7 Points for Increasing Power Generation: Start by Looking at Shade Countermeasures

When you want to increase the power generation of a solar power system, the first thing to check is the impact of shading. Causes of low generation include dirt, temperature rise, equipment malfunctions, wiring losses, snowfall, and aging, but shading tends to occur depending on local conditions and can change with the season and time of day, making it an easily overlooked factor. If you consider adding panels or replacing equipment without checking the impact of shading, the power generation may not increase as much as expected. This article explains seven points for looking at shade countermeasures as an entry point to improving power generation, aimed at practitioners who search for "発電量 上げ方".

Table of Contents

• Why consider shading countermeasures first when increasing power generation

• Point 1: Identify suspected shading from monthly and time-of-day data

• Point 2: Check shadows from rooftop equipment and surrounding buildings

• Point 3: Focus on shadows in winter and during mornings and evenings

• Point 4: Don't overlook shadows caused by growth of trees and vegetation

• Point 5: Don't force panels into shaded areas

• Point 6: Also check for temporary obstructions from fallen leaves, snow, and dirt

• Point 7: Validate power generation after shading countermeasures using data

• Verifying cases where power generation does not increase with shading countermeasures alone

• Summary

Why Shadow Mitigation Should Be the First Consideration When Increasing Solar Power Output

When considering ways to increase the output of a solar power system, the first thing to examine should not be equipment replacement or expansion, but the factors that are currently reducing its output. Among these factors, shading is relatively easy to detect and to devise countermeasures for; however, because it varies with season and time of day, it is easily overlooked if on-site inspections are insufficient.

Solar panels generate electricity by receiving solar radiation. If part of a panel is shaded, the solar radiation received by that portion is reduced, and the power output decreases. The effect of shading is not determined solely by the shaded area. The impact on power generation varies depending on the time of day the shading occurs, the panel layout, the connection units, the operation of power conversion equipment, and the relationship with neighboring panels. Even a small shadow can have a large effect on annual energy production and self-consumption if it falls during times when generation would be high.

What makes shadows troublesome is that they don’t always appear in the same place or with the same shape. Because the sun’s position is different in the morning and evening, the direction of shadows changes. Because the sun’s altitude differs between summer and winter, the length of shadows changes. Even if a site appears shadow-free when visited in summer, surrounding buildings, trees, or rooftop equipment can cast much longer shadows in winter. If power output is low only in winter, weak only in the morning, or suddenly drops in the evening, you should suspect the influence of shadows.

Also, shading can increase after installation. Trees that were short at the time of installation may grow, nearby buildings or facilities may be added, or new piping or HVAC equipment may be installed on the roof, creating shading that was not included in the initial simulation. In other words, shade mitigation is not only a pre-installation check but also relevant to post-installation power generation management.

The reason to start with shading countermeasures when aiming to increase power generation is that, before adding capacity, you might be able to recover lost generation opportunities from the equipment you already have. By identifying the causes of shading and avoiding heavily shaded areas, managing trees and other obstructions, or revising the layout, you may be able to improve actual generated output even with the same installed capacity. To increase power generation, the basic step is to first confirm why generation is not occurring.

Point 1: Find suspected shading from monthly and time-of-day data

The first step in shading countermeasures is to identify suspected shading from power generation data. By checking monthly generation and generation by time of day before visiting the site, you can more easily narrow down the seasons and times of day when shading may be occurring. Even if you feel the generation is low, rather than inspecting everything on-site at once, it is more efficient to first narrow down the possibilities from the data.

Looking at monthly power generation, you can see the seasonal changes in output. If generation is significantly lower only in winter, you need to check not only the shorter daylight hours but also winter shadows. Because the sun’s altitude is lower in winter, shadows from surrounding buildings, trees, rooftop equipment, railings, and roof structures such as penthouses tend to extend farther. Places that were not shaded in summer may cast shadows on panels in winter.

Looking at power generation by time of day makes it easier to estimate the direction of shadows. If morning generation does not rise as expected, shadows from buildings, trees, or equipment on the east side may be suspected. If generation suddenly drops in the evening, check for shadows on the west side. If there is an unusual dip around midday, nearby obstructions such as rooftop structures, piping, air-conditioning equipment, or handrails close to the panels may be casting shadows.

What’s important is to separate variations caused by weather from those caused by shading. On cloudy or rainy days overall power output decreases, but shading tends to appear at specific times of day or on specific surfaces. Even when looking at data from sunny days, if output drops unnaturally during a particular time period you should suspect shading or equipment problems. If the power output curve is not smooth and dips at similar times every day, the likelihood of shading increases.

If data for each installation surface is available, assessment becomes even easier. If the overall power generation is not low but only a specific roof surface or a particular circuit is underperforming, focus on checking whether that area is shaded. When the south-facing side is normal but only the east-facing side is low, or only a particular row is low, inspecting on-site obstacles and the direction of shadows makes it easier to identify the cause.

When considering ways to increase power generation, data analysis is the starting point for countermeasures. If you can identify the months, time periods, and installation surfaces suspected of being shaded, on-site inspections become more efficient and unnecessary measures can be avoided. Shade countermeasures should be based on generation data, not on intuition.

Point 2: Check shadows from rooftop equipment and surrounding buildings

The next thing to check for shading is shadows from rooftop equipment and nearby buildings. For rooftop solar installations, equipment around the panels can cast more shadow than expected. Air-conditioning units, piping, rooftop penthouses, ventilation equipment, railings, lightning protection equipment, antennas, and inspection structures can cast shadows on the panels depending on the time of day and the season.

Shadows from rooftop equipment can affect power generation even over a short period because the equipment is located close to the panels. In particular, when tall equipment is situated very near the panels, shadows lengthen during times of low solar elevation. Shadows from rooftop equipment can be difficult to assess accurately from installation drawings or photos alone. Unless the equipment’s height, position, distance to the panels, and the sun’s direction are confirmed, the extent of the shadow cannot be determined.

Shadows from nearby buildings are also important. If adjacent buildings or tall structures are close, they can cast long shadows in the mornings and evenings or during winter. Even if the roof surface itself faces south and conditions are good, if the period during which shadows from surrounding buildings fall on it is long, the amount of power generated may be lower than expected. In urban areas and densely built-up locations, it is important not to underestimate the shadows from surrounding buildings.

As a mitigation measure, first identify the source of the shading. Determine which equipment is casting shadows on which panels and at what times. Areas where shading has a significant impact may be treated as exclusion zones when changing the layout or during system expansion. For existing installations it may be difficult to relocate surrounding equipment, but organizing the power generation data and the positions of the shadows makes it easier to explain the causes of reduced power output.

When checking shadows cast by rooftop equipment, we also consider maintenance access routes. Equipment that causes shadows is also subject to inspection and repair. If solar panels are placed too close to existing equipment, it not only makes inspections and repairs more difficult but also increases the likelihood that the panels will be affected by shading. Even when adding panels to boost power generation, it is important to leave adequate clearance around rooftop equipment.

Shadows cast by rooftop equipment and surrounding buildings are a direct cause of reduced power generation. To increase power generation, it is necessary to identify the sources of shading, assess their impact on generation, and review placement and management methods.

Point 3: Focus on shadows in winter and during mornings and evenings

One thing often overlooked in shadow mitigation is shadows in winter and during mornings and evenings. Even if a site appears shadow-free in the summer daytime, shadows can lengthen in winter and at dawn or dusk and fall on the panels. When considering ways to increase power generation, it is important not to judge shadows based on a single time of day, but to check them across seasons and times of day.

In winter, because the sun's altitude is low, shadows from surrounding buildings, trees, and rooftop equipment become long. Shadows that did not reach the panels in summer may cover a wide area in winter. If winter power generation is lower than expected, you should not simply assume it is due to shorter daylight hours; you need to check for winter shadows.

Shadows in the morning and evening also affect power generation. In the morning, obstacles on the east side are more likely to cast shadows, while in the evening, obstacles on the west side are more likely to do so. Morning and evening generation is often lower than around midday, but it can be important from the perspective of self-consumption. For example, if a facility starts operating in the morning and its power demand is high, reduced morning generation due to shading can affect efforts to reduce purchased electricity. For facilities with high demand in the afternoon, shadows on the west side can be problematic.

Viewing power generation data by time of day makes it easier to identify shading in winter and during mornings and evenings. Even on sunny days, if generation drops at the same time every day, shading may be the cause. If generation falls at the same time only in a particular season, seasonal shading is suspected. It is important to check whether the decreases in generation occur in a similar pattern each day.

As a mitigation measure, identify the areas that are shaded during winter and in the morning and evening, and assess whether they have a significant impact on power generation. For existing installations, major layout changes may be difficult, but tree management, reviewing the planned scope of future expansions, updating generation simulations, and reflecting the findings in maintenance plans are possible. For new installations or expansions, deciding panel layouts with winter shading in mind makes it easier to prevent a decline in power generation after installation.

When planning shade mitigation, pay attention to the time of day when you inspect the site. It's important to check not only during clear daytime but also while accounting for shadows in the mornings, evenings, and in winter. Not overlooking winter and morning/evening shadows is a crucial point for increasing power generation.

Point 4: Don't Overlook Shadows from Tree and Vegetation Growth

Shadows cast by trees and plantings are also a common cause of reduced power generation. Unlike buildings or rooftop equipment, trees grow over time, so areas that had little shading at installation can affect power output after a few years. When considering ways to increase power generation, it's important to check not only current trees but also their future growth.

The shadows of trees also change with the seasons. For deciduous trees, the darkness of the shadow varies between the season when leaves are present and the season when they are absent. Evergreen trees can cast shadows year-round. In summer, dense foliage strengthens the shadows, while in winter, because the sun’s altitude is lower, even bare branches can cast long shadows. How shadows fall varies depending on the tree species, location, height, and distance to the panels.

Trees create not only shade but also effects from fallen leaves and birds. When leaves accumulate on panels, they block sunlight and reduce power generation. In places where birds tend to gather, soiling from bird droppings also occurs. At sites where trees are nearby, shade, fallen leaves, and soiling need to be checked together.

As a mitigation measure, first confirm whether the trees are on the property or on neighboring land. If the trees are on the property and can be managed, consider pruning or branch management. If the trees are on neighboring land and cannot be dealt with freely, reflect their shading impact in the simulation and make the power generation forecast realistic. If the trees are likely to continue growing, manage them as a long-term shading risk.

Also, the appearance of tree shadows changes depending on the timing of the on-site inspection. If you inspect during a season when leaves are sparse, you may overlook the effects of summer shading or the influence of fallen leaves. Conversely, if you only inspect in summer, you may miss shadows caused by the low winter sun. It is important to combine power generation data with on-site inspections to determine which seasons tree shadows are having an impact.

To increase power generation, tree shade should not be treated merely as part of the surrounding environment but as a factor to be managed because it affects generation. By regularly checking the growth of trees and plantings and managing them as needed, it becomes easier to prevent declines in power output.

Point 5: Don’t force adding panels in shaded areas

When you want to increase power generation, you might be tempted to add panels to available roof surfaces or land. However, adding panels into shaded areas by force may not boost generation as much as you expect.

When considering how to increase generation, the important thing is not simply to increase installed capacity, but to place panels where they can generate power most effectively.

If panels are installed in shaded areas, the total installed capacity increases. Therefore, the simulated annual generation may also appear to increase. However, in locations where shading lasts for long periods, the generation per unit of capacity may be lower. It can happen that, although the installed capacity has increased, the actual generation and self-consumption do not increase as much as expected.

Particularly, areas that experience strong shading in winter or during mornings and evenings require attention. For facilities with high demand in winter, winter power generation is important. For facilities with high electricity demand in the morning or afternoon, morning and evening shading affects self-consumption. If the purpose of increasing generation is to reduce electricity bills or the amount of purchased electricity, it is important to check the overlap between shaded time periods and facility demand.

As countermeasures, you can exclude areas with heavy shading from the installation target, prioritize surfaces with less shading, and prioritize shadow-mitigation measures and cleaning of existing equipment over adding panels. Even when increasing capacity to raise power generation, check the generation per unit of capacity and judge whether the impact of shading is too great.

Also, deciding to avoid shaded areas entirely is not always the correct choice. If the shading is temporary and has little impact on power generation, or if there is little shading during the times when the generated electricity can be used effectively, those areas can still be utilized. The important thing is not to increase the number of panels without understanding the effects of shading.

To increase power generation, you must identify where to add capacity before increasing equipment capacity. Rather than forcibly adding panels in shaded areas, it is more effective to accurately pinpoint areas with favorable conditions and arrange them in a layout that maximizes generation efficiency and maintainability.

Point 6: Check for temporary shading from fallen leaves, snow, and dirt

When people think about shading, they tend to imagine shadows cast by buildings or trees, but fallen leaves, snow accumulation, and dirt temporarily covering the panel surface can also cause reductions in power output. These are not strictly shadows, but in terms of blocking sunlight their effect on power generation is similar. To increase power output, you need to check not only fixed shadows but also seasonal and temporary obstructions.

Fallen leaves are a common issue for roofs and land located near trees. Not only in autumn, but on windy days and after pruning leaves can also accumulate on panels. If leaves are dry and are blown away quickly, the impact may be small; however, if they become wet from rain and stick to the panel surface or collect at the lower edge of the panels, they can affect power generation. When leaves build up around drains, they can also affect building maintenance.

Snow accumulation is a major factor that greatly reduces power generation in winter. When snow covers the surface of panels, they cannot receive sunlight, causing periods when no electricity is generated. Not only the time it is snowing but also the time snow remains after a snowfall is important. If the roof pitch is shallow, snow may be less likely to slide off. Even after snow has slid off, it can accumulate at the lower part of the panels or around them and cast shadows.

Also check for soiling as a temporary obstruction. When bird droppings, sand and dust, pollen, exhaust-derived dirt, or other particulates adhere to the panel surface, light is less able to reach it. Because soiling often accumulates gradually, the decrease in power output progresses slowly and may go unnoticed. If only a particular surface shows lower power output, check whether that surface is in conditions that make it more prone to soiling.

As a countermeasure, it is effective to set inspection timings by season. During seasons with many fallen leaves, after snowfall, in periods with high pollen or dust, and in times when birds are likely to cause issues, check power generation data and on-site conditions. If cleaning or removal is necessary, prioritize safety and choose methods that will not damage the panels or the roof.

Fallen leaves, snowfall, and dirt can be seasonal and occur only at certain times, unlike fixed shadows. However, because they can recur every year, they are important for managing power output. To increase power generation, check not only visible shadows but also temporary factors that obstruct the panel surface.

Point 7: Verify power generation after shadow mitigation with data

Shadow mitigation does not end with implementation. It is important to verify with data how much power generation has improved after the measures. Even if you remove the causes of shading, manage trees, or revise the layout, you cannot judge the effectiveness unless you confirm that power generation has actually improved.

In the evaluation, compare power output before and after the countermeasures. However, simply comparing with the previous or following month is affected by seasonal and weather variations. If possible, compare with the same month in the previous year, sunny days from the same season, simulated values, and time-of-day generation curves. It is important to check whether power output has improved during the time periods when shade-mitigation measures were implemented.

For example, if you manage trees on the east side, check whether morning power generation has improved. If you mitigate shading from obstacles on the west side, check evening power generation. If you arrange the layout to avoid shadows around rooftop equipment, see whether the generation curve around midday has become smoother. The effectiveness of shading measures is easier to understand if you check not only the annual total but also the time periods when shading occurred.

Also check not only power generation but also self-consumption. Even if power generation increases due to shading countermeasures, if that increase only becomes surplus, the improvement in the effectiveness of the installation will be limited. Check whether generation is increasing during the facility’s demand hours, or whether self-consumption is increasing. It is important to distinguish between improvements in power generation and improvements in the installation’s effectiveness.

If you record data after implementing shading countermeasures, it will help inform future improvement decisions. If you can determine how much effect each measure had, you can apply them to other roof surfaces and equipment. If the effect is small, recheck causes other than shading, such as soiling, thermal losses, equipment condition, wiring, or snow accumulation.

To increase power output, it's important to repeatedly implement countermeasures and verify them. Shading countermeasures should not be left to intuition; confirming their effectiveness with generation data turns them into practical, actionable improvements for field operations.

Checking when power generation does not increase with shading countermeasures alone

If you implement shading countermeasures but power generation does not increase as much as expected, you need to check causes other than shading. Power generation declines are often caused by multiple overlapping factors, and even if you only improve shading, you may not see the expected improvement if soiling, temperature losses, equipment faults, wiring losses, snow accumulation, or aging remain.

The first thing to check is dirt on the panel surface. Even if you reduce shading, if sand and dust, pollen, fallen leaves, bird droppings, or other particulate matter adhere to the panel surface, it cannot receive sufficient sunlight. If power output remains low after shading countermeasures, check whether dirt is still present on the same surface.

Next, check for temperature-related losses. In summer, even with high solar irradiance, power output can decrease because panel temperatures rise. Even if reducing shading increases solar irradiance, in environments where panel temperatures tend to be high, energy generation may not increase as much as expected. Check roof ventilation, the space behind the panels, and heat buildup from nearby equipment.

The condition of equipment and wiring should also be inspected. If power output is low across the board, rather than only during certain times or on specific arrays, check the power conversion equipment, wiring, connections, and output limitations. If only some systems are showing low power output, there may be a fault in the equipment or wiring of those systems.

In snowy areas, the effects of snow and lingering snow should also be considered. Even if shading countermeasures are implemented, if snow remains on the panels during winter, power generation will decrease. Check the snow drop-off area and snow storage space, and whether snow is casting shadows on the lower parts of the panels. Fallen leaves and dirt are likewise factors that can obstruct the panel surface.

Also check that you are not confusing power generation with self-consumption. Even if generation improves, if the additional output is not used within the facility and becomes surplus, the practical effect may seem small. It is important to separate and check power generation, self-consumption, and surplus electricity.

Shading countermeasures are an effective means of improving power generation, but they are not a panacea.

If power generation does not increase, it is important to check other causes of generation loss in sequence and address them in combination.

Summary

When considering how to increase power generation, shading mitigation should be the first important point to check. Shadows are caused by surrounding buildings, rooftop equipment, trees, utility poles, slopes, and variations in terrain elevation, and they change with the seasons and time of day. Even if shadows are not noticeable in summer, they can lengthen in winter or during mornings and evenings and reduce power generation. To increase generation, it is essential to first understand where, when, and to what extent shading occurs.

Point 1: Identify suspected shading using monthly and time-of-day data. If power generation is low only in specific months or time periods, suspect shading.

Point 2: Check for shadows from rooftop equipment and nearby buildings. Even small equipment can cast long shadows in winter or in the morning and evening.

Point 3: Focus especially on shadows in winter and during the morning and evening, because periods and times with low sun angles tend to increase the impact of shading.

In Point 4, it is important not to overlook shadows caused by the growth of trees and plantings. Trees grow and create not only shade but also falling leaves and effects from birds.

In Point 5, confirm that panels are not forcibly added into shaded areas. Even if system capacity is increased, generation per unit of capacity may be lower in heavily shaded zones.

In Point 6, check for temporary obstructions from falling leaves, snow accumulation, and soiling. These also block sunlight and lead to reduced power generation.

In Point 7, verify post-mitigation generation with data. Compare monthly and time-of-day generation before and after the measures to confirm whether there has been an actual improvement.

If generation does not increase with shading countermeasures alone, also check for soiling, temperature losses, equipment faults, wiring issues, snow accumulation, system degradation, and mismatches with self-consumption. Because drops in generation are often caused by multiple overlapping factors, it is important not to limit consideration to shading alone but to combine data analysis with on-site inspection to isolate the causes.

And to carry out shade mitigation measures accurately, precise on-site information is indispensable. If the installation area, rooftop equipment, obstacles, trees, site boundaries, orientation, slope, and inspection access routes can be accurately identified, it becomes easier to pinpoint the causes of shading and to devise measures to increase power generation.

If you want to accurately record on-site installation extents, obstacles, trees, rooftop equipment, site boundaries, orientation, slope, inspection routes, and so on, and advance power generation improvement through shade mitigation, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. By obtaining high-precision location information on site, it becomes easier to organize the causes of shading, feasible installation areas, maintenance routes, and positions of surrounding obstructions, and you can more seamlessly proceed from on-site verification for power generation improvement to simulation comparisons and post-installation performance management. To consider increasing power generation through shade mitigation, it is important not to rely solely on desk-based assumptions but to accurately grasp the site and appropriately address the shading causes that are reducing power generation.