9 Inspection Checks to Increase Solar Power Output

When you want to increase solar power output, it's premature to immediately consider adding panels or updating equipment. The reason output doesn't improve is often due to multiple overlapping factors, not just panel performance: shadows, dirt, fallen leaves, snow accumulation, temperature rise, wiring, connection points, power conversion equipment, changes in the surrounding environment, and so on. To increase output, you should first inspect whether the current equipment is delivering its expected power, and choose improvement measures appropriate to the cause. This article, aimed at practitioners searching for "how to increase power generation", explains the inspection checks you should confirm to raise solar power output, divided into nine items.

Table of Contents

• Inspections to increase solar power generation should start with isolating the cause

• Check 1: Verify seasonal decreases using monthly generation data

• Check 2: Check for shading and abnormalities using generation by time of day

• Check 3: Inspect panel surfaces for dirt, fallen leaves, and bird droppings

• Check 4: Inspect for shading from buildings, trees, and rooftop equipment

• Check 5: Check for output reductions caused by high temperatures, poor ventilation, or the installation environment

• Check 6: Check for changes after snow accumulation, typhoons, and strong winds

• Check 7: Inspect wiring, connection points, and power conversion equipment

• Check 8: Verify orientation, tilt, and layout conditions

• Check 9: Review inspection records and verify the effects of improvements

• Decisions to avoid during inspection checks

• Summary

Inspections to Increase Solar Power Output Start with Isolating the Cause

For inspections aimed at increasing solar power generation, the most important thing is not to assume a single cause for low output. When you feel the output is low, it's tempting to suspect panel degradation or equipment failure, but in reality it may be a natural fluctuation due to weather or seasonal changes. Conversely, if you leave it alone thinking it's just seasonal variation, it may actually be caused by shading, dirt, or equipment shutdown.

Solar power generation varies greatly depending on solar irradiance, temperature, solar elevation, weather, and the surrounding environment. In winter, sunlight hours are short and the sun’s elevation is low, so power generation tends to decline. In summer, although solar irradiance is high, panel temperatures rise and output can sometimes decrease. In spring, pollen and yellow dust, and in autumn, fallen leaves and post-typhoon dirt can affect power generation. In other words, the causes of insufficient power generation also change with the seasons.

In inspections aimed at increasing power generation, we first review the generation data and then assess the on-site conditions. We examine monthly generation to identify seasonal trends, and analyze generation by time of day to look for possible shading or equipment abnormalities. Based on that, we inspect panel surfaces, surrounding obstructions, trees, rooftop installations, wiring, equipment, and inspection routes. By combining data and on-site verification, it becomes easier to avoid unnecessary cleaning or unnecessary equipment replacement.

Also, increasing power generation is not the same as increasing self-consumption. Even if generation increases, if that generation is concentrated at times when the facility cannot use it, it may only lead to larger surpluses. During inspections, you need to distinguish whether the amount of generation itself is low or whether there is generation that is not being used. To correctly determine how to increase generation, the starting point is isolating the causes.

Check 1: Confirm seasonal declines using monthly power generation

The first inspection check is to review the monthly power generation. Looking only at the total annual generation does not reveal in which seasons generation is dropping. To increase generation, you need to check the generation for each month and determine whether the decrease is a reasonable seasonal fluctuation or an improvable generation loss.

If power generation is low only in winter, check for shortened sunshine hours, low solar altitude, winter shading, and the effects of snow. If power generation does not increase in summer as expected, it may not be due to insufficient solar irradiance but rather rising panel temperatures or high-temperature conditions of equipment. If power generation lags in spring, pollen, yellow sand (Asian dust), or dust deposition may be involved. If power generation is low in autumn, suspect fallen leaves, post-typhoon dirt, or debris blown in by strong winds.

When examining monthly generation, a simple comparison with the previous month is not sufficient. Because solar power generation varies seasonally, a lower output than the previous month is not necessarily abnormal. Comparing with the same month in the previous year, with sunny days in the same season, and with the simulation values at the time of installation makes it easier to determine whether the change is a natural fluctuation or an abnormal decline.

In inspections aimed at increasing power generation, you first identify the months in which output has declined and then check for causes that are likely to occur in those seasons. Once seasonal trends are understood, it becomes easier to prioritize actions such as cleaning, shade mitigation, snow checks, and equipment inspections. Monthly power generation is an important check that serves as the entry point for the overall inspection.

Check 2: Check for shading and abnormalities in power generation by time of day

The second inspection check is to examine power generation by time of day. Monthly generation figures reveal seasonal trends, but shading and equipment faults can appear during specific hours of the day. By looking at generation by time of day, you can more precisely narrow down the causes of underperforming output.

If the power output in the morning does not increase, consider shadows on the east side caused by buildings, trees, utility poles, or rooftop equipment. If the power output falls rapidly in the evening, check for shadows on the west side. If there is an unusual drop around midday, you need to check for shadows from nearby obstructions such as rooftop structures, piping, handrails, and air-conditioning equipment, as well as output limiting of power conversion equipment and faults at connection points.

When examining generation by time of day, it is important to use data from sunny days. Cloudy or rainy days generally show reduced generation overall, so they are not suitable for distinguishing between shading and equipment faults. If generation falls at the same time each day even on sunny days, the cause may be site conditions or equipment conditions rather than the weather.

If data by installation surface or by system is available, you can examine it in more detail. If there are trends—such as only a particular roof surface underperforming in the morning, only a particular system dipping at midday, or only a specific surface dropping off early in the evening—you can narrow the scope of checks for shading, wiring, and equipment. Time-of-day data is an important clue for finding the causes during inspections aimed at increasing power generation.

Check 3: Inspect the panel surface for dirt, fallen leaves, and bird droppings

The third inspection check is to inspect the condition of the panel surface. Solar panels generate electricity from sunlight striking their surface, so when dirt, fallen leaves, bird droppings, dust, or other debris accumulate on them, power output decreases. Dirt often builds up gradually, making drops in power output easy to overlook.

Causes of soiling include sand and dust, pollen, yellow sand (Asian dust), exhaust-derived dirt, particulate matter, fallen leaves, bird droppings, and residual deposits after snowfall. Areas with many trees nearby are more prone to fallen leaves and bird droppings. If unpaved land, farmland, construction sites, or high-traffic roads are nearby, soil dust and particulate matter are more likely to adhere. On rooftops, panels located near vents or exhaust equipment can also become locally soiled.

During inspections, check whether the dirt is thinly spread across the entire surface or is localized. Localized obstructions such as bird droppings or fallen leaves can affect power output more than they appear. If power output does not recover after rain, or if only a particular surface shows reduced output, it is worth checking for surface dirt.

When performing cleaning, prioritize safety and the protection of equipment. Work on roofs is hazardous, and methods such as vigorously scrubbing with hard tools, using unsuitable detergents, or applying high-pressure water can negatively affect panels and equipment. The decision to clean should be made after cross-checking generation data with on-site conditions, and after cleaning it is important to confirm whether generation has improved.

Check 4: Verify shadows cast by buildings, trees, and rooftop equipment

The fourth inspection check is to check for shading. Even if the panel surface is clean, shading will prevent power output from increasing. Shading is a direct cause of reduced power generation, yet it is easily overlooked because it varies with the seasons and time of day.

Sources of shadows include surrounding buildings, rooftop equipment, tower housings, railings, piping, air conditioning equipment, ventilation equipment, trees, utility poles, signs, slopes, and differences in terrain elevation. Even if there were few shadows at the time of installation, shadows may increase later as trees grow, rooftop equipment is added, or new structures are built nearby.

Particular attention should be paid to shading in winter. In winter the sun is lower in the sky, and shadows that did not reach the panels in summer can fall on them. If power generation is significantly lower only in winter, check not only the shorter hours of sunlight but also the extent and timing of the shading. Morning and evening shading is also important. If generation is weak in the morning, check for obstructions on the east side; if it drops off early in the evening, check for obstructions on the west side.

In shadow inspections, we combine power generation data with on-site verification. We check which time periods show drops in generation and determine from which directions shadows are likely to appear during those times. If trees are the cause and can be managed, consider pruning or trimming branches; if rooftop equipment or surrounding buildings are the cause, treat them as subjects for layout review or as exclusion zones when expanding. To increase power generation, it is important to prioritize areas with less shading.

Check 5: Verify output degradation due to high temperature, ventilation, and installation environment

The fifth inspection check is to verify high temperatures, ventilation, and installation conditions. While solar power generation tends to be greater with higher solar irradiance, output can decrease when panel temperature rises. If power output does not increase on a sunny summer day, it is necessary to check for output reduction due to high temperatures.

Panels installed on roofs tend to run hotter because roofing materials absorb heat, and poor ventilation behind the panels allows temperatures to rise. Heat also tends to build up when a low mounting rack is used on a flat roof or when many rooftop installations nearby impede airflow. Even for ground-mounted systems, temperature conditions can be affected if overgrown vegetation obstructs airflow or if surrounding structures cause air to stagnate.

In the generation data, check whether the power output around midday on clear summer days is not increasing as much as expected. Even if spring or autumn appears to produce more stable generation, temperature-related losses may be involved. It is important to check ventilation around the panels, the condition of surrounding vegetation, and the temperature environment around the equipment.

As countermeasures, consider managing vegetation and obstacles that impede ventilation, ensuring heat dissipation around equipment, and reviewing layout and racking conditions. However, because changes to rack height and tilt angle also affect wind loads and constructability, decisions should not be made based on power generation alone. High-temperature measures need to be considered together with power generation, maintainability, and safety.

Check 6: Confirm changes after snowfall, typhoons, and strong winds

The sixth inspection check concerns changes after snowfall, typhoons, and strong winds. Because solar power generation equipment is installed outdoors, power output can decrease following severe weather conditions. To improve power generation, it is important not only to carry out routine inspections but also to perform checks after weather events.

In snowy regions, there are periods when snow covers the panel surface and prevents power generation. Not only the time it is snowing, but also the time snow remains after a snowfall affects power generation. If the panel tilt is small, snow is less likely to fall off, and when snow accumulates under or in front of the panel it can cast shadows. If winter power generation is low, check for snowfall and residual snow.

After typhoons and strong winds, fallen leaves, branches, airborne debris, sand and dust, and particulate matter can remain on panels and roofs. Even if debris does not directly cover the panels, accumulation in drains and inspection walkways can affect maintenance. If power generation suddenly drops after strong winds, check the panel surfaces, mounting structures, wiring, equipment, and surrounding obstructions for changes.

After weather events, inspections should prioritize safety above all. Avoid attempting to work on roofs with remaining snow or at sites immediately after strong winds. First check the power generation data and assess on-site conditions from areas that appear safe. Recording inspection results will also be useful for future checks after typhoons or snowfall.

Check 7: Inspect Wiring, Connections, and Power Conversion Equipment

The seventh inspection check covers the wiring, connections, and power conversion equipment. Even if there are no problems with the panel surface or shading, losses or faults in the electrical pathways will prevent power generation from increasing. The electricity generated by the solar panels passes through wiring and equipment to become usable by the facility. If problems occur during that process, the amount of electrical energy actually available for use is reduced.

If power generation suddenly drops, or if only a particular system shows low output, you need to check the wiring, connection points, and power conversion equipment. If wiring distances are long, connection points are difficult to inspect, or wiring routes are complex, fault detection can be delayed. During new installations or expansions, confirm the wiring routes and equipment installation locations as conditions that can also affect power generation.

The condition of power conversion equipment is also important. If the equipment is stopped, the amount of electricity available to the facility decreases even if the panels are generating. If output plateaus around midday, check the equipment capacity and output conditions. If the equipment is located in places prone to high temperatures, exposed to rain or snow, or difficult to inspect, consider the long-term operational risks.

Because electrical inspections require specialized expertise and safety measures, operational personnel should not be forced to make judgments; instead, it is important to organize generation data and on-site conditions and clarify the necessary scope of inspection. Inspections aimed at increasing power generation must check not only the panels but also the pathways that deliver the electricity.

Check 8: Verify orientation, tilt, and placement conditions

The eighth inspection check is orientation, tilt, and placement conditions. Power generation varies depending on which direction the panels face and at what angle they are installed. For existing installations, major changes may not be possible, but this is an important item to check for understanding why power output is not increasing.

Surfaces that face close to south tend to produce more electricity over the year. However, east- and west-facing surfaces are not necessarily worse. East-facing surfaces tend to generate more in the morning, while west-facing ones tend to generate more in the afternoon. If a facility’s power demand is high in the morning or afternoon, generation from east and west faces can help with self-consumption. To increase power generation, also check the relationship between the time of generation and the facility’s demand.

Tilt angle also affects power generation. If the angle is small, dirt and snow are more likely to remain, while if the angle is large, inter-row shading and wind effects can occur. For flat roofs and ground-mounted installations, check the balance between tilt angle, inter-row spacing, and the number of panels that can be installed. In layout planning, it is also important to ensure that panels are not being forced into shaded areas or areas that are difficult to maintain.

During inspections, record the orientation and tilt as on-site conditions and compare them with the power generation data. If only a specific surface shows low power generation, check that surface’s orientation, tilt, shading, soiling, and wiring. Understanding the placement conditions makes it easier to determine which surface to prioritize when performing expansions or upgrades.

Check 9: Confirm inspection records and the effectiveness of improvements

The ninth inspection check is the verification of inspection records and the effects of improvements. Even if inspections and cleaning are carried out, without records they cannot be applied next time. To increase power generation, it is important to record what was checked, what was improved, and how the power output changed.

Items to record include the inspection date and time, weather, the scope/area checked, the condition of power generation, the presence or absence of dirt/soiling, sources of shading, the condition of fallen leaves or snow accumulation, the results of equipment and wiring checks, and the actions taken. Recording photos and location information together makes it easier to check the same place at the next inspection.

When evaluating the effectiveness of improvements, compare power generation before and after inspection. However, power generation naturally changes with different weather and seasons. Compare with similar sunny days, the same month of the previous year, simulation values, generation by time of day, and generation by installation surface. Check whether power generation returned after cleaning, whether generation during specific time periods improved after shadow mitigation, and whether system-specific generation recovered after equipment inspection.

As inspection records accumulate, site-specific trends become apparent. If you can identify tendencies such as heavy dust in spring, leaves tending to accumulate in autumn, strong shadows at particular times in winter, or certain surfaces becoming dirty after typhoons, it becomes easier to plan future inspections. Records and verification are the foundation for continuously improving power generation output.

Judgments to Avoid During Inspection Checks

What you should avoid in inspection checks is performing cleaning or equipment replacement without confirming the cause of low power generation. Cleaning is effective if dirt is the cause, but if the cause is shading, equipment shutdowns, wiring faults, thermal losses, or snow, cleaning alone will not improve the situation. It is important to check the power generation data and on-site conditions and to choose countermeasures appropriate to the cause.

Avoid attempting unsafe work on roofs. Solar panels are often installed on roofs or other elevated locations, which carries risks of falls and equipment damage. Working on wet roofs, sloped roofs, in strong winds, or during snowfall is particularly dangerous. Areas that cannot be safely inspected should be checked under appropriate arrangements.

Be careful about judging based solely on annual generation. Annual totals do not reveal which months or times of day have problems. To increase generation, it is important to check by month, by time of day, by installation surface, and by system. Also, in addition to generation, you should check self-consumption and surplus electricity to ensure that improvements are translating into practical benefits.

Not recording inspection results is a decision that should be avoided. Without records, you can't compare when the same issue recurs. Inspections to increase power generation are not completed with a single check; they require continuous improvement.

Summary

In inspection checks to increase solar power output, it is important to check in order: monthly generation, generation by time of day, panel surfaces, shading, high temperatures, snow accumulation, wiring, equipment, orientation, tilt, layout, and inspection records. The causes of stagnant generation are not limited to a single factor and may involve multiple overlapping issues. Combining data analysis with on-site verification to isolate the causes is the fundamental approach to improving power generation.

In Check 1, seasonal declines are checked using monthly power generation. In Check 2, shading and anomalies are checked using power generation by time of day. In Check 3, dirt, fallen leaves, and bird droppings on the panel surface are checked. In Check 4, shading caused by buildings, trees, and rooftop equipment is checked. In Check 5, output reductions due to high temperatures, ventilation, and the installation environment are checked. In Check 6, changes after snow accumulation, typhoons, and strong winds are checked. In Check 7, wiring, connections, and power conversion equipment are checked. In Check 8, orientation, tilt, and layout conditions are checked. In Check 9, inspection records and the effects of improvements are checked.

To increase power generation, rather than carrying out cleaning or equipment replacement without checking the cause, it is important to specifically identify the factors that are reducing output. After inspection, verify by data how much the power output has improved and use that information to inform the next maintenance.

And to improve the accuracy of inspection checks, accurate on-site information is indispensable. If you can ascertain the installation area, rooftop equipment, obstacles, trees, site boundaries, orientation, slope, inspection access routes, and candidate connection points, it becomes easier to organize issues related to shading, soiling, temperature, wiring, and maintainability.

To accurately record installation areas, obstacles, trees, rooftop equipment, site boundaries, orientation, tilt, inspection routes on site—and to carry out inspection checks efficiently to increase solar power generation—using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. If you can acquire high-precision local position information, it becomes easier to organize the causes of shading, areas prone to soiling, the ranges that should be inspected, wiring routes, and maintenance routes, and to consistently proceed with inspection records, verification of generation improvements, and post-installation performance management. To increase solar power generation, it is important not to rely on subjective inspections but to accurately understand the site and address the causes that are lowering generation in order.