7 Monitoring Items Households with Low Power Generation Should Review

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If you feel your power generation is low, check the monitor first, rather than assuming a 'fault'.

It is not uncommon for households that have installed solar power systems to feel, "the amount of power generation seems low lately," "it's less than the simulation," or "the income from selling electricity isn't increasing as much as I expected." In particular, if you check the numbers displayed on the monitor every day, you are more likely to become concerned about changes in generation.

However, even if the power generation appears low, it is premature to immediately conclude that the solar panels or the power conditioner have failed. The amount of power generated fluctuates due to various conditions such as weather, season, temperature, solar irradiance, shading, dirt, power consumption, voltage suppression, and output control.

What you need to be especially careful about is confusing "generated electricity" with "sold electricity." A solar power monitor displays the amount of electricity generated, the amount used at home, the amount sold to the utility, and the amount purchased from the utility. If you don't distinguish these correctly, you may mistakenly think that "generation is low" even though your system is actually generating power.

When you feel the power generation is low, it's important to first check the items displayed on the monitor in sequence. Rather than looking at a single number, combining information such as daily, monthly, and time-of-day breakdowns, power consumption, amount of electricity sold, and the status of the power conditioner can narrow down the cause considerably.

This article explains, divided into seven monitoring items, what to review when you feel the power output of your home solar power generation is low. It organizes the points you should check before suspecting a malfunction, common misconceptions, and cases in which you should request an inspection, so please refer to it if you want to calmly assess the condition of your home's solar power system.

7 Monitoring Items Households with Low Power Generation Should Review

The seven monitoring items you should check when you feel the power generation is low are as follows.

By checking these seven items in order, it becomes easier to determine whether the power output has actually decreased, whether it only appears low, or whether an equipment inspection is necessary.

1. View monthly power generation, not just the day's generation

When people feel their power generation is low, the first thing many check is "today's power generation".

Of course the day's power generation is important, but judging based on only one day's worth can be misleading.

Solar power generation is strongly affected by the weather. On days that are sunny only in the morning and cloudy from the afternoon, days with many thin clouds, days with a lot of yellow dust or pollen, or days when the sky looks whitish and hazy even though it isn’t raining, the power output may not increase much even if it appears sunny.

Therefore, when determining whether power generation is low, check not only the generation for the day but also the monthly generation.

The three points to look at are the following.

For example, if power generation is low for only a few days, it is likely due to the weather. On the other hand, if monthly power generation is clearly low despite many sunny days, you need to check the condition of the equipment and the surrounding environment.

Also, the power output from solar panels also varies with the seasons. In summer, longer hours of sunlight generally mean higher output, but if the temperature becomes too high the panels’ generation efficiency can drop. In winter, even though temperatures are low, sunlight hours are shorter and the sun’s altitude is lower, so roof orientation and shading are more likely to affect performance.

In other words, whether power generation is low should be determined not just by "today's numbers" but by comparing them with "past data from the same period." If your monitor can display year-on-year comparisons for the same month or monthly graphs, be sure to check them.

Guidelines for assessing monthly power generation

When reviewing monthly power generation, the following ways of looking at it are helpful.

• Isn't it extremely low compared with the same month of the previous year?

• Is the power generation not increasing despite the many sunny days?

• Has the power generation remained low for more than a week, even on sunny days?

• Is it showing a decline that cannot be explained by seasonal factors alone?

In particular, you should be cautious if performance has dropped significantly compared with the previous year under the same season and weather conditions. There may be some underlying cause, such as panel soiling, increased shading, a malfunctioning power conditioner, or voltage suppression.

2. Verify whether the power generation is reasonable given the weather and solar irradiance

If you feel the power output is low, don't just rely on the monitor's numbers; check them against the day's weather and solar irradiance conditions.

Solar power generation is a system that produces electricity by receiving sunlight. Therefore, it is natural for power output to be low on cloudy or rainy days. However, even if you felt it was "sunny," there may have been conditions that made it difficult for generation to increase.

For example, on days like the following, power generation tends to decrease.

If you can view a time-of-day power generation graph on the monitor, check the generation curve. On an ideal sunny day, power generation gradually increases from the morning, reaches a peak around midday, and then decreases toward the evening, forming a mountain-shaped graph.

On the other hand, the graph becomes jagged on cloudy days. If the power output suddenly rises and falls, it may be due to clouds rather than an equipment malfunction.

Points to check when power generation is low even on sunny days

If the power generation is low despite sunny weather, please check the following points.

• Are there any shadows during the peak power generation hours?

• Is there no noticeable dirt on the panel surface?

• Is the power conditioner operating normally?

• Are any indicators for voltage suppression or output control being displayed?

• Is your power consumption higher than usual, with only the amount of electricity you sell decreasing?

If, on a sunny day, the power generation graph doesn't form a peak and doesn't rise above a certain level, possible causes include output limiting by the power conditioner, voltage suppression, or a fault in part of the panels.

However, it can be difficult to definitively identify the cause using only consumer-grade monitors. It is important to observe whether the same trend occurs over multiple consecutive days.

3. Check the generated power itself, not the amount of electricity sold

A common occurrence in households that think their power generation is low is that they assume “low electricity sales = low power generation.”

However, the amount of electricity generated and the amount of electricity sold are not the same.

Electricity generated by solar power is used in the home first. Only the surplus electricity that cannot be consumed at home is sold back to the grid. In other words, even if the amount of electricity sold has decreased, the actual amount generated may not have declined if a lot of electricity is being used at home.

For example, in the following cases, the amount of electricity sold is likely to decrease.

Thus, a low amount of electricity sold does not necessarily mean that the amount of power generated is low.

When viewing the monitor, always check "generated power", "consumption", "sold power", and "purchased power" separately.

How to Distinguish Between Generated Electricity and Sold Electricity

Monitor display names vary by manufacturer, but generally include the following items:

To determine whether the amount of power generated is truly low, you need to look at "generated power" rather than "sold power".

Especially during periods when electricity prices rise or when time spent at home increases, the proportion of generated electricity used at home tends to increase, so the amount of electricity sold back to the grid is likely to decrease. In such cases, even if income from selling electricity falls, it may be helping to reduce electricity bills by lowering the amount of electricity purchased.

Be careful: if you judge that "power generation is low" based solely on electricity sales revenue, you may misinterpret the actual effects.

4. Check whether power consumption has increased

If you feel the power output is low, make sure to check not only the generation side but also any changes on the consumption side.

The effectiveness of solar power generation is not determined solely by the amount of electricity generated. Depending on how much electricity is used within the household, the amounts of electricity sold to and purchased from the grid can vary greatly.

For example, even if power generation is the same, if daytime electricity consumption increases, the amount of electricity sold decreases. On the monitor it displays "There is little surplus electricity to sell", so it can feel as though power generation has dropped.

The common causes that tend to increase electricity consumption are as follows.

In particular, air conditioners, clothes dryers, dishwashers, electric water heaters, induction cooktops, and electric vehicle charging are appliances that tend to consume large amounts of electricity. If you use these during the daytime, they will consume the electricity generated by solar power within the household, reducing the amount of power sold back to the grid.

Tips for interpreting energy consumption

When checking the power consumption on the monitor, confirm the following three items.

The first is daytime consumption. If power consumption increases during the hours when solar power generation is operating, the amount of electricity sold decreases.

The second is seasonal consumption. In summer and winter, electricity use increases due to cooling and heating, so the amount of electricity sold tends to decrease.

The third is a comparison with the same month of the previous year. Even if power generation is the same as the previous year, if consumption has increased, the amount of electricity sold will decrease.

When you feel that "power generation is low," it's important to look at not only the generation figures but also the same day's electricity consumption.

5. Viewing the power conditioner's display and operating status

When the power output from a solar power system is low, you should always check the condition of the power conditioner.

A power conditioner is an important device that converts the direct current electricity produced by solar panels into alternating current electricity that can be used in homes. Even if the solar panels are generating power, if the power conditioner is stopped or showing an error, you cannot use the electricity at home or sell it.

The items to check on the monitor and main unit display are as follows:

If there are consecutive days of low power generation, first check whether the power conditioner is operating normally. In particular, it may be stopped after a power outage, a lightning strike, breaker operation, or a long absence.

Actions to take when an error message is displayed

If an error code is displayed on the power conditioner, check it according to the instruction manual or the manufacturer's guidance. Depending on the error, some issues will automatically recover after a temporary shutdown, while others will require contacting the retailer or the installation company.

Be careful not to disassemble or touch the internal parts on your own. Power conditioners and solar power systems contain components that carry high voltages, posing a risk of electric shock or equipment failure.

Limit verifications to the monitor display, the unit display, the breaker status, and the scope described in the instruction manual.

Be aware of power conditioner degradation

Solar panels are equipment that can be used for a long time, but because power conditioners are electronic devices, they undergo degradation over time. If many years have passed since installation, reduced conversion efficiency and component deterioration can affect power generation.

In particular, be cautious if you have any of the following symptoms.

• Power generation does not start even though it is sunny.

• Stops frequently during the day

• An error keeps appearing.

• The power generation graph suddenly cuts off midway.

• There are unusual noises and a burnt smell.

In such cases, you should consult a professional as soon as possible.

6. Review the history of voltage suppression and output control

Voltage suppression and output control are often overlooked causes of low power generation.

Voltage suppression is a function whereby the power conditioner reduces its output when the power grid voltage becomes too high. It is an action required for safety, but if it occurs frequently, the amount of electricity that can actually be output is reduced even when the solar panels are able to generate power.

Check whether any of the following messages are displayed on the monitor or power conditioner.

If voltage curtailment is occurring, the power-generation graph may flatten around midday on sunny days. If a graph that would normally form a peak instead levels off at a constant output, it may indicate that curtailment is being applied.

Signs of Suspected Voltage Suppression

When voltage suppression is occurring, the following tendencies may be observed.

• Only during the daytime on clear days does power generation fail to increase.

• The top of the power generation graph becomes unnaturally flat.

• A suppression indicator appears on the monitor.

• There are many households in the neighborhood with solar panels installed.

• Output drops only during specific time periods

Voltage suppression involves not only household equipment but also the condition of the local power grid. Therefore, it may not be something that can be easily resolved on the household side.

However, because the issue may be improved by adjusting settings, wiring, or consulting the power company, if curtailment warnings appear frequently it is important to consult your installer or the power company.

Please provide the Japanese text you would like me to translate into English.

Depending on the region, contract terms, and equipment configuration, output control may be implemented. Output control is a mechanism that curtails the output of solar power generation under certain conditions to maintain the supply-demand balance of electricity.

On days when output curtailment occurs, power generation can be lower than expected even if it’s sunny. If the monitor or dedicated app displays a history of output curtailment, check whether it coincides with days of low generation.

7. Check power generation differences for each panel and each string

Some monitors and dedicated apps allow you to check the power generation status at the panel level, circuit level, or system level. It isn't available in every household, but when it can be checked it is a very important item.

Because it allows you to determine whether the low power output is due to overall weather conditions or to a problem with some panels or circuits.

The points to look for are as follows:

For example, if the overall power generation is low, weather or seasonal effects may be responsible. On the other hand, if only a specific system has low generation, the cause may lie in the panels, wiring, junction boxes, or the input circuits on the power conditioner connected to that system.

Main causes of low power generation in only part of the system

If only some panels or strings show low power output, the following causes may be responsible.

• Part of the panel is shaded.

• The panels are dirty with bird droppings and fallen leaves.

• Snow and frost remain only in some areas.

• The surrounding trees have grown, increasing the amount of shade.

• There are shadows cast by antennas and rooftop equipment.

• There is a problem with the wiring or the connection points.

• Some of the panels and equipment are malfunctioning.

In particular, the growth of trees and changes to nearby buildings are causes that are easily overlooked. Even if there were no problems at the time of installation, a few years later, trees may grow or additional buildings or equipment may be added to neighboring properties, causing shadows to occur during certain hours of the day.

Solar panels can see their power generation efficiency affected even if only part of them is shaded. If the amount of power generated suddenly drops at a particular time of day, visually inspect the roof and the surrounding environment.

Procedures for Isolating Causes of Low Power Generation

If you feel that the power output is low, it is important not to rely only on your impressions and to check things in order. Following the steps below will make it easier to identify the cause.

Step 1: First, separate generated power and sold power

The first thing to check is whether the low figure is the "power generation" amount or the "power sold" amount.

If only the amount of electricity sold is low, it may be that household electricity consumption has increased. If the power generation itself is low, you need to check the weather, equipment, shading, and curtailment.

Step 2: View by month instead of by day

Next, check the power generation on a monthly rather than daily basis. If it’s low for just a few days, it may be due to the weather. If it’s low throughout the month, suspect changes in equipment or the environment.

It's particularly useful if you can compare it with the same month in the previous year. If generation has fallen substantially despite being the same season, it may not be due merely to differences in the weather.

Step 3: View the power generation graph on a sunny day

Graphs from sunny days are useful for assessing power generation. If the generation curve looks abnormal despite a sunny day, there may be some underlying cause.

The graph for a near-normal clear day rises from morning to noon, peaks around midday, and falls in the evening, forming a mountain-shaped curve.

Graphs suspected of being abnormal have the following characteristics.

Step 4: Check the power conditioner display

Next, check the display of the power conditioner. If error codes, warnings, stop indicators, or curtailment indicators are shown, they can provide clues to a reduction in power generation.

If an error occurs, it's also important to record it. When consulting a service provider, providing the error code, the date and time it occurred, any changes in power generation, and the weather will make it easier to explain the situation.

Step 5: Visually check for shadows and dirt

Check the condition around the roof and panels from a safe location. There is no need to climb onto the roof. Inspect from the ground, a balcony, or any other area that appears safe.

The key points to note are as follows.

• Whether the tree branches are not extending

• Are antennas or roof-mounted equipment casting shadows?

• Are bird droppings and fallen leaves noticeable?

• Is there any snow or frost remaining?

• Are shadows from neighboring buildings increasing?

Even if there is dirt, it is dangerous to climb onto the roof and clean it by yourself. Working at height carries the risk of falling and may also damage the panels. Consult a professional contractor if necessary.

Decisions You Should Not Make When Power Generation Is Low

When you think the power output is low, making a hasty, incorrect judgment can lead to unnecessary inspection costs or equipment replacement. Avoid the following judgments.

Concluding that power generation is defective based solely on electricity sales revenue

A decrease in revenue from electricity sales does not necessarily mean that power generation is low. Electricity tariff plans, the selling price of electricity, household consumption, battery charging, time spent at home, and other factors can affect revenue from electricity sales.

First, let's check the actual power generation.

Deem it to be malfunctioning immediately after a period of continuous rain or cloudy weather

A decline in power generation over several days is often due to the weather. It's natural for generation to be low during extended periods of rain or cloudiness.

Looking at trends over several days to several weeks, including at least some sunny days, makes it easier to judge.

Compare using only one day's power generation

Solar power generation fluctuates greatly on a daily basis. A decrease compared with the previous day or with last week alone does not necessarily indicate an anomaly.

When comparing, it's important to do so in the same month, the same season, and under similar weather conditions.

Disassembling Equipment Yourself

Disassembling power conditioners, junction boxes, or areas around breakers on your own is dangerous. There is a risk of electric shock and equipment failure.

Limit actions to checking the monitor, verifying the display, and performing only those operations within the scope of the instruction manual; if you suspect any abnormalities, consult a qualified professional.

Cleaning panels in your own way

If the panels look dirty, you might be tempted to spray them with water or scrub them with a brush yourself. However, working on the roof is dangerous, and you may also damage the panel surfaces.

Light dirt may be washed away by rain. If bird droppings or fallen leaves are severe, or if the impact on power generation persists, it is safer to consult a professional.

Cases that require inspection or consultation

If checking the monitor does not reveal the cause, or if an obvious malfunction is suspected, contact the retailer, installation company, manufacturer, or maintenance/inspection contractor.

In particular, you should consider an inspection in the following cases.

When consulting, preparing the following information will make the process smoother.

• Installation period

• Solar panel capacity

• Power conditioner model number

• When you first began to notice reduced power output

• Presence or absence of error codes

• Monthly power generation data

• Power generation graph on a sunny day

• Changes in Electricity Sold and Electricity Consumption

• Presence or absence of shadows or dirt

• Recent events such as power outages, lightning strikes, and construction work.

By providing this information, the technician will find it easier to infer the cause. If possible, save photos of the monitor screen and screenshots of the power generation graph.

Frequently Asked Questions

Could low power generation on a day indicate a malfunction?

If power generation is low for just one day, it does not necessarily indicate a fault. Power generation can vary significantly due to clouds, rain, thin clouds, yellow dust, pollen, shadows, and other factors. First, it is important to observe the trend over a period of several days to a month.

However, if it does not generate power even on sunny days, if errors are being reported, or if the power-generation graph is unnaturally interrupted every day, consider having it inspected.

Is the decrease in the amount of electricity sold due to low power generation?

That's not necessarily the case. The amount of electricity sold is the remainder after subtracting the electricity used within the household from the electricity generated. If daytime electricity consumption increases, the amount of electricity sold will decrease even if generation stays the same.

If there are changes such as spending more time at home, using the air conditioner for longer, or introducing a storage battery or an electric vehicle, the amount of electricity sold is likely to decrease.

What causes low power generation even when it is sunny?

If power generation is low despite sunny conditions, possible causes include thin clouds, yellow sand, dirty panels, shading, voltage suppression, output control, and malfunctioning power conditioners.

In particular, if the power generation graph plateaus around midday, there may be voltage suppression or output curtailment. If it drops only during specific time periods, shading effects should also be considered.

Does dirt on solar panels affect power generation?

Soiling can have an impact depending on its severity. When bird droppings, fallen leaves, dust, pollen, or yellow sand adhere to the panels, they can block sunlight and reduce power generation.

However, light dirt may be washed away by rain. Climbing onto the roof to clean it yourself is dangerous, so if the dirt is severe or a decline in power output continues, consult a professional.

Can a power conditioner cause a decrease in power generation?

Yes. If the power conditioner has stopped, is displaying an error, or has deteriorated with age, it will affect power generation.

Check the operating status, error codes, inhibited indications, and stop history on the monitor or the unit display. If any abnormal indications appear, refer to the user manual and, if necessary, consult your dealer or the manufacturer.

When power generation is low, how long should you monitor the situation?

If the drop is temporary due to the weather, it becomes easier to judge after monitoring it for a few days to about a week. However, if it does not generate power even on sunny days, displays error messages, produces unusual noises or smells, or trips the breaker, you should consult someone sooner rather than later.

A significant drop in monthly power generation compared with the same month of the previous year can also serve as a guideline for considering an inspection.

Is there anything I can do myself when power generation is low?

What you can do yourself is check the monitor, compare generated and sold electricity, check energy consumption, check the power conditioner display, and visually inspect for shadows and dirt.

On the other hand, avoid climbing onto the roof, disassembling equipment, touching wiring, or cleaning panels yourself. It's important to leave any work that goes beyond what you can safely inspect to a professional.

Summary

If you notice low power output, instead of immediately assuming a malfunction, it's important to check the monitor items in order.

Please provide the Japanese text you would like me to translate.

The causes of low power generation can be natural, such as weather and seasons, or they can be issues that require corrective action, such as increased electricity consumption, shading, soiling, voltage suppression, and equipment malfunctions.

First, don’t judge solely by the amount of electricity sold; check the actual power generation. Then, by reviewing the monthly data, generation graphs for sunny days, the amount of electricity consumed, the power conditioner’s display, curtailment history, and generation differences by grid, it becomes easier to sort out the cause.

If the power output is extremely low despite sunny weather, error messages are displayed, the generation graph looks abnormal every day, or only a specific system is not producing power, it is recommended to consult a specialist promptly.

When you feel the power generation is low, it's especially important to stay calm and examine the figures separately. By correctly checking the items on the monitor, you can reduce unnecessary anxiety and decide on necessary inspections or countermeasures at the right time.