Five Things to Note About the Price and Gross Yield of Solar Power Plants

Table of Contents

• Treat the gross yield of a solar power plant as an initial screening metric

• Note 1: Verify the assumptions used to calculate the gross yield

• Note 2: Check whether past generation performance is being assumed to continue into the future

• Note 3: Check that maintenance and repair costs are not omitted

• Note 4: Verify the remaining term together with equipment degradation

• Note 5: Confirm that land conditions and site risks are reflected

• Practical points to check for properties with a high gross yield

• Even properties that appear to have a low gross yield can have value worth considering

• Summary: Prioritize on-site evidence over the gross yield figure

Consider the gross yield of a solar power plant as an initial indicator

When considering the purchase or acquisition of a solar power plant, many practitioners are likely to check the gross yield along with the price. In project documents, gross yield is sometimes used as an indicator of how much electricity sales revenue can be expected relative to the price of the plant. When comparing multiple properties, projects with a high gross yield may appear attractive, while those with a low gross yield may be deprioritized.

However, the surface yield of a solar power plant should be regarded only as an initial metric for comparison. Surface yield is often calculated from the expected revenue from electricity sales and the acquisition price, but it may not adequately reflect maintenance and management costs, future repair expenses, the risk of equipment downtime, the burden of land management, or uncertainties caused by insufficient documentation. If you judge based solely on the numbers, unexpected costs or hassles may arise after purchase, and the actual financial results can change significantly.

A solar power plant is not merely equipment. It is a business asset that integrates solar panels, power conversion equipment, mounting structures, foundations, cables, monitoring devices, fences, drainage facilities, land, power purchase terms, management contracts, and the site environment.

Even if revenue from electricity sales appears stable, equipment deterioration, heavy burdens from vegetation or drainage management, or uncertainties in land contracts can make the stated yield figures look better than the reality.

What a practitioner searching for "solar power plant price" wants to know is not simply how to find projects with high gross yields, but how to assess whether that figure can be trusted. Rather than taking a high gross yield to mean a bargain and a low one to mean a loss, it is important to verify why that number is what it is, which costs are included, and which risks are not included.

This article outlines five points to pay attention to when looking at the price and gross yield of a solar power plant. Rather than specific prices or numerical values, it focuses on the mindset and considerations practitioners should check before purchase, when comparing options, and when explaining internally. Using the gross yield figure as an entry point, by confirming generation performance, operation and maintenance costs, equipment degradation, remaining term, land conditions, and on-site risks, you will be able to judge the reasonableness of the price more realistically.

Point 1: Verify the assumptions used to calculate gross yield

When looking at the gross yield of a solar power plant, the first thing to check is the calculation assumptions. Gross yield is an easy-to-understand metric, but the meaning of the figure can vary greatly depending on which electricity sales revenue is used, what price is taken as the basis, and which costs are not included. Even gross yields that appear similar can differ in their reliability as a basis for comparison if the assumptions are different.

First, what I want to confirm is the basis for the power sales revenue. I check whether it is based on past performance or future assumptions, whether only certain favorable periods are being used, and whether monthly or yearly fluctuations have been averaged out. If the solar power plant is already operating, you should be able to verify past generation and power sales records. If assumptions rather than actual results are the main basis, you need to confirm that those assumptions match the local conditions.

Next, check what is included in the purchase price at the time of acquisition. Whether the land is included, whether you will assume an existing leasehold agreement, whether only the equipment is included, or whether a management contract, warranties, or completed repairs are included will change the actual evaluation even if the gross yield appears the same. Even deals that look to have a high gross yield can become a substantial burden in practice if many additional procedures, repairs, or the establishment of a management system are required after purchase.

Also, gross yield may be presented as an indicator before deducting operation and maintenance costs and future repairs. If costs such as regular inspections, power generation monitoring, mowing, cleaning, drainage maintenance, fence repairs, equipment replacement, and emergency responses are not included, the actual returns will be lower than the stated figures. The higher the gross yield of a project, the more carefully you need to check which costs have been omitted.

The calculation period is also important. Your assessment will differ depending on whether you assume electricity sales revenue for the first year, an average over multiple years, or the entire remaining operational period. Projects that look good in the first year may yield a different long-term evaluation once future equipment degradation, repairs, output curtailment, and management burdens are considered. When looking at the gross yield, it is important not to focus only on the appearance in a single year but to consider whether it will remain stable over the entire remaining period.

Deals for which the assumptions used to calculate gross yield are clear make internal explanations and comparative evaluations easier. Conversely, for deals with vague assumptions, even if the figures look high they are a weak basis for decision-making. When comparing price and gross yield, the first step to prevent losses is to confirm "what this figure includes and what it does not include."

Note 2: Check that the assumption that past power generation performance will continue into the future has not been made

As a caution regarding gross yield, it is important to check whether past generation performance is being assumed to continue unchanged into the future. A solar power plant that has produced steadily in the past is not guaranteed to maintain the same output going forward. Equipment degrades with age, and the surrounding environment can change. Vegetation can grow, drainage channels can become clogged, and power conversion equipment and monitoring devices may also develop faults.

When evaluating power generation performance, do not judge based solely on the annual total. Although the annual figures may appear stable, a month-by-month analysis can reveal drops in generation during specific seasons. For example, weeds growing in summer may cast shadows on panels; surrounding trees or terrain can cast longer shadows in winter; generation may be affected by snow or falling leaves; or there may be equipment outages or maintenance stoppages. Monthly generation records can reveal these site-specific issues.

You should also check trends over multiple years. Even if the power generation performance for a single year looks good, that year may simply have benefited from favorable weather. Check whether output is stable across multiple years, is gradually declining, or has suddenly dropped from a certain point. If it is decreasing year by year, possible causes include panel soiling, equipment deterioration, growth of surrounding trees, insufficient vegetation management, or malfunctions in electrical equipment.

Also verify the differences between the power generation simulation and actual performance. If the planned generation and the actual results differ significantly and you cannot explain the reasons, the assumptions behind the surface yield become unstable. Clarify whether the simulation was overly optimistic, whether shading or output curtailment were not adequately accounted for, whether there were many equipment shutdowns, or whether on-site management was insufficient. If the basis for the generation estimate is weak, even if the surface yield looks good on paper, it should be treated cautiously in practical decision-making.

To assess whether power generation can be maintained in the future, verifying on-site conditions is essential. Check whether surrounding trees have grown, whether vegetation management can be continued, whether drainage channels are free of blockages, and whether inspections around the equipment can be carried out easily. It is important to determine whether stable generation performance is due to appropriate maintenance or simply because past conditions were favorable.

Gross yield is an indicator often evaluated based on expected future revenues from electricity sales. Therefore, you must check whether past performance is being simply extrapolated into the future. By separately verifying the stability of generation performance and the sustainability of that performance going forward, it becomes easier to assess the reliability of the gross yield in relation to the price.

Point 3: Confirm that maintenance and repair costs have not been omitted

What you should pay particular attention to when looking at gross yield is whether maintenance and repair costs have been omitted. Gross yield is an apparent indicator based on revenue from electricity sales, so it may not adequately reflect the costs required to maintain a power plant. Because a solar power plant is not something you buy and then forget about, and must be managed over the long term, it is risky to judge it based solely on figures that exclude maintenance costs.

Maintenance and management include regular inspections, power generation monitoring, grass cutting, cleaning, inspection of electrical equipment, drainage channel management, repair of fences and gates, management of surrounding trees, and on-site response in case of abnormalities. The burden of these tasks varies greatly depending on the plant’s location and local environment. A plant on flat, easily accessible land and a plant in forested or sloped terrain can differ greatly in ease of management even with the same installed capacity.

Grass cutting and cleaning also affect power generation. If weeds cast shadows on the panels, power output may decrease. In areas where fallen leaves or dirt remain on the panels, the need for cleaning may increase. At power plants where drainage channels easily accumulate sediment and fallen leaves, inspections and cleaning after heavy rain are necessary. These tasks are carried out to maintain revenue from electricity sales and are not merely expenses but management measures to preserve the value of the plant.

Future repairs also need to be checked. Solar panels, power conversion equipment, mounting structures, foundations, cables, connection equipment, monitoring devices, fences, and drainage facilities may require maintenance or replacement during the operational period. Even if they are operating without problems now, if repairs become concentrated during the remainder of the operational period, the apparent gross yield can change substantially. Even projects with a high gross yield can carry a heavy actual burden if many repairs remain unaddressed.

When reviewing past operations and maintenance costs, do not simply take low costs as a positive sign. Low costs may indicate that necessary maintenance was not carried out sufficiently. If inspection reports are merely formal and there is no history of corrective actions for identified items, you cannot accurately assess the power plant’s condition. When evaluating maintenance cost records, you need to check the scope of work, frequency, reports, and on-site condition together.

To use gross yield for practical decision-making, you need to view it net of maintenance and repair costs. Even if the headline numbers look high, the assessment can change once you factor in management expenses and future repairs. When comparing price and gross yield, always confirm not only the revenue from electricity sales but also that the costs required to maintain that revenue have not been omitted.

Point 4: Check remaining service life together with equipment degradation

When evaluating the gross yield of a solar power plant, it is important to consider the remaining term and equipment degradation together. Even if the gross yield figure appears high, if the remaining term is limited or equipment degradation has advanced, the actual project value will be affected. You need to confirm not only the single-year figures but whether they are sustainable over the entire remaining operational period.

The first thing to check is the remaining period during which the terms for selling electricity remain in effect. For an operating power plant, a certain period has passed since the start of operations. If the remaining period is long, many future opportunities to sell electricity remain, but the likelihood of equipment deterioration and the need for repairs during that time also increases. If the remaining period is short, whether the plant can generate power stably over that short period becomes important, and the impact of any major repairs becomes more significant.

Equipment degradation strongly affects the assessment of remaining service life. Solar panels, power conversion equipment, mounting structures, foundations, cables, monitoring devices, fences, and drainage systems deteriorate over time. Even if current power generation performance is good, when equipment is nearing its replacement time, has a history of frequent shutdowns, or has unresolved issues noted during inspections, it will impact future power generation and maintenance costs.

Also check the downtime history. Verify which equipment stopped in the past, when and to what extent it stopped, what the causes were, and whether the recovery actions were appropriate. The fact that there was downtime is not necessarily a problem, but if recovery has occurred without identifying the cause or the same issue is recurring, a risk of future downtime remains. If the assumptions underlying the nominal yield do not reflect downtime risk, the figures may appear better than reality.

When a case has a short remaining term and significant equipment deterioration, it becomes difficult to determine to what extent repairs should be carried out. Even if major repairs are undertaken, there may be only a limited period in which those costs can be recouped. For cases with a long remaining term, it is necessary to plan for repairs and replacements in a systematic way. In either situation, it is important to anticipate not only the gross yield but also the maintenance and repairs that will be required during the remaining term.

For deals that appear cheap with a high gross yield, you need to check whether there are underlying factors such as the remaining term or equipment deterioration. Even for deals that are expensive and whose gross yield looks modest, if the equipment is in good condition and the risk of repairs during the remaining term is low, there is value in stable operation. The gross yield figure only has practical meaning when considered together with the remaining term and the condition of the equipment.

Point 5: Confirm that it reflects land conditions and on-site risks

One aspect that is often overlooked when looking at gross yield is land conditions and on-site risks. Solar power plants are installed on land and operated outdoors for long periods. Land rights, boundaries, road access, drainage, shading, vegetation, and disaster risks affect power output, maintenance costs, and downtime risk. However, these on-site risks may not be adequately reflected in the gross yield figures.

First, you should check the form of land use. Confirm whether the land is owned or leased, whether the land-use contract period is sufficient, and what the renewal and termination conditions are. In the case of leased land, if the land-use rights are not adequately secured for the power sales period and the planned operation period, concerns will remain about future business continuity. If there are unclear points in the land contract, you should be cautious even if the gross yield appears high.

Boundaries and the scope of use are also important. Check whether fences, panels, mounting racks, drainage channels, maintenance access paths, and cable routes are contained within the site. Even if the drawings appear to show no issues, on site the boundary markers may be hard to identify, fences may be located near the boundary, or drainage facilities may involve neighboring land. If there are uncertainties about the boundary, adjustments may be required during post-purchase management or repairs.

Also check drainage and topography. If conditions include drainage channels that are easily clogged, easy inflow of sediment, areas where water tends to pool, or unstable slopes, inspections and repairs after heavy rain will be necessary. Poor drainage can lead to scour around foundations, impacts on cables and electrical equipment, and deterioration of maintenance access routes. These risks affect long-term maintenance costs and downtime risk.

The risks of shade and vegetation must not be overlooked. If surrounding trees grow and cast shade, power output may decrease. Weeds can also cast shadows beneath panels. Fallen leaves can clog drainage channels, fallen trees can affect equipment, and wildlife damage can affect cables. Even if generation performance is good now, future power output may change if the local site environment changes.

Road access and ease of recovery are also factors that are not easily reflected in gross yield. For power plants that are difficult to access on site, it may take longer to inspect and restore operations in the event of an anomaly. If downtime is prolonged, it will affect revenue from electricity sales. When assessing gross yield, it is necessary to check how land conditions and on-site risks will affect income and expenses.

Practical Points to Check for Properties with High Gross Yields

Properties with a high gross yield can appear attractive at first glance. However, it's risky to judge them without confirming why the gross yield is high. Depending on whether the price has been kept low, the assumptions for income from electricity sales are set too optimistically, or costs and risks are not fully reflected, the actual situation can be very different.

First, verify the basis for revenue from electricity sales. Check whether it is based on past actual performance, on assumed generation, or whether only the best periods have been used. Review monthly and annual generation records to confirm whether output is stable, whether there are any abnormal drops, and whether any shutdown history is explained. Projects that show a high gross yield while the basis for generation is unclear should be treated with caution.

Next, check maintenance costs and future repairs. For properties that appear to have high gross yields, costs for mowing, cleaning, inspections, drainage management, equipment repairs, and emergency responses may not be fully reflected. Even if past management costs have been low, that may simply mean necessary maintenance was not being performed. Review inspection reports and repair histories to see if there are any outstanding items that have not been addressed.

You also need to check the land conditions. There may be reasons the price is kept low, such as unclear boundaries, poor road access, inadequate drainage, shadows from nearby trees, and the heavy burden of vegetation maintenance. For properties with significant on-site risks, even if the gross yield appears high, the post-purchase burden may increase.

Also, the consistency of the documentation is important. Verify that the project summary, power generation performance, power sales conditions, land contracts, drawings, inspection reports, and site photographs are all consistent. If documentation is insufficient, a high yield may not indicate low risk; rather, the price may be depressed because the risk cannot be verified.

When considering properties with a high gross yield, it's important not to take the high figure at face value but to break down why it appears high. Determining whether the risks are remediable or structurally difficult to resolve makes practical decision-making easier.

Even properties that appear to have a low gross yield are worth considering

Properties that appear to have a low gross yield can seem disadvantaged at the comparison stage. However, a low gross yield does not necessarily mean the property is not worth considering. Even if the gross yield is modest, if the power plant has stable generation performance, good equipment condition, favorable land conditions, and is easy to maintain, it can be a manageable asset for long-term operation.

Power plants with stable generation performance make it easier to forecast future revenue. If there are no major anomalies in monthly or annual results, few outage records, and the causes of reduced generation are clear, it also becomes easier to explain internally. Stability, which is hard to reflect in surface yield figures alone, is a practically important value.

You should also assess the condition of the equipment. If the solar panels, power conversion equipment, mounting racks, foundations, cables, monitoring devices, fences, and drainage facilities are in good condition, and inspection reports and repair histories are well organized, it becomes easier to anticipate future repair risks. If the reason the price appears somewhat high is the good condition of the equipment, you may not want to judge solely by the gross yield.

Well-prepared land conditions also add value. A power plant with clear boundaries, good road access, stable drainage, easy vegetation management, and that is easy to restore after a disaster tends to have lower long-term management burdens. While these conditions are not readily reflected in the surface yield, they have a major impact on stable operation after purchase.

In addition, power plants with well-organized documentation and on-site information are easier to manage after transfer. When drawings match the actual site, the photo locations in inspection reports are clearly identified, and repair histories are organized, post-purchase uncertainty can be reduced. Even if the apparent gross yield looks low, projects with clear decision-making materials and low risk provide practical reassurance.

Gross yield is a useful starting point for comparison, but it's premature to rule out a property solely because of a low figure. It is important to judge the reasonableness of the price after looking at stability, ease of management, low repair risk, land conditions, and the state of documentation.

Summary: Prioritize on-site evidence over gross yield figures

When looking at the price and gross yield of a solar power plant, it is important to check five things: the assumptions used to calculate the gross yield, the future prospects of the plant’s generation performance, operation and maintenance costs and repair costs, the remaining term and equipment degradation, and land conditions and on-site risks. Gross yield can be useful as an entry point for comparison, but it is dangerous to make a purchase decision based on that number alone.

There are reasons why projects with high gross yields appear to be high. You need to verify whether the assumptions for electricity sales revenue are overly optimistic, whether the suppressed price reflects equipment deterioration or land-related risks, or whether operation, maintenance, and repair costs have not been adequately accounted for. Conversely, even projects that appear to have low gross yields can be easier to consider for long-term operation if their generation track record is stable, equipment condition is good, and land conditions are favorable.

What matters for practitioners is not to use the gross yield as the final determinant in internal explanations. They need to compile power generation performance, electricity sale conditions, remaining term, operation and maintenance costs, repair history, land conditions, and on-site risks, and explain the reasonableness of the price on that basis. Especially for used solar power plants, it is essential to reconcile past operational records with current on-site conditions.

During on-site surveys, it is important to accurately record inspection points that are likely to affect surface yield. By recording trees that cause shading, the extent of vegetation growth, drainage channels, cable damage, equipment deterioration, fence damage, and inspection points near boundaries together with location information, you can more easily organize the basis for reduced power generation and future costs.

If you want to make a realistic assessment of a solar power plant's surface yield, using LRTK (an iPhone-mounted GNSS high-precision positioning device) can also be effective. If you can record equipment locations within the plant, drainage channels, causes of shading, extent of vegetation, candidate repair sites, and caution points near boundaries along with high-precision positional information, you can reconcile discrepancies between drawings and the field and make it easier to share the same information among stakeholders. When judging the price and surface yield of a solar power plant, it is important to build up not only desk-based figures but also on-site verifiable evidence.