6 Items to Assess the Day-Night Power Balance in Solar Power Generation Calculations

When calculating solar power generation, looking only at annual or monthly generation figures does not allow you to fully determine whether it will suit actual power operations. Because solar power generates mainly during the daytime, it becomes easier to evaluate installation benefits and operational policies only after clarifying how much can be used during the day, how much shortfall will occur after the evening, and how surplus power will be handled.

Especially in practice, it is necessary to look not only at the total amount of power generation but also at consumption by time of day, daytime self-consumption, nighttime electricity purchases, the presence or absence of a storage battery, differences between holidays and weekdays, seasonal variations, and so on. Even if a large amount of power is generated during the day, surplus increases if electricity is not used during that time. Conversely, even if annual generation appears sufficient, facilities with high nighttime consumption are more likely to still need to purchase electricity.

This article explains six items that operations personnel searching for information on "solar power generation calculation" should check to assess the day–night power balance. Rather than merely providing a rough estimate of generation, it summarizes an approach for organizing usable decision-making material for the field by taking into account the time difference between generation and consumption.

Table of Contents

• Solar power generation calculations assume the time difference between day and night.

• Item 1: Organize daytime electricity consumption by time period

• Item 2: View solar power generation as a daytime generation curve

• Item 3: Check self-consumption and surplus electricity separately

• Item 4: Evaluate nighttime electricity purchases and the need for a storage battery

• Item 5: Review the day-night balance according to season, weather, and weekdays/holidays

• Item 6: Linking power balance to operational improvements and equipment planning

• Summary: Visualize day-night misalignment and leverage power generation calculations in practical operations

Assume a day-night time difference in solar power generation calculations

When calculating solar power generation, the first point to grasp is that the times when power is generated and when electricity is used do not necessarily coincide. Because solar power generates electricity from solar radiation, generation is concentrated during daytime. On the other hand, electricity use in residences, offices, factories, shops, warehouses, and other facilities varies greatly depending on the building’s purpose and operating hours. Some facilities consume a lot of electricity during the daytime, while others have usage centered in the evening and at night.

When you look only at the annual total of generated electricity, it may appear that solar power can cover a substantial portion of electricity consumption. However, in reality you need to treat separately the electricity that can be used at the moment it is generated and the electricity required at night. If the electricity generated during the day cannot be used on site, it will either be exported as surplus power or stored in batteries. Because solar generation cannot be relied on at night, you must either use electricity stored in batteries or buy power from the grid.

Therefore, when calculating solar power generation, it is important not only to consider "how many kWh are generated per day" but also to look at "how much is generated at what times" and "how much electricity is used during those time periods." To look at the day-night power balance means overlaying generation and consumption on a time axis and separately grasping the electricity available for use during the day, the excess electricity, and the electricity that is lacking at night.

A common mistake in practice is to determine the installation size solely by comparing monthly electricity consumption and projected power generation. For example, even if monthly consumption and monthly generation are similar, the amount that can be self-consumed is limited if daytime consumption is low. Conversely, at facilities where daytime use of air conditioning, refrigeration/freezing, pumps, processing equipment, lighting, and so on is high, generated power is easier to use on site and is more likely to reduce daytime electricity purchases.

Also, considering the balance between daytime and nighttime usage is important when deciding system capacity. Increasing generation capacity will raise annual generation, but it can also increase surplus that cannot be used during the daytime. If you increase system capacity without considering how to handle surplus, the self-consumption rate may not improve as much as expected. Conversely, if you adjust system capacity to match daytime consumption, it's easier to use the generated electricity without waste.

When considering the day-night power balance, first separate and organize the terms "generated energy", "consumption", "self-consumption", "surplus energy", and "nighttime purchased electricity". Generated energy is the amount of electricity produced by the solar PV system. Consumption is the amount of electricity used by the building and equipment. Self-consumption is the portion of the generated electricity used on-site. Surplus energy is the portion of the generated electricity that could not be used during that time period. Nighttime purchased electricity is the amount of electricity purchased from external sources during periods when solar generation is not available.

By dividing the analysis in this way, solar power generation calculations become not merely forecasts of generation but materials for power operations planning. It becomes easier to determine how effectively electricity generated during the daytime can be used, to what extent nighttime shortfalls can be offset, and whether battery storage or operational changes are required.

Item 1: Organize daytime power consumption by time period

The first step in assessing the day–night electricity balance is to organize daytime electricity consumption by time of day. No matter how accurately you calculate solar power generation, if the demand-side information remains coarse you cannot properly estimate how much can be self-consumed. This is because monthly energy consumption figures alone do not show whether the electricity is used during the day or at night.

In practice, verify electricity consumption on an hourly basis whenever possible, and on 30-minute intervals if feasible. Use utility usage data, records of power receiving equipment, monitoring device data, and building management system logs to examine daily electricity usage patterns. Even when detailed data are not available, it is important to ask about operating hours, run-times of major equipment, and differences between holidays and weekdays in order to create time-of-day estimates.

When assessing daytime electricity consumption, rather than simply calculating the total, identify which time periods experience the highest load. For example, in facilities where air conditioning and equipment all start up together at the beginning of the workday, electricity use may increase in the morning. In factories where many production machines run in the afternoon, generation peaks and consumption peaks may easily coincide. In food service and retail establishments, loads can be higher during lunchtime and evening customer periods.

When organizing daytime consumption, roughly divide the day into the time periods when solar generation can be expected. Generation is low in the early morning, increases from the morning into midday, and then gradually decreases toward the afternoon. It varies with the season and installation conditions, but how much electricity is used during the core daytime hours greatly affects the ease of self-consumption.

One point to note is that even if daytime consumption appears high, the generation peak and the consumption peak can be out of sync. In facilities that use a lot of electricity in the morning and see consumption drop in the afternoon, afternoon generation can become surplus. Conversely, in facilities where consumption increases in the evening and later, solar power alone may find it difficult to directly meet that load.

Also, daytime consumption includes fixed loads and variable loads. Fixed loads are power that occurs continuously during the day, such as lighting, ventilation, standby power, and equipment that runs at a constant setting. Variable loads are power that changes depending on temperature, workload, and operating conditions, such as air conditioning, refrigeration, heating, processing machines, and conveying equipment. Fixed loads are easy to allocate as recipients of on-site solar self-consumption, whereas variable loads require consideration of day-to-day variability.

When analyzing daytime electricity consumption, check not only weekdays but also holidays. In factories and offices, daytime consumption may be high on weekdays, but operations are reduced on holidays and surplus increases. In stores and commercial facilities, consumption may be higher on holidays. Treating weekdays and holidays under the same conditions can lead to misestimating annual self-consumption and surplus electricity.

Furthermore, daytime electricity consumption also changes with the seasons. In summer, many facilities see higher air-conditioning loads, which can increase daytime consumption. Conversely, solar power generation is influenced by sunlight conditions, temperature, installation orientation, and regional differences, so summer is not necessarily the period with the highest output. In winter, consumption can rise due to heating, hot water demand, and longer lighting hours, while in regions or periods with reduced sunlight conditions generation may struggle to increase. For these reasons, it is advisable not to judge based on a single representative month but to check daytime consumption for each season.

When daytime consumption can be organized, the accuracy of solar power generation calculations improves. It becomes easier to determine how much of the generated electricity can be used on-site, which time periods are prone to surplus, and whether increasing system capacity will increase self-consumption or only increase surplus. Before starting calculations on the generation side, arranging time-of-day consumption data is an essential preparation for assessing the day–night balance.

Item 2: Viewing solar power generation as the daytime generation curve

Next, what we want to look at is viewing solar power generation as a daily generation curve. When calculating solar power output, it is common to estimate annual or monthly generation, but that alone is insufficient for examining the day–night power balance. By understanding around what times generation increases and decreases, you can check how it overlaps with consumption.

On clear days, the daily output of solar power generation gradually increases from the morning, peaks around midday, and declines toward the evening. However, the actual generation curve varies depending on installation orientation, tilt angle, surrounding shading, ambient temperature, cloud movement, equipment specifications, and other factors. South-facing installations tend to concentrate generation around the central daytime hours; installations oriented more toward the east tend to generate more in the morning, while those oriented more toward the west tend to generate more in the afternoon.

When evaluating the day‑night power balance, the overlap between the generation curve and the consumption curve is important. If the peak of the generation curve occurs during periods of low consumption, surpluses are more likely to arise. Conversely, if high generation coincides with consumption from equipment, air conditioning, lighting, and so on, self‑consumption tends to increase. Even if the monthly generation is the same, the amount that can be self‑consumed varies depending on the shape of the generation curve.

The basic concept for calculating power generation is to multiply system capacity, solar irradiance, and losses. In practice, estimates take into account the solar conditions at the installation site, the orientation and tilt of the panel surface, system capacity, output reduction due to temperature, losses from wiring and conversion, and degradation from soiling and aging. However, if you want to see the day-night balance, you need to break it down by day or by time of day instead of summarizing it only as one-month or one-year totals.

Even if it is difficult to calculate generation by time of day in detail, classifying trends into morning, midday, afternoon, and evening makes it easier to see the relationship with consumption. For example, in facilities with high morning consumption, east-facing roofs or layouts may better align with the consumption period. In facilities with high afternoon loads, west-facing generation may overlap more with consumption. However, because installation conditions are also influenced by roof shape, site conditions, safety, and constructability, it is important not to judge based on generation alone.

When examining a power generation curve, focus not only on the moment of maximum output but also on the periods during which generation remains above a certain level. Even if an instantaneous peak is large, if consumption is low at that time it results in excess generation. Conversely, when the generation peak is broad and prolonged, it is more likely to overlap with consumption across a wide daytime period. For the day-night power balance, it is important to consider not only the peak height but also the time span during which generation is available.

Shading also has a major effect on the power generation curve. If shading occurs only in the morning, generation during the morning will decrease. If shading occurs in the evening, generation in the latter half of the afternoon will decrease. If shading occurs during the midday peak hours, it can have a large impact on overall generation. Shadows cast by surrounding buildings, equipment racks, trees, handrails, rooftop machinery, and other objects change position with the seasons and time of day, so they need to be checked throughout the year.

The power generation curve is also relevant when considering battery storage systems. If there are periods during the day when generation is high and consumption is low, one approach is to charge the battery with the surplus and use it at night. However, effectiveness varies depending on the battery’s capacity, charge/discharge control, and intended use. If you decide on battery capacity without understanding the power generation curve, you may be unable to fully charge the battery or may not be able to make full use of it.

In solar power generation calculations, you should not stop at simply totaling the generated energy; you need to consciously overlay the generation curve on the consumption curve. By visualizing when power is generated and when it can be used, the relationships between self-consumption, surplus, and nighttime shortfalls become clear. This forms the foundation for examining the day-night power balance.

Item 3: Confirm self-consumption and surplus electricity separately

After organizing daytime consumption and the generation curve, the next step is to separate and check self-consumption and surplus electricity. In calculating solar power generation, treating all generated energy as fully usable can lead to a risk of overestimating the actual effect. Of the electricity generated, the portion that can be used within the building during that time is self-consumption, and the portion that cannot be used is surplus electricity.

Self-consumption is easiest to understand if you think of it, for each time period, as the smaller of "generation" and "consumption." For example, even if generation is high during a certain period, if consumption is low, the amount you can self-consume is limited to the consumption. Conversely, in periods when consumption exceeds generation, you can self-consume the entire generation, but the shortfall will be made up by purchased electricity. By summing this approach across time periods, you can estimate daily, monthly, and annual self-consumption and surplus electricity.

What is important here is that total power generation and self-consumption are not the same. Even if annual generation is large, if there are many daytime periods when you cannot use all the produced power, the amount of self-consumption will be hard to increase. Conversely, even if generation itself is moderate, if it aligns well with daytime consumption, the self-consumption rate may become high. When considering the effects of installation, you need to look not only at the amount of generation but also at the proportion that can be self-consumed.

The self-consumption rate is the proportion of generated electricity that is consumed on-site. It can be approximated by dividing the amount consumed on-site by the amount generated. On the other hand, when assessing the degree of energy self-sufficiency from solar power, you check the share of the building’s total consumption that was covered by solar. These two are similar but have different meanings. Even if the self-consumption rate is high, if the system capacity is small, its contribution to total consumption is limited. Conversely, when system capacity is large, the contribution to total consumption may increase, but excess generation can also rise and the self-consumption rate may fall.

Checking the amount of surplus electricity is important for verifying the appropriateness of equipment capacity. If surplus is small, the generated electricity is readily usable on-site. However, if equipment capacity is reduced too much to make surplus extremely small, the contribution from generation may become small. Conversely, if surplus is large, there is room to consider battery storage, operational changes, demand shifting, or reviewing equipment capacity.

It is also important to check the time periods when surplus occurs. Countermeasures vary depending on whether surplus appears only during part of the daytime, whether sunny days produce long periods of surplus, or whether surpluses are large on holidays. If the surplus is only temporary during daytime on weekdays, major measures may not be necessary. On the other hand, if surpluses become large on holidays or during off-peak periods, it is necessary to look at the annual surplus energy and carefully consider equipment capacity and operational methods.

Separating self-consumption and surplus electricity makes the daytime-nighttime balance easier to see. If there is a surplus during the day but a lot of purchased electricity at night, you can determine that a time-shift issue is the problem. In that case, possible measures include using battery storage to shift surplus to nighttime, moving equipment that can be operated during the day to daytime operation, and adjusting operating schedules. Conversely, if there is little surplus during the day and purchased electricity remains at night, it may be preferable to first review the generation capacity or the daytime load profile rather than relying on battery storage.

Also, to increase self-consumption, not only adding equipment but also operational adjustments are important. Check whether there are pieces of equipment whose operating hours can be shifted to daytime, whether charging, heating, cooling, etc. can be moved to daytime, and whether any large loads are being stopped during break times or setup times. Rather than forcing changes to equipment operation, it is practical to consider ways of using equipment aligned with generation hours within a range that does not affect work quality or safety.

By separating and checking self-consumption and surplus electricity in this way, solar power generation calculations become practical information for decision-making. It is not just about whether the amount of generation is large or small; distinguishing usable generation from surplus generation is central to assessing the day–night power balance.

Item 4: Assess nighttime electricity purchases and the need for battery storage

In the day–night power balance, it is also essential to check how much electricity is purchased at night. Solar power generation is primarily produced during the day and basically does not generate at night. Therefore, unless you understand how much electricity is used at night, you cannot determine how much of the electricity burden can be reduced by solar power alone.

When looking at nighttime purchased electricity, first check the breakdown of the loads occurring at night. In residences, consider lighting, air conditioning, water heating, household appliances, charging, etc. In offices or stores, there are lighting, air conditioning, refrigeration equipment, ventilation, standby power, security equipment, and information/IT equipment. In factories and warehouses, nighttime-operating production equipment, refrigeration and freezing, pumps, compressed-air-related equipment, and continuously operated equipment are involved.

If nighttime load is small, the main effect of solar power generation is to reduce daytime electricity purchases. In that case, adding battery storage for nighttime use may have only limited benefit. Conversely, if nighttime load is large and there is a lot of surplus power during the day, the idea of storing the surplus for nighttime use becomes easier to consider. However, decisions about installing battery storage need to be made comprehensively, taking into account capacity, the number of charge/discharge cycles, intended use, how it will be used during outages, installation space, safety, and maintenance.

Before considering the need for a storage battery, confirm the relationship between daytime surplus electricity and nighttime electricity purchases. If there is little surplus during the day, there is little electricity that can be charged into the storage battery, so the effectiveness of nighttime use tends to be limited. Conversely, when there is a large daytime surplus and there is steady consumption at night, there is room to shift surplus to nighttime. However, because storage batteries incur losses during charging and discharging, the daytime surplus cannot be used entirely at night as is.

When checking nighttime electricity purchases, look not only at the average but also at the peak and minimum loads. Facilities that have a consistently steady load throughout the night make it easier to plan battery discharge schedules. In facilities where nighttime load varies greatly from day to day, there may be days when a fully charged battery cannot be fully utilized, and conversely days when capacity is insufficient. Whether nighttime usage is stable affects consideration of battery capacity.

Also, the approach changes depending on whether your sole objective is to reduce electricity purchases at night or you also prioritize preparedness for power outages. If there are essential pieces of equipment you want to keep running during an outage, you need to define the loads and operating hours required in an emergency separately from the normal power balance. Confusing the day-night balance calculation with the emergency-use calculation can lead to misjudging the battery capacity and operating conditions.

The amount of electricity purchased at night can in some cases be reduced through operational improvements. Check whether unnecessary equipment is running at night, whether standby power is excessive, and whether the operating hours for air conditioning and ventilation match actual usage. If the purpose of solar power generation calculations is to optimize electricity costs or save energy, it is important to review not only the generation equipment but also the nighttime load itself. Reducing unnecessary nighttime consumption will improve the overall power balance before relying on solar power or batteries.

Even when considering battery storage, rather than assuming you will store all daytime surplus, look at the amount that can actually be used during the night. If capacity is too large, you may see more days when it cannot be fully charged or fully discharged. If capacity is too small, you may not be able to make sufficient use of the surplus. Therefore, battery capacity should be determined by balancing daytime surplus, nighttime load, intended use, and operating conditions.

By reviewing how much electricity is purchased at night, you can realistically evaluate the results of solar power generation calculations. It becomes clear whether daytime generation alone is sufficient, whether measures for nighttime loads are necessary, whether it makes sense to consider battery storage, or whether operational improvements should be prioritized. In assessing the balance of power between day and night, nighttime electricity purchases are as important to check as generation.

Item 5: Review the Day-Night Balance by Season, Weather, and Weekdays/Holidays

Solar power generation and the balance of electricity between day and night cannot be assessed using calculations for just a single day. This is because both generation and consumption change with the seasons, the weather, and differences between weekdays and holidays. If you judge the effect of an installation based only on calculations for a representative day, you may overlook surpluses or shortages that occur over the course of a year.

Seasonal differences have a significant impact on solar power generation calculations. Solar irradiance, day length, solar elevation, temperature, and weather trends change with the seasons. Separating periods when generation tends to increase from those when it tends to decrease makes it easier to understand the annual power balance. In particular, because the load on the consumption side also changes between summer and winter, it is necessary to examine not only generation but also consumption by season.

In summer, facilities with large air-conditioning loads tend to see increased daytime consumption, which can often coincide with solar power generation. If daytime consumption is also high during periods when generation is relatively large, self-consumption is likely to increase. On the other hand, depending on the region and installation conditions, output can be affected by the rainy season, typhoons, or temperature-driven output declines. In periods with many holidays or business closures, even if generation is high, consumption may be low and surpluses can increase. Don’t judge based only on summer generation; also check the number of operating days and the operational schedule.

During winter, power generation may decrease depending on the region and installation conditions. Shorter hours of sunlight and a lower solar altitude can make shadowing more likely. Conversely, in facilities where heating, lighting, and hot-water loads increase, energy consumption may rise. When generation drops in winter and nighttime consumption increases, a lack of balance between daytime and nighttime becomes more noticeable.

Variations due to weather are also important. On sunny days, generation increases and daytime surpluses tend to occur. On cloudy or rainy days, generation decreases and it may be necessary to purchase electricity even during the daytime. Looking only at the annual average generation makes it difficult to see the surpluses on sunny days and the shortfalls on bad-weather days. In practice, separating an average day, a high-generation day, and a low-generation day makes it easier to understand operational risks.

Do not overlook the differences between weekdays and holidays. In offices and factories that operate on weekdays, generation and consumption may overlap on weekdays, but consumption can be lower on holidays and surplus may increase. In commercial and service facilities, consumption may be higher on holidays. Calculating with a simple average without reflecting a facility’s operating calendar can lead to inaccurate estimates of self-consumption and surplus electricity.

Also, there are effects from long holidays, busy seasons, and slow seasons. In manufacturing, power consumption can change depending on production volume. In schools and public facilities, usage can vary greatly during vacation periods. In warehouses and logistics facilities, fluctuations in inbound and outbound shipment volumes can affect power usage. When using solar power generation output calculations in practice, it is important to reflect actual operating patterns rather than rely solely on simple monthly averages.

By taking seasons, weather, and weekdays and holidays into account, the day-night power balance becomes closer to reality. For example, even if the self-consumption rate looks high over the year, surpluses may be concentrated in specific periods. Conversely, even if the annual average appears to show a large surplus, it may be nearly exhausted during busy seasons. Understanding this difference makes consideration of equipment capacity, storage batteries, and operational changes more concrete.

When analyzing by season, check the monthly generation and consumption, and further dividing them into daytime and nighttime makes it more practical. By lining up monthly daytime consumption, monthly nighttime consumption, monthly generation, monthly self-consumption, and monthly surplus electricity, you can see when benefits are likely to occur and when shortages are likely. Even if you don't put it into a table, it is important to keep this classification in your calculations.

When evaluating the day-night power balance in solar power generation calculations, it is important not to draw conclusions based solely on averages. By checking multiple scenarios that take into account seasonal changes, weather, and differences between weekdays and holidays, you can make assessments that more closely reflect the actual situation after installation.

Item 6: Linking Power Balance to Operational Improvements and Equipment Planning

The purpose of calculating the day-night power balance is not just to know the amount of generation. It is important to use the calculation results to guide operational improvements and equipment planning. When generation, daytime consumption, self-consumption, surplus, and nighttime electricity purchases become clear, it is easier to judge where there is room for improvement.

First, consider whether there are power uses that can be shifted to daytime. Because solar power generates electricity during the day, the more loads that can be used during daytime, the easier it is to increase self-consumption. For example, if you have equipment whose timing can be adjusted—such as charging, heating, cooling, cleaning, pump operation, ventilation, or operations related to thermal or cold storage—check whether they can be moved to the generation period. However, any adjustments should be considered only to the extent that they do not affect operational efficiency, safety, quality, or worker burden.

Next, examine the time periods when a surplus occurs to confirm whether the system capacity is appropriate. If the surplus is consistently large, the system capacity may be too big for the consumption pattern. Conversely, if there is little surplus and you are purchasing a lot of electricity even during the daytime, you may be able to consider adding generation capacity, taking into account available installation area, contractual terms, and equipment constraints. When determining system capacity, it is important not only to maximize generation but also to consider its overlap with consumption.

Consideration of battery storage should also proceed while reviewing the results of the power balance. If there is a large daytime surplus and a large amount of purchased electricity at night, the approach of using a battery to shift daytime surplus to nighttime is more likely to be viable. Conversely, if daytime surplus is small, installing a battery may still offer limited charging opportunities. If nighttime load is low, the battery may also not be fully utilized. Be clear about the battery’s purpose and evaluate normal electricity use and emergency preparedness separately.

When improving operations, reducing unnecessary electricity use is also important. Before increasing daytime power generation, check for nighttime standby power, excessive air conditioning, unnecessary lighting, and equipment that runs for excessively long periods. If overall consumption decreases, the way you think about required generation and battery capacity will also change. Rather than treating energy conservation and solar generation calculations separately, it is practical to view them within the same power balance.

Also, the day-night balance calculation results can be used as explanatory materials for stakeholders. Rather than showing only generation amounts, explaining how much can be used during the daytime, how much will be surplus, and how much purchased electricity will still be required at night makes it easier to convey a picture of post-installation operation. It also makes it easier to share the same assumptions among management, on-site personnel, facility managers, and construction personnel, helping to prevent excessive expectations and misunderstandings.

In practice, it is important not to treat the calculation results as a one-time deliverable. After operations begin, check the measured data and examine the differences between assumptions and actual results. If there is more surplus than expected, review daytime usage patterns and how energy storage is utilized. If generation is lower than expected, check for shading, soiling, equipment condition, weather conditions, and measurement methods. If nighttime power purchases are higher than expected, re-examine the breakdown of nighttime loads and the operating schedule.

Continuously reviewing the power balance leads to operational improvements after introducing solar power generation equipment. Pre-installation calculations are merely hypotheses, and it is desirable to improve their accuracy through post-installation measurements. By periodically checking generation, consumption, surplus, and the amount of purchased electricity, you can adjust equipment usage to match on-site conditions.

In this way, the day–night power balance broadly involves equipment capacity, storage batteries, operational improvements, energy conservation, stakeholder communication, and post-installation verification. To make solar power generation calculations useful in practice, you must not leave the results as mere numbers but adopt a perspective that leads to concrete decisions and improvements.

Summary: Visualize day-night discrepancies and apply power generation calculations to practical operations

To assess the day-night electricity balance when calculating solar power generation, it is important to consider not only the total generation but also generation and consumption by time of day together. Because solar power generation occurs mainly during the daytime, you need to separately check how much can be used during the day, how much surplus is produced, and how much electricity will need to be purchased at night.

First, organize daytime electricity consumption by time of day. Monthly usage alone does not reveal the overlap between generation hours and consumption hours. Next, view solar power generation as a daytime generation curve. Whether the generation peak and the consumption peak coincide significantly affects the amount of self-consumption.

On that basis, we separate and verify self-consumption and surplus electricity. Because not all generated electricity can necessarily be used, it is practical to distinguish the portion that can be consumed from the portion that will be excess. We also review nighttime electricity purchases to assess the need for battery storage and the potential for operational improvements. The measures to take vary depending on whether nighttime demand is high or there is a large daytime surplus.

Also, by taking into account differences in season, weather, and weekdays versus holidays, you can bring the annual power balance closer to reality. Calculations based only on representative days can overlook biases toward surpluses or shortages. Verifying under multiple conditions makes it easier to assess equipment capacity and operational methods.

Finally, it is important to use the calculation results to inform operational improvements and equipment planning. Verify whether there are loads that can be shifted to daytime, whether surplus generation is excessive, whether nighttime loads can be reduced, and whether the purpose of using batteries is clear. After installation, continue to review measured data and compare assumptions with actual performance; by doing so, you can more easily increase the utilization of solar power generation.

When you visualize the day-night power balance, solar power generation calculations become not merely rough estimates but documents that can be used for decisions about installation, operational design, and improvement proposals. It is important to consolidate generation, consumption, self-consumption, surplus electricity, and nighttime electricity purchases, and make decisions tailored to the actual conditions on site.

When you want to use solar power generation calculation results to inform on-site decisions, a system that can capture not only generated output but also time-of-day consumption, the effects of shading, and day–night mismatches is useful. Rather than basing the approach solely on specific product or service names, it is effective to combine on-site surveys, electricity usage data, generation simulations, and checks of operating conditions to connect generation calculations with on-site verification.