Solar Panel Stringing: Series vs Parallel Wiring

String configuration is the bridge between your panel layout and your inverter. Get it wrong and you lose production, trip overcurrent protection, or void warranties. Get it right and every panel operates near its peak power point across all seasons.

This guide covers series vs parallel fundamentals, string sizing math with worked examples, NEC 690.7 temperature derating, mismatch rules, shade-aware strategies, DC wiring requirements, and how solar design software handles all of this automatically.

What this guide covers:

• Series, parallel, and series-parallel wiring fundamentals with a comparison table
• String sizing formulas with two worked examples using real panel and inverter specs
• NEC 690.7 temperature correction factors and a cold-weather derating walkthrough
• Rules for mixing different wattage panels on the same string
• Shade-aware stringing strategies: bypass diodes, string splitting, MLPE
• DC cable sizing, MC4 connectors, grounding, rapid shutdown, and labeling
• How design software automates string configuration and catches errors before permit submission

Chapter 1: Series, Parallel, and Series-Parallel Fundamentals

Every solar array uses one of three wiring configurations. The choice depends on inverter input specifications, roof layout, and shading conditions.

Series Wiring

In a series string, the positive terminal of one panel connects to the negative terminal of the next. Voltage adds up across the string. Current stays constant at the level of the weakest panel.

A string of 10 panels rated at 37.2 V Vmp and 11.47 A Imp produces:

• String voltage: 37.2 V x 10 = 372 V
• String current: 11.47 A

Series wiring is the standard for residential and commercial grid-tied systems. String inverters need high DC voltage, with MPPT windows starting at 150-200 V and peaking at 500-600 V. You need series strings to reach those levels.

Parallel Wiring

In a parallel configuration, all positive terminals connect together and all negative terminals connect together. Current adds up. Voltage stays constant at the level of the lowest-voltage panel.

Two parallel strings of 11.47 A each produce:

• Combined voltage: 372 V (same as one string)
• Combined current: 11.47 A x 2 = 22.94 A

Parallel wiring is common in battery-based off-grid systems (12 V, 24 V, or 48 V) and for connecting multiple series strings to a single MPPT input.

Series-Parallel (Hybrid) Wiring

Most real-world systems use a combination. Panels are wired in series to form strings, then multiple strings connect in parallel to an MPPT input. Series sets the voltage; parallel scales the power.

A 12 kW system might use three strings of 10 panels each. Each string produces 372 V at 11.47 A. The three strings connect in parallel to one MPPT tracker at 372 V and 34.41 A combined.

Comparison Table

Why Most Residential Systems Use Series

A typical residential string inverter has an MPPT range of 150-500 V. A single 400 W panel produces about 37 V at maximum power. You need at least 5 panels in series to reach 150 V and can fit up to 13 before hitting 500 V. Since most residential roofs hold 8-16 panels, series strings are the natural fit.

Parallel-only configurations require inverters designed for low-voltage, high-current DC input, standard in off-grid but not grid-tied residential work.

Chapter 2: String Sizing — Matching Panels to Inverter Voltage Windows

String sizing determines how many panels to wire in series so the string voltage stays within the inverter’s operating window across all temperature conditions.

Reading the Datasheet

You need four numbers from the panel datasheet (all at Standard Test Conditions, STC = 25 C cell temperature, 1000 W/m2 irradiance):

• Voc (Open-Circuit Voltage): The voltage a panel produces when no current flows. This is your maximum voltage reference.
• Vmp (Maximum Power Voltage): The voltage at which the panel produces peak power. This is your operating voltage reference.
• Temperature Coefficient of Voc: How much Voc changes per degree Celsius. Always negative for silicon panels. Typically -0.25% to -0.35% per C.
• Temperature Coefficient of Pmax (optional but useful): How peak power changes with temperature.

From the inverter datasheet, you need:

• Maximum DC Input Voltage: The absolute ceiling. Exceeding this damages the inverter and voids the warranty.
• MPPT Voltage Range (Vmin to Vmax): The operating window where the inverter tracks maximum power. Your string Vmp must stay inside this range at all temperatures.
• Maximum Input Current per MPPT: Limits how many parallel strings you can connect to one tracker.

The Two Boundaries

String sizing has an upper limit and a lower limit:

Upper limit (maximum panels per string): Your string Voc at the coldest expected temperature must not exceed the inverter’s maximum DC input voltage. Cold weather increases voltage.

Lower limit (minimum panels per string): Your string Vmp at the hottest expected temperature must stay above the inverter’s MPPT minimum voltage. Hot weather decreases voltage.

Formulas

Cold-weather maximum Voc per panel:

Voc_cold = Voc_STC x [1 + (TempCoeff_Voc / 100) x (T_min - 25)]

Hot-weather minimum Vmp per panel:

Vmp_hot = Vmp_STC x [1 + (TempCoeff_Vmp / 100) x (T_max_cell - 25)]

Cell temperature is not ambient temperature. On a hot day with 35 C ambient, cell temperature can reach 55-65 C. A common approximation adds 25-30 C to peak ambient for rooftop panels.

Maximum panels per string:

N_max = floor(Inverter_Max_DC_Voltage / Voc_cold)

Minimum panels per string:

N_min = ceil(Inverter_MPPT_Vmin / Vmp_hot)

Your string length must satisfy: N_min ≤ N ≤ N_max

Worked Example 1: Residential System

Panel: 440 W monocrystalline (common 2025-2026 residential panel)

Inverter: Single-phase hybrid, 600 V max DC input

Site conditions: Coldest expected ambient = -10 C. Hottest expected ambient = 38 C (cell temp estimate: 63 C).

Step 1: Cold-weather Voc

Voc_cold = 37.20 x [1 + (-0.27 / 100) x (-10 - 25)] Voc_cold = 37.20 x [1 + (-0.0027) x (-35)] Voc_cold = 37.20 x 1.0945 Voc_cold = 40.72 V

Step 2: Maximum panels per string

N_max = floor(600 / 40.72) = floor(14.73) = 14 panels

Step 3: Hot-weather Vmp

Vmp_hot = 31.10 x [1 + (-0.34 / 100) x (63 - 25)] Vmp_hot = 31.10 x [1 + (-0.0034) x (38)] Vmp_hot = 31.10 x 0.8708 Vmp_hot = 27.08 V

Step 4: Minimum panels per string

N_min = ceil(150 / 27.08) = ceil(5.54) = 6 panels

Result: This system can use strings of 6 to 14 panels. A typical residential install with 12 panels on one roof face would run a single string of 12 panels at 372 V nominal. That sits comfortably inside the 150-550 V MPPT window.

Worked Example 2: Commercial Rooftop

Panel: 580 W bifacial (commercial-grade)

Inverter: Three-phase string inverter, 1100 V max DC input

Site conditions: Cold climate, coldest expected ambient = -20 C. Hottest expected ambient = 36 C (cell temp: 61 C).

Step 1: Cold-weather Voc

Voc_cold = 51.80 x [1 + (-0.26 / 100) x (-20 - 25)] Voc_cold = 51.80 x [1 + (-0.0026) x (-45)] Voc_cold = 51.80 x 1.117 Voc_cold = 57.86 V

Step 2: Maximum panels per string

N_max = floor(1100 / 57.86) = floor(19.01) = 19 panels

Step 3: Hot-weather Vmp

Vmp_hot = 43.40 x [1 + (-0.32 / 100) x (61 - 25)] Vmp_hot = 43.40 x [1 + (-0.0032) x (36)] Vmp_hot = 43.40 x 0.8848 Vmp_hot = 38.40 V

Step 4: Minimum panels per string

N_min = ceil(200 / 38.40) = ceil(5.21) = 6 panels

Result: Strings of 6 to 19 panels. A 100 kW system (172 panels) could use 10 strings of 17 panels across 4 MPPT inputs. Each string produces 737.8 V nominal, well within the 200-1000 V MPPT range.

For a deeper look at matching panels to inverters, see our solar inverter sizing guide.

Chapter 3: Temperature Derating

Temperature is the most common source of string sizing errors. Panels are rated at 25 C (STC), but real cell temperatures range from below zero to 65+ C. Ignoring voltage swings causes permit rejections, equipment damage, or chronic underperformance.

Why Cold Weather Is the Voltage Risk

Silicon solar cells produce higher voltage at lower temperatures. A panel rated at 37.2 V Voc at 25 C might produce 42.7 V at -20 C. Across a 14-panel string, that is 598 V instead of the expected 521 V.

If 598 V exceeds the inverter’s 600 V maximum, you have a code violation, a warranty issue, and potential equipment failure.

NEC 690.7 Requirements

NEC 690.7 requires that the maximum PV system voltage be calculated using the sum of open-circuit voltages corrected for the lowest expected ambient temperature. The code provides two methods:

Method 1: Table 690.7(A) correction factors. Use when manufacturer temperature coefficients are not available. Multiply rated Voc by the factor corresponding to the site’s lowest expected temperature.

Method 2: Manufacturer temperature coefficients. When the panel datasheet provides a temperature coefficient of Voc (which nearly all modern panels do), NEC 690.7(A) requires you to use it instead of the table.

Method 2 is standard for all new installations because every major manufacturer publishes temperature coefficients.

NEC Table 690.7(A) Correction Factors (Crystalline Silicon)

These factors are conservative approximations. Manufacturer-specific coefficients often yield slightly different (and more accurate) results.

Worked Example: String Exceeding Limits at -15 C

Scenario: An installer in Minnesota designs a 13-panel series string using 440 W panels (Voc = 37.20 V, TempCoeff Voc = -0.27%/C) on an inverter with a 600 V maximum. At STC: 13 x 37.20 V = 483.6 V, well under 600 V.

Minnesota’s ASHRAE 99.6% design temperature is -27 C. The installer uses -15 C as the lowest expected ambient for this suburban site.

Using manufacturer coefficient:

Voc_cold = 37.20 x [1 + (-0.0027) x (-15 - 25)] Voc_cold = 37.20 x [1 + (-0.0027) x (-40)] Voc_cold = 37.20 x 1.108 Voc_cold = 41.22 V per panel

String voltage at -15 C = 13 x 41.22 = 535.8 V

That is under 600 V. The design passes.

Now check with 14 panels (a common temptation to add one more):

String voltage at -15 C = 14 x 41.22 = 577.1 V

Still under 600 V, but with minimal headroom. And if the actual temperature drops to -25 C:

Voc_extreme = 37.20 x [1 + (-0.0027) x (-25 - 25)] Voc_extreme = 37.20 x 1.135 Voc_extreme = 42.24 V per panel

String at -25 C = 14 x 42.24 = 591.4 V

That is 8.6 V from the inverter’s absolute maximum. Most AHJs would reject this design. Keep corrected string voltage at least 5-10% below the inverter’s maximum DC rating.

Cross-check with Table 690.7(A):

At -15 C, the table factor is 1.16.

String Voc (table method) = 14 x 37.20 x 1.16 = 14 x 43.15 = 604.1 V

The table method shows this 14-panel string exceeding 600 V. Table factors are more conservative than manufacturer coefficients. When in doubt, use whichever method produces the higher voltage.

Hot Weather and the Low-Voltage Boundary

While cold weather pushes voltage up, hot weather pulls it down toward the MPPT minimum. If string Vmp drops below the MPPT threshold, the inverter loses tracking ability or shuts down entirely.

Cell temperature is significantly higher than ambient. A rooftop panel in 38 C ambient can reach 60-68 C. Use the panel’s NOCT value to estimate:

T_cell = T_ambient + ((NOCT - 20) / 800) x Irradiance

For a panel with NOCT of 45 C at 800 W/m2 irradiance and 38 C ambient at peak sun (1000 W/m2):

T_cell = 38 + ((45 - 20) / 800) x 1000 = 38 + 31.25 = 69.25 C

That is 44 C above STC. With a Vmp temperature coefficient of -0.34%/C, each panel loses about 15% of its rated Vmp voltage.

Chapter 4: Mixing Different Wattage Solar Panels

Installers sometimes need to combine panels of different wattages, typically when expanding an existing system. The answer depends on how you wire them.

Series Mixing and Imp Mismatch

In a series string, every panel carries the same current, limited to the lowest Imp. A 400 W panel (11.47 A) in series with nine 440 W panels (14.15 A) forces the entire string to 11.47 A. Those nine panels each lose about 19% of their current capacity.

The math:

That is a 17.3% loss across the string compared to rated capacity. The loss is permanent, every day, all year.

Parallel Mixing and Vmp Mismatch

In parallel, the MPPT tracker picks one voltage for all connected strings. Two parallel strings at 372 V and 347 V Vmp might track at 360 V. Neither operates at peak power.

Rules for Safe Mixing

1. Same string, same panel. The strongest rule: every panel in a series string should be identical in model, wattage, and age. Different models with the same Imp can work, but check datasheets carefully.

2. Match Imp for series strings. If you must mix, choose panels with Imp values within 0.5 A of each other. A 14.15 A panel and a 13.80 A panel lose less than 3% from mismatch.

3. Match Vmp for parallel strings. When connecting strings in parallel to the same MPPT, keep Vmp within 5% across strings. A 372 V string and a 360 V string (3.2% difference) will work. A 372 V string and a 310 V string will not.

4. Use separate MPPT inputs for mismatched strings. Modern inverters with 2-4 MPPT inputs let you isolate different string configurations. Put your 440 W string on MPPT 1 and your 400 W string on MPPT 2. Each tracker optimizes independently.

5. Never mix cell technologies. Monocrystalline and polycrystalline panels have fundamentally different I-V curves. Mixing them on the same string or MPPT causes chronic mismatch losses.

When to Avoid Mixing Entirely

• When the Imp difference exceeds 1.5 A between panels in a series string
• When mixing panels from different decades (degradation rates differ)
• When one panel type has bypass diodes and another does not
• When the customer expects full rated output (mixing always costs some production)

For more on common configuration errors, read our guide to solar string design mistakes.

Chapter 5: Shade-Aware Stringing Strategies

A single shaded panel in a series string can cut output by 30-70%. Understanding how shade interacts with string configuration is the difference between a system that performs and one that chronically underproduces.

How Shading Affects Series Strings

In a series string, current passes through every panel. When one is partially shaded, the entire string matches the lower current. A 14-panel string with one 50%-shaded panel might lose 20-40% of total output, not just 1/14th.

Without bypass diodes, a shaded cell becomes a load instead of a generator, creating hot spots that can damage cells and cause fire hazards.

Bypass Diodes: The Built-In Safety Net

Modern panels include 2-3 bypass diodes, each protecting roughly one-third of the cells. When a cell group’s output drops, the bypass diode routes current around it.

A partially shaded panel loses roughly one-third of its output per activated bypass diode instead of dragging down the entire string. If one-third of one panel is shaded, you lose about 33% of that panel’s contribution, not 33% of the string.

String Splitting to Isolate Shade

When shade affects a specific area of the roof, you can split your layout into separate strings to isolate the shaded zone.

Example: A residential roof has 16 panels. A chimney shades 3 panels during morning hours. Instead of running one string of 16 panels where the chimney shade affects all 16 panels’ output:

• String 1: 13 unshaded panels (south-facing, clear)
• String 2: 3 panels near the chimney (separate MPPT input)

String 1 operates at full capacity all day. String 2 takes the morning shade hit independently. Total system production is significantly higher than a single combined string.

This approach requires an inverter with at least two MPPT inputs, which is standard on most modern residential inverters.

When to Use Microinverters

Microinverters convert DC to AC at each panel. Every panel operates independently, making them the best technical solution for complex shade conditions.

Use microinverters when:

• Multiple shade sources affect different parts of the array at different times
• The roof has dormers, vents, or chimneys creating irregular shade patterns
• Panels face two or more orientations (east/west split, for example)
• The customer demands maximum production from a partially shaded roof

Trade-offs: Higher cost per watt, more roof connections, and more components that can fail. For unshaded roofs, the production gain does not justify the premium.

When to Use Power Optimizers

Power optimizers sit behind each panel and perform module-level MPPT. The optimized DC feeds into a dedicated string inverter. Each panel operates at its own maximum power point regardless of neighbors.

Advantages over microinverters:

• Lower cost per watt than microinverters
• DC-to-DC conversion is more efficient than DC-to-AC at the module level
• The string inverter handles grid interaction, which simplifies system architecture

Advantages over standard string inverters:

• Module-level optimization eliminates series mismatch from shade
• Panel-level monitoring identifies individual underperformers
• More flexible string lengths (wider voltage windows with fixed output voltage per optimizer)

Shade Assessment Before Stringing

Before deciding on string configuration, you need:

• Which panels are shaded and when (hour by hour, month by month)
• The severity of shading (full shade vs. partial)
• Whether shade is seasonal (low winter sun) or permanent (adjacent building)

Professional shadow analysis tools generate hour-by-hour shade maps that show exactly which panels are affected throughout the year. This data directly informs your stringing decisions.

For a comprehensive look at shading assessment methods, see our guide to solar shading analysis tools.

Chapter 6: Wiring Best Practices and Safety

Physical wiring, connectors, grounding, and code compliance determine whether your system is safe, inspectable, and insurable.

DC Cable Sizing

PV DC cables carry high voltage and must be sized for both current capacity and voltage drop. NEC 690.8 requires that PV source circuit conductors be rated at 125% of the short-circuit current (Isc) of the connected modules.

Sizing steps:

1. Calculate maximum circuit current: Isc x 1.25 (NEC 690.8 continuous current factor)
2. Apply an additional 1.25 factor for conductor ampacity (total = Isc x 1.56)
3. Check voltage drop (target under 2% for DC runs)
4. Select cable gauge from NEC Table 310.16 based on the higher requirement

Common DC cable sizes for residential solar:

Always use PV Wire or USE-2 rated cable for exposed outdoor DC runs. Standard THWN is not rated for the UV exposure and temperature extremes of rooftop installations.

MC4 Connectors

MC4 connectors are the industry standard for solar DC connections. The “4” refers to the 4 mm contact pin diameter. Key requirements:

Never cross-mate brands. NEC and UL 6703 require all connectors from the same manufacturer. An Amphenol pin in a Staubli housing may fit but will not maintain contact pressure. This causes arcing, heat buildup, and fire risk.

Use the correct crimping tool. Each manufacturer specifies a tool. Hand-crimped connections are the leading cause of DC arc faults in residential solar.

Never connect or disconnect under load. MC4 connectors are not load-break rated. Shut down the inverter and verify zero current first.

Follow torque specifications. Over-tightened cable glands crack housings; under-tightened glands allow moisture ingress. Typically 2-3 Nm for the cable gland and hand-tight plus quarter-turn for the lock.

Grounding

NEC 690.41 requires one of two grounding approaches:

1. Grounded systems: One conductor (usually negative) is solidly grounded. Requires a ground-fault detection and interruption (GFDI) device.
2. Ungrounded systems: Neither conductor is grounded. Requires a ground-fault protection device that detects faults on both conductors. Most modern string inverters use this approach.

Equipment grounding: All exposed metal parts (module frames, racking, junction boxes) must be bonded to an equipment grounding conductor per NEC 690.43. Use listed grounding lugs or WEEB (Washer, Electrical Equipment Bond) clips rated for the specific racking system.

Rapid Shutdown: NEC 690.12

NEC 690.12 requires that PV systems on buildings include a rapid shutdown function. The 2020 and 2023 NEC editions establish specific requirements:

Outside the array boundary (more than 1 foot from the array): Conductors must be reduced to 30 V or less within 30 seconds of rapid shutdown initiation.

Inside the array boundary: Conductors must be reduced to 80 V or less within 30 seconds, or the system must use a listed PV Hazard Control System (PVHCS).

Compliance methods:

• Module-level power electronics (MLPE): Microinverters and DC power optimizers with rapid shutdown capability satisfy both inside and outside boundary requirements.
• String-level rapid shutdown devices: Dedicated devices installed at each string that disconnect and discharge conductors on command.
• Listed PVHCS: A system-level approach certified to UL 3741 that manages hazard control without module-level devices.

2023 NEC exception: PV systems on detached, non-enclosed structures (carports, pergolas, ground mounts that enter equipment-only buildings) are exempt from 690.12 rapid shutdown requirements. This is a significant cost reduction for commercial carport installations.

Labeling

NEC 690.31(G) and 690.56 require specific labels at multiple points in the system:

• At the main service panel: “WARNING: SOLAR ELECTRIC SYSTEM CONNECTED” with the rated AC output
• At the inverter: Maximum DC voltage, maximum DC current, and rapid shutdown type
• On DC conduit: “SOLAR CIRCUIT” labels at every access point and every 10 feet
• At the rapid shutdown initiator: Operating instructions for first responders
• On the PV disconnect: “SOLAR DISCONNECT” with voltage and current ratings

Labels must be reflective, weather-resistant, and conform to ANSI Z535.4 color coding. Red background with white text is standard for high-voltage warnings.

Chapter 7: How Design Software Automates String Configuration

Manual string sizing works for simple systems: one roof face, one panel type, no shade. Real-world projects have panels on multiple orientations, chimney shadows, and HVAC obstructions.

This is where solar design software changes the workflow.

Auto-Stringing

Modern design platforms analyze your panel layout and automatically assign panels to strings based on:

• Inverter voltage window (max DC input, MPPT range)
• Panel electrical specifications (Voc, Vmp, temperature coefficients)
• Site temperature data (ASHRAE design temperatures for the location)
• Shading analysis results (which panels are affected, when, and how severely)
• Panel orientation and tilt (panels on different faces go to different strings)

The software tests every possible string combination, selecting the configuration that maximizes annual production while staying within all electrical limits.

Automatic Temperature Derating

Design software pulls site-specific temperature data and applies derating automatically. Select a location and every string length is validated against temperature-corrected voltage limits. This eliminates the most common permit rejection cause: incorrect or missing derating calculations.

String Visualization

Good solar software shows which panels belong to which string, color-coded on the roof layout. You see at a glance whether shaded panels are isolated, string lengths are balanced, and voltage windows are respected.

When a customer asks “why did you put those three panels on a separate string?”, you can show the shade map and string assignment in one view.

Production Simulation by String

Advanced tools simulate production at the string level. Compare two strings of 8 panels versus one of 10 plus one of 6, and the software calculates which produces more over 25 years. This takes seconds versus hours by hand.

Integration with Proposals

The design flows directly into solar proposal software for customer-facing documents. Layout, string configuration, production, and financial returns all come from the same engineering model. No re-entry, no copy-paste errors.

For more on designing efficient panel layouts before stringing, see our solar panel layout design guide.

Why Automated Stringing Matters for Installers

A miscalculated string can damage an inverter on the first cold morning or waste production every hot afternoon for 25 years. Automated stringing in SurgePV catches these problems at design time, before equipment is purchased or permits submitted.

Conclusion

Solar panel stringing comes down to three things:

1. Size strings for both temperature extremes. Calculate cold-weather Voc for the upper limit and hot-weather Vmp for the lower limit. Every string must stay inside the inverter’s voltage window year-round.

2. Isolate shade. Put shaded panels on separate strings or use module-level electronics. A single shaded panel in an un-split series string costs far more production than the price of an extra MPPT channel.

3. Wire to code. Matched MC4 connectors from one manufacturer, properly sized PV Wire, equipment grounding on every frame, and NEC 690.12 rapid shutdown compliance. These are not optional.

Manual string sizing is straightforward for simple systems. For anything with mixed orientations, partial shade, or multiple MPPT inputs, solar design software pays for itself on the first project by catching errors that would otherwise cost time and money in the field.

Frequently Asked Questions

Should solar panels be wired in series or parallel?

Most residential grid-tied systems use series wiring because string inverters and hybrid inverters require high DC voltage input. Series strings add the voltage of each panel while keeping current constant. Parallel wiring is used when you need to keep voltage low, such as with battery-based systems or when adding panels to fill an MPPT channel. Many commercial systems use series-parallel combinations to balance voltage and current within inverter limits.

How many solar panels can you put on one string?

The maximum number of panels per string depends on the inverter’s maximum DC input voltage and the panel’s open-circuit voltage at the coldest expected temperature. Divide the inverter max voltage by the cold-weather corrected Voc per panel. For example, with a 600 V inverter limit and panels producing 40.7 V Voc at -10 C, the maximum is 14 panels per string. Always check minimum string length against the MPPT low-voltage threshold too.

Can you mix different wattage solar panels on the same string?

Mixing different wattage panels in series forces the entire string to operate at the lowest current (Imp) of any panel, which wastes capacity from higher-current panels. In parallel, mixing panels with different Vmp values causes similar mismatch losses. The safest approach is to keep identical panels on each string. If mixing is unavoidable, group panels with matching Imp values in series strings or matching Vmp values in parallel strings, and use separate MPPT inputs for different panel types.

What happens if one solar panel in a string is shaded?

When one panel in a series string is shaded, its current output drops. Because series strings carry identical current through every panel, the shaded panel becomes a bottleneck and drags down the output of the entire string. Bypass diodes in the panel’s junction box route current around shaded cell groups, limiting losses to roughly one-third of that panel’s output per activated diode. Power optimizers or microinverters eliminate this problem by allowing each panel to operate independently.

How do you calculate the maximum panels per string for an inverter?

Use this formula: Max panels = floor(Inverter max DC voltage / Panel Voc at coldest temperature). To get cold-weather Voc, apply the temperature coefficient: Voc_cold = Voc_STC x (1 + (TempCoeff_Voc x (T_min - 25))). For a panel with 37.2 V Voc, -0.27%/C coefficient, and a site minimum of -10 C, the corrected Voc is 40.7 V. With a 600 V inverter limit, that gives 14 panels maximum per string. Always verify the minimum string length for hot-weather Vmp as well.