Collect the evidence before calculating
Module data
Use the exact module datasheet: Voc, Vmp, Isc, Imp, voltage temperature coefficient, maximum system voltage and connector information.
Receiving equipment
Use the exact inverter, charge-controller or portable-power manual: absolute maximum PV input voltage, MPPT range, input-current limits and permitted array configurations.
Site conditions
Record the project minimum design temperature. Do not substitute the current weather, daytime average or module operating temperature.
Series path
List every component exposed to string voltage, including connectors, cable, disconnects, fuses, SPDs, combiner equipment and measuring devices.
Cold-weather Voc calculation workflow
PV module Voc normally rises as cell temperature falls. When the datasheet provides a negative percentage coefficient, use its magnitude for a conservative cold correction. Confirm the required method with the module manufacturer and the applicable project standard.
N × Voc,cold < lowest absolute maximum voltage in the series path
In the formula, βVoc is expressed as a decimal per degree Celsius. A datasheet value written as a percentage must be converted before use. This page intentionally provides no universal module count because every result depends on exact datasheets and site temperature.
- Confirm the exact module model and its Voc temperature coefficient.
- Establish the project minimum design temperature from an approved source.
- Calculate corrected Voc using the method required by the project standard or manufacturer.
- Multiply corrected Voc by the proposed series count.
- Compare against every component's maximum DC voltage—not only the inverter label.
- Separately check hot-weather Vmp against the minimum MPPT operating voltage.
- Record assumptions, datasheet revisions and calculation results for design review and commissioning.
Can different PV module models be connected in series?
Sometimes a design review can demonstrate compatibility, but equal wattage is not enough. Series current is constrained by the electrical behaviour of the modules in the string, while the sum of operating voltages must remain inside the receiving MPPT window across temperature and irradiance.
| Check | Why it matters | Evidence |
|---|---|---|
| Imp and Isc | Large current differences can increase mismatch loss and change protection calculations. | Both module datasheets |
| Vmp and Voc | The combined string must remain inside MPPT and absolute voltage limits. | Module and controller/inverter data |
| Temperature coefficients | Cold and hot boundaries may diverge even when STC values look similar. | Manufacturer coefficients |
| Technology and bypass layout | Different I-V behaviour, shading and bypass operation can produce unstable or inefficient operation. | Module construction documentation |
| Connectors and cable | Mating appearance does not prove electrical or mechanical compatibility. | Exact connector and cable instructions |
If replacement modules cannot be matched, consider a separately controlled MPPT input only when the receiving equipment manufacturer permits that architecture. Do not parallel unlike strings by assumption.
Australia and UAE project checks
Australia
Confirm the current AS/NZS requirements, equipment instructions, local network rules and licensed-electrician responsibilities. This guide does not establish regulatory compliance.
United Arab Emirates
For Dubai projects, check the current DEWA DRRG standards, connection guidelines, eligible-equipment process and project documents. Other emirates may have different authority requirements.
PV string design FAQ
Should I use Vmp or Voc to determine maximum series count?
Use temperature-corrected Voc for the absolute maximum voltage check. Use temperature-adjusted Vmp separately to verify that the string remains inside the MPPT operating window.
Does a portable power station's published voltage include extra margin?
Do not assume unpublished margin. Treat the manufacturer's absolute maximum PV input voltage as a hard boundary and follow its permitted module configuration instructions.
Can two 200 W panels be considered compatible?
No. Compare Voc, Vmp, Isc, Imp, temperature coefficients, maximum system voltage, connector system and MPPT limits. Nominal wattage alone is insufficient.