Independent Technical Review for PV Projects with Economic Significance
For larger photovoltaic projects, glossy project documentation and yield forecasts are not enough. What matters is whether the design, material selection, protection concept, cable routing, string configuration, grid connection, documentation and construction quality are technically sound. This is precisely where a PV tender expert comes in.
A technical review of a photovoltaic project is particularly relevant when tenders are being prepared or evaluated, a solar park is to be acquired, banks require technical evidence, or investors need to realistically assess a project's risks. The objective is not formality, but a substantiated decision-making basis.
Contents
When a PV Tender Expert Is Needed
- When preparing or evaluating a PV tender
- Before purchasing a solar park or project portfolio
- For banks, investors or family offices prior to financing
- For EPC awards and plausibility review of proposals
- Before technical acceptance or commissioning
- When project documentation appears incomplete, contradictory or overly optimistic
- For repowering, expansion or refurbishment projects
Typical Questions Addressed
- Is the technical concept plausible for the site, roof or open area?
- Are the yield forecast, wiring and component selection realistic?
- Is the documentation sufficient for financing, operation and warranty?
- Are there risks in the protection system, grid connection, cable routing or installation?
- Are the tender documents formulated so as to avoid critical gaps?
- Where are the technical or economic red flags in the project?
Scope: Technical Review of Photovoltaic Projects
| Review Area | Content | Benefit |
|---|---|---|
| Tender Documents | Scope of work, technical specifications, interfaces, quality requirements, documentation obligations | Reduces change orders, gaps and ambiguity |
| Design and Configuration | String layout, inverter concept, protection measures, cable dimensioning, cable routing, grid connection | Identifies technical weaknesses before construction or purchase |
| Components and System Architecture | Modules, inverters, mounting structure, storage, monitoring, interfaces | Assesses suitability, consistency and risks |
| Documentation | Circuit diagrams, string plans, test protocols, acceptance documents, labelling, as-built documentation | Ensures traceability for operation, financing and disputes |
| Solar Park Due Diligence | Technical plausibility review, risk analysis, condition, bankability, yield shortfall and damage potential | Improves investment decision and negotiating position |
Technical Due Diligence for Lenders, Developers and EPCs
In a financing context, the technical review of a PV project is called technical due diligence, or TDD. Whoever finances a photovoltaic project or portfolio appoints an independent technical adviser for this purpose. The internationally used role name is lender's technical advisor (LTA). In both cases the task is the same: to test the technical assumptions of a project far enough that a capital decision can rest on them.
The neutrality of the role is essential. The reviewer sits between the sponsor or developer on one side and the financing bank or investor on the other. He represents neither position, but describes the technical facts so that both sides can work with them.
| Client role | Guiding question | Typical deliverable |
|---|---|---|
| Lender, financing bank | Do the technical assumptions support the assumed yields and operating costs? | TDD report with risk rating and proposed conditions |
| Investor, fund, asset manager | Which technical risks are not yet reflected in the purchase price? | Red flag report with prioritisation and cost impact |
| IPP, operating company | Is the asset documented and built the way it is being sold? | Asset condition review with defect and documentation list |
| Developer, sponsor | Will the design withstand a lender's review? | Pre-check before submission, remediation list |
| EPC contractor | Are the bid and the specification technically coherent? | Tender evaluation, bid and specification review, interface clarification |
The term bankability does not describe a technical threshold but the outcome of this review: a project is bankable when yield assumptions, build quality, documentation and the operating concept are substantiated well enough for the remaining risks to be named and priced.
Tendering support works the same way in the opposite direction: before a contract is awarded, the specification is checked for gaps that would later turn into variation orders.
Yield Assessment: What P50, P75 and P90 Mean
Yield forecasts for photovoltaic projects are not stated as a single figure but as a probability. P50, P75 and P90 denote exceedance probabilities: the P90 value is the annual yield that is reached or exceeded with 90 percent probability. It therefore lies below the P50 value.
| Metric | Meaning | Typical use |
|---|---|---|
| P50 | Expected value, statistically exceeded in half of all years and missed in the other half | Planning, economic modelling, comparison of options |
| P75 | Reached or exceeded in 75 percent of years | Sensitivity case, intermediate scenario |
| P90 | Reached or exceeded in 90 percent of years | Conservative case, the customary reference in project finance |
What matters for the review is less the figure itself than how it was produced. A P90 value without a disclosed uncertainty calculation is not a substantiated number. At minimum the following must be checked:
- source of the irradiation data, length of the time series and comparison against a second independent source
- interannual variability of irradiation at the specific site
- model uncertainty of the simulation used and the assumed performance ratio
- degradation assumed per operating year and its derivation from datasheet and warranty curve
- availability assumption plus losses from shading, soiling and curtailment
- reference period of the P90: a single year yields a different figure than a ten-year mean
How a yield shortfall against the forecast is proven technically is described under PV yield assessment. An overview of the other report types is given under types of PV expert report.
Red Flag Checklist for the Technical Review
In practice the following points are the most frequent triggers of renegotiation, lender conditions or later disputes. They serve as a pre-check before a full review is commissioned.
| No. | Review point | Why it matters |
|---|---|---|
| 1 | Irradiation data from a single source, with no time series stated | The yield forecast is not cross-checked, the spread is unknown |
| 2 | Performance ratio assumed as a flat figure, with no loss breakdown | Optimistic assumptions stay invisible |
| 3 | Degradation assumption departs from the warranty curve without justification | Yield in the later operating years is overstated |
| 4 | Shading analysis missing or ignoring self-shading between rows | Systematic yield shortfall across the whole term |
| 5 | String plan missing or inconsistent with the as-built documentation | Fault finding becomes expensive, warranty claims hard to enforce |
| 6 | DC/AC ratio and inverter sizing not derived | Clipping losses or overload in the part-load range |
| 7 | Cable cross-sections, routing and voltage drop not evidenced | Permanent losses and thermal risk |
| 8 | Earthing, lightning and surge protection concept not documented | Insurance-relevant, a frequent cause of consequential damage |
| 9 | Grid connection agreement, connection conditions and curtailment rules missing | Export, and therefore yield, is not secured |
| 10 | Test reports to IEC 62446-1 missing or incomplete | The condition at commissioning is not evidenced |
| 11 | Handover protocol missing or signed without reservation of defects | Burden of proof and the start of limitation periods shift against the operator |
| 12 | O&M contract without an availability definition and without maintenance history | Operating cost and outage risk cannot be calculated |
Point 11 belongs to the full handover logic: which records must exist at which moment is covered under PV handover and acceptance protocol.
How a Technical Due Diligence Proceeds
- Data room and document request. The existing data room is compared against a fixed requirement list. How robust the documentation is becomes visible at this stage already.
- Document review. Yield assessment, design, component datasheets, grid connection, test and handover records, and the technical parts of the contracts.
- Site visit and sampling. Visual inspection, thermography, insulation and I-V curve measurements on selected strings, design compared against as-built.
- Report. Findings separated into evidenced, calculated scenario and statement by a party, plus a prioritised red flag list with technical and commercial classification.
- Queries and follow-up. Open points clarified with sponsor, operator or EPC, with re-inspection after remediation where required.
Data Room Requirements
These documents are regularly required for a technical review. If several are missing, that is a finding in itself.
- yield assessment including uncertainty calculation and simulation file
- site layout, module layout, string plan, single-line diagram
- datasheets and warranty terms for modules, inverters and mounting system
- grid connection agreement, connection conditions, curtailment rules
- test reports to IEC 62446-1, insulation and I-V curve measurements
- handover protocol, defect list, evidence of remediation
- as-built documentation and labelling of plant components
- O&M contract, maintenance and fault history
- monitoring data at string level, ideally across several operating years
- insurance documents and claims history
Effort and Fees
The effort of a technical review depends on three things: installed capacity, the number of sites and above all the quality of the data room. A fully documented project is faster to review than a smaller one with gaps in its records.
- Desktop pre-check. Data room screening, plausibility check of the yield assessment, short red flag list. Suitable as a basis for deciding whether a full review is worthwhile.
- Full technical due diligence. Document review, site visit with measurements, report with risk rating and proposed conditions.
- Accompanying review. Handover supervision, re-inspection after remediation, support during tendering and award.
Fees are charged on a time basis with a record of hours, guided by the German JVEG scale. A written estimate of effort is provided before appointment. The pricing structure for smaller reports is set out under cost of a PV expert report.
Solar Park Due Diligence: What Really Matters
A due diligence for a solar park must identify the critical points that subsequently affect yield, operational safety, CAPEX/OPEX or liability. This includes not only visible defects, but above all systemic weaknesses in the technical concept.
- Plausibility of yield assumptions and site data
- Comparison of design, component selection and actual execution
- Review of protection and safety concepts
- Assessment of documentation quality and completeness
- Identification of risks for yield shortfall, change orders or subsequent damage
- Transparent summary for management, financing and negotiation
What Clients Receive
- Clear technical assessment rather than vague generalities
- Structured risk overview with prioritisation
- Substantiated notes on open items and documentation gaps
- Technical argumentation basis for acquisition, financing or contract award
- Comprehensible summary for decision-makers without information loss
Depending on the assignment, the focus may be on tender review, technical due diligence, acceptance support or a combined project review.
Who This Service Is For
This service is aimed at stakeholders who need more than a general assessment – they require a technically substantiated review with economic relevance. It is particularly valuable for larger rooftop systems, ground-mounted systems, solar park acquisitions, portfolios and complex projects with multiple interfaces.
FAQ
What is a technical due diligence (TDD)?
The technical review of a photovoltaic project ahead of an acquisition or financing decision. Yield assumptions, design, execution, documentation and the operating concept are examined so that the remaining technical risks can be named.
What is a lender's technical advisor?
The technical adviser to the financing side. Appointed by the lender, he tests whether the technical assumptions of the project support the assumed yields and operating costs, while remaining neutral towards sponsor and operator.
What do P50, P75 and P90 mean?
They are exceedance probabilities for the annual yield. The P90 value is reached or exceeded with 90 percent probability and therefore lies below the P50 value. What matters is the disclosed uncertainty calculation behind it, not the figure alone.
Which documents are needed for a technical due diligence?
Yield assessment with uncertainty calculation, site and string plans, single-line diagram, datasheets and warranty terms, grid connection agreement, test reports to IEC 62446-1, handover protocol, as-built documentation, O&M contract and monitoring data at string level.
What is a red flag report?
A condensed review listing and prioritising only the decision-relevant risks. It serves as a fast basis for deciding whether a project is pursued further and a full review commissioned.
What does a PV tender expert do?
Tender evaluation: review of technical documents, specifications, the plausibility of the project concept, documentation requirements and risks, so that clients can decide on an informed basis before award.
When is due diligence for a solar park advisable?
Before acquisition, financing, refinancing and technical re-assessment, and whenever the quality of the project documentation or of the execution is not clearly substantiated.
Are operating assets and portfolios reviewed as well?
Yes. For operating assets the track record replaces the forecast: monitoring data, fault and maintenance history and the documented condition are set against the original assumptions. Portfolios are reviewed on a sampling basis with selection criteria agreed in advance.
Request a Technical Review for Your PV Project
If you would like a PV tender, an ongoing photovoltaic project or a solar park due diligence to be technically reviewed, a brief initial assessment is usually the quickest way to get started.
Email: info@gutachterpv.org
Profile: Andreas Benz – Expert Profile