Quick answer
Software-assisted assignment of modules to series strings and inverter inputs. Supported checks, design conditions and practical routing require review; generated maps do not establish installation approval.
What Is Auto-Stringing?
Answer: Auto-stringing uses module, inverter and layout inputs to propose module series connections and assignments to inverter inputs. Its usefulness depends on the supported equipment rules and verified design conditions. Review voltage, current, input architecture, practical routing and remaining assumptions. A generated string map records proposed connections; it is not proof of complete electrical design, permit acceptance or approval to install.
Auto inverter selection compares candidate equipment. Auto-stringing allocates modules within the chosen architecture. Keep both aligned with the actual stringing electrical design and its released revision.
Inputs and Checks That Matter
| Input or check | What to establish |
|---|---|
| Exact module specifications | Voc, Vmp, Isc, Imp and applicable temperature coefficients |
| Design temperatures | Required cold-voltage and operating conditions, with their basis |
| Exact inverter limits | Absolute voltage, operating window, operating current and short-circuit constraints |
| Input architecture | Independent MPPTs, physical connectors, supported parallel strings and per-input limits |
| Array grouping | Orientation, shading, module type and permitted configuration |
| Routing and identifiers | Practical paths, stable module/string/input labels and field verification needs |
Series module voltages add for the relevant operating condition. Parallel strings contribute current to their shared input. A physical connector is not necessarily an independent MPPT, and a maximum usable input-current figure is not automatically a short-circuit-current limit.
SMA’s STP 15000TL-10 technical table, for example, separately lists input A/B current limits, short-circuit-current limits, independent MPP inputs and strings per input. Use the exact equipment table and footnotes rather than a generic “one string per connector” rule.
Voltage Calculations Need the Baseline Term
PVsyst’s voltage-sizing documentation separates operating-voltage checks from cold-condition open-circuit-voltage limits. Its default temperatures are software settings, not automatically the required conditions for every site.
For an illustrative linear correction with a relative Voc coefficient expressed per °C:
Voc(T) = Voc at reference temperature × [1 + βVoc × (T − reference temperature)].
The 1 + term preserves the reference voltage. Multiplying only by the coefficient and temperature difference does not calculate the corrected voltage. Convert a coefficient stated in percent per °C to a fraction per °C; an absolute V/°C coefficient needs a different additive expression. Use the manufacturer’s applicable data and required design method.
For arithmetic only, suppose a hypothetical module has Voc = 50 V at 25°C, βVoc = −0.25%/°C = −0.0025/°C, and the evaluated module temperature is −10°C:
Voc = 50 × [1 + (−0.0025) × (−10 − 25)] = 54.375 V per module.
18 modules in series = 978.75 V; 19 modules = 1,033.125 V.
Against a hypothetical 1,000 V absolute limit, 19 fails this arithmetic check. Eighteen is below the limit for the stated assumptions, but is not an approved design: applicable margins, other equipment ratings, temperature basis, tolerances, operating voltage and current constraints remain to be established.
A Formula Is Not the Entire String Design
A preliminary maximum count from absolute voltage is floor(allowed voltage / evaluated module Voc) under the defined assumptions. A hot-condition MPPT minimum can inform a lower count using ceil(minimum operating voltage / evaluated module Vmp). Neither is a complete compatibility test.
Also check cold operating voltage, start/full-power conditions, current and supported parallel-input configuration. Do not infer Vmp’s temperature behavior from a power coefficient without an applicable method.
For illustration, two identical parallel strings with 10 A operating current and 11 A short-circuit current each give arithmetic totals of 20 A operating and 22 A short-circuit current under those stated conditions. They are different quantities, and both require their own applicable comparison and design treatment.
Grouping similar irradiation conditions can help review mismatch, but different orientations do not imply a fixed loss percentage or a universal requirement for a separate MPPT. Validate the configuration against the exact architecture and modeling assumptions. Plain DC strings, optimizer-based systems and microinverter AC branches have different rules; do not apply one algorithm to all three without verifying support.
Review the Generated Map
- Verify module count and exact input assignments against the selected equipment.
- Review voltage/current checks and their conditions, not only a green status indicator.
- Check the proposed physical sequence and routing against accessible site conditions.
- Reconcile identifiers with the string map, single-line diagram, equipment schedule and material quantities.
- Close findings through the design review workflow and identify the applicable released revision.
- Route field changes through required review, then update as-built drawings with accepted installed details.
Commissioning measurements require qualified personnel, appropriate procedures and exact equipment instructions. Do not use a universal “within 5%” Voc rule or this hypothetical example as a live testing or connection procedure.
Designers: expose missing inputs and excluded checks. Installers: confirm the released map and report deviations before affected work. Sales teams: do not claim that auto-stringing completes every electrical calculation or guarantees energy recovery from optimizers or microinverters.
Evaluate the workflow in a SurgePV demo using your actual module and inverter configuration. Confirm supported architectures, output fields and human review responsibilities.
Frequently Asked Questions
Does auto-stringing guarantee a compliant installation?
No. Supported checks depend on verified inputs and rules. Exact manufacturer constraints, remaining electrical design, professional review and required acceptance remain separate responsibilities.
Is a microinverter branch the same as a DC string?
No. Microinverters convert module DC to AC, and their supported AC branch arrangements follow the exact product and applicable requirements. Do not use plain DC string-length formulas for an AC branch.
Should every orientation use a separate MPPT?
Evaluate the actual architecture, manufacturer requirements and modeled mismatch. Separate tracking can be useful, but there is no universal orientation rule or fixed production-loss percentage here.
Does a passing cold Voc check settle string sizing?
No. Operating voltage, current, inputs, other equipment limits and applicable conditions still require review. Passing one arithmetic comparison is not approval.
Related Glossary Terms
About the Contributors
Editorial contributor · SurgePV
Rainer Neumann is credited as an editorial contributor on SurgePV content. This profile does not assert engineering credentials, project totals, software-testing experience, education, speaking engagements, or media citations because independent verification evidence is not retained in the publication record.
CEO & Co-Founder · SurgePV
Keyur Rakholiya is identified by SurgePV as its CEO and a company co-founder. His SurgePV author page lists only role information that can be tied to the public profile below; credentials, project totals, testing claims, media appearances, and speaking engagements are not asserted without retained evidence.
