7 Steps to Check the Price and Power Generation of a Solar Power Plant

Table of Contents

• Check the price of a solar power plant together with its generation output

• Step 1: Align the project overview and comparison conditions

• Step 2: Check monthly and annual generation records

• Step 3: Interpret the assumptions of the generation simulation

• Step 4: Examine causes of reduced generation from equipment and the site environment

• Step 5: Verify the power sale conditions and remaining term alongside the generation output

• Step 6: Reflect maintenance and management costs and outage risks in the generation output

• Step 7: Confirm discrepancies between the drawings and actual conditions during on-site inspection

• Mistakes to avoid when comparing price and generation output

• Summary: Verify the basis for the generation output on site and judge the price

Check the price of a solar power plant together with its power output.

When considering the purchase or acquisition of a solar power plant, the price is often the first thing you notice. However, the price of a solar power plant cannot be judged solely by its installed capacity or apparent size. A power plant is an asset that creates business value through the electricity it generates. Therefore, to determine whether the price is reasonable, you must always check how stably it actually generates power.

Even for power plants with similar installed capacities, valuations can differ greatly between projects with stable generation and those that experience frequent output declines or shutdowns. Actual power generation can vary significantly due to solar irradiance conditions, orientation, tilt, shading from the surroundings, vegetation overgrowth, equipment degradation, drainage conditions, and the quality of operation and maintenance. Even if the installed capacity on the documents is large, if the site is not generating sufficient power in practice, one cannot say the project has business value commensurate with its price.

On the other hand, power plants that may appear somewhat expensive can be easier to consider as long-term investments if they have a stable record of past power generation, few stoppages, well-maintained equipment and land, and well-organized management records. Conversely, projects that may look inexpensive can lead to unexpected expenses and additional effort after acquisition if their output is unstable for unknown reasons and repairs or on-site management become burdensome.

What someone responsible for operations who searches "solar power plant price" wants to know is not just a rough market price. It is important to determine whether the quoted price is reasonable relative to the expected power generation, whether the basis for the reported generation performance can be trusted, whether the plant will be able to generate similarly in the future, and how to explain this in internal approval processes. Rather than looking at price and generation separately, confirming the conditions under which the generation figures were produced is the first step in preventing failure.

This article explains seven steps to verify the price and power output of a solar power plant before purchase. Rather than specific price levels, it focuses on practical verification methods for judging the reasonableness of the price. It checks, in order, generation track record, simulations, equipment condition, feed-in conditions, operations and maintenance, and on-site inspections, organizing decision criteria so you won’t be misled by surface-level numbers.

Step 1: Align project overview and comparison criteria

The first step in checking the price and generation of a solar power plant is to align the project overview and the comparison criteria. When comparing multiple projects, you cannot make a proper judgment if you compare prices alone while factors such as installed capacity, location, start of operations, power sale conditions, land use type, and management status differ. First, you need to organize the information so it can be reviewed from the same perspective.

In the project overview, we confirm the installed capacity, the number of panels installed, the configuration of power conversion equipment, the start date of operations, the location of the power plant, the land area, the form of land ownership or usage, road access conditions, and the management framework. Installed capacity is an easy-to-understand metric for initial comparisons, but judging power generation capability by that alone is risky. Actual power generation varies depending on installation conditions, the local environment, and the condition of the equipment, so always verify installed capacity together with actual generation performance.

When standardizing comparison conditions, clarify whether the power plant is a new-build project or an existing, already-operational secondhand project. For pre-construction projects, the assumptions used in simulations become important, whereas for already-operational projects, historical generation performance is a major factor in decision-making. For secondhand projects, because you may be able to verify generation records, outage histories, inspection reports, repair histories, and on-site photographs, you should place greater emphasis on actual performance than on desk-based assumptions.

Also, when comparing prices, you need to confirm what is included with the power plant. Whether land is included, whether leasehold rights are being transferred, whether management contracts will be taken over, and how much of the equipment warranties and repair histories can be verified will change the meaning of the same price. Rather than looking only at the headline price, sort out what you are acquiring, what you are taking over, and which risks you will bear.

At this stage, the important thing is not to compare items while leaving unknowns ambiguous. If you know the equipment capacity but the power generation record is insufficient, have a land contract but the renewal terms are unclear, or have inspection reports but the repair measures are unknown, it becomes difficult to judge whether the price is reasonable. When comparing before purchase, first separate confirmed information and unconfirmed information for each project, and consider how the unconfirmed parts might affect the price.

Standardizing project overviews is not merely clerical work. It is the foundation for correctly interpreting the relationship between price and power generation. If this foundation remains unclear, it becomes difficult to organize subsequent generation performance and on-site inspection results. By setting the comparison criteria at the outset, it becomes easier to discern why prices are high or low and why power generation is strong or weak.

Step 2: Check monthly and annual power generation performance

The next thing to check is the monthly and annual generation performance. When assessing the price of a solar power plant, how much it has generated in the past is extremely important information. In particular, for plants already in operation, actual generation data is available, allowing you to verify real operational results rather than estimates.

When reviewing power generation performance, a point to be careful about is not judging based solely on the annual total. Even if the annual total looks fine, examining the data by month can reveal that output drops sharply in specific seasons. For example, weeds growing in summer can cause shading; in winter the sun’s lower angle can extend shadows from surrounding trees; snow or fallen leaves can have an impact; and equipment shutdowns may occur after heavy rain. Monthly trends can reveal site-specific issues.

Year-by-year trends are also important. Even if the power generation in a single year looks good, you cannot tell whether that is a temporary effect caused by weather or the result of a stable equipment condition. Check whether output is stable over multiple years, is gradually declining, or has suddenly dropped at some point. If it is gradually declining, factors such as aging, soiling, vegetation growth, increased shading, or inadequate maintenance may be involved. If there is a sudden drop, you should suspect equipment failure, wiring faults, output control (curtailment), or extended shutdowns.

If you find a month with low power generation, always check the reason. Determine whether it can be explained by the weather, whether there was equipment downtime, whether mowing or cleaning was insufficient, or whether it was stopped for inspection or repair. If the cause is clear and has been addressed, it becomes easier to anticipate future risk. On the other hand, if an unexplained decline continues, you should be cautious in your judgment even if the price appears low.

When reviewing power generation performance, we also check the reliability of the monitoring data. We confirm whether the data are continuous, whether there are any missing periods, whether abnormal values have not been left unaddressed, and whether the relationship between equipment downtime and power output is explained. For projects where generation data are not organized, there is insufficient information to assess the reasonableness of the price.

Power generation track record is one of the most realistic bases for backing up a price. For high-priced projects, check whether stable generation performance is the reason. For low-priced projects, check whether reduced or unstable generation is the reason for the low price. By carefully examining generation performance month-by-month and year-by-year, you can more easily uncover the on-site issues behind the numbers.

Step 3: Interpreting the assumptions of the power generation simulation

Alongside actual generation performance, you should check the assumptions behind the power generation simulation. Simulations are an important reference for forecasting future generation, but their results can vary greatly depending on the assumptions. When reviewing price and expected generation, it’s important not to focus on the simulation numbers themselves but to interpret the conditions under which they were calculated.

In simulations, assumptions include solar radiation conditions, orientation, tilt, equipment capacity, loss rates, shading effects, aging degradation, output control, and downtime. If these conditions do not match the actual site, the projected power generation will diverge from reality. Especially for used power plants, past performance should be compared with the simulation to confirm the extent of any discrepancy between assumptions and actual results.

If the difference between simulation and actual performance is small and stable over the long term, it becomes easier to forecast power generation. On the other hand, if actual performance continually falls short of the simulation, it is necessary to identify the reasons. We determine whether the impact of shading was underestimated, vegetation management or cleaning was insufficient, equipment degradation has progressed, or output curtailment and shutdowns are occurring more than expected.

Conversely, if actual results exceed the simulation, you must also verify the reasons. Check whether the result was due only to a period of favorable weather, because the design assumptions were conservative, or because the system has been well maintained. Even if the numbers look good, it is risky to assume the same power generation in the future unless the reasons can be reproduced.

In pre-purchase due diligence, simulations are not treated as absolute figures but used as a reference for comparison to understand actual power generation performance. Simulations are desk-based projections, while actual results are what occurred on site. By comparing the two, differences in the plant’s design conditions, the local environment, and the state of management become apparent.

When considering future power generation, you also need to factor in age-related degradation and changes in the surrounding environment. Even if past performance has been good, that does not guarantee the same will continue. Power generation can change due to the growth of nearby trees, worsening drainage, equipment deterioration, the timing of major component replacements, and changes in management practices. When reviewing simulations, check not only the current figures but also whether they include factors that could reduce output in the future.

To judge whether a price is reasonable, it is important that the assumptions underlying the power generation simulation are realistic. A price based on optimistic generation estimates will create discrepancies in financial results after acquisition. Reconciling actual generation performance with the simulation and verifying the basis for the figures will improve the accuracy of price assessments.

Step 4: Assess the causes of reduced power generation from equipment and on-site environmental factors

When checking generation performance, if a decline or instability in power output is found, we investigate the causes from both the equipment and the on-site environment. A decrease in power output at a solar power plant is not necessarily caused by a single factor. Equipment degradation, equipment malfunctions, wiring problems, shading from vegetation, soiling, poor drainage, snow accumulation, fallen leaves, output curtailment, and other factors may overlap.

In terms of equipment, we inspect the condition of solar panels, racking, foundations, cables, junction boxes, power conversion equipment, and monitoring systems. Cracks, discoloration, dirt on panels; loosened fastenings; corrosion of racking; settlement or scour around foundations; damage to cable sheathing; and deterioration of connection points can affect power output and increase the risk of shutdown. Even if everything looks fine from a distance, there may be deterioration hidden by vegetation or on the rear side of equipment.

Also check the equipment downtime history. If generation was low in a particular month, see whether converters or connection equipment were down during that period and how long it took to restore them. A failure in itself is not necessarily a problem. What matters is whether the cause was identified, properly repaired, and measures were taken to prevent recurrence. Unexplained shutdowns or repeated occurrences of the same fault should be carefully checked before purchase.

On-site, we check shading, vegetation, drainage, topography, and surrounding structures. If surrounding trees have grown and are casting shadows, their impact may increase in the future. If weeds are covering the undersides of panels or nearby equipment, they can affect not only power generation but also inspection work. If drainage channels are clogged or there are areas where water tends to accumulate, this can lead to equipment deterioration and ground instability.

Whether the causes of reduced power generation can be remedied is also important. If they can be improved by mowing, cleaning, or minor equipment repairs, it may be possible to address them by incorporating those measures into the post-purchase management plan. On the other hand, if the causes are terrain-related shading, trees on neighboring land, inadequate road access, poor drainage conditions, or constraints in the land contract, they may not be easy to remedy.

In low-priced projects, the causes of reduced power generation may already be reflected in the price. Even in such cases, it is important to understand the cause and to be able to establish a response plan. A cheap project acquired while the cause is unknown may lead to unexpected burdens after acquisition. When you detect a drop in power generation, it’s important not to stop at the numbers alone but to investigate the causes from both the on-site conditions and the equipment.

Step 5: Check the power sale conditions and remaining period together with power generation

To assess the price of a solar power plant, you need to check the power purchase conditions and the remaining contract period together with the plant’s power generation. Power purchase conditions directly affect the plant’s revenue, but if it cannot actually generate power reliably, those conditions cannot be fully utilized. Conversely, even if generation is stable, unfavorable factors in the remaining period or contract terms will change how the price is perceived.

Before purchase, confirm the terms of the power sales contract, the start date of operation, certification-related information, the procedures required for succession, interconnection conditions, and whether output control is in place. With second-hand power plants, previous owners or managers may be involved, so it is important to check for any discrepancies in the names on documents, addresses, installed capacity, and contract terms. If there are unclear points in the documents, they may affect post-acquisition procedures and management.

The remaining period relates to the outlook for how long future income can be earned. Projects with a long remaining period have more time left for operation, but they also require consideration of equipment deterioration and repairs associated with long-term operation. For projects with a short remaining period, it is important that they can generate power reliably in the short term, and the impact of major repairs will be greater.

Rather than viewing power generation and feed-in conditions separately, it is important to consider both together. Even if feed-in conditions are favorable, if power generation has declined the revenue outlook will weaken. Even if power generation is stable, if the remaining period is limited you need to plan future operations carefully. For high-priced projects, confirm whether the feed-in conditions and the stability of power generation justify that price. For low-priced projects, check whether the remaining period or restrictions in the conditions are the reasons for the low price.

Output control and shutdown risks must not be overlooked. Even if generation equipment is capable of operating sufficiently, if opportunities to actually sell electricity are restricted, the relationship between generated output and revenue changes. Review past control records and shutdown histories to confirm whether they have been appropriately reflected in expected returns and cash-flow projections.

Feed-in conditions can often appear attractive, but it is risky to judge the price based on them alone. By checking the feed-in conditions, remaining term, generation track record, equipment condition, and repair risk together, you can assess the relationship between price and power generation in a way that more closely reflects reality.

Step 6: Reflect operation and maintenance costs and downtime risk in power generation

Power generation at a solar power plant will not be maintained automatically simply by installing the equipment. Stable generation continues only with maintenance such as daily inspections, grass cutting, cleaning, monitoring, drainage management, and response to abnormalities. When checking price and power output, it is important to reflect maintenance costs and downtime risk in the power generation forecast.

Maintenance and management include periodic inspections, checks of electrical equipment, power generation monitoring, mowing, weeding, general cleaning, emergency response, cleaning of drainage channels, repair of fences and gates, and management of surrounding trees. The burden of these tasks varies greatly depending on the plant’s location and the condition of its equipment. Even with the same installed capacity, a plant that is flat and easily accessible is easier to manage than one located in forested or sloping terrain.

Vegetation management directly affects power generation. If weeds cast shadows on the panels, power output may decrease. As nearby trees grow, the area of shading can expand seasonally. At power plants where mowing and branch pruning are insufficient, actual power generation can decline year by year. Before purchasing, check the past mowing frequency, the on-site vegetation conditions, and the maintenance work that will be required going forward.

Downtime risk is also important. A power plant may be temporarily shut down due to failures of conversion equipment or connection facilities, communication failures, cable damage, natural disasters, effects of poor drainage, and so on. If the outage period is prolonged, it will affect both the plant’s actual power generation and its financial performance. If there have been shutdowns in the past, check the causes, duration, recovery measures, and measures to prevent recurrence.

When looking at maintenance costs, it is important not to simply take low past expenditures as a positive sign. Low costs may instead indicate that necessary maintenance was not carried out sufficiently. When reviewing past expenses, verify the work performed, its frequency, reports, and the on-site condition together to judge whether appropriate management was conducted.

When forecasting power generation, it is necessary to assume that maintenance and management will continue. If management weakens, generation may decline, and if you switch to appropriate management, costs may increase. Even projects that appear inexpensive can see their effective valuation change once maintenance costs and outage risks are reflected.

When comparing the price and power generation of solar power plants, don’t just look at the historical generation figures—also check the management framework that supports those figures. Plants with stable management make it easier to forecast future generation. Plants with inadequate management may appear to have strong past generation performance but can still carry risks going forward.

Step 7: Confirm discrepancies between drawings and actual conditions during the site survey

Finally, an on-site survey is indispensable. Even if the documented price, projected power generation, simulations, and inspection reports are all in order, there are many things you won't know unless you check the site. Solar power plants are outdoor facilities, and local topography, shading, drainage, vegetation, equipment deterioration, and maintenance access routes have a major impact on power generation.

In an on-site survey, first confirm whether the drawings match the actual arrangement. Check the panel layout, mounting structures, inverters, junction boxes, fences, gates, access walkways, drainage channels, and the condition near the boundaries. At a used power plant, repairs or modifications carried out during operation may have altered the site from the older drawings. If the drawings and the site differ, confirm when and why the changes were made and whether the related documents have been updated.

Checking for shadows is also important. Check whether surrounding trees, buildings, utility poles, or variations in terrain elevation are casting shadows on the panels. Shadows change with the time of day and season, so even if no shadows are visible during an on-site inspection, it is necessary to compare with periods of reduced power generation. If shadows occur in winter or in the morning and evening, they may be affecting the monthly generation performance.

We also check drainage conditions on site. We look at which direction rainwater flows, whether drainage channels are clogged, whether sediment or fallen leaves have accumulated, and whether there are places where water tends to pool. Poor drainage can lead to scour around foundations, weakening of the ground, impacts on cables and electrical equipment, and deterioration of maintenance access routes. Special care is required on slopes and reclaimed or filled land.

We also check the equipment's condition on site in detail. We look for cracked or dirty panels, corrosion of the mounting structure, loosened fastenings, cable deterioration, the condition around junction boxes, ventilation around power conversion equipment, fence damage, and damage hidden by vegetation. Sometimes issues that are not recorded in the inspection report are discovered on site.

Information obtained during on-site inspections should be recorded not only with photographs but also in a way that clearly indicates locations. If you can organize which trees are causing shadows, which drainage channels are prone to clogging, which equipment is showing deterioration, and which areas near boundaries require attention, the information becomes much easier to use for internal briefings, instructions to property management companies, and repair estimates.

The on-site survey is the final step to verify the validity of the price and power generation. If the figures in the documents match the actual conditions observed on site, the reliability of the assessment increases. Conversely, if significant discrepancies are found on site, it will be necessary to review the assumptions about price and power generation.

Common Mistakes to Avoid When Comparing Price and Power Generation

When comparing the price and power output of solar power plants, what you should avoid is judging them solely by installed capacity. Installed capacity is an important basic piece of information, but it does not guarantee actual power generation. Even with the same capacity, generation can vary depending on the local environment, shading, vegetation, equipment degradation, and maintenance condition. Rather than simply assuming that larger capacity means higher value, you need to look at actual generation performance and its stability.

Another thing to avoid is becoming complacent based solely on annual electricity generation. The annual total is an easy-to-understand metric, but it can hide monthly anomalies. If there is a significant drop in a particular season, there may be site-specific risks. Check the monthly and yearly trends and confirm that you can explain the reasons for any declines.

Blindly trusting simulation figures can also be dangerous. Simulation results change depending on the assumptions. If the effects of shading, aging-related degradation, downtime risk, output control, and operation and maintenance are not adequately reflected, estimates can be more optimistic than actual power generation. Especially when judging profitability before purchase, it is important to compare with actual performance and expect realistic generation.

You should avoid immediately assuming that a low price is advantageous. Cheap deals may involve reduced power generation, a short remaining term, equipment deterioration, land risks, management burdens, and insufficient documentation. If the reasons for the low price are clear and a plan to address them can be formulated, the deal can be considered, but it is dangerous to make a decision without understanding the reasons.

Conversely, it is also wrong to assume that a high price guarantees peace of mind. You need to verify whether the reasons for the high price can be explained by power generation track record, terms of electricity sales, land stability, equipment condition, and maintenance history. If there are only abstract explanations without supporting documents or on-site evidence, you cannot conclude that the price is justified.

Delaying on-site inspections is also a major misjudgment. Even if the paperwork shows no problems, on site there can be issues with shading, drainage, vegetation, deterioration, property boundaries, and road access. The price and power output of a solar power plant are closely tied to the actual conditions on site. It is important to prioritize evidence that can be confirmed on site, not just desk-based materials.

Summary: Verify on-site the basis for power generation and determine the price

To verify the price and power output of a solar power plant, it is important to check the following seven steps in order: organizing the project overview, monthly and annual power generation performance, assumptions of the power generation simulation, causes of generation decline, power sale terms and remaining period, operation and maintenance costs and shutdown risks, and on-site inspection. Rather than judging a price as high or low based only on the price itself, you need to confirm what level of power generation that price is based on.

Power generation is the central factor that underpins the value of a solar power plant. However, generation is not determined by installed capacity alone. It varies with solar irradiance, installation conditions, equipment condition, vegetation management, shading, drainage, operation and maintenance, and outage history. By confirming whether past generation performance has been stable, whether anomalous values can be explained, and whether site conditions will allow generation to be maintained in the future, it becomes easier to judge the reasonableness of the price.

What matters for operational staff is leaving behind supporting evidence that can be used for internal explanations. Organize power generation records, simulations, inspection reports, repair histories, power purchase conditions, land documents, and site photos so that you can explain which factors are affecting the price. Especially for used power plants, it is essential to reconcile past operational history with the current on-site condition.

During on-site surveys, it is important not only to take photographs but also to accurately record where and what kinds of risks exist. By documenting—along with location information—equipment near boundaries, drainage channels, trees that cause shading, the extent of vegetation growth, cable damage, fence damage, and spots requiring repairs, it becomes easier to explain the causes of reduced power generation and the reasonableness of the price.

If you want to carry out on-site inspections of solar power plants more accurately, using LRTK (iPhone-mounted GNSS high-precision positioning device) can also be effective. If you can record inspection points within the plant along with high-precision location information, it becomes easier to share among stakeholders the discrepancies between drawings and the actual site, risks from shading and drainage, equipment deterioration locations, and the areas that require vegetation management. When judging the price and power generation of a solar power plant, building up on-site verifiable evidence—not just desk-based figures—is a crucial step to prevent mistakes.