Can I skip this step if I chose microinverters?

Mostly yes. Microinverters convert DC to AC at each panel, so you are not building high-voltage series strings into one central box. You still need compatible equipment, but the string-length maths in this step is a string-inverter job.

What if my string only fails the cold Voc check?

Reduce panels per string, choose an inverter with a higher maximum DC voltage, or pick panels with lower Voc — do not assume the installer will fix it on site. The string voltage calculator shows which limit you are hitting.

What is DC:AC ratio and does this step set it?

DC:AC ratio is how much panel DC capacity you connect relative to the inverter's AC rating (e.g. 6 kW of panels on a 5 kW inverter ≈ 1.2). Step 7 checks whether a proposed string length is electrically safe and inside MPPT; oversizing strategy is a separate sizing decision.

7. Strings and electrical match | Photonik Design Guide

Previous step — Choosing an inverter set your inverter type. If you chose string or hybrid, this step checks how many panels you can wire together before you hit electrical limits. Microinverter systems can skip most of this.

Grid-connected string and hybrid systems — this step is about matching panel strings to a central inverter. If you chose microinverters in Step 6 — Choosing an inverter, each panel is its own mini-string; you can skim this and move on to Step 8 — Battery storage.

Who needs this step?

String inverter — yes. All your panels on an MPPT input share one operating voltage.
Hybrid inverter — yes. Same string rules as a string inverter (plus battery wiring later in step 8).
Microinverters — largely skip. The inverter under each panel handles voltage on its own.

You should already have a shortlisted panel model and inverter type from Step 6 — Choosing an inverter. Step 7 is not about picking brands — it is about checking the electrical fit before you lock how many panels sit on each string.

The two checks (in plain English)

Cold mornings — do not over-voltage. Panel voltage rises when it is cold. Add up the panels in series and check the string's open-circuit voltage (Voc) at your site's coldest expected temperature. It must stay below the inverter's maximum DC voltage — or the inverter can shut down or be damaged.
Hot afternoons — stay inside MPPT. Operating voltage falls when panels are hot in the sun. Check the string's minimum power voltage (Vmp) at your hottest expected cell temperature. It must stay inside the inverter's MPPT window (between MPPT min and MPPT max) or the inverter cannot track maximum power.
Series vs parallel: panels wired in series add voltage; parallel strings add current. This step is mostly about how many panels you put in one series string on each MPPT input.

Infographic: cold weather raises string Voc toward the inverter maximum DC limit; hot cell temperatures lower Vmp toward the MPPT minimum; panels in series add voltage. — The diagram uses one voltage scale for simplicity. Check **Voc** on cold mornings and **Vmp** on hot afternoons. The hot example (~70°C) is **cell temperature** on the panel, not air temperature.

Voltage Calculation in Photonik

Gather these from the panel and inverter datasheets (or our panel and inverter directories):

From the panel: Voc and Vmp at standard test conditions, and the temperature coefficient of Voc (usually a small negative % per °C).
From the inverter: MPPT minimum voltage, MPPT maximum voltage, and maximum DC input voltage (the hard ceiling).
From your site: a realistic minimum and maximum temperature range for where the array will sit (or use defaults and refine later).

Off-grid note: string voltage rules still apply on battery systems with a solar charge controller or hybrid inverter. Voltage windows are often tighter than grid-tied gear. Skip grid export topics; focus on whether the string fits the controller’s MPPT range at your site’s temperatures.

In Photonik Pro, open System Design → String Voltage Check. Set max string length, site temperature range, and cell temperature rise — read calculated Vmp and Voc against each inverter’s minimum and maximum columns.

String Voltage Check in Photonik with string length, temperature inputs, and inverter min and max voltage columns. — String Voltage Check — panels per string vs inverter limits.

Worked example: string voltage vs panel cell temperature for 8, 11, and 5 panels in series using Trina Vertex S+ 440 W and Sungrow SG5.0RS; eleven panels exceed the inverter maximum DC voltage when cold, five panels fall below the recommended Vmp range when hot, eight panels stay in range. — Worked example on paper: Trina Vertex S+ 440 W panel and Sungrow SG5.0RS inverter.

Without Pro, use the string voltage calculator or follow the string voltage walkthrough.

Ready for storage? Step 8 — Battery storage covers whether and how to add a battery.

DC:AC ratio (a quick concept)

Inverters are sold with an AC power rating (e.g. 5 kW), but you can often attach more panel DC capacity than that nameplate — sometimes 1.2× to 1.5× or more, depending on climate and inverter limits. That ratio is called DC:AC ratio (or oversizing).

Why do it? Panels rarely hit their lab rating in the real world. A modest oversize captures more energy in good conditions without changing the inverter box.
Why not go wild? Too much DC for the inverter means more clipping on sunny days (power the panels could make but the inverter cannot export). The inverter and local rules still cap what you can connect.
For this step: DC:AC ratio is a sizing conversation for later — step 7 is about whether a given string length is electrically valid, not about maximising kW on the roof.

7. Strings and electrical match

Who needs this step?

The two checks (in plain English)

Voltage Calculation in Photonik

DC:AC ratio (a quick concept)

Frequently asked questions

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