7 Checks to Prevent Post-Installation Problems in Solar Power Generation Simulations

Solar power generation simulations are important documents for confirming annual generation and self-consumption before installation. However, if you rely on simulation results as-is when proceeding with installation, you may encounter post-installation problems such as “it doesn’t generate as much as expected,” “there is too much surplus power,” “roof or land maintenance is difficult,” or “the cause of generation decline is unknown.” To prevent these issues, it is important not only to look at the generation numbers but also to check calculation assumptions, on-site conditions, constructability, maintainability, and post-installation performance management. This article explains seven points that practitioners searching for “solar power generation simulation” should check to prevent post-installation troubles.

Contents

• Concept for preventing post-installation problems with solar power generation simulations

• Check 1: Confirm that the basis for the annual generation is clear

• Check 2: Confirm monthly generation and seasonal variations

• Check 3: Separate and confirm self-consumption and surplus power

• Check 4: Confirm generation reduction due to shading, orientation, and tilt

• Check 5: Confirm loss rates such as temperature, soiling, and snow

• Check 6: Confirm that constructability and maintainability are realistic

• Check 7: Confirm post-installation performance management methods

• Decisions to avoid to prevent post-installation problems

• Summary

Concept for preventing post-installation problems with solar power generation simulations

Solar power generation simulations are documents for predicting generation before installation. They can show annual generation, monthly generation, system capacity, self-consumption, and surplus power, and are used for installation decisions, internal approvals, and comparing vendors’ proposals. However, simulations are predictions based on assumptions and do not guarantee actual generation after installation.

Many post-installation problems arise not from the simulation results themselves but from insufficient checking of the assumptions. For example: treating the roof or land’s total area as fully usable for installation, not adequately reflecting shading, underestimating losses from temperature and soiling, overestimating daytime demand of the facility, or failing to secure maintenance access.

Problems are not limited to insufficient generation; even if generation occurs, it may not be consumed on-site, surplus power may be excessive, inspections and cleaning may be impossible, roof equipment maintenance may be hindered, or mowing and drainage management on land may be difficult. These issues are hard to see from generation numbers alone.

To prevent post-installation problems, use solar power generation simulations not as materials to “make installation performance look good” but as materials to “identify potential post-installation problems in advance.” The larger the proposed generation, the more carefully you must check why that generation is possible, what area is being used, which losses are assumed, and whether the layout is maintainable.

It is also important to separate initial simulations from those after on-site surveys. Drawings and aerial photos cannot capture roof equipment, piping, drains, trees, slopes, elevation differences, shading, and maintenance paths completely. Recalculate after reflecting conditions found in on-site surveys and check generation based on the final layout to reduce gaps after installation.

The basis for preventing post-installation problems is to separate and confirm generation, usable energy, surplus energy, potentially reducible energy, and manageable scope. Below are seven practical points to check in order.

Check 1: Confirm that the basis for the annual generation is clear

The first check to prevent post-installation problems is whether the basis for the annual generation is clear. Annual generation is the most scrutinized figure in a solar power generation simulation. However, a large annual generation figure alone is not a basis for reassurance. You need to confirm what system capacity, what installation area, and what solar radiation assumptions were used to calculate that generation.

Annual generation tends to increase with larger system capacity. Therefore, when comparing multiple proposals, looking only at total generation can make higher-capacity proposals look better. But if capacity is increased by using shaded or hard-to-maintain areas, actual generation may not meet expectations and management may become difficult after installation.

For roof projects, separate the roof’s total area from the actually usable area. It is important to consider roof equipment, piping, penthouses, railings, drains, inspection openings, waterproofing clearances, and inspection passages. Simulations that fill the roof entirely with panels may show large initial generation but may require reducing the number of panels before construction.

For land projects, check not only the total site area but also site boundaries, slopes, elevation differences, trees, drainage channels, existing structures, maintenance paths, and potential grid connection points. Even on large land, not all area can be used for generation. Considering mowing, inspections, drainage, equipment replacement, and snow storage space, the actually usable area may be smaller than assumed.

When checking the basis for annual generation, it is effective to look at generation per capacity. Even if total generation is large, low generation per capacity may indicate inclusion of poor-condition areas. Conversely, a modest total generation with high generation per capacity that carefully reflects site conditions may be a prediction closer to post-installation performance.

When you have the annual generation figure, ensure you can explain “why this number is achieved.” Vague basis for annual generation can cause post-installation problems. Clear basis makes it easier to explain adjustments after on-site surveys and differences with actual performance after installation.

Check 2: Confirm monthly generation and seasonal variations

The second check is monthly generation and seasonal variations. Even if annual generation looks sufficient, actual monthly generation can vary greatly. Solar generation is affected by sunlight hours, solar altitude, irradiance, temperature, weather, shading, and snow, so it does not produce uniformly throughout the year.

If you install without checking monthly generation, you may find after installation that “although the annual figures looked good, generation is low in months with high demand.” For example, if a facility has high winter power demand and winter generation drops significantly, expected reduction effects may not be achieved. For facilities with high summer air-conditioning demand, you need to check summer generation and temperature losses.

Winter requires particular attention. Solar altitude is lower and daylight hours are shorter; shadows from surrounding buildings, trees, roof equipment, railings, and penthouses tend to stretch. In snowy regions, snow on panels can create periods with no generation. If a simulation shows unusually high winter generation, shading or snow may not have been sufficiently reflected.

In summer, while irradiance is high and generation tends to increase, panel temperature rise can lower output. High irradiance does not automatically mean maximum generation. When reviewing monthly generation, check whether summer temperature losses are reflected.

Rainy seasons, typhoons, prolonged rainy periods, and cloudy seasons also affect generation. In some regions, certain months within the annual total may show much lower generation. If monthly generation is unnaturally flat, confirm whether regional characteristics and seasonal weather variation have been sufficiently reflected.

To prevent post-installation problems, compare monthly generation with the facility’s monthly consumption. If high-generation months coincide with high demand, self-consumption is easier. If generation peaks when demand is low, surplus may increase. Looking at monthly alignment of generation and demand reduces post-installation gaps compared to relying on annual totals alone.

Check 3: Separate and confirm self-consumption and surplus power

The third check is to separate and view self-consumption and surplus power. Electricity generated by solar power is divided into the portion used within the facility and the portion that remains unused (surplus). Installing without confirming this difference can lead to situations where generation meets expectations but expected benefits are not realized.

Self-consumption refers to the amount of generated electricity used within the facility. Because it directly reduces purchased electricity, it is a central metric for judging installation benefits. Surplus power is the generated electricity that cannot be consumed within the facility at the same time. How surplus is handled greatly affects the installation’s effectiveness.

Even proposals with large total generation may provide limited on-site usable power if self-consumption is small. Facilities that primarily operate at night or have low weekend demand may generate daytime power that cannot be consumed. Even facilities with high annual consumption may not see increased self-consumption if generation times do not align with demand.

Relying solely on self-consumption rate is risky. Small system capacities tend to show high self-consumption rates but may have low self-consumption volume. Larger system capacities can lower self-consumption rate but may increase self-consumption volume. To prevent post-installation problems, check self-consumption rate, self-consumption volume, and surplus power together.

When increasing system capacity, confirm whether the extra generation will be consumed on-site or become surplus. Up to a certain capacity, self-consumption will increase, but beyond that point, only surplus may increase. Increasing capacity in that situation may raise generation without delivering the expected benefits.

If combining battery storage, separate results for with and without batteries. A battery does not increase generation; it shifts surplus power to other times. Viewing only battery-included results can hide the surplus risk for PV alone. Consider charge/discharge losses and capacity constraints and confirm how effectively surplus can be utilized.

To prevent post-installation problems, check usable energy, not just potential generation. Separating self-consumption and surplus power helps avoid situations where “it generates but yields no benefit.”

Check 4: Confirm generation reduction due to shading, orientation, and tilt

The fourth check is shading, orientation, and tilt-related generation losses. These factors significantly affect simulation results. Insufficient pre-installation checks can lead to lower-than-expected generation after installation.

Sources of shading include surrounding buildings, roof equipment, penthouses, railings, piping, HVAC exhausts, trees, utility poles, signs, slopes, and terrain elevation differences. Shadows change with season and time of day. Even if there is no problem in summer, winter’s low solar altitude can cause long shadows. Morning and evening shadows are also easily overlooked.

When checking shading, it’s helpful to compare generation with and without shading. If reflecting shade reduces generation, that’s not bad; it’s a necessary adjustment to approach real post-installation performance. A realistic shade-reflected generation is more effective in preventing post-installation problems than an unrealistically high generation that ignores shading.

Orientation matters as well. South-facing surfaces tend to yield higher annual generation, but east- or west-facing surfaces can be useful depending on a facility’s demand hours. Facilities with high morning demand may benefit from east-facing generation, and those with high afternoon demand from west-facing generation. Don’t judge orientation solely by annual generation; check it against the facility’s usage hours.

Tilt angle affects seasonal irradiance capture, row-to-row shading, wind, snow shedding, and soiling retention. Roof projects often follow existing roof pitch, so ideal angles may not be selectable. On flat roofs or land, racking angle can be set, but increasing angle can affect row spacing, inter-row shading, and wind loads.

To prevent post-installation problems, check orientation, tilt, and shading based on actual site conditions rather than ideal assumptions. Make the final decision using a simulation that reflects shading, obstacles, orientation, and tilt after on-site survey rather than a preliminary estimate.

Check 5: Confirm loss rates such as temperature, soiling, and snow

The fifth check is loss rates such as temperature, soiling, and snow. Solar power generation simulations subtract various losses from ideal generation to estimate more realistic output. If these loss rates do not match site conditions, actual generation after installation may be lower than assumed.

Temperature loss is the reduction in output due to panel temperature rise. This requires special attention in summer and for roof installations. Even in high-irradiance seasons, high panel temperature can limit expected generation. If summer generation looks excessively high, check whether temperature loss has been adequately reflected.

Soiling loss is the generation decline caused by dust, pollen, fallen leaves, bird droppings, exhaust-related soiling, and particulates on panel surfaces. Locations with many surrounding trees, nearby unpaved areas, dust-prone environments, or places where birds congregate should not downplay soiling impacts. Rain may wash panels naturally, but depending on soiling type and panel angle, residues may remain.

In snowy regions, you must account for generation declines due to snow. Snow on panels creates periods with no generation. Check snow-shedding angles, snow storage areas, ease of snow removal and inspection, and snow-load capacity. If winter generation looks high in a simulation, ensure snow and residual snow are sufficiently reflected.

Wiring losses, power conversion losses, equipment downtime, and aging effects also relate to loss rates. Power generated at panels travels through wiring and equipment to be used in the facility, and losses occur along the way. Confirm whether the simulation’s reported generation is panel-side generation or the usable energy after conversion.

Loss rates may be summarized as a single comprehensive number. In that case, confirm which components—temperature, shading, soiling, snow, wiring, conversion, aging—are included. Proposals with low loss rates make generation look larger but may hide downside risks after installation.

To prevent post-installation problems, do not understate loss rates to make generation look better; realistically estimate losses according to site conditions.

Check 6: Confirm that constructability and maintainability are realistic

The sixth check is whether constructability and maintainability are realistic. Simulations may propose layouts that maximize generation by using the roof or land to the fullest. But layouts that cannot actually be constructed or maintained can lead to problems after installation.

For roof projects, check structure, waterproofing, loads, roof equipment, drains, inspection openings, and inspection paths. Filling a roof with panels may increase apparent generation, but it can make drain cleaning, waterproofing repairs, HVAC maintenance, and piping repairs difficult. Layouts that interfere with building management become causes of post-installation problems.

For land projects, check site boundaries, slopes, elevation differences, drainage, ground conditions, maintenance paths, mowing, equipment installation areas, and connection candidates. Lining panels across the entire site increases capacity but can make inspections, mowing, cleaning, and equipment replacement difficult. Poorly drained land can hinder maintenance during rain or snowmelt.

Maintainability is directly linked to preserving generation. If soiling, shading, equipment faults, or wiring issues cannot be checked on-site, identifying causes will be delayed. Layouts lacking inspection paths, with difficult equipment access, or where panel surroundings are hard to clean can prolong generation declines.

Considering constructability and maintainability may reduce system capacity from the initial simulation because you need to secure inspection paths, leave space around drains, avoid roof edges, provide maintenance paths, and reserve snow storage areas. Generation may drop somewhat, but these measures are important to reduce long-term operational troubles.

To prevent post-installation problems, adopt a layout that can be constructed, maintained, and managed long-term rather than one that simply maximizes generation. Re-simulate with the final layout and check generation, self-consumption, and surplus power.

Check 7: Confirm post-installation performance management methods

The seventh check is post-installation performance management methods. Solar power generation simulations serve as pre-installation decision documents and as management baselines after installation. If post-installation generation differs from assumptions, you need to decide how to check, where to inspect, and how to improve; otherwise, response to problems may be delayed.

First, retain monthly generation as a baseline. Annual generation alone does not show which months are underperforming. Low winter output points to shading or snow; low summer output suggests temperature loss or soiling; low spring or autumn output can indicate pollen, fallen leaves, or dust. Monthly data provide clues for investigation.

Hourly generation and per-installation-surface generation are also important. If morning generation is low, check east-side shading; if generation drops early in the evening, check west-side shading; if there is an unnatural dip around midday, check roof equipment shading or equipment issues. If a specific mounting surface underperforms, focus on that surface’s soiling, shading, wiring, and connections.

Manage actual self-consumption and surplus power. Even if generation matches expectations, changes in facility operation can alter self-consumption. Conversely, slight generation drops may only reduce surplus and have little impact on self-consumption. To judge post-installation effects, check both used and leftover electricity, not only generation.

In performance management, record the simulation’s assumptions. If equipment capacity, installation area, orientation, tilt, shading assessment, loss rates, irradiance conditions, power usage data, presence of batteries, and maintenance conditions are documented, it becomes easier to analyze deviations. Without recorded assumptions, it is hard to determine whether generation declines are due to weather, equipment, or site conditions.

Also, establish verification procedures for when generation falls short. Creating a sequence to check weather, irradiance, shading, soiling, snow, equipment stoppages, wiring, and demand changes makes problem response smoother. Confirming post-installation performance management methods enables you to leverage simulations for long-term operation.

Decisions to avoid to prevent post-installation problems

To avoid post-installation problems, do not judge solely by the size of annual generation. While important, annual generation tends to increase with larger system capacity. If you don’t check whether a large generation figure is due to good site conditions, large capacity, or underestimated loss rates, expected and actual outcomes may diverge after installation.

Also avoid failing to separate self-consumption and surplus power. Not all generated electricity is used within the facility. Judging installation benefits only by total generation can lead to excessive surplus and lower-than-expected benefits after installation.

Avoid using pre-site-survey simulations as the final decision. Drawings and aerial photos may not accurately capture roof equipment, piping, drains, inspection paths, trees, slopes, elevation differences, shading, and connection candidate points. Re-simulate after on-site survey and reflect conditions.

Underestimating loss rates is also dangerous. If temperature, soiling, snow, shading, wiring, conversion, and aging are not sufficiently considered, generation will be overestimated. For proposals with high generation, check the breakdown of loss rates.

Avoid postponing maintainability considerations. Layouts lacking inspection paths, impossible-to-clean configurations, or difficult equipment access make post-installation response to generation decline hard. Choose layouts that can maintain generation long-term rather than those that only maximize initial generation.

To prevent post-installation problems, don’t decide based only on favorable numbers; confirm deteriorating conditions and management methods too. Use solar power generation simulations not just to show expected effects but as documents to prevent post-installation issues.

Summary

To prevent post-installation problems with solar power generation simulations, comprehensively check annual generation, monthly generation, self-consumption, surplus power, shading, orientation, tilt, loss rates, constructability, maintainability, and performance management. It is important that large generation figures are based on site conditions and that the plan is manageable after installation.

Check 1 confirms the basis for annual generation: system capacity, usable installation area, irradiance conditions, and loss rates so you can explain why the generation is achieved. Check 2 confirms monthly generation and seasonal variations: identify seasons with likely lower generation such as winter, summer, rainy season, and snowy periods.

Check 3 separates self-consumption and surplus power: focus on usable energy, not just potential generation, to judge installation benefits. Check 4 confirms shading, orientation, and tilt-related generation declines: use effective generation based on site conditions rather than ideal assumptions.

Check 5 confirms loss rates such as temperature, soiling, and snow: simulations with unrealistically low loss rates may overstate generation. Check 6 confirms constructability and maintainability: without inspection, cleaning, drainage, mowing, and equipment access, long-term operation will have issues. Check 7 confirms post-installation performance management methods: enable comparison of monthly generation, hourly generation, self-consumption, and surplus power with actual performance.

Decisions to avoid include judging only by annual generation, using pre-site-survey estimates as the final decision, mixing up generation and self-consumption, and deferring maintainability. Reflecting site and operational conditions correctly in simulations rather than making numbers look better will reduce post-installation troubles.

The foundation for preventing post-installation problems is accurate site information. If you can accurately grasp candidate installation areas, roof equipment, obstacles, trees, site boundaries, orientation, tilt, inspection paths, and connection candidate points, the simulation assumptions become clear and it becomes easier to proceed consistently from pre-construction checks to post-installation performance management.

If you want to accurately record candidate installation areas, roof equipment, obstacles, trees, site boundaries, orientation, tilt, inspection paths, and connection candidate points on site and use solar power generation simulations to improve their effectiveness in preventing post-installation problems, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. With high-precision on-site location data, you can better organize shading and obstacles, usable installation areas, wiring routes, and maintenance paths, making it easier to compare vendor proposals, perform pre-construction checks, and manage maintenance after installation. To prevent post-installation problems with solar power generation simulations, it is important not to rely solely on desk-based generation figures but to accurately understand the site and translate that into a plan that is manageable long-term.