Vertical integration changes how a supplier controls production, sources cells and handles material changes. It does not automatically mean higher output, lower prices or a better warranty. Buyers should compare the exact module, its production records and the contract rather than pay a premium for the manufacturing label alone.
What Changes in Your Purchase
| Buying decision | Vertically integrated manufacturer | Module assembler | Evidence to request |
|---|---|---|---|
| Cell sourcing | Can coordinate its own cell and module production, but may also buy cells externally. | Buys cells from outside suppliers and controls their selection and assembly. | Cell source and production site for your order. |
| Material consistency | Can manage changes across several production stages internally. | Relies on supplier agreements, incoming inspection and change controls. | Approved bill of materials and written substitution rules. |
| Price | May benefit from coordinated production, while carrying upstream factory costs. | Can shop among cell suppliers, but remains exposed to external pricing. | Comparable delivered prices, payment terms and quote validity. |
| Delivery | Depends on internal production schedules and available stock. | Depends on purchased-cell availability and assembly capacity. | Allocated stock, shipping dates and partial-delivery terms. |
| Warranty and repairs | Responsibility depends on the warranty issuer and contract. | Responsibility also depends on the warranty issuer and contract. | Covered costs, claims procedure and replacement policy. |
Integration does not require ownership of every factory from raw silicon to finished modules. A supplier may combine cell and module production, or extend further upstream. The IEA identifies five main manufacturing stages: polysilicon, ingots, wafers, cells and modules.[1]
Tongwei’s business includes high-purity crystalline silicon, solar cells and finished modules. For a purchase, the useful follow-up is specific: which facilities and material sources will supply the model on your quotation?
Check the Module, Not Just the Factory
An assembler can buy high-quality cells and apply strict production controls. An integrated manufacturer can also deliver different module designs from different factories. Neither label establishes a fixed efficiency or degradation advantage.
Higher efficiency mainly helps when installation space is limited. As a simple calculation, a 450W module at 22% efficiency needs about 2.05m² of module area; at 23%, it needs about 1.96m². Two systems with the same 10kW rating do not automatically produce different annual energy just because their module efficiencies differ.
Rated power is measured under standard test conditions, including irradiance of 1,000W/m² and cell temperature of 25°C. Actual output also changes with sunlight and operating temperature.[2]
Compare the model code, factory, certificate coverage and material configuration. IEC 61215-2 describes design-qualification tests intended to assess electrical characteristics and resistance to prolonged outdoor exposure. It does not establish a universal performance gap between integrated manufacturers and assemblers.[3]
For extended reliability testing, ask for the test conditions, sample configuration and measured result. “Less than 2% loss” means little without knowing which test was run. It cannot be converted directly into a 25-year energy forecast.
Compare Prices on the Same Basis
Ask both suppliers to quote the same capacity, delivery location and scope. Check whether tax, freight, unloading and inspection are included. A factory-gate module price is not comparable with a delivered system price that includes inverters, mounting equipment and installation.
Illustrative price comparison: a difference of CNY 0.10/W equals CNY 1,000 on a 10kW order and CNY 10,000 on a 100kW order. These are calculations, not market quotes or typical savings from choosing an assembler.
If every other system cost stays unchanged, the module discount is also the system saving. There is no basis for turning a CNY 1,000 module discount into several thousand yuan of additional savings.
For repairs, request separate figures for the replacement module, transport, roof access, removal and installation. Access equipment and labour may be shared across several replacements, so a flat per-module repair estimate can be misleading.
Read the Warranty Costs
A product warranty covers specified defects. A power warranty sets a minimum output level under stated conditions. A 30-year power warranty does not necessarily include 30 years of free roof access, labour or shipping.
Check who issues the warranty, who can make a claim and which remedy the supplier may offer. Replacement, repair and financial compensation can leave the buyer with different costs. Silence about labour is a reason to obtain written clarification—not proof that every related cost belongs to the buyer.
For an illustrative linear power warranty, a 1% first-year reduction followed by 0.4 percentage points per year gives a year-25 minimum of 89.4%: 100% − 1% − (24 × 0.4%). That is a contractual power floor, not a forecast of annual energy production.
Use the version of the warranty applicable to your model and sales region. Tongwei’s product document downloads provide a starting point for checking specifications; obtain any missing warranty or installation documents before signing.
Put Delivery and Substitutions in Writing
Ask whether the quoted modules are finished stock, scheduled production or dependent on a future cell purchase. Record the dispatch date separately from the arrival date. For a phased project, specify which quantities must arrive together.
At 500W per module, a 500kW order contains 1,000 modules. A shortfall of 200 modules leaves 100kW undelivered. Whether that delays the entire project depends on the electrical layout and commissioning plan.
The purchase agreement should identify the approved bill of materials—the cells, glass, encapsulant and other key components—and explain how substitutions are approved. A change may require a review of certification coverage or additional testing. An electroluminescence image alone does not establish that a substitute material has equivalent long-term performance.
Agree on delay remedies and notification periods for the actual project. There is no universal daily penalty or lead time that applies to either manufacturing model.
Plan for Replacement Modules
Matching dimensions are only part of a replacement decision. The installer also needs to check voltage, current, connectors, mounting zones and the inverter’s operating limits. NREL’s guidance explains why string sizing must account for module open-circuit voltage, site minimum temperature and inverter voltage limits.[4]
A discontinued model does not automatically require replacing the whole string. Ask the supplier how it approves substitute models, whether compatible stock is held locally and who pays for any necessary mounting or wiring changes.
Before accepting Tongwei modules, buyers can use the module authenticity query to check product identity. Keep the serial-number list with delivery records and warranty documents. Authenticity verification does not replace inspection for damage.
Use a Documented Acceptance Check
The following is a suggested procurement workflow, not a report of a completed factory audit or field trial.
- Before payment: match the quotation, datasheet, certificate coverage and warranty to the exact model. Confirm the seller, manufacturer and warranty issuer.
- Before dispatch: obtain the packing list and agreed inspection records. Set the sampling method and acceptance criteria before inspection begins.
- At delivery: photograph packaging damage, check quantities and serial numbers, and record visible defects before installation.
- At commissioning: retain the installer’s test records, system layout and baseline performance data.
- For a claim: record the affected serial numbers, fault date, photographs and relevant test results. Keep the supplier’s response in the same file.
For hail-prone sites, request the tested ice-ball diameter and impact speed rather than relying on glass thickness alone. DOE guidance describes the basic 25mm hail test and recommends stronger evidence for severe hail exposure. It also recommends baseline imaging to help distinguish later storm damage.[5]
Choose for the Project
For a home or small commercial roof, compare the installed design, roof suitability and local service arrangements. Ask who handles a leaking roof, a failed connector and a defective module; these may involve different parties. The installer’s scope matters as much as the module supplier’s manufacturing structure.
For a financed project, send the proposed manufacturer, module and warranty package to the lender and insurer before committing to a non-refundable order. Approval requirements, review times and loan pricing are project-specific. Vertical integration alone does not establish eligibility or a lower interest rate.
For distributors and larger buyers, focus on batch consistency, change approval, repeat-order availability and replacement handling. Ask for references from comparable installations and discuss actual claims experience—not just shipment volume.
An integrated supplier is worth paying more for when its offer includes verifiable advantages: reserved production, traceable materials, clear change controls or stronger contractual support. An assembler can be the better purchase when it provides equivalent product evidence and service at a lower delivered cost.
Request a model-specific module quotation
Send Tongwei your project capacity, installation type, delivery country and required arrival date. Include your shortlisted model, if available, and request its datasheet, applicable warranty, certification coverage and delivery terms.
Send Your Project RequirementsAbout This Guide
This is a source-based purchasing guide, not a firsthand product review. The calculations are labelled examples, and no factory visits, laboratory tests or customer purchases are claimed. External references support the technical points beside them; Tongwei links identify its own products and services.