How to explain the basis for generation estimates in solar power generation simulations

Annual and monthly generation figures shown in solar power generation simulations are essential numbers for adoption decisions, internal explanations, and comparing vendor proposals. However, simply presenting generation figures is unlikely to convince stakeholders unless you can explain why those figures are expected. To explain the basis for generation, it is important to separate and organize equipment capacity, installable area, insolation, orientation, tilt, shading, loss rates, self-consumption, and on-site survey results. This article explains, for practitioners who search for "太陽光発電量 シミュレーション", how to clearly explain the basis for generation estimates.

Table of contents

• Why explaining the basis for generation is important in solar power generation simulations

• Explain equipment capacity and installable area

• Explain insolation and regional conditions

• Explain orientation, tilt, roof surfaces, and land conditions

• Explain generation reductions due to shading and obstacles

• Explain loss rates such as temperature, soiling, and snow

• Separately explain self-consumption and surplus energy

• Explain revisions after on-site surveys

• Explain as a benchmark for performance comparison

• Summary

Why explaining the basis for generation is important in solar power generation simulations

The purpose of explaining the basis for generation in a solar power generation simulation is not merely to show technical calculations. It is to enable stakeholders before installation to judge how much they can trust the generation figures, under what conditions benefits can be expected, and under what conditions outcomes might be lower than expected.

In solar proposals, annual and monthly generation figures are often shown prominently. Larger annual generation can make the benefits look greater. However, if it is unclear what roof area, equipment capacity, insolation assumptions, orientation, tilt angle, shading, and loss rates those figures were calculated from, the numbers can become disconnected from reality.

If adoption decisions proceed with ambiguous bases for generation, it becomes difficult to explain changes in generation after detailed design or on-site surveys. An initial proposal may appear to generate a lot, but after on-site surveys reflecting rooftop equipment, shading, and inspection walkways, generation can decrease. If you had originally explained the bases separately, stakeholders are more likely to understand the reasons for changes.

Explaining the basis for generation is also important when comparing multiple vendor proposals. Even for the same facility or land, proposed annual generation may differ. The difference might come from different equipment capacities, different insolation assumptions, or different expectations for shading and loss rates. If you can decompose and explain the bases, you can choose a proposal that matches on-site conditions rather than simply the one with the largest generation.

Moreover, generation simulations are useful not only before deployment but also for post-deployment performance management. If actual generation after installation is lower than expected, you need to check which assumptions were off. If you retain the bases for monthly generation, shading conditions, loss rates, self-consumption, and surplus energy, it becomes easier to analyze discrepancies with actual performance.

Explaining the basis for generation is not only about persuading for adoption but also about sharing risks accurately. Rather than showing only favorable numbers, explaining both the conditions under which the generation is achieved and the conditions that would cause downside makes the simulation more trustworthy in practice.

Explain equipment capacity and installable area

When explaining the basis for generation, the first items to organize are equipment capacity and installable area. Solar generation tends to increase with larger installed capacity. Therefore, when explaining annual generation figures, first clarify what kW of equipment is assumed and from what area that capacity was calculated.

For rooftop projects, separate the roof’s total area from the actually usable area. Even if a roof appears large, rooftop equipment, piping, penthouses, railings, drains, inspection hatches, waterproofing clearances, and inspection walkways mean not all area can be used for panels. If you present the plan-view roof area as the installable area, it will be hard to explain later reductions in generation.

The same applies to land projects. Total land area and the actual panel-placement area differ. You need to consider site boundaries, slopes, elevation differences, drainage channels, trees, existing structures, maintenance paths, potential connection points, and snow storage spaces. Even a large site may have a limited area usable for generation equipment.

When explaining generation bases, separating maximum installable capacity and realistic installable capacity makes the explanation clearer. Maximum installable capacity shows the theoretical limit. Realistic installable capacity accounts for inspection, construction, maintenance, shading, drainage, and access. For adoption decisions, the latter is closer to reality and therefore a better reference.

Also include generation per unit capacity to convey proposal validity. This clarifies whether a large annual generation is simply due to large capacity or because panels are efficiently placed in favorable locations. Low generation per unit capacity may indicate that shaded or unfavorably oriented surfaces are being used. Conversely, a proposal that limits capacity to good surfaces may have high reliability despite smaller capacity.

When explaining equipment capacity and installable area, show which ranges were used and which were excluded before presenting generation figures. This makes it easier to explain that the generation numbers are realistic and based on on-site conditions.

Explain insolation and regional conditions

Next to explain as a basis for generation are insolation and regional conditions. Solar panels generate from sunlight, so the expected amount of sunlight in a given region is the foundation of generation forecasts. Even with the same equipment capacity, annual generation will vary with insolation conditions.

When explaining insolation, it is important to present not only annual insolation but also monthly insolation conditions. Annual insolation provides an easy-to-understand overall guideline but cannot fully represent seasonal generation variations. Regions with abundant summer insolation, regions prone to winter declines, regions affected by the rainy season or frequent clouds, and snowy regions require different views of monthly generation.

Indicate that local meteorological conditions are reflected in the simulation. Prediction accuracy changes depending on whether conditions near the installation site or broader average conditions were used. Insolation in mountainous areas, coastal areas, basins, snowy regions, or areas with many tall surrounding buildings can vary even within the same municipality.

Also explain the relationship between insolation and temperature. While higher insolation generally increases generation, panel output can drop due to elevated panel temperature in summer. Therefore, if summer generation appears high, explain whether temperature losses were included. Explaining insolation alone can overstate summer generation.

For winter, explain shorter daylight hours, lower solar altitude, snow, and the increased length of shadows. Lower winter generation is not just due to bad weather but to fundamentally different insolation conditions. In snowy regions, the time snow remains on panels affects generation. Clarifying how much winter generation you expect helps align post-installation expectations with reality.

A simple statement like “this region will generate this much” is insufficient. Explaining monthly generation, temperature, snowfall, cloudiness, and local characteristics clarifies the basis for generation.

Explain orientation, tilt, roof surfaces, and land conditions

Orientation and tilt are very important when explaining the basis for generation. The direction panels face and their installation angle change the way they receive sunlight, the hours they generate, and monthly generation. Even with identical capacity, orientation and tilt differences affect generation.

For orientation, surfaces closer to south tend to yield higher annual generation. However, the optimal orientation is not always simply south. East-facing surfaces generate more in the morning; west-facing surfaces generate more in the afternoon. Depending on a facility’s power usage hours, east-west generation may contribute effectively to self-consumption.

When explaining generation bases, separate orientation by installation surfaces. Presenting the roof or land as a single generation figure makes it hard to see which surfaces contribute. If you can explain capacity and generation for south, east, west, flat roof sections, and land installation zones, the basis becomes clearer.

Tilt should also be explained. For roof projects, panels are often installed to match existing roof pitch, so ideal tilt angles are not always selectable. On flat roofs or land sites, rack angles can be set, but larger angles affect inter-row shading, wind loads, spacing, and maintainability. Smaller angles can allow greater installable capacity but influence seasonal generation and the persistence of soiling.

For land projects, include terrain conditions. Whether the site is flat, sloped, has berms or elevation differences, or sits lower than surroundings affects generation and shading. If land assumed flat in simulation is found to be sloped during on-site survey, you must revise the basis for generation.

When explaining orientation, tilt, roof surfaces, and land conditions, do not present only the conditions that maximize generation; explain conditions that are actually constructible. Ideal conditions may yield high generation, but if they do not match actual roof pitch or terrain, post-installation results will diverge.

If you can explain how much will be installed on which orientation, at what tilt, and how much generation each surface produces, stakeholders will more easily understand the validity of the generation figures.

Explain generation reductions due to shading and obstacles

Shading and obstacles are particularly important when explaining the basis for generation. Shadows on panels reduce the amount of sunlight received and therefore lower generation. Simulations that ignore shading can overestimate generation. Therefore, make clear to what extent shading is reflected in the generation figures.

Sources of shading include surrounding buildings, rooftop equipment, penthouses, railings, piping, air-conditioning and exhaust equipment, trees, utility poles, signs, slopes, and terrain elevation differences. For rooftop projects, rooftop equipment and adjacent building shadows are main checks; for land projects, trees, surrounding structures, and terrain are primary concerns.

Shading varies by time of day and season. Shadows that are short in summer can be long in winter due to lower solar altitude. Morning shading tends to come from the east, evening shading from the west. When explaining the basis for generation, describe not only the annual average but also how much winter and morning/evening shading are expected.

Comparing shaded and unshaded cases is effective when explaining shading impacts. Showing generation without shading versus with shading communicates the magnitude of shading loss. If you exclude areas with heavy shading, explain how capacity and generation change as a result.

Shading also affects self-consumption. If shading occurs during a facility’s peak demand hours, it can reduce the reduction in purchased electricity. For example, a facility with high morning demand and strong east-side shading will see impacts on self-consumption as well as generation. Explaining the effects of shading on annual generation and on generation timing is practically useful.

Obstacles affect not only shading but also soiling and maintainability. Trees cause shading and can increase leaves and bird droppings. Rooftop equipment influences not only shading but inspection and maintenance space. When explaining generation bases, describe obstacles not just as shading sources but also as contributors to generation loss and maintenance constraints.

A thorough explanation of shading and obstacles helps stakeholders understand that conservative generation figures can still be realistic simulations.

Explain loss rates such as temperature, soiling, and snow

Explaining loss rates is essential for the basis of generation. Solar systems do not always generate at maximum under ideal conditions. In practice, temperature, wiring, power conversion, shading, soiling, snow, system downtime, and aging reduce generation. How much of these losses are assumed affects simulation reliability.

Temperature loss refers to output reduction due to elevated panel temperature, and it is especially important in summer and for rooftop installations. Even with high insolation, high panel temperature can limit expected generation. When explaining summer generation, show that temperature losses were included.

Soiling loss arises from dust, pollen, leaves, bird droppings, exhaust deposits, and particulates on panel surfaces. Consider soiling where there are many surrounding trees, nearby unpaved areas, sources of dust, or bird congregation. Ease of cleaning and inspection affects long-term generation maintenance.

In snowy regions, explain generation reductions due to snow. When snow remains on panels, generation is lost for the duration. Whether panels have a steep enough tilt to shed snow, whether there is snow storage space, and whether winter inspection and snow removal are feasible all affect winter generation. Be clear about how much snow impact is assumed.

Wiring losses and power conversion losses are also important. Power generated by panels travels through wiring and equipment before use, and losses occur along the way. Clarify whether the simulation figures represent generation at the panel output or the energy available after conversion, as this affects stakeholder understanding.

Loss rates are often shown as a single aggregate number. However, presenting only an overall loss rate can obscure what is included. When explaining the basis for generation, separate items such as temperature, shading, wiring, conversion, soiling, snow, and aging, and communicate how much loss is assumed for each.

Carefully explaining loss rates demonstrates that generation figures are not inflated but reflect on-site conditions and long-term operation. This is especially important for internal explanations and vendor comparisons.

Separately explain self-consumption and surplus energy

When explaining the basis for generation, you must separate total generation into self-consumption and surplus energy. Electricity generated by solar is divided between what is used on-site and what remains unused. If you do not distinguish these, there is a risk that stakeholders will misunderstand total generation as equivalent to the economic benefit.

Self-consumption is the portion of generated electricity consumed within the facility. It directly reduces purchased electricity and is the central metric for explaining benefits. Surplus energy is the portion generated but not consumed at the same time; whether surplus is exported, stored in batteries, or curtailed changes the evaluation.

To explain self-consumption, overlay generation and the facility’s electricity usage by time of day. Even a facility with large annual usage may have mostly nighttime demand, making solar compatibility limited. Conversely, a facility with modest annual usage but a steady daytime base load may more easily use generated power.

Distinguishing generated and usable energy is important. A proposal with large annual generation but substantial surplus may have limited actual reduction in purchased electricity. High self-consumption ratios can be misleading if they simply reflect small capacity. Explain self-consumption ratio, self-consumption volume, and surplus energy together to convey realistic benefits.

Monthly and hourly breakdowns are also effective. For facilities with high summer cooling load, summer generation may align well with self-consumption. Facilities with low operation on holidays may see increased surplus. Facilities with morning- or afternoon-weighted demand may see different self-consumption depending on installation orientation.

When combining batteries, separate explanations for cases with and without batteries are necessary. Batteries can shift surplus to other times but involve charge-discharge losses and capacity constraints. Presenting only the battery-enabled case can obscure the standalone solar generation and surplus situation.

Separating self-consumption and surplus energy turns generation bases into the basis for benefits. This perspective is crucial for internal approvals and customer explanations.

Explain revisions after on-site surveys

Making clear the revisions after on-site surveys is essential when explaining the basis for generation. Initial simulations are sometimes based on drawings, aerial photos, and outline information. On-site surveys reveal conditions not apparent at the initial stage, such as rooftop equipment, piping, drains, inspection paths, trees, site boundaries, elevation differences, shading, and potential connection points.

It is not uncommon for generation to change after on-site surveys. Installable area may decrease. Incorporating shading may reduce generation. Panel layouts may be revised to secure inspection walkways and maintenance space. For land projects, berms, drainage, and access paths may reduce capacity.

These revisions are not intended to worsen generation but to make simulations more realistic. When explaining, organize the differences between the initial simulation and the post-survey simulation and explain why generation changed.

For example, explain that capacity decreased because area around rooftop drains was excluded, monthly generation dropped because winter shading was reflected, layouts were revised to secure inspection walkways, or parts of the land were excluded due to tree shading. Such concrete explanations help stakeholders understand that revisions are reasonable.

After on-site survey revisions, you must recalculate not only annual generation but also self-consumption and surplus. Changes in capacity and generation timing alter the overlap with facility demand. Using initial proposal self-consumption values unchanged can misrepresent benefits.

When explaining the basis for generation, communicate both preliminary estimates before on-site survey and higher-accuracy values after on-site survey. The final adoption decision should use the post-survey simulation. Carefully explaining revisions increases stakeholder acceptance and reduces gaps after installation.

Explain as a benchmark for performance comparison

The purpose of explaining the basis for generation in a solar simulation is not only for pre-installation decisions. It is also important to create benchmarks that can be used to compare actual performance after installation. If the bases for generation are recorded, it becomes easier to identify causes when actual generation differs from expectations.

For performance comparison, retain not only annual but also monthly generation figures. Having monthly expected values allows you to see which months are underperforming. Low winter generation may suggest shading or snowfall issues; low summer generation may suggest temperature loss or soiling; low spring or autumn generation may suggest pollen, leaves, or dust.

Hourly generation and per-surface generation are also useful. If morning generation is low, suspect east-side shading; if generation falls early in the evening, suspect west-side shading; if there is an abnormal dip around midday, check rooftop equipment shadows or equipment problems. If only one installation surface underperforms, inspect that surface for soiling, shading, wiring, or connection issues.

Retain benchmarks for self-consumption and surplus as well. Even if generation matches expectations, changes in facility operation can alter self-consumption. Conversely, a slight drop in generation may only reduce surplus, leaving self-consumption largely unaffected. For post-installation management, check both used and surplus energy as well as generation.

It is also important to record simulation assumptions. If equipment capacity, installation surfaces, orientation, tilt, shading assessment, loss rates, insolation conditions, power usage data, battery presence, and maintenance conditions are recorded, analyzing gaps with actual performance is easier. Without recorded assumptions, it is hard to tell whether underperformance is due to weather, equipment, or site conditions.

Ideally, explanations of generation bases in pre-installation documents should be preserved as benchmarks for post-installation management. Linking simulations to actual performance enables early detection of generation declines, revision of maintenance plans, and improved accuracy in future proposals.

Summary

To explain the basis for generation in a solar power generation simulation, do not present only annual generation figures. It is important to separate and organize the assumptions that compose the generation figures. By explaining equipment capacity, installable area, insolation, regional conditions, orientation, tilt, shading, loss rates, self-consumption, surplus energy, and post-survey revisions in order, stakeholders can more easily understand the validity of the generation numbers.

First, explain equipment capacity and installable area. Show that generation was calculated based on usable area, not total roof or land area. Next, explain insolation and regional conditions. Present not only annual insolation but also monthly generation, temperature, snowfall, cloudiness, and regional characteristics so the foundation of generation forecasts is clear.

Orientation, tilt, roof surfaces, and land conditions are also important. Explain how much is installed on which surfaces, at what orientation and angle, so the breakdown of generation is easy to understand. For shading and obstacles, provide shaded vs. unshaded comparisons, describe winter and morning/evening shading, and explain generation reductions due to obstacles. Even if accounting for shading lowers generation, you can show that the simulation is realistic.

Also separate and explain loss rates such as temperature, soiling, snow, wiring, power conversion, and aging. Since a single aggregate loss rate can be unclear, organize which generation losses are assumed and to what extent. For self-consumption and surplus, separate the generated amount from the amount usable on-site and clarify that generation is not identical to economic benefit.

Carefully explain revisions after on-site surveys. If generation changes due to rooftop equipment, inspection paths, drains, trees, boundaries, elevation differences, or shading, showing the reasons increases stakeholder acceptance. Additionally, keep simulations in a form usable as post-installation performance benchmarks. Recording monthly, hourly, and per-surface generation, self-consumption, surplus energy, and loss-rate assumptions makes post-installation analysis easier.

A simulation whose basis for generation can be explained is useful across adoption decisions, internal explanations, vendor comparisons, pre-construction checks, and post-installation performance management. Conversely, generation figures with unclear bases lose practical credibility even if they look large.

The foundation of explaining generation bases is accurate on-site information. If you can accurately capture the installation candidate area, rooftop equipment, obstacles, trees, site boundaries, orientation, tilt, inspection routes, and potential connection points, the simulation assumptions become clear and the basis for generation is easier to explain.

If you want to accurately record installation candidate areas, rooftop equipment, obstacles, trees, site boundaries, orientation, tilt, inspection routes, and potential connection points on-site and improve the accuracy of explaining generation bases in solar power generation simulations, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. High-precision on-site positioning makes it easier to organize shading and obstacles, installable areas, wiring routes, and maintenance routes, enabling consistent progress from vendor comparisons and pre-construction checks to post-installation performance management. To clearly explain the basis for generation in solar power generation simulations, it is important not only to perform desk calculations but also to accurately understand the site and organize that information as the assumptions for generation.