Note
Year-One Solar Output: Reading the Numbers
The installation quote included a projected annual output in kilowatt-hours. Twelve months later, the factory’s engineering team pulls the monitoring data or the PEA/MEA meter export and compares it to that figure. Most of the time, the numbers are not identical.
A contractor who has reviewed this data, and can explain the gap before the factory raises it, is in a different conversation from one seeing the numbers for the first time in the meeting room.
What Does “As Promised” Actually Mean for Solar Output?
Solar output projections are built from three variables: installed capacity in kilowatts, historical solar irradiance for the location, and an assumed performance ratio. Each variable contains uncertainty.
Installed capacity is fixed at commissioning and is the one variable the contractor controls entirely.
Solar irradiance for the design is taken from historical averages for the region. Actual irradiance for any specific twelve-month period will differ from those averages. A year with a longer wet season or above-average cloud cover will produce lower output even from a perfectly functioning system.
Performance ratio (PR) is the efficiency of the conversion from available sunlight to usable electricity. It depends on panel temperature, soiling, shading, inverter efficiency, and cable losses. For a well-maintained C&I solar system in Thailand’s tropical climate, a performance ratio of 70 to 80% is typical.
The design projection is an estimate built from those three variables, not a guarantee of exact output. The year-one review is the first time that estimate gets tested against a full year of real data, and both sides benefit from understanding what it means before the comparison is made.
What Numbers Should You Prepare Before the Review?
Before meeting the factory, pull four things:
- Actual energy generated: total kWh for the twelve months, from the inverter monitoring platform or the PEA/MEA export meter reading
- Design projection: the annual kWh estimate from the original system design or quote document
- Performance ratio: most inverter monitoring platforms report this directly; if not, it is actual kWh divided by the theoretical output based on measured irradiance
- Service history: dates of panel cleaning visits, any inverter events or alarms logged during the year, and the figures captured in the commissioning baseline record
If the monitoring platform does not record irradiance data separately, the design document should state the irradiance assumption used. Comparing actual output to projected output without an irradiance reference tells you there is a gap. Adding the irradiance comparison tells you how much of that gap is weather and how much is system behavior. Those are two different conversations.
How Much Variation Is Normal, and What Causes It?
For a C&I solar installation in Thailand, a gap of up to 10% below the design projection often traces to weather variation and normal soiling rather than a fault. A gap larger than 10% warrants a specific explanation.
Four causes account for most shortfalls:
Soiling: panels in industrial areas accumulate dust faster than residential rooftops. Factories with heavy vehicle traffic, exhaust emissions, or significant bird activity see soiling build up faster between cleaning visits. The monitoring data usually shows a recognizable pattern: gradual output decline between cleans and a step recovery immediately after each cleaning visit.
Temperature: panels lose efficiency as surface temperature rises. In Thai summers, panel temperatures well above 40 degrees Celsius are common. This is a characteristic of photovoltaic technology, not a fault. High ambient temperature is already partly accounted for in any design using Thailand-specific irradiance data, but peak summer performance will still run below the standard test conditions the manufacturer uses for rated output.
Shading from changes after installation: if new rooftop equipment, signage, or structures were added after installation, they may introduce shading that was not part of the original design. A brief walkdown of the roof before the review identifies this quickly, and it is worth doing before the meeting so you are not discovering it together with the factory.
Equipment faults not caught promptly: an inverter that tripped and went unreset for several days, or a string with a loose connection, can remove a significant share of a system’s output for the affected period. The inverter event log shows this directly. If the service history confirms the fault was identified and resolved on the next scheduled visit, the impact is limited and documented.
When Does a Gap Trigger a Warranty Action?
A gap that is explained by weather, temperature, or soiling between planned cleaning visits is a maintenance discussion, not a warranty claim.
A warranty action is appropriate when the gap traces to a fault in equipment that was installed correctly and maintained as agreed, and the fault occurred within the warranty period. An inverter failing before the manufacturer’s warranty expires, or panels measuring below their rated output degradation after only two years, are cases where a claim is justified.
The critical factor is the documentation trail. A warranty claim to a manufacturer typically requires: the original commissioning report showing the system passed initial performance checks, the monitoring data showing when the performance decline started, and a site inspection report confirming the fault. If the commissioning baseline record and monitoring data are in the site register, assembling this takes an afternoon. Without them, some of the required evidence may not be recoverable.
FAQ
What if the monitoring data and the PEA/MEA meter show different totals?
The export meter from PEA/MEA is the authoritative figure for energy delivered to the grid or consumed on site. A difference of 1 to 2% between the inverter monitoring platform and the meter is common due to measurement method differences and is not a fault. A larger discrepancy is worth investigating: check the monitoring platform’s data window for gaps, verify the platform is reading from the correct inverter input, and compare both against the physical meter reading.
What if the original design projection document is missing?
The commissioning baseline record should carry the design irradiance assumption and the projected annual output figure the system was sized to achieve. If neither document exists, the system size in kilowatts and the location’s historical irradiance data can be used to reconstruct a projection. Be explicit with the client that this is a reconstruction, not the original design figure; the difference matters if a dispute develops later.
How do you handle a factory that insists the shortfall is a warranty claim?
Start with the data. Show the irradiance comparison for the period, the cleaning history, and the performance ratio. If weather and maintenance explain the gap, say so clearly and put it in writing. If after that analysis a residual gap remains that the data does not explain, further investigation is warranted, which is a different conversation from accepting a claim for a gap that has a documented maintenance explanation.
If you want to see how TRACE 30 holds the commissioning baseline record and the site register alongside the maintenance calendar, so the data you need for a year-one review is already in one place when the factory asks, the program overview is at /program/. You can also book a short call to walk through how that fits your current solar portfolio.