Eight checks before requesting a solar power generation simulation

Before requesting a solar power generation simulation, it is important to organize the installation site, power usage, objectives, and on-site conditions. If you request a simulation while the necessary information is unclear, estimates of generation and self-consumption can easily diverge from reality, and it becomes harder to compare vendor proposals. This article explains eight points that practitioners who are researching "solar power generation simulation" should confirm before requesting a simulation, from a practical, usability-focused perspective.

Table of contents

• The accuracy of a solar power generation simulation depends on preparation before requesting it

• Check 1: Clarify the purpose of installation

• Check 2: Organize actual power usage

• Check 3: Understand the conditions of candidate installation sites

• Check 4: Confirm shading factors and the surrounding environment

• Check 5: Decide on the approach to system capacity

• Check 6: Organize the policy on self-consumption and surplus power

• Check 7: Consider the presence of batteries and emergency use

• Check 8: Align request conditions to make comparisons easier

• How to read simulation results after requesting

• Improving the accuracy of on-site information raises request quality

• Summary

The accuracy of a solar power generation simulation depends on preparation before requesting it

A solar power generation simulation is an important document for predicting how much electricity the planned solar power equipment will generate. By checking annual generation, monthly generation, self-consumption, surplus power, and generation losses, you can concretize the expected operation after installation. However, a simulation does not automatically produce an accurate answer simply because it is requested. The reliability of the results varies greatly depending on the input conditions and the information shared at the time of request.

A common situation for practitioners is receiving simulations from multiple vendors with differing estimates of generation and reduction effects, leaving them unsure which to trust. Such differences arise not only from each vendor’s calculation methods but also from differences in the granularity and assumptions of the information provided at the time of request. If you give one vendor only drawings while another receives site photos and power usage data, you cannot directly compare the results.

To improve the accuracy of a solar power generation simulation, it is essential for your team to organize the information that should be confirmed before requesting. Knowing the candidate site area and orientation, usable roof or ground area, surrounding shading, facility power consumption, operating hours, and planned future equipment changes helps vendors calculate under conditions closer to reality. Conversely, if information is insufficient, vendors will use general assumptions and approximate conditions, which may require major revisions later.

The pre-request checks do not mean performing specialist calculations in-house. What practitioners should do is organize the on-site and operational information that forms the simulation’s assumptions so that the same conditions can be communicated to vendors. This makes proposal comparisons easier and helps determine whether differences in generation estimates stem from design choices or differing assumptions.

A solar power generation simulation is not just a generation forecast; it is a foundation for making an installation decision. If you confirm the key points before requesting, you can read the results more precisely and have more concrete discussions with vendors. The following sections explain the eight items to check before requesting, in order.

Check 1: Clarify the purpose of installation

Before requesting a solar power generation simulation, the first thing to organize is the installation purpose. If the purpose is vague when you request a simulation, vendors tend to produce proposals aimed at maximizing generation. However, the optimal solar design depends on what you prioritize. The simulation results to focus on differ depending on whether you want to increase self-consumption, prioritize electricity cost reduction, prepare for emergencies, or introduce the system as part of environmental initiatives.

If you prioritize self-consumption, what matters is not only the annual generation but how much the facility’s usage hours overlap with generation hours. Facilities with high daytime demand can more easily use generated power directly. Conversely, facilities that mainly operate at night will have times that are hard to self-consume with solar alone, so batteries or operational changes may need to be considered.

If you prioritize electricity cost reduction, focus on the portion of generation that reduces purchased electricity. Even with high generation, large surpluses may not directly translate to the expected cost reductions. Therefore, when requesting a simulation, it is important to communicate objectives like “I want to know the self-consumable generation,” or “I want to confirm the reduction in purchased electricity,” rather than simply “maximize generation.”

If emergency use is a priority, you need a perspective separate from normal self-consumption. Clarify which equipment you want to run during outages, how long you expect to operate, and how you view the relationship between daytime generation and storage. Operating strategies that fully consume batteries during normal times versus reserving charge for emergencies will change the simulation results.

If the installation purpose is clear, you can specify the simulation contents to vendors. Instead of simply asking to “know the solar generation,” say things like “I want monthly generation and surplus power on a self-consumption basis,” “I want to check overlap with daytime demand,” or “Please compare with and without batteries.” Such requests are more likely to produce practical results. Clarifying the purpose is the starting point for a solar power generation simulation.

Check 2: Organize actual power usage

To obtain practical simulation results, organizing the facility’s power usage is indispensable. If you only want to predict generation amounts, the primary information centers on the installation site and system capacity. But if you are considering electricity cost reductions or self-consumption, you must know when and how much power the facility uses.

First, confirm the annual power consumption. Knowing the annual usage level helps you gauge the scale of the solar system. However, annual totals alone are insufficient. Because solar generates during the daytime, a large annual total may still be hard to self-consume if the facility’s usage is concentrated at night. Monthly and hourly data are important to correctly assess the installation’s effectiveness.

Organizing monthly power usage reveals seasonal demand variations. Facilities with high air-conditioning loads in summer, heating or production loads in winter, or distinct busy and slow seasons will show large peaks and valleys. Since solar generation also varies seasonally, comparing monthly usage and monthly generation clarifies when self-consumption is easy and when surpluses are likely.

Hourly power usage further improves simulation accuracy. Solar generation begins in the morning, increases around midday, and decreases toward evening. The more the facility’s load curve overlaps this generation curve, the easier it is to self-consume. Facilities operating machinery or HVAC during the day may match well, while those with demand concentrated in the evening or night may see limited reduction effects from solar alone.

How you treat holidays and non-operating days is also important. Even if weekday daytime demand is high, operations may stop on holidays, causing generated power to become surplus. Annual averages can hide these differences. Before requesting a simulation, organize operating days, holidays, seasonal operating patterns, and any special operating schedules for a more realistic estimate.

Organizing actual power usage is the foundation for using a solar simulation to assess electricity bill reductions and self-consumption. Rather than proceeding based only on generation estimates, comparing generation with facility demand helps determine system capacity and the need for batteries.

Check 3: Understand the conditions of candidate installation sites

Before requesting a simulation, understand the candidate installation site conditions as much as possible. Solar generation depends greatly on the site’s area, orientation, tilt, shading, and surrounding environment. Even with the same system capacity, a good site and a poor site can produce different annual generation. Therefore, if site information is vague, the simulation results tend to remain approximate.

For rooftop installations, first confirm the roof surface shape and usable area. Consider roof area, pitch, orientation, material, locations of existing equipment, inspection routes, handrails, rooftop structures, piping, and lightning protection. Although plans may indicate ample usable area, in reality equipment and required clearances for safety can limit installable area. If you can convey the actual roof conditions when requesting a simulation, you reduce the risk of later design changes.

For ground-mounted systems, check site shape, elevation changes, boundary with neighboring land, existing structures, drainage, maintenance paths, surrounding buildings, trees, and future planned uses. Even if the site is large, you cannot use all of it for solar. Consider vehicle access, inspection routes, disaster-prevention clearances, and separations from surrounding equipment. Simulating at maximum capacity without these considerations can lead to discrepancies with the actual plan.

Orientation and tilt are also important. Generally, south-facing orientations tend to yield higher annual generation, but east- or west-facing surfaces are not necessarily poor. Depending on facility demand hours, morning- or afternoon-weighted generation can be advantageous. Roof pitch and mounting angle also affect monthly generation. Having a rough grasp of orientation and tilt before requesting helps you understand proposals.

If you have multiple candidate sites, organize each condition separately. Treating south, east, and west roof faces and ground space as a single candidate makes it hard to see which areas contribute to generation. Request results that show generation and capacity by location so you can decide which sites to prioritize or exclude.

Understanding candidate site conditions not only improves simulation accuracy but also makes vendor proposals easier to compare. If you convey accurate on-site conditions, differences among vendors’ proposals become more visible as design-policy differences.

Check 4: Confirm shading factors and the surrounding environment

Before requesting a solar power generation simulation, it is very important to confirm shading factors. Solar generation depends on solar irradiance, so shading reduces generation. Moreover, shading effects are not determined solely by shaded area; the time of day, season, panel layout, and electrical connection configuration all affect the impact on generation.

Sources of shading include surrounding buildings, rooftop equipment, rooftop structures, handrails, piping, chimneys, signs, trees, utility poles, and neighboring structures. On rooftops, even small equipment that is usually overlooked can cast shadows depending on season and time of day. For ground-mounted systems, site elevation changes and on-site structures also create shading.

Shading changes by season. In summer, the sun’s altitude is high so shadows are short, but in winter the sun’s altitude is low and shadows lengthen. A site that seems fine in summer may have panel shading from surrounding buildings or equipment in winter. When requesting a simulation, ask vendors to include winter shading in their assessment.

Underestimating shading leads to overly optimistic simulated generation. After installation, actual generation may fall short of expectations. Pay particular attention to areas shaded in the morning and evening, places where shadows lengthen in winter, locations near rooftop equipment, and places where tree growth is expected. Organizing site photos and the positions of obstacles before requesting helps vendors evaluate shading.

The surrounding environment also affects soiling and maintenance. Sites with frequent dust, leaf accumulation, bird activity, or exhaust and particulate matter may experience generation reductions due to dirty panels. Reflect these environmental factors in loss assumptions if needed for a more realistic simulation.

Shading and the surrounding environment are difficult to capture from drawings alone. Inspect the site before requesting and list anything likely to affect generation to increase simulation reliability. In practice, checking how thoroughly vendors incorporate on-site shading is as important as chasing larger generation figures.

Check 5: Decide on the approach to system capacity

Before requesting a solar power generation simulation, decide how you want to consider system capacity. System capacity is a key condition directly linked to generation. Increasing capacity tends to increase annual generation, but a larger capacity is not always the optimal proposal. Appropriate capacity depends on installation site, power usage, self-consumption policy, and treatment of surplus power.

If you request capacity maximization, the simulation may place as many panels as possible on the roof or site. In that case, annual generation appears larger, but the layout may include shaded or hard-to-maintain areas. Using poor-generation areas can reduce generation per unit of capacity.

If you prioritize self-consumption, consider a capacity matched to facility demand. Excessive generation can increase unusable surplus during the day. A smaller capacity may raise self-consumption rates and be easier to operate. However, making capacity too small reduces total self-consumed energy, so it is important to balance generation and usage.

When requesting simulations, it is effective to compare multiple capacity patterns, not only the maximum. For example, compare the maximum installable capacity, a capacity limited to the most efficient surfaces, a self-consumption-focused capacity, and a capacity that allows future expansion. Comparing multiple scenarios as simulation conditions—not just as article or proposal formats—helps determine the scale that fits your objectives.

Maintainability also relates to capacity decisions. Whether to secure inspection routes, leave work space around rooftop equipment, or plan for future equipment replacement affects installable capacity. Focusing solely on short-term generation maximization can create inconveniences for long-term operation.

Capacity should be chosen not to fill the site but to be easy to generate from, use, and manage. Before requesting a simulation, clarify whether you want to know the maximum capacity, the appropriate capacity, or the capacity that suits self-consumption so your request is clear.

Check 6: Organize the policy on self-consumption and surplus power

Before requesting a solar power generation simulation, organize your policy on self-consumption and surplus power. Generated solar power is divided into the portion used on-site and the portion left unused. If electricity cost reduction is the main objective, the amount of power that can be self-consumed is particularly important.

If you prioritize self-consumption, the simulation should report not only generation but also self-consumed energy, self-consumption rate, and surplus power. Even with high annual generation, large surplus means limited on-site usable power. Conversely, a modest annual generation that matches facility demand well can yield a plan that is easy to self-consume.

How you handle surplus affects capacity and battery considerations. If your policy is to minimize surplus, you may plan for capacity that matches daytime demand. If you intend to utilize surplus in other ways, include batteries or operational changes in the simulation. Before requesting, decide whether you will tolerate, minimize, or utilize surplus to make vendor proposals easier to compare.

Facility operating patterns are important when considering self-consumption. Facilities that operate steadily during daytime are easier to self-consume. Facilities with holidays or long shutdowns may see increased surplus during those periods. Confirm whether the simulation can account for weekdays, holidays, and seasonal variation.

Also consider future changes in power demand. If you expect future electric equipment installations, HVAC upgrades, production changes, or shifts in operating hours, judging self-consumption on current usage alone may not match the future. If you have firm future plans, share them at request time for a more practical simulation.

If the policy on self-consumption and surplus is clear, you will have a clearer basis for evaluating simulation results. Instead of only asking if generation is large, you can evaluate how effectively generated power can be used.

Check 7: Consider the presence of batteries and emergency use

Before requesting a solar power generation simulation, decide whether to consider batteries and whether to assume emergency use. Including batteries changes how you interpret the simulation. For solar alone, overlap between daytime generation and daytime demand is central, but with batteries you can consider using daytime surplus in the evening or night.

However, adding a battery does not always increase benefits. Facilities with little surplus cannot charge batteries much. Conversely, if surplus is large but demand during discharge times is low, batteries may not be fully utilized. Request comparisons with and without batteries to see how self-consumption and surplus change and facilitate decision-making.

If you consider batteries, separate normal operation and emergency use. Under normal operation, batteries store daytime surplus for use when generation is zero to increase self-consumption. For emergency use, batteries supply power to necessary equipment during outages. These are different operational policies. Using batteries until depleted in normal times may leave insufficient charge for emergencies. Reserving capacity for emergencies reduces usable capacity for normal times.

If emergency use is a consideration, decide which equipment to prioritize. Will the battery cover the entire facility, or only essential lighting, communications, and control systems? The necessary approach differs. You must also consider nights and bad-weather periods when solar is not generating.

For simulations that include batteries, check charging/discharging losses. Not all energy stored in a battery is available later; conversion and charge/discharge processes incur losses. When requesting, ask that the simulation report self-consumption, surplus, charge and discharge amounts, and remaining state under battery scenarios to avoid overestimating benefits.

If you organize whether to include batteries and emergency use in advance, the scope of the simulation becomes clear. Indicate whether you want to analyze solar alone, include batteries, emphasize normal-time savings, or place emphasis on emergency preparedness to obtain more practical results.

Check 8: Align request conditions to make comparisons easier

When requesting solar power generation simulations from multiple vendors, align the request conditions. If conditions differ, you cannot correctly compare the results. If you request maximum capacity from one vendor and self-consumption-focused scenarios from another, it is natural that generation and surplus differ. For meaningful comparisons, base requests on the same assumptions.

First, share the same site information with each vendor. Organize and provide roof plans, site maps, site photos, obstacle locations, installable ranges, and areas you want excluded. If information differs, you cannot tell whether result differences stem from vendor design capability or different input data.

Next, share the same power usage data. Provide annual, monthly, hourly usage, and operating/holiday schedules to the extent possible. The granularity of power usage data greatly affects results when assessing self-consumption. To avoid different vendor assumptions, standardize the base data on your side.

Also, standardize the simulation items you want. In addition to annual generation, specify monthly generation, self-consumption, surplus power, system capacity, generation per unit capacity, treatment of shading and losses, and differences with and without batteries. Even if vendor proposals use different formats, having the same items shown makes comparisons easier.

Align system capacity conditions as well. Decide whether to compare maximum capacity, the same capacity, or ask each vendor to propose an optimal capacity for self-consumption. Comparing the same capacity reveals differences in generation efficiency and condition settings. Requesting optimal capacities shows each vendor’s design philosophy.

Aligning request conditions is not only for fair vendor comparison. It also clarifies decision-making within your organization. If you can compare high-generation, low-surplus, self-consumption-friendly, and maintenance-focused proposals under the same assumptions, you will have greater confidence in your decision.

How to read simulation results after requesting

After requesting a solar power generation simulation, do not accept the numbers at face value; interpret them by checking assumptions and breakdowns. Annual generation tends to catch attention first, but that alone cannot determine a proposal’s quality. Annual generation is an important metric, but must be viewed together with system capacity, site conditions, shading, losses, and self-consumption assumptions.

First confirm the relationship between system capacity and annual generation. Larger capacity tends to increase generation, so simply comparing generation favors larger capacities. Looking at generation per unit capacity helps verify the plausibility of site and calculation assumptions. If a number is unusually high, check whether the assumed irradiance or loss factors are overly optimistic.

Next, review monthly generation. Monthly trends reveal seasonal peaks and valleys. If a site expected to have strong winter shading shows high winter generation, or if a region with snow or persistent cloud shows unnaturally stable generation, review the assumptions. Monthly data helps spot inconsistencies that annual totals mask.

Self-consumed energy and surplus power are also important. If electricity cost reduction is the goal, how much of the generation can be used on-site matters. A high self-consumption rate with small capacity may still yield a small amount of self-consumed energy; conversely, a lower rate with a much larger capacity can result in a large self-consumed energy increase. Separate percentage rates from energy amounts when assessing.

Also check how losses are treated. Confirm assumptions for temperature, conversion, wiring, soiling, shading, and aging losses. Smaller assumed losses yield larger generation but can create large gaps with post-installation performance. Reliable simulations not only show larger generation but also explain factors that reduce output.

Simulation results are not a single correct answer but material for decision-making. When reading the results, confirm not only the magnitude of the numbers but the assumptions from which they arose. Organizing conditions before requesting makes result interpretation easier and helps you ask vendors concrete follow-up questions.

Improving the accuracy of on-site information raises request quality

To improve the quality of solar power generation simulations, increase the accuracy of on-site information. Simulations predict generation based on site conditions. If roof or site shape, orientation, tilt, obstacles, and surrounding environment are not accurately known, results will be unstable.

If site information is vague when you request a simulation, vendors will calculate from drawings and approximate assumptions. That is acceptable for initial studies, but when you reach a decision-making stage you need data that reflects on-site realities. Equipment not shown on drawings, subsequently installed piping, inspection spaces, adjacent buildings, and grown trees can all affect generation and installable area.

Accurate on-site information allows realistic judgments of usable area. By clarifying usable roof faces, obstacles to avoid, areas affected by shading, and areas to retain for maintenance routes, you make simulation assumptions clear. Consequently, estimates of system capacity, generation, self-consumption, and surplus become closer to reality.

The accuracy of on-site information also strongly affects vendor comparisons. Sharing the same on-site conditions with each vendor enables fair comparison of proposals. Conversely, if each vendor interprets site conditions differently, you cannot tell what drives differences in simulation results. Organizing on-site information on your side is effective for improving comparison accuracy.

On-site information should include location data. If you accurately record candidate locations, obstacle positions, surrounding structures, site boundaries, inspection targets, and existing equipment positions, you can use this information not only for simulation but also for pre-construction checks and maintenance management. Because solar systems operate long-term, organizing site information before installation helps future management.

Summary

Before requesting a solar power generation simulation, it is important to organize eight items: installation purpose, power usage, candidate sites, shading factors, system capacity, self-consumption and surplus policy, presence of batteries and emergency use, and comparison conditions. If you request without confirming these, simulation results tend to remain approximate and vendor proposal comparisons become difficult.

Clarifying the installation purpose determines whether you want to maximize generation, prioritize self-consumption, or consider emergency preparedness. Organizing actual power usage makes it easier to check overlap between generation and demand. Understanding candidate site conditions and shading factors brings generation forecasts closer to on-site realities.

For system capacity, consider not only maximum capacity but appropriate capacity. Choose a capacity that is easy to generate from, use, and manage rather than simply filling available space. Organizing self-consumption and surplus policy links to electricity cost reduction and battery considerations. When considering batteries, separate normal-time use and emergency use.

When requesting from multiple vendors, align request conditions. Sharing the same site information, power usage data, and checklist items makes proposals easier to compare. After receiving simulations, interpret not only annual generation but also monthly generation, self-consumed energy, surplus power, loss assumptions, and the relationship with system capacity.

The basis for improving request quality is accurate on-site information. If you correctly grasp roof or site shape, orientation, tilt, obstacles, surrounding structures, and maintenance routes, simulation assumptions become clear and vendor comparisons are easier. Reflecting actual site conditions rather than relying solely on desk calculations is fundamental to making solar power generation simulations a trustworthy basis for decisions.

If you want to accurately record candidate sites, obstacles, existing equipment, site boundaries, and inspection routes on-site and prepare consistent request conditions for simulations, using LRTK, an iPhone-mounted GNSS high-precision positioning device, is effective. If you can obtain high-precision location information on-site, it becomes easier to organize pre-request data, share conditions with vendors, compare proposals, perform pre-construction checks, and manage maintenance. To ensure thorough preparation before requesting a solar power generation simulation, it is important to accurately assemble both power data and on-site information.