the morning and evening. Also, even if there are no problems in summer, shadows can lengthen in seasons when the sun’s elevation is lower. Shadows should be treated as something that changes over time and with the seasons, not as a single point in time.

Do not overlook shadows cast by surrounding structures and added equipment. Installing new equipment within the power plant, or adding fences, signs, monitoring poles, etc., can create shadows at certain times of day. If power generation drops at the same time of day even after cleaning, suspect the effect of fixed shadows rather than dirt. To increase power generation, it is important not only to reduce existing shadows but also to operate in a way that does not create new ones.

When performing weeding or pruning, prioritize the areas that have the greatest impact on power generation. Rather than aiming only to make the entire site uniformly tidy, focus on the areas in front of the panels, around equipment, inspection walkways, and the directions where shadows are likely to extend. After work, record whether shadows were actually eliminated, whether inspections have become easier, and whether ventilation has improved. By checking for shadows before cleaning, you can separate the priorities of where cleaning is needed and where weeding is needed.

Step 5: Check connection points, conversion devices, and drainage status to prevent recurrence

The last thing to check before cleaning is power losses other than dirt and shading. Even if you clean the panel surface, power generation may not improve sufficiently if there are problems with connection points, cables, inverters or other conversion equipment, or drainage conditions. In solar power systems, panels not only need to receive sunlight, but the electricity they generate must be properly extracted, converted, and transmitted stably. If there is a fault anywhere along that path, cleaning alone will not solve it.

First, check for generation differences at the string level. Even if the total generation of the plant does not appear to be a major problem, some strings may have reduced output. Compare equipment under the same conditions, and if a particular area consistently shows lower output, suspect not only soiling or shading but also poor connections, cable damage, or equipment-side issues. If abnormalities tend to appear after rain, moisture ingress or the condition around connection points may be involved.

Connection parts and cable faults can include loose terminals, poor contact, damage to cable sheathing, damage caused by animals, damage during mowing operations, and deterioration due to aging. Because these are often difficult to detect from appearance alone, rather than having on-site personnel forcibly touch equipment to make a judgment, it is important to organize the equipment showing abnormalities, the time of occurrence, changes in power generation, on-site photos, and the surrounding environment, and, if necessary, arrange for a professional inspection. If these possibilities are checked before cleaning, the next decision will be quicker if there is no improvement after cleaning.

Check the shutdown history and alarm history of the power conversion equipment. If the equipment that converts the generated electricity has been stopped or its output restricted, generation will not increase even with sufficient solar irradiance. Even short stoppages can cause large losses if they occur during daytime when output is high. If the generation curve on clear days levels off, also check for output curtailment, equipment capacity limits, temperature rise, and measurement anomalies. Because a drop in generation due to soiling and limitations on the equipment side cannot be distinguished by appearance alone, it is necessary to cross-check the histories with the generation curve.

Don't overlook the environment around equipment. If weeds are growing around the equipment, ventilation is poor, there is a lot of dust or debris buildup, or heat tends to accumulate, operational efficiency and the risk of shutdown can be affected. By checking the area around equipment during a pre-cleaning inspection, you can more easily identify power generation losses not only on the panel surfaces but across the entire power plant.

Furthermore, drainage conditions also affect improvements in power generation. In areas where puddles remain after rain, weeds are more likely to grow and dirt and sediment are more likely to accumulate. Muddy walkways delay inspections and cleaning, and also delay the detection of abnormalities. Where sediment flows in, it can accumulate beneath panels and around cables, causing dirt and damage. If the same places become dirty again soon after cleaning, drainage or terrain problems should be suspected.

To avoid treating cleaning as a one-time measure, it is important to inspect connection points, conversion equipment, and drainage conditions, and to record locations that are prone to recurrence. To increase power generation, it is necessary not only to remove dirt but also to improve on-site conditions that cause dirt and abnormalities to recur.

Management methods to sustain improvements in power output after cleaning

After cleaning, check how the power generation changed. Cleaning is not something you do and forget; only by verifying whether it led to an improvement in power generation can you use that information for future decisions. By keeping records of the power generation before and after cleaning, the cleaning scope, the condition of dirt before cleaning, photos after cleaning, and the weather conditions, it becomes easier to confirm the effect of the cleaning. If power generation improved, you can conclude that soiling was a major factor in generation loss at that site.

On the other hand, there are cases where power generation does not improve significantly after cleaning. In such cases, rather than assuming the cleaning was pointless, consider that another source of generation loss remains. Recheck shading, weeds, trees, connection points, cables, conversion equipment, output curtailment, temperature rise, poor drainage, and so on. If you recorded data and the on-site conditions before cleaning, it will be easier to narrow down which causes to check next.

When comparing the effect of cleaning, pay attention to weather conditions. If the weather is significantly different before and after cleaning, you cannot simply compare power output. Compare days with clear skies and similar solar irradiance conditions as much as possible. Also, if you can compare cleaned equipment and uncleaned equipment under the same conditions, it will be easier to judge the effect of cleaning. To make power output improvements part of regular practice, you need the habit of verifying work results with numerical data and on-site photographs.

Record keeping is also important. If you record the places you cleaned, the places that were heavily soiled, the places prone to recurrence, the places where shadows appeared, and the places where water collected, it will be easier to determine the priorities for the next inspection. If you can identify trends—such as the same places getting dirty every year, bird damage occurring in the same rows, or sediment washing into the same aisles—you can take proactive measures before power generation drops significantly.

When multiple people are responsible for management, being able to accurately share the same location is important. In large power plants, where similar rows and equipment are lined up, photos alone can make it difficult to identify the location. If you record the equipment number, location information, and photos together, it becomes easier for on-site personnel, managers, inspectors, and repair staff to confirm the same location. Improving power generation is not only about noticing issues on site, but also about recording that information in a form that stakeholders can share.

In post-cleaning management, we continuously monitor power output data. If output improves only immediately after cleaning but declines again within a short period, it is necessary to reassess the causes of recurring soiling, drainage, and the surrounding environment. If power output remains stable after cleaning, the timing and scope of the cleaning were likely appropriate. In this way, tracking power output after cleaning reveals the optimal management approach for each site.

Efforts to increase power generation only become effective when cleaning, weeding, inspections, repairs, and record-keeping are linked. By identifying causes before cleaning, verifying results after cleaning, and recording locations prone to recurrence, improvements in power generation can be turned from one-off tasks into continuous operational improvements.

Summary

Cleaning is important for increasing solar power generation, but if you skip checks before cleaning, you may not see as much improvement as expected. The causes of reduced power output are not limited to dirt on the panel surface. Multiple factors can combine to lower output, such as weather and solar irradiance conditions, shading that varies by time of day, weeds and trees, faults in connections and cables, inverter shutdowns or output curtailment, poor drainage, and site conditions that make inspection difficult.

Before cleaning, the first thing to look at is the power generation data. Check not only monthly and annual totals but also generation by time of day, by equipment unit, and generation curves on clear days. Next, separate out weather and solar irradiance conditions to determine whether there are generation losses that can be improved on the equipment side. Then, on site, check the types of soiling, where it occurs, soiling at the lower edges, bird droppings, fallen leaves, and dust. Furthermore, by also checking shadows, weeds, trees, surrounding structures, connection points, power conversion equipment, and drainage conditions, it becomes easier to determine whether cleaning is truly the priority measure.

After cleaning, it is important to check how power generation has changed. By recording before-and-after photos, the area cleaned, power generation data, and weather conditions, you can verify the effect of the cleaning. If an improvement is observed, it is easier to conclude that soiling was the main cause of the generation loss. If the improvement is small, check for other causes such as shading, connections, equipment, or drainage. Improving power generation is not a one-time operation; it becomes established by repeating root-cause identification, countermeasures, effect verification, and record updates.

Especially at large power plants, a system for accurately sharing problem locations is important. If rows prone to soiling, areas where shadows occur, places where water accumulates, abnormal strings, repair locations, cleaning extents, and inspection photos are recorded together with location information, stakeholders can more easily confirm the same location. By combining power generation data with on-site location information, it becomes easier to explain priorities for cleaning, weeding, and repairs, and to streamline recurrence checks in subsequent inspections.

If you want to accurately manage efforts to increase solar power generation—from pre-cleaning checks through post-cleaning effectiveness verification—using LRTK can also be effective. As an iPhone-mounted GNSS high-precision positioning device, LRTK is useful for recording inspection locations within a solar power plant, areas prone to soiling, points where shadows occur, locations with poor drainage, abnormal equipment, cleaning areas, and site photos together with high-precision location information. By recording the items to be checked before cleaning along with their location information, it becomes easier to pursue generation improvements based on field data rather than on intuition.