The handover from the EPC contractor is the moment that sets that baseline. This guide explains degradation in plain terms, how performance guarantees and warranties fit together and which documents and tests an owner should require before accepting the plant.
What degradation is
Degradation is the gradual loss of output of a module over time. There is often a larger loss in the first period of exposure to light, followed by a slow, steady decline. Causes include light induced effects, thermal cycling, moisture ingress, cell cracks and potential induced degradation.
Manufacturers publish expected rates and guarantee a minimum output at set years. Actual results vary with climate, quality and handling, which is why measured data from your own plant matters.
Three layers of protection
Owners have three types of protection. The EPC contract provides a defects liability period and a performance guarantee at handover. Manufacturers give product warranties against defects and performance warranties against excess degradation. Insurance covers some physical damage and loss.
These layers have different durations and different proof requirements. Know which applies to a given problem. See our overview of what an EPC contract is for the structure.
The performance ratio and capacity test
At commissioning, the plant is tested to show it delivers the guaranteed output. Typical tests include a capacity test, comparing measured power with expected power under measured irradiance and temperature, and a performance ratio test over a period, which compares actual energy with the energy that the installed capacity should produce.
Define the test method, instruments, weather corrections and acceptance criteria in the contract. Disputes often arise from methods that were vaguely written.
Creating the baseline
A good handover includes a baseline data set: string-level currents and voltages, inverter outputs, insulation resistance results, thermographic images, IV curve tests on a sample of strings and a full set of as-built drawings. Take the data when the plant is new, under defined conditions.
Compare later measurements with the baseline. Without it, an owner cannot show whether a loss is degradation or a defect.
Sampling modules for flash testing
Warranty claims on module output usually depend on measured power in a recognised laboratory. Setting aside a few spare modules, or taking samples at handover for testing, creates reference points. Keep spares in storage, and record the batch and serial numbers.
Our note on module handling and storage explains how to avoid damage that could otherwise void a claim.
Warranty documents and transfer
Collect the warranty certificates for modules, inverters, trackers, transformers and monitoring equipment. Check that they are issued to the owner or can be assigned, that the terms match the contract and that the start dates are clear.
Check the conditions: some warranties require specific installation methods, cleaning practices or environmental limits. Record how these were met.
Defects liability period
The defects liability period is typically one or two years after handover, during which the contractor repairs defects at its cost. Use it. Run a full inspection before it ends, including thermography, and issue a list of defects in writing within the period.
Make sure a lender or technical adviser reviews the final inspection if required by financing.
Records to maintain during operation
Keep monthly production, availability, weather data, cleaning records, inverter logs, fault reports and maintenance reports. Compare actual output with the expected output from the energy model, corrected for weather.
Check commissioning methods in our guide to PV commissioning tests so that later measurements can follow the same procedures.
Practical tips for owners and asset managers
Keep a simple dashboard that compares monthly actual energy with expected energy, corrected for weather. A persistent gap is the first signal of a problem, and the sooner it is investigated, the more likely it is within a warranty period.
Schedule yearly thermography and string tests, and file the results with the baseline. Small changes year after year are easier to see in a consistent set of data.
Handover meeting agenda
A good handover meeting covers test results against guarantees, open defects and agreed completion dates, the warranty register, spare parts and tools handed over, training completed, document status and the start dates of each warranty and the defects liability period.
Record decisions in minutes signed by both parties. Verbal agreements fade quickly, and a signed record is what resolves a disagreement later.
Why early-life data matters most
The first year of operation shows teething problems, such as loose connectors, string faults and inverter settings that were not optimised. Capturing them within the defects liability period shifts the cost to the contractor.
Plan an early review at around six months and another before the period ends, with the contractor present and the data on the table.
Questions to ask the EPC contractor at handover
Ask for the test certificates of every inverter and transformer, the thermography report, the as-built string layout, the list of spare parts, the commissioning data in electronic form and the contacts for each manufacturer’s warranty desk. Ask what was found and fixed during commissioning, not just what passed.
Honest answers to these questions give the asset manager a head start for the whole life of the plant.
Making a claim
A claim needs evidence: the baseline, the measurements showing a loss beyond the guarantee, the test reports from an accredited laboratory and proof that the plant was operated and maintained as required. Notify the manufacturer or the contractor in writing and within the deadlines of the warranty.
Be prepared for the process to take time. A well-kept record reduces the argument.
Who writes this
Handover evidence and warranty files are what our solar commissioning engineers prepare with owners. Insight here is from the USP&E EPC team. The company, USP&E, is accountable for the EPC and O&M work it sells and is not a broker. Experience: 25,000 MW contracted since 2002, 24+ years in the field, 150+ power projects in 45+ countries. Read how we run power plant EPC projects through handover and operation.
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Questions about solar handover and warranties
How much do solar modules degrade each year?
Rates are given in manufacturer warranties and vary with product and climate. Measured data from your own plant is the real answer.
Why is a baseline test needed?
It lets the owner show later that a loss is real and beyond the guarantee.
Who is responsible for defects after handover?
The EPC contractor during the defects liability period, then manufacturers under their warranties.
What can void a warranty claim?
Poor handling, wrong installation, missing records or failure to follow the warranty conditions.
Preparing a solar plant for handover?
Send us the contract test clauses and the plant data, and our engineers will review the baseline and warranty package.
An engineer will reply if you email info@uspeglobal.com, call +27 10 822 2324 or fill in the project enquiry form. Generation equipment for hybrid plants is listed in the USP&E inventory.