8 Points to Review: Tilt, Orientation, and Shading to Increase Power Generation

When you want to increase the power output of a solar PV system, focusing only on the number of panels or the system capacity can sometimes fail to deliver the expected improvement. Actual generation varies greatly depending on the tilt angle at which panels are installed, the azimuth (orientation) they face, and the times of day when they receive shading. Furthermore, even when reassessing tilt and orientation, you need to consider inter-row shading, soiling, snow accumulation, wind, maintenance access routes, and the facility’s hours of electricity use. This article, aimed at practitioners searching for "how to increase power generation", explains in eight points the tilt, azimuth, and shading review items you should check to raise generation.

Table of Contents

• To increase power generation, consider angle, orientation, and shading together

• Item 1: Accurately confirm the orientation of the roof surface or installation surface

• Item 2: Cross-check the power generation time windows for each orientation with facility demand

• Item 3: Examine how the tilt angle affects monthly power generation

• Item 4: Check the balance between inter-row shading and the number of panels that can be installed

• Item 5: Pay special attention to shading in winter and during mornings and evenings

• Item 6: Check shading from rooftop equipment, trees, and surrounding buildings

• Item 7: Consider the effects of soiling, snow, and wind together with angle

• Item 8: Verify power generation after layout changes with data

• Decisions to avoid when reassessing angle, orientation, and shading

• Summary

To increase power generation, consider angle, orientation, and shading together

To increase the power output of a solar PV system, it is important to check angle, orientation, and shading together rather than separately. Even if the panel tilt is good, if the orientation does not match the facility's demand periods it will be difficult to boost self-consumption. Even on near-south-facing surfaces, generation drops if they are shaded in winter or in the morning and evening. Even in locations with little shading, if the tilt is too small so that dirt or snow easily remains, maintaining long-term generation becomes challenging.

A common oversight when considering how to increase power generation is the difference between maximum generation capacity and the generation that can actually be used. A layout that maximizes annual generation does not necessarily maximize the effectiveness of the installation. For facilities that prioritize self-consumption, it is important that electricity is generated during the hours when it can be used on-site. For facilities with high demand in the morning, east-facing generation can be effective, while for those with high demand in the afternoon, west-facing generation may work better.

Also, increasing the angle does not necessarily always increase power generation. Increasing the tilt angle can make panels receive more sunlight in winter, but it can also cause shadows on the front and rear rows of panels or make them more vulnerable to wind. Decreasing the angle can make it easier to install more panels, but dirt and snow may be more likely to remain. To increase power output, you need to consider not only short-term generation but also the conditions that allow stable generation over the long term.

The same goes for shadows. The impact of shading cannot be judged from a single site visit. Even if there is little shading during summer daytime, long shadows in winter mornings and evenings can fall on the panels. Trees grow, rooftop equipment is added, and the surrounding environment changes. Therefore, when reviewing measures to increase power generation, it is essential to combine generation data with on-site inspections.

Reviewing angles, orientation, and shading is not just a matter of design theory. It is practical work: analyzing power generation data, inspecting the site, considering placement to match the facility’s electricity usage periods, and ensuring the system will be maintainable after installation. From here, we will explain, in order, the eight specific items you should check to increase power generation.

Item 1: Accurately confirm the orientation of the roof and mounting surfaces

The first item to check is the orientation of the roof planes and installation surfaces. The direction the solar panels face affects both annual energy production and time-of-day generation profiles. Surfaces closer to south tend to yield higher annual generation, but east- and west-facing surfaces also have roles. To increase output, it is important not to treat the entire building as a single orientation, but to verify the orientation of each roof plane and each installation surface.

In gable and hip roofs, multiple roof planes face different orientations. Even for the large roofs of factories and warehouses, flat roofs, corrugated metal roofs, and ground-mounted installations, the way each section receives solar radiation can vary. Even if a building appears to face south overall, it may actually include a mix of southeast-, southwest-, east-, and west-facing surfaces. If you look at power generation with orientation left ambiguous, you cannot tell which surface is contributing to the generation.

When checking orientation, it is important to verify it not only from the drawings but also on site. Drawings may be misaligned with the actual building layout, or there may be additional equipment or obstructions on site. By recording the orientation, tilt, and available installation area for each roof surface, you will make it easier to confirm the assumptions used in power generation simulations and contractor proposals.

For existing installations, we also check generation data by orientation. If the south-facing surface is not generating as much as expected, there may be shading, soiling, or equipment faults. If the east-facing surface is effectively generating in the morning, it may match the facility's morning demand. The west-facing surface may contribute to afternoon demand. It is important to view orientation not only in terms of generation amount but together with the generation time periods.

To increase power generation, you need to determine which surfaces to prioritize. Prioritizing surfaces that are close to south-facing with minimal shading, east- and west-facing surfaces that align with demand periods, and surfaces that are easy to maintain will make it easier to improve both generation and self-consumption. Checking orientation is the foundational task before reviewing angles and shading.

Item 2: Match generation time periods by orientation with facility demand

The second item is to match the generation time windows for each orientation with the facility's electricity usage patterns. Even if you increase the amount of power generated, if the electricity generated cannot be used within the facility, the benefits of installation may be limited. It is important to check not only the total power generation but also when it is being generated.

Surfaces that face nearly south tend to generate more electricity around midday. In facilities with high daytime demand for air conditioning, lighting, production equipment, and office work, south-facing generation is more likely to be consumed on-site. Conversely, in facilities with low demand around midday, increased south-facing generation can lead to greater surplus energy.

East-facing surfaces tend to generate electricity in the morning. For factories, warehouses, shops, and offices that start operating in the morning, east-facing generation may match the facility's startup demand. West-facing surfaces tend to generate electricity in the afternoon. In facilities where cooling loads increase in the afternoon or that operate through the evening, west-facing generation can contribute to self-consumption.

Thus, evaluating orientation solely by whether it faces south is insufficient. You should check when the facility uses electricity and overlay which panel orientations are generating during those time periods. Even if generation is high, if it does not align with demand it will result in surplus. In practice, it is very important to verify whether increases in generation lead to increases in self‑consumption.

Overlaying generation and consumption by time of day reveals where improvements are needed. If the amount of electricity purchased is large in the morning but east-facing generation is weak, check for shading or layout on the east side. If the amount purchased is large in the afternoon but west-facing generation is weak, check for shading or equipment condition on the west side. If there is a large surplus around midday, simply increasing south-facing generation may have only limited effect.

When reviewing tilt and orientation to increase power generation, consider total generation and self-consumption separately. The orientation that maximizes generation may differ from the orientation that is most convenient for facility use. By matching generation time periods with facility demand, it becomes easier to translate generation improvements into better implementation outcomes.

Item 3: Examine the effect of tilt angle on monthly power generation

The third item is to examine how the tilt angle affects monthly power generation. The tilt angle of solar panels determines which seasons they receive sunlight more effectively. Adjusting the angle can sometimes improve generation, but evaluating only annual generation may cause you to miss seasonal differences.

In winter, because the sun's altitude is low, having some tilt can make it easier to receive solar radiation. Conversely, in summer the sun's altitude is high and solar radiation is greater, so how power generation varies with angle differs from winter. If a facility's electricity demand is high in winter, winter generation should be prioritized. If cooling demand is large in summer, summer generation and temperature-related losses should be evaluated together.

When reassessing the tilt angle, compare the annual energy yield, monthly energy yield, winter energy yield, and summer energy yield separately. Even if the annual total shows little difference, the tilt that improves winter yield may differ from the tilt that tends to increase summer yield. If you do not clearly identify which season's generation you want to increase, it will be difficult to judge the practical effect.

Also, the tilt angle affects soiling and snow. At low angles, dust, pollen, leaves, and snow are more likely to remain. At steeper angles, snow may slide off more easily, but you need to check where the snow will fall and the space available for snow accumulation. It’s important not only for power generation but also whether the angle makes it easy to maintain the surface condition.

On existing roofs, installations are often aligned with the roof pitch, so the tilt angle can be difficult to change easily. Even in such cases, knowing the tilt angle makes it easier to understand the causes of reduced power output. For surfaces with a shallow pitch where dirt tends to remain, strengthen cleaning schedules; for surfaces where snow tends to persist in winter, perform checks after snowfall—these measures can be used to guide maintenance.

The tilt angle is not simply a design parameter for improving power generation efficiency. It is a management factor related to monthly power generation, soiling, snow accumulation, and maintainability. To increase power generation, it is important to check the angle in conjunction with seasonal power output.

Item 4: Check the balance between inter-row shading and the number of panels that can be installed

The fourth item is the balance between inter-row shading and the number of panels that can be installed. On flat roofs and ground-mounted installations, panels are sometimes arranged in multiple rows. In such cases, inter-row shading can occur, with panels in the front row casting shadows on panels in the rear rows. Increasing the tilt angle can make the panels more exposed to sunlight, but it can also lengthen the inter-row shading.

To avoid inter-row shading, it is necessary to increase the spacing between front and back panels. However, widening the spacing can reduce the number of panels that can be installed on the same roof or land area. Even if increasing the tilt angle raises the output per panel, if the number of installed panels decreases, the total system output may not increase as much as expected.

Conversely, reducing the tilt angle and increasing the number of panels makes it easier to increase the total installed capacity. However, shallower angles can make it more likely for dirt and snow to remain, which also affects seasonal power generation. In other words, to increase generation you need to comprehensively compare tilt angle, inter-row shading, number of panels, susceptibility to soiling, and maintainability.

Inter-row shading tends to be particularly problematic in winter and during mornings and evenings. When the sun's elevation is low, shadows from the front rows easily extend to the rear rows. Increasing the tilt angle to try to improve winter generation can actually increase inter-row shading and reduce the output of the rear rows. When considering changes to tilt angle or layout, always check for inter-row shading in winter.

When performing power generation simulations, we examine how the number of installed panels changes when the tilt angle is altered for the same installation area. In addition to annual generation, we also check monthly generation, generation per capacity, the times when inter-row shading occurs, and maintenance access routes. Maximizing generation is neither about cramming panels together nor about increasing the tilt angle. It is about finding the balance that yields the highest effective generation for the site conditions.

Item 5: Pay special attention to shadows in winter and during mornings and evenings

The fifth item is checking shadows in winter and in the mornings and evenings. The impact of shading cannot be judged from just one site visit. Even if there appears to be little shading during summer daytime, long shadows can fall on the panels in winter or in the mornings and evenings. To increase power generation, it is necessary to focus on checking the conditions that are likely to cause shading.

In winter, because the sun's altitude is lower, shadows from surrounding buildings, trees, and rooftop equipment extend farther. Panels that were not shaded in summer may become shaded in winter. If winter power generation drops significantly, check not only the shorter hours of sunlight but also the extent of winter shading.

Morning and evening are times when shadows tend to lengthen. In the morning, shadows from buildings, trees, utility poles, and equipment on the east side are more likely to appear, while in the evening shadows on the west side tend to be problematic. If a facility's power demand is high in the morning or afternoon, morning and evening shadows can also affect self-consumption. It is important to check not only the total amount of power generation but also whether shadows are cast during the demand periods.

Viewing generation data by time of day makes it easier to detect suspected shading. If generation drops at the same time every day even on sunny days, shading or equipment conditions may be involved. Check for trends such as a slow morning ramp-up, an early drop in the evening, or an unnatural dip around midday.

During on-site shadow inspections, pay attention to the time periods when power generation data shows a decline. If output is low in the morning, check the east side; if it's low in the evening, check the west side; if it's low in winter, check for obstacles that cast long shadows at low solar elevations. If you record the cause of the shadow, the area affected, and the times when shadows occur, you can use that information when revising the layout or deciding on expansions.

Shadows in winter and in the morning and evening are an important but easily overlooked factor in increasing power generation. When improving power output, it is essential to check not only midday, when generation is highest, but also the times of day and seasons when shadows lengthen.

Item 6: Check for shadows caused by rooftop equipment, trees, and surrounding buildings

The sixth item is to specifically identify the sources of shading. Shading can result from rooftop equipment, trees, or surrounding buildings. Because each type casts shade differently and varies in how easily it can be mitigated, they need to be categorized by cause to increase power generation.

Rooftop equipment includes rooftop penthouses, air-conditioning equipment, piping, ventilation equipment, handrails, antennas, and inspection structures. These are often located close to panels and can cast strong shadows even over short periods. Especially in winter and in the morning and evening, even low-lying equipment can cast long shadows. On the roof, it is important to check the equipment’s height, position, and distance from the panels.

Trees change the shadows they cast as they grow. Trees that produced little shade when first planted may, after several years, extend their branches and leaves and cast shade on panels. Evergreen trees can create shade year-round, and even deciduous trees produce denser shade during the seasons when they have leaves. Trees can cause not only shade but also fallen leaves and bird droppings. If the trees can be managed on-site, consider pruning and other maintenance.

Shadows cast by surrounding buildings can be difficult to deal with freely. If there are adjacent buildings or tall structures, they can create long shadows, especially in the morning and evening and during winter. Shadows that cannot be removed by the company should be accounted for as an assumption when estimating power generation. When adding capacity or changing the layout, it is necessary to avoid areas that are heavily affected by shadows from surrounding buildings.

When checking for shading, determine whether the cause of the shading is controllable. If it is controllable, consider pruning, changing the layout, and ensuring clearance around equipment. If it is not controllable, incorporate it into the power generation simulation and set expectations realistically. Ignoring shading and expecting high output can lead to the problem of actual generation being lower than expected after installation.

By clearly identifying the causes of shading, it becomes easier to determine the priority of countermeasures. To increase power generation, rather than viewing shadows vaguely, it is important to understand which obstacles are casting shadows on which surfaces at which times of day.

Item 7: Consider the effects of dirt, snow accumulation, and wind together with angle

The seventh point is to consider the effects of dirt, snow accumulation, and wind together with the tilt angle. When reviewing the tilt and orientation to increase power generation, people tend to focus only on how sunlight is received, but in practice it is also important whether the panel surface can be kept in good condition and whether it can cope with snow and wind.

When the tilt angle is small, sandy dust, pollen, yellow sand, fallen leaves, bird droppings, and particulate matter tend to remain. Some dirt will be washed away by rain, but when the tilt angle is small, water does not run off easily, and dirt can accumulate at the lower edge of the panels and around the frames. When dirt accumulates, power generation decreases even under the same solar irradiance conditions.

In snowy regions, the angle affects how snow accumulates and remains. A smaller angle makes snow more likely to stay, which can lengthen the periods when power generation is not possible. Increasing the angle can make snow more likely to slide off, but you need to check where the snow will fall and the space for piled snow. If the fallen snow affects walkways, equipment, or neighboring properties, another problem can arise.

The effect of wind cannot be ignored. Increasing the angle can increase the surface area exposed to wind. On rooftops or in open terrain, consideration for wind is necessary. Changing the angle to increase power output must not create problems with safety, constructability, or maintainability. When changing the angle, it is necessary to consider not only power output but also wind, mounting conditions, and ease of inspection comprehensively.

Dirt, snowfall, and wind can be difficult to capture when calculating annual power generation alone. Even if the first year’s generation appears high, a layout that tends to retain dirt, does not shed snow easily, or is difficult to maintain may lead to a long-term decline in generation. To increase generation, it is necessary to consider both short-term generation and long-term maintenance.

When reviewing angle, orientation, and shading, check not only the conditions for receiving sunlight but also the conditions that reduce factors that obstruct sunlight. Choosing an arrangement and tilt that keep the panel surface in good condition will lead to improved power generation.

Item 8: Verify the power output after layout changes using data

The eighth item is to verify the power generation after layout changes using data. Reviewing angle, orientation, and shading is not completed simply by implementing the changes. After carrying out layout changes, cleaning, shading countermeasures, tree management, expansion, etc., it is necessary to confirm whether the actual power generation has improved.

In verification, we compare the power generation before and after the change. However, because power generation naturally varies with weather and seasons, simply comparing to the previous day or the next month is insufficient. We compare using similar sunny days, the same month of the previous year, the same time periods, the same installation surface, and the same system. It is important to focus on and check the time periods and surfaces that should have improved due to the layout change.

For example, if you adopt a placement that avoids shadows on the east side, check whether morning power generation has improved. If you increase west-facing placements, check afternoon power generation and self-consumption. When you change the tilt angle, also check monthly power generation, how soiling persists, and recovery after snowfall. If you implement shadow-mitigation measures, look at whether the generation curve during the hours when shadows occurred has improved.

Check not only generation but also self-consumption and surplus electricity. If generation increases but the additional output simply becomes surplus, the improvement in the installation’s effectiveness is limited. If the purpose of increasing generation is to reduce purchased electricity, it is important to verify whether the increased generation is being used within the facility.

Keep a record of your verification results. If you document the changes made, implementation date, scope, on-site photos, changes in power output, shadow variations, and the condition of soiling or snow cover, you can use them to inform future improvement decisions. Improving power output is not completed in a single review. Site conditions change, and seasonal challenges recur. Continuously validating with data increases the accuracy of improvements.

Decisions to Avoid When Reassessing Angles, Orientations, and Shadows

When reassessing angle, orientation, and shading, you should avoid simply adopting angles and orientations that are generally considered good. While a layout close to south-facing or a consistent tilt angle can be advantageous in some cases, the optimal conditions change depending on local conditions, shading, facility demand, snowfall, wind, and ease of maintenance. If you base decisions only on generalities, actual power generation and the effectiveness of the installation may fall short.

Also, you should avoid judging solely by annual power generation. Even if annual generation increases, if generation is concentrated during periods when the facility cannot use it, surplus may increase. If you prioritize self-consumption, you need to check monthly generation, time-of-day generation, self-consumption amounts, and surplus electricity separately.

Underestimating shadows can be dangerous. If you judge there is no problem because there is little shade during summer daytime, you may overlook shadows in winter or at dawn and dusk. Forcibly adding panels to shaded areas may increase installed capacity but can reduce power generation per unit of capacity. To increase power output, you need to prioritize areas with less shading.

You should also avoid making decisions that sacrifice maintainability. Even if changing angles or layouts increases power generation, if inspections and cleaning become difficult, it will be harder to sustain power output over the long term. It is important to compare power generation after ensuring inspection routes, drainage, equipment access, and ease of cleaning.

You should also avoid making judgments based solely on a desktop layout without on-site verification. There are obstacles, shadows, piping, equipment, trees, terrain, slopes, and drainage that cannot be discerned from drawings. Reviews of angles, orientation, and shading need to be carried out by combining power generation data with on-site verification.

Summary

When reviewing angle, orientation, and shading to increase power generation, it is important to comprehensively check the orientation of the mounting surface, its relationship with facility demand, the tilt angle, inter-row shading, winter and morning/evening shadows, shading from rooftop equipment and trees, soiling and snow accumulation, and verification of power generation after layout changes. Judging angle alone, orientation alone, or shading alone is unlikely to lead to practical improvements.

In Item 1, we accurately confirm the orientation of the roof and mounting surfaces. In Item 2, we compare the power generation time periods for each orientation with the facility's demand. In Item 3, we examine the impact of the tilt angle on monthly power generation. In Item 4, we check the balance between inter-row shading and the number of panels that can be installed. In Item 5, we focus on shadows in winter and during the morning and evening. In Item 6, we check shadows from rooftop equipment, trees, and surrounding buildings. In Item 7, we consider the effects of soiling, snow accumulation, and wind together with the tilt angle. In Item 8, we validate the power generation after layout changes using data.

When reviewing tilt, orientation, and shading, avoid simply applying generic optimal settings, judging solely by annual energy production, or downplaying shading and maintainability. To increase generation, you must choose conditions tailored to the local site that make generation easier, are practical for facility use, and are easy to manage over the long term.

And to accurately reassess angles, orientation, and shading, the accuracy of on-site information is indispensable. If you can accurately grasp the installation area, rooftop equipment, obstructions, trees, site boundaries, orientation, slope, inspection routes, and candidate connection points, it becomes easier to sort out the causes that are reducing power generation.

If you want to accurately record on-site installation areas, obstacles, trees, rooftop equipment, site boundaries, orientation, slope, inspection routes, and so on, and efficiently advance power-generation improvements by reviewing angles, orientation, and shading, using LRTK — an iPhone-mounted GNSS high-precision positioning device — is effective. By obtaining highly accurate on-site location information, it becomes easier to organize roof and land orientation, slope, causes of shading, installable area, wiring routes, and maintenance access, and to carry out on-site verification, simulation comparisons, and post-installation performance management for power-generation improvements in an integrated way. When reviewing angles, orientation, and shading to increase power generation, it is important not to judge based solely on general desk-based theory, but to accurately grasp the site and translate that understanding into conditions that improve both generation and self-consumption.