# Table of Contents

• The mindset to prevent power shortfalls in solar power generation simulations

• First organize the main causes of power shortfalls

• Misreading insolation data makes simulations prone to error

• Verify orientation and tilt angle according to on-site conditions

• View shadow impacts by time of day and season, not just annually

• Consider actual generation conditions, not only panel capacity

• Account for losses from power conditioners and grid conditions

• Do not underestimate temperature rise and aging degradation

• Reflect region-specific risks such as snow and soiling

• In self-consumption systems, check mismatches with demand patterns

• Link simulation results to maintenance plans and operational improvements

• Improve the accuracy of on-site measurements to prevent shortfalls

• Summary

# The mindset to prevent power shortfalls in solar power generation simulations

Solar power generation simulations are not merely work to predict annual generation. In practice, it is important to use them as a means of verification to prevent issues after installation such as “not generating as expected,” “actual results not matching the business plan,” or “insufficient electricity available for self-consumption.” In other words, the purpose of simulation is not to produce a high generation figure but to correctly interpret on-site conditions, avoid overestimation, and identify potential generation shortfalls in advance.

Solar generation is not determined by system capacity alone. Even with the same panel capacity, actual generation can vary greatly depending on regional insolation, roof or land orientation, tilt angle, shadows from surrounding buildings or trees, panel temperature, wiring losses, equipment conversion losses, aging degradation, and the effects of snow or soiling. To prevent generation shortfalls with simulation, these conditions need to be input as realistically as possible, and results should be read not as “average values” but as “projections that include risks.”

What practitioners should be particularly careful about is not to judge simulation results by a single number. Even if annual generation looks sufficient, monthly figures may fall sharply in winter. Even if monthly figures show no problem, generation in the morning and evening could be weaker than expected, preventing self-consumption rates from rising. Also, even if the first year after installation meets expectations, generation shortfalls may emerge years later due to changes in the surrounding environment or equipment degradation. Preventing generation shortfalls requires checking from multiple perspectives: annual, monthly, hourly, seasonal, and long-term operation.

Solar power generation simulations play different roles at each stage: before design, before proposal, before investment decision, before construction, and after operation begins. Before design, they are used to compare candidate sites; before proposals, to explain expected values and risks; before investment decisions, to confirm the safety of financial projections; before construction, to finalize layout and equipment selection; and after operation begins, to serve as the baseline for analyzing differences from actual generation. By continuously using simulations from planning through operation, rather than as a one-off task, the ability to prevent generation shortfalls is enhanced.

# First organize the main causes of power shortfalls

To prevent generation shortfalls, you must first classify the causes. The reasons solar generation falls short of expectations can broadly be divided into misreading natural conditions, overestimating design conditions, insufficient site surveys, incorrect equipment performance assumptions, variability in construction quality, and insufficient operation and maintenance. In simulation, it is important to check to what extent each of these elements is reflected.

When misreading natural conditions, insolation and weather trends are often judged only by averages. Even if a region’s annual insolation looks sufficient, areas with long cloudy seasons during the rainy season or winter can see generation drop significantly in particular months. For corporate facilities or factories that want to cover a certain amount of power with solar, installing systems based only on annual totals can mean required power is not available at needed times.

Overestimating design conditions often involves assuming panels can be installed at ideal orientations and angles. Actual roofs may have ridges, steps, equipment, lightning protection, maintenance walkways, and the entire surface may not be freely usable. For ground-mounted systems, constraints may arise from site development conditions, neighboring boundaries, fences, maintenance access, and drainage. Even if a simulation shows an ideal layout, if the layout changes during construction, generation will change as well.

Insufficient site surveys are also a major cause of generation shortfalls. Shadows from surrounding buildings, utility poles, trees, mountain shading, and rooftop equipment can’t always be accurately grasped from drawings alone. In particular, because solar altitude is lower in winter, shadows that were not noticeable during summer checks can affect generation. If simulations do not adequately account for shadow impacts, post-installation shortfalls in morning, evening, or winter generation are likely to be revealed.

Incorrect assumptions about equipment performance require understanding the difference between nameplate output and actual operating conditions. Panel output is given under standard test conditions, so unless site-specific temperature, ventilation, installation method, soiling, wiring distance, and conversion efficiency are reflected, differences from actual generation will occur. Furthermore, if long-term financial planning ignores aging degradation, generation shortfalls several years later may be overlooked.

# Misreading insolation data makes simulations prone to error

Insolation data is the foundation of solar generation simulations. Insolation indicates the amount of solar energy reaching the ground or an inclined surface and is a key factor determining the upper limit of generation. However, you cannot rely on a single insolation number. Since it varies by region, year, season, time of day, terrain, and cloud propensity, results change depending on which data you use and how you interpret it.

To prevent generation shortfalls, first verify that the insolation data used in the simulation reflects conditions close to the planned installation site. Even with the same city or region name, coastal, inland, mountainous, basin, and snowy areas have different insolation tendencies. Using data from a location tens of kilometers away can fail to adequately reflect local cloud formation or fog effects. For large-scale projects or projects where downside risk in generation is a significant concern, using meteorological conditions as close to the installation site as possible is desirable.

It is also important to look at monthly insolation, not only annual averages. Even if annual generation appears sufficient, regions with large winter declines affect not only annual finances but seasonal power supply and demand. For households, heating demand in winter and cooling demand in summer matter; for corporate facilities, the relationship between operating days/hours and generation peaks is important. To prevent generation shortfalls, confirm not simply “how much is generated annually” but “how much is generated when it is needed.”

When examining insolation data, considering years with lower-than-average insolation is also useful. Solar generation is affected by weather, so generation is not the same every year. If planning is based very close to average values, bad-weather years are more likely to cause generation shortfalls. In simulation, in addition to a standard case, check whether the plan holds up under somewhat lower-than-average generation to improve practical safety.

# Verify orientation and tilt angle according to on-site conditions

Panel orientation and tilt angle are fundamental conditions that greatly affect generation. Generally, the closer the orientation and angle are to those that efficiently receive sunlight, the higher the generation. But in practice, roof shapes and site conditions often prevent ideal installations. To prevent generation shortfalls in simulation, accurately input the orientation and tilt angle that can actually be installed, not ideal conditions.

For rooftop installations, the orientation on drawings can differ slightly from the actual orientation. Judging orientation from building layout or roof plans alone can overlook deviations from true north. Although the impact on generation may seem small, when installing across multiple roof surfaces or using east-west faces, orientation input errors affect monthly and hourly generation. Especially when prioritizing self-consumption, consider not only maximizing generation on south-facing surfaces but also how to use east and west faces to match morning and evening demand.

Tilt angles also need to be verified according to on-site conditions. When using actual roof pitch, tilt angles differ by building. For flat roofs and ground mounts, angles can be adjusted with racking, but constraints include strong wind measures, snow measures, shading on adjacent rows, maintenance access, and aesthetic conditions. Even if you set the angle to maximize generation, if shadows increase, the number of installable panels decreases, or maintainability worsens, the overall plan’s rationality may decline.

In discussing orientation and tilt angle, check not only conditions that maximize annual generation but also seasonal generation. Increasing tilt angle can improve winter insolation reception while affecting summer generation and installation efficiency. Reducing tilt can allow more panels to be installed but may inhibit soiling runoff and lead to longer snow retention. In simulation, compare multiple patterns and check not just annual numbers but generation in seasons prone to shortfalls.

# View shadow impacts by time of day and season, not just annually

Confirming shadows is very important for preventing generation shortfalls in solar simulations. Even shadows affecting only part of a panel array can impact generation, and losses depending on the time of day and season can be hard to see from annual figures alone. If rooftop equipment, adjacent buildings, trees, mountains, signs, utility poles, or fences are nearby, carefully evaluate shadow impacts.

Avoid the mistake of visiting a site once and concluding “shadows are not a problem.” The sun’s position changes with the seasons, so shadows that are short in summer can lengthen in winter. A site may be fine in the morning but suffer shadows from adjacent buildings in the afternoon. Conversely, an impact on annual generation may appear small while morning shadows pose a major problem for self-consumption projects expecting morning generation.

In simulation, it is desirable to evaluate shadows not only as an annual loss rate but also by month and time of day. For example, if shadows extend long on winter evenings, the annual impact may seem limited. However, for facilities with high winter power demand, reduced generation at that time directly affects self-consumption plans. To prevent shortfalls, read shadow impacts not only as “what percentage is reduced overall” but as “when, on which surface, and by how much.”

Be careful with tree shadows as well. Even if trees are not a problem at the site survey, growth over several years can increase shading. Deciduous trees also change shading seasonally. Surrounding buildings may also change insolation conditions due to future extensions or neighboring development. While it is difficult to predict everything perfectly, checking the possibility of changes around the site during simulation and allowing margin where necessary contributes to preventing long-term generation shortfalls.

# Consider actual generation conditions, not only panel capacity

In solar planning, people tend to think that larger system capacity means more generation. Capacity is certainly an important metric, but judging generation by capacity alone can miss the risk of shortfalls. Panel capacity indicates output under standard conditions and does not guarantee that such output will be available on site at all times. Actual generation varies with insolation, temperature, installation angle, shadows, equipment efficiency, wiring, and grid conditions.

To prevent generation shortfalls, before increasing installed capacity, check whether there are conditions that make generation difficult. For example, even if panels cover the roof area fully, if parts are prone to shading or orientations are significantly off, generation may not scale with capacity. Increasing panel count can complicate layouts and make wiring or grid configuration inefficient. In simulation, compare a capacity-increased case with cases that prioritize efficiency by avoiding shadows and losses.

Panel layout also relates to maintainability. Narrowing access for the sake of slightly higher generation or installing panels in hard-to-inspect locations makes cleaning and inspection difficult, and over the long term soiling and delayed fault detection can reduce generation. A layout that looks high-performing in initial simulation can lead to operational shortfalls if it is hard to operate and maintain.

When considering panel capacity, examine not only peak generation but operational states throughout the year. If capacity is too large, output may hit limits during favorable conditions, creating generation that cannot be fully utilized. In self-consumption systems, excess generation during times of low demand increases uneconomic hours. To prevent generation shortfalls, design not by simply enlarging capacity but to stably obtain the necessary amount during required times.

# Account for losses from power conditioners and grid conditions

Electricity generated by panels is not directly usable as-is. The generated DC power is converted to AC by power conditioners and sent to building loads or the grid. Conversion losses occur in this process. Losses and constraints also arise from wiring, combiner boxes, protection devices, power receiving and transformation equipment, and grid-interconnection conditions. To prevent generation shortfalls in simulation, check not only panel-side generation but how much electricity is actually usable.

Power conditioner sizing affects generation. If the inverter capacity is smaller than panel capacity, output can be limited during periods of strong insolation. Conversely, selecting an excessively large capacity is not always good; consider low-output efficiency, installation location, maintainability, and operating range. In simulation, it is important to look at generation after conversion to AC, not only the assumed DC-side generation.

Wiring losses cannot be ignored. Longer distances from installation to equipment or complex wiring routes can increase electrical losses. When roofs are divided into multiple faces or ground-mounted systems are distributed across a wide site, wiring planning affects generation efficiency. Even if detailed wiring design is not finalized at the simulation stage, it is important to conservatively evaluate likely losses according to on-site conditions.

Grid conditions can also constrain generation. Even if generation capability exists, grid interconnection conditions or constraints of the facility’s receiving equipment may require output suppression. In self-consumption systems, when loads are low, controls may reduce generation. If such controls occur frequently, differences arise between simulated generation and actually usable energy. To prevent generation shortfalls, consider not only the generation capability of equipment but also the conditions of the power receiving side.

# Do not underestimate temperature rise and aging degradation

While panels tend to generate more with stronger insolation, their output decreases as panel temperature rises. Summer often yields higher generation potential due to more insolation, but roof or ground surface temperature rises, poor ventilation, and installation methods can limit expected generation. To prevent generation shortfalls in simulation, appropriately account for temperature-related output losses.

On rooftops, panel temperature varies with roofing material and ventilation conditions. When the gap with the roof is insufficient or the surrounding structure inhibits airflow, panel temperature tends to increase. For flat roofs and ground mounts, installation height, racking structure, surrounding reflections, and ground conditions change temperature conditions. Even with the same insolation, different temperature conditions cause actual generation to vary, so reflecting site-like conditions in simulation is important.

Aging degradation is also an indispensable perspective to prevent generation shortfalls. Because solar installations are used long-term, judging solely by first-year generation risks misestimating generation several years or a decade later. Solar panels, power conditioners, wiring, connection parts, racking, and protection devices change in performance and condition over time. During planning, estimate not only first-year generation but how much generation will decline over the long term.

Especially for financial projections and self-consumption plans, do not rely too heavily on first-year generation. Even if the first year looks sufficient, considering future generation declines may reveal little margin relative to required energy. In simulation, separate first-year, several-years-later, and long-term operational generation to understand when generation shortfalls may occur.

# Reflect region-specific risks such as snow and soiling

Simulations should reflect region-specific risks. Snow, salt damage, dust, volcanic ash, yellow sand, bird droppings, falling leaves, pollen, and industrial dust can affect generation depending on the region and installation environment. If these factors are not sufficiently accounted for, simulations may show no issues while actual generation falls short.

In snowy regions, consider not only winter insolation but the period panels remain covered by snow. When panels are covered, generation drops substantially during that period. With shallow tilt angles or roof shapes that prevent snow shedding, generation may be unavailable longer than expected. Also, snow fall locations and surrounding safety measures affect design and require operational considerations; conservatively accounting for winter outages and reductions in simulation helps grasp shortfall risks.

Soiling impacts are often overlooked. While some dirt is washed away by rain, low-tilt panels, dusty environments, sites where birds congregate, or areas where leaves accumulate can retain dirt and decrease generation. Even if no problem appears immediately after installation, soiling can accumulate over time and gradually reduce generation. Simulations should account for soiling losses and consider ease of cleaning and inspection.

In coastal or industrial areas, consider salt and dust effects on equipment. These affect not only generation but equipment degradation and connection issues. To prevent generation shortfalls, consider equipment specifications, installation methods, and inspection frequency suited to the local environment, and link simulation results to operational plans. Rather than only looking at generation numbers, confirm whether the environment can maintain those numbers.

# In self-consumption systems, check mismatches with demand patterns

In self-consumption systems, it is important that not only generation amounts but generation timing match consumption timing. Even with high annual generation, if generation concentrates during times of low demand, usable energy is limited. Conversely, if generation is insufficient during high-demand periods, solar’s reduction effect will be smaller than expected. To prevent shortfalls, combine generation simulations with demand data.

For households, ease of self-consumption differs between families often absent during daytime and those at home a lot. For corporate facilities, whether operations are on weekdays or holidays, daytime or nighttime, and whether loads vary seasonally affects solar effectiveness. Factories, warehouses, retail, offices, welfare facilities, and schools all have very different load profiles. In simulation, examine not only annual generation but the overlap of demand and generation curves.

For self-consumption systems, evaluating by time of day as well as by month is effective to prevent shortfalls. Facilities with large daytime cooling loads in summer may align well with solar generation. Conversely, facilities with high evening demand will often face times when solar alone cannot meet needs. Facilities with morning-peaking demand may benefit from using east-facing roofs, increasing practical value even if annual generation is not maximized.

Also, increasing capacity to avoid generation shortfalls can simply increase surpluses if demand does not match. To raise self-consumption rates, consider capacity, orientation, presence of storage, load operation times, and control methods comprehensively. Solar generation simulations should be used not only to confirm equipment performance but also as material to review overall facility power usage, reducing the sense of insufficiency after installation.

# Link simulation results to maintenance plans and operational improvements

To prevent generation shortfalls, do not let simulation remain just a pre-installation prediction. After operation begins, compare actual generation with simulation results and analyze causes when differences arise. If actual generation is less than expected, identify whether the cause is weather, shadows, soiling, equipment faults, or output control to guide countermeasures.

When comparing, it is important to look at not just annual totals but monthly, daily, and hourly data. Even if annual differences are small, a large shortfall in a particular month may indicate seasonal factors, shadows, snow, or soiling. Comparing generation curves on clear days can reveal trends such as partial panel shading, output drops at specific times, or plateaus at equipment limits.

Integration with maintenance planning is also important. Maintaining simulated generation requires inspections, cleaning, equipment checks, connection checks, and management of surrounding trees. Rather than reacting after a shortfall occurs, having mechanisms to detect early signs of generation decline minimizes losses. For managers of multiple facilities, operations that compare simulated and actual values and prioritize inspection of anomalous sites are effective.

Operational improvements can include adjusting loads. In self-consumption systems, shifting some equipment operation to high-generation periods, adjusting HVAC or charging times, and reexamining relationships with demand peaks can increase effective use of generation. Solar generation simulations serve both as materials for installation decisions and as standards for post-operation improvements. Continuously compare plan and actual values and use differences to drive improvements to prevent generation shortfalls.

# Improve the accuracy of on-site measurements to prevent shortfalls

Improving the accuracy of solar generation simulations requires improving input data quality. No matter how advanced the calculations, coarse site understanding yields results that differ from reality. Roof and land dimensions, orientation, tilt, positions of surrounding obstacles, heights of structures causing shadows, installable area, and maintenance access directly affect simulation results.

Running simulations with insufficient on-site measurements can lead to overestimating panel layouts at the design stage, overlooking shadows, or needing layout changes during construction. This can prevent securing the originally expected generation. To prevent generation shortfalls, acquire spatial information on site as accurately as possible early in planning and clarify installable areas and constraints.

For rooftop installations, accurately capture roof shape, pitch, orientation, obstructions, parapets, equipment bases, and inspection hatch positions. For ground mounts, consider site boundaries, elevation differences, development conditions, drainage direction, surrounding structures, trees, fences, and access ways. Estimating generation while leaving these ambiguous causes a mismatch between construction conditions and simulation assumptions, leading to post-installation shortfalls.

Recently, the importance of efficiently acquiring on-site position and shape information and using it in design and simulation has increased. To improve simulation accuracy, reflect accurate coordinates and dimension information obtained on site in design data rather than relying solely on desk-based organization. Especially when comparing multiple candidate sites or when roof/site constraints are complex, the precision of on-site measurement forms the foundation for preventing generation shortfalls.

# Summary

To prevent generation shortfalls in solar power generation simulations, it is important not to look only at annual generation figures but to check the assumptions behind those numbers. Many factors affect generation: insolation data, orientation, tilt angle, shadows, system capacity, conversion losses, wiring losses, temperature rise, aging degradation, snow, soiling, and demand patterns. Overlooking any one of these can lead to post-installation problems of “not generating as expected.”

The basic principle to prevent shortfalls is not to produce maximum values under optimistic conditions but to simulate with realistic assumptions that reflect site conditions. Also check downside scenarios: years with low insolation, winter declines, times of day with significant shadow impact, and post-degradation performance. Visualizing risks at the planning stage allows revising capacity, layout, equipment configuration, maintenance plans, and operation methods.

Simulations should be used not only before installation but also after operation begins. Comparing actual generation with planned values and analyzing differences enables early detection of soiling, shadows, equipment faults, output control, or mismatches with demand. Since solar installations are intended for long-term operation, it is important to continually check and improve generation, not rely only on the first year.

Supporting simulation accuracy is the correctness of on-site information. Accurately grasping roof or site dimensions, orientation, tilt, and obstructions reduces the gap between design assumptions and reality. If you want to streamline on-site measurement and reflect accurate positional information in design and simulation, utilizing LRTK that can be attached to an iPhone for high-precision positioning is effective. This facilitates consistent handling of site surveys for solar installation candidates, roof and site position checks, identification of surrounding obstacles, and pre- and post-construction record management, supporting the creation of on-site data to prevent generation shortfalls.