9 Items to Check in a Solar Power Generation Simulation Report

A solar power generation simulation report is not a document that only shows the annual generation figure. By interpreting the equipment capacity, installation conditions, monthly generation, shadow effects, generation losses, self-consumption, surplus energy, the relationship with power consumption, and the validity of underlying assumptions, you can realistically judge the post-installation generation and the electricity cost reduction effect. This article explains the nine items you should always check in a report for practitioners gathering information with the term "solar power generation simulation," presented in a way that makes it easy to compare vendor proposals and use in internal deliberations.

Table of contents

• A simulation report for solar power generation is a document to check the basis of the numbers

• Check equipment capacity and installation area

• Check annual generation and generation per capacity

• Check monthly generation peaks and troughs

• Check assumptions about irradiance and weather conditions

• Check orientation, tilt, and installation layout

• Check shadow effects and the surrounding environment

• Check generation losses and long-term degradation

• Check self-consumption and surplus energy

• Check the overlap with power consumption

• Verify on-site information to increase report reliability

• Summary

A simulation report for solar power generation is a document to check the basis of the numbers

When you receive a solar power generation simulation report, your eyes are first drawn to the annual generation figure. How much can be generated annually is important for the installation decision. However, the true value of the report lies less in the number itself than in being able to confirm under what conditions that number was derived. A report that shows a large generation figure is not necessarily good; it is important to read whether it matches site conditions and power consumption and whether the assumptions are not overly optimistic.

A solar power generation simulation is calculated based on installation area, orientation, tilt, regional irradiance, equipment capacity, shadows, generation losses, and so on. In other words, if the input conditions change, the results will also change. Even for the same building or site, different vendors may show different annual generation and self-consumption rates. The differences arise not only from the calculation methods used but also from how well on-site information is reflected, the evaluation of shadows, the estimation of losses, and differences in installation layout.

When practitioners review a report, they need to confirm whether the calculation assumptions are reasonable, not just whether the generation is large or small. By checking whether the roof or site shape is correctly reflected, whether surrounding shadows are considered, whether generation losses are realistically estimated, and whether the facility’s power usage aligns with generation times, you can reduce discrepancies after installation.

Also, simulation reports can be used as a common document to compare vendor proposals. When comparing multiple proposals, looking only at annual generation can make proposals with larger equipment capacity look favorable. However, by also examining generation per capacity, self-consumption amount, surplus energy, and how shadows and losses are treated, you can judge which proposal better suits practical needs.

Knowing the items to check in a report makes your questions to vendors more specific. You can ask why a certain generation figure was obtained, which installation surfaces contribute to generation, how winter generation decline is treated, and which power data were used to calculate the self-consumption rate. A solar power generation simulation report is not a document to receive and stop at; it is a document to be read to improve the accuracy of the installation decision.

Check equipment capacity and installation area

The first things to confirm in a report are equipment capacity and installation area. Equipment capacity is basic information indicating the overall scale of the solar panels to be installed. Generally, larger equipment capacity tends to result in higher annual generation. However, a larger capacity does not necessarily mean the proposal is optimal. If it does not match the site conditions or the facility’s power usage, surplus power may increase or panels may be placed in areas with low generation efficiency.

In the report, check which roof faces or site areas have what capacity allocated. For roof installations, conditions differ for each face, such as south-facing, east-facing, or west-facing. For ground-mounted installations, the site shape, elevation differences, access paths, neighboring boundaries, and relationship with surrounding structures are relevant. Even if the installation area is large, not all of it may be suitable for generation.

When reviewing installation area, confirm not only the size but whether the actually usable area is realistic. Consider whether roof edges, inspection paths, rooftop equipment surroundings, drainage routes, safety clearances, and space for future equipment replacement are accounted for. Although the report may appear to place many panels, the number of panels may be reduced during detailed design or construction. If the assumed installation area underlying the simulation is overstated, the annual generation may also appear overstated.

Equipment capacity should also be checked in relation to the facility’s power usage. If self-consumption is emphasized, too large a capacity may produce more power than can be used during the day. Conversely, if capacity is too small, the generation itself may be insufficient, and electricity cost reduction or decarbonization effects may be limited. It is important to confirm how the equipment capacity was determined in the report.

Equipment capacity and installation area form the foundation of the entire report. If these conditions do not match site reality, subsequent numbers for generation, self-consumption, and surplus energy will be difficult to trust. The first step in interpreting the report is to carefully check where and how much is assumed to be installed.

Check annual generation and generation per capacity

Next, check the annual generation and generation per capacity. Annual generation is the most straightforward indicator in a solar power generation simulation. It indicates how much electricity is expected to be generated in one year after installation, and it is often used for internal explanations and vendor comparisons. However, judging based only on annual generation risks overlooking differences in equipment capacity.

Proposals with larger equipment capacity tend to have larger annual generation. Therefore, when comparing multiple reports, looking only at total generation can make higher-capacity proposals appear advantageous. What matters, however, is how efficiently the installed capacity generates power. By checking generation per capacity, it is easier to assess whether the installation conditions and calculation assumptions are reasonable.

If generation per capacity is high, it may indicate favorable orientation, tilt, and irradiance conditions, with few shadows or losses. However, if it is excessively high, you need to confirm whether the assumptions are optimistic. The apparent high generation may be due to insufficient consideration of shadows, too low a loss rate, or installation angles being more ideal than actual construction conditions.

Conversely, if generation per capacity is low, the proposal may include faces with less favorable conditions. Including north-leaning faces, shadow-affected areas, unfavorable tilts, or locations constrained by the surrounding environment can increase total capacity while lowering efficiency. In such cases, rather than maximizing capacity, narrowing installation to better faces and adjusting capacity may lead to a more practically acceptable plan.

When reviewing annual generation, also check whether it refers to first-year generation or long-term generation that includes degradation. Solar power equipment is used over a long period, so judging solely by initial generation can mislead long-term outlooks. If the report shows assumptions about long-term degradation, check those assumptions.

Annual generation is important, but it alone does not determine quality. Only by looking at equipment capacity, installation conditions, losses, shadows, and the relationship with self-consumption can you understand the meaning of the generation figure. Checking generation per capacity together allows you to interpret the report’s numbers more objectively.

Check monthly generation peaks and troughs

Always check the monthly generation in a solar power generation simulation report. While annual generation is convenient for grasping the overall picture, monthly variations are important for actual operation. Solar generation varies by season because monthly irradiance, daylight hours, solar altitude, temperature, weather, snowfall, and shadow length differ.

By looking at monthly generation, you can see which seasons have high generation and which have low. Generation tends to increase from spring to summer, while rainy season, typhoons, short winter daylight hours, and snowfall can reduce generation. Although summer brings abundant irradiance, high temperatures can reduce generation efficiency. Therefore, it is important to confirm whether the monthly peaks and troughs are natural.

Pay particular attention to winter generation. In winter, the low solar altitude causes shadows from surrounding buildings and rooftop equipment to extend. If winter generation is unnaturally high despite shadow factors at the site, the shadow evaluation may not have been adequately reflected. In regions where snowfall is expected, if winter generation is estimated high, confirm how snowfall impact is treated.

Monthly generation is also important for assessing compatibility with the facility’s power usage. In facilities with high air-conditioning demand in summer, summer generation can directly lead to savings. Conversely, for facilities with high winter power demand, failing to account for winter declines can lead to misinterpretation if you only look at annual averages. In reports, consider monthly generation alongside monthly usage.

Additionally, monthly generation helps judge whether equipment capacity is appropriate. If surpluses are large in high-generation months and shortages occur in high-demand months, increasing capacity may not yield the expected benefits. A balance may look good in total annual figures but reveal operational issues when viewed monthly.

Monthly generation is a key item for checking the realism of the report. By confirming seasonal variation, winter shadows, and alignment with local climatic conditions—things not visible from annual totals—you can make simulation results more usable in practice.

Check assumptions about irradiance and weather conditions

Simulation results are heavily influenced by assumptions about irradiance and weather conditions. Since solar power generates electricity from irradiance, the regional irradiance conditions form the basis of generation. With the same equipment capacity, annual generation varies between locations with high and low irradiance. In the report, it is important to check what irradiance data and weather conditions were used for the calculation.

When checking irradiance assumptions, confirm whether data close to the installation site were used. If calculations use only broad-area averages, regional characteristics such as mountainous areas, coastal zones, urban areas, or snowfall regions may not be adequately reflected. There can be differences in irradiance conditions even among nearby locations depending on the surrounding environment. If a report’s generation looks high, verify whether the irradiance assumptions match the actual conditions.

Temperature conditions are also important. Solar panels generate from irradiance, but panel output decreases when panel temperature rises. In summer, while irradiance is high, temperature-related generation losses can occur. Calculating generation based on irradiance alone may produce results that are more optimistic than reality. Check whether temperature effects are reflected in generation losses in the report.

Handling of snowfall and cloudy conditions is important in some regions. In areas with snowfall, panels may be covered by snow, causing periods with no generation. In regions with many cloudy or rainy periods, monthly generation should reflect that trend. If the report’s monthly generation does not align with the local climate, check the weather assumptions.

Practitioners do not need to perform detailed calculations of irradiance and weather, but they can check whether the report’s generation substantially contradicts the site’s regional characteristics. Reports that do not clearly state irradiance assumptions make it difficult to verify the basis of generation. Ask the vendor what weather conditions were used and whether monthly generation reflects regional characteristics.

Irradiance and weather assumptions are hidden but critical factors in simulations; confirming them in the report helps you judge the reliability of the numbers.

Check orientation, tilt, and installation layout

In a solar power generation simulation report, check orientation, tilt, and installation layout. The direction panels face, the angle at which they are installed, and which surfaces they occupy all affect generation. Even with the same equipment capacity, different layout conditions can produce differences in annual and monthly generation.

Regarding orientation, surfaces closer to south-facing tend to achieve higher annual generation. However, east- or west-facing orientations are not necessarily disadvantageous. East-facing surfaces tend to generate more in the morning, while west-facing surfaces generate more in the afternoon. Depending on the facility’s power usage pattern, not only the total generation but also the time of generation can be important. Reports that show generation or capacity by orientation make it easier to assess compatibility with power usage.

Tilt angle also affects generation. For roof installations, angles often follow the existing roof slope and cannot be freely chosen. For flat roofs or ground-mounted installations, racking can set the angle, but increasing the angle affects wind exposure, inter-row shading, installation spacing, and maintainability. Check whether the tilt angles in the report match actual construction conditions.

In the installation layout, verify whether panels are placed sensibly. If the layout aims to make generation look large by filling the roof or site, inspection paths and safety clearances may be insufficient. If panels are placed near rooftop equipment, in likely shadow zones, or around drainage routes, the layout may change during detailed design.

If multiple installation surfaces exist, check how much each surface contributes to generation. The evaluation of a proposal changes depending on whether sufficient generation can be expected from favorable surfaces alone or whether capacity is increased by including less favorable surfaces. Even if total generation is high, including low-efficiency surfaces may require reconsideration in terms of maintainability and surplus power.

Orientation, tilt, and installation layout connect the simulation to real-world planning. If the report includes layout diagrams and installation conditions, review them together with annual generation to judge whether the plan is realistically constructible.

Check shadow effects and the surrounding environment

Shadow effects are an item to pay special attention to in a solar power generation simulation report. Since panels generate from irradiance, any shadow reduces generation. The impact of shadow is not determined solely by the shadowed area; it varies with the time of day, season, panel arrangement, and how connections are configured.

Sources of shadows include surrounding buildings, rooftop equipment, railings, roof structures, piping, chimneys, signs, trees, utility poles, and neighboring structures. On roofs, equipment that looks small in normal conditions can cast long shadows in winter or at dawn and dusk. For ground installations, surrounding trees, buildings, and on-site elevation changes can cause shadows.

In the report, check how shadows are considered. Is the shadow impact reflected in generation? Are shadowed areas excluded from installation? Is shadow treated as a fixed loss? If the surrounding environment includes shadow sources but the report lacks shadow explanation, be cautious.

Winter shadows are particularly important. With low solar altitude, shadows from surrounding buildings and equipment extend in winter. A site that looks fine in a summer visit can have significant shadows in winter. If monthly generation shows unreasonably high winter output, verify whether shadow evaluation was adequately reflected.

The surrounding environment affects generation in ways other than shadows. Dirt, fallen leaves, bird droppings, exhaust, and dust settling on panel surfaces reduce generation. In areas with many trees or where dust is likely, check assumptions about losses due to soiling and the maintenance plan.

Shadows and the surrounding environment are indispensable elements for bringing simulated generation closer to reality. A report that looks conservative after accounting for shadows may actually be more realistic. Rather than focusing only on whether generation is large, check how honestly the report accounts for factors that reduce generation.

Check generation losses and long-term degradation

In a solar power generation simulation report, verify how generation losses and long-term degradation are treated. Solar power does not always produce maximum output under ideal conditions. In reality, generation is reduced by various factors. How these generation losses are estimated greatly affects the report’s reliability.

Generation losses include output reduction due to temperature rise, conversion losses during power conditioning, wiring losses, soiling of panel surfaces, shadows, snowfall, equipment downtime, and variability among equipment. These may be estimated individually or summarized into a comprehensive loss rate. In either case, the important point is whether the loss assumptions can be explained.

Temperature-related losses are easily overlooked. Although panels generate from irradiance, their output decreases as panel temperature rises. In summer, while irradiance is high, performance loss due to high temperature may occur. If summer generation is estimated extremely high, check whether temperature losses are reflected.

Losses from conversion and wiring are also important. Electricity generated by panels is not used directly but passes through equipment and wiring, causing some loss. Confirm whether the report’s figures refer to generation on the panel side or to electrical energy close to what can actually be used, to avoid misunderstanding the numbers.

Long-term degradation is indispensable for long-term operation. Solar equipment is intended for long-term use, and performance can change over time. Check whether the report presents only first-year predictions or includes a long-term outlook that considers degradation.

If generation losses and degradation are underestimated, generation will appear higher. In actual operation, losses cannot be avoided. More reliable reports do not just inflate generation but realistically address factors that reduce it. By checking the breakdown and rationale for generation losses, you can evaluate simulation results more calmly.

Check self-consumption and surplus energy

For judging electricity cost reductions and the appropriateness of equipment capacity, self-consumption and surplus energy are important in a simulation report. Even with large generation, if the power cannot be used within the facility, it will not directly reduce purchased electricity. In practice, how much of the generated power can be self-consumed is more important than total generation.

Self-consumption amount refers to the portion of generated power consumed within the facility. This amount can potentially reduce the electricity purchased from outside by the same amount. The self-consumption rate indicates the percentage of generation used on-site. While a high self-consumption rate may seem efficient, judging by percentage alone is risky.

When equipment capacity is small, the self-consumption rate tends to be high because the smaller generation is easier to consume on-site. However, if the self-consumption amount itself is small, the electricity cost reduction effect is limited. Conversely, with large capacity, the self-consumption rate may fall while the self-consumption amount increases. In reports, check self-consumption rate and self-consumption amount together.

Surplus energy is also important. Surplus refers to generated power that cannot be used by the facility at that time. Large surpluses may indicate that equipment capacity is too large relative to demand. Particularly if surpluses increase during holidays, lunch breaks, or low-activity seasons, problems may be hidden that are not visible in annual averages.

When combining batteries, part of the surplus can be stored and used at other times. However, batteries do not eliminate all surplus. The usable energy depends on battery capacity, charge/discharge losses, the demand to which discharge can be applied, and policies for maintaining emergency reserves. Comparing reports with and without batteries helps assess the effect.

By reading self-consumption and surplus energy, you can see how well the generation matches facility operations. In a solar power generation simulation report, it is important to separate generated, usable, and surplus energy rather than only looking at total generation.

Check the overlap with power consumption

Finally, check the overlap between generation and the facility’s power consumption. Solar power generates during the day, so the more power is used during daytime, the easier it is to self-consume. Even with large generation, if the timing of power usage does not match generation, the electricity cost reduction effect may be limited.

Looking at overlap with power consumption requires more than annual consumption numbers. A facility with large annual consumption but concentrated at night will have weak compatibility with solar generation. Conversely, a facility with moderate annual consumption but steady daytime demand can efficiently use generated power.

Monthly overlap is also important. Facilities with high air-conditioning demand in summer often see demand coincide with high generation. Conversely, facilities with high winter demand may see limited reductions due to winter generation decline. In reports, compare monthly generation and monthly usage to see which seasons are likely to produce effects.

Viewing overlap by time of day gives an even more realistic judgment. If generation peaks at midday while facility demand peaks in the morning or evening, surplus or shortages are likely. If the daytime generation peak coincides with the facility’s usage peak, self-consumption is easier. If there is a large mismatch, consider adjusting capacity, adding batteries, or reviewing operating hours.

Overlap with power consumption is also important when considering the impact on basic charges. Even if purchased energy decreases due to solar generation, if maximum demand occurs at times when generation is not available, contract-related aspects may be less affected. If you expect peak reduction, check when maximum demand occurs and how much solar generation or batteries can contribute at that time.

The overlap between generation and power consumption is a key perspective affecting the practical effectiveness of solar power. If this relationship is not shown in the report, ask the vendor and have them explain the basis for self-consumption and surplus energy. For practitioners, the most important reading is not how much can be generated, but how much can be used.

Verify on-site information to increase report reliability

To correctly read a solar power generation simulation report, you must also check the accuracy of on-site information. Generation varies with the shape, orientation, tilt, shadows, and surrounding environment of the installation site. If on-site information is inaccurate, even the most detailed report may diverge from reality.

For roof installations, roof surface dimensions, shape, orientation, tilt, rooftop equipment, railings, piping, inspection paths, and drainage routes are important. Although a drawing may appear to allow installation, obstructions or safety clearances can limit installable area. For ground installations, site boundaries, elevation differences, surrounding structures, trees, access paths, and future use plans are relevant.

A report created with ambiguous on-site information may be useful for initial consideration but requires caution for decision making. The reliability of the simulation depends on whether an on-site survey was conducted, whether it was calculated from drawings alone, and whether photos and location information were reflected. When you receive a report, check what on-site information was used for the calculation.

Accurate on-site information also makes it easier to compare proposals from multiple vendors. If the same site conditions are shared, differences in generation and self-consumption can be evaluated as differences in design policy. Conversely, if each vendor uses different on-site assumptions, it becomes difficult to determine the cause of differences in results.

On-site information is useful not only for simulation but also for pre-construction checks and maintenance management. Accurately recording candidate installation spots, obstacles, equipment positions, site boundaries, and inspection routes allows consistent use after installation. Since solar power equipment is intended for long-term operation, organizing on-site information before installation is important.

Summary

The items to check in a solar power generation simulation report go beyond annual generation. By checking equipment capacity and installation area; annual generation and generation per capacity; monthly generation; irradiance and weather conditions; orientation, tilt, and installation layout; shadow effects; generation losses and long-term degradation; self-consumption and surplus energy; and overlap with power consumption, you can judge the report’s practicality.

By examining equipment capacity and installation area, you can understand the assumptions about where and how much will be installed. Checking generation per capacity as well as annual generation lets you verify generation efficiency and the validity of assumptions. Reviewing monthly generation makes it easier to confirm seasonal variation, winter shadows, and consistency with regional weather.

Irradiance and weather conditions, orientation, tilt, and installation layout form the foundational assumptions for generation. It is also important to see whether shadows, the surrounding environment, generation losses, and long-term degradation are realistically accounted for. Rather than only making generation look large, evaluating how carefully the report reflects factors that reduce generation helps judge its reliability.

When considering electricity cost reduction and self-consumption, self-consumption amount, surplus energy, and overlap with power consumption are key. Even if generation is large, it does not directly reduce costs unless it can be used on-site. Check whether daytime demand, monthly usage, holiday operation, and time-of-day usage patterns align with generation.

Finally, accurate on-site information supports the report’s reliability. If the roof or site shape, obstacles, surrounding structures, and inspection routes are not correctly understood, the simulation assumptions become unstable. Reflecting actual site conditions, not just desk calculations, leads to reports usable in practice.

If you want to improve the accuracy of site records—such as candidate installation spots, obstacles, equipment positions, site boundaries, and inspection routes—and thereby improve the accuracy of solar power generation simulation reports, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. High-precision local positioning makes it easier to proceed consistently from assumption verification and vendor proposal comparison to pre-construction checks and maintenance management. To make simulation reports reliable decision-making materials, it is important to accurately gather both power data and on-site information.