Designing a string with optimisers: a worked example

A common worry about panel-level optimisers is that they'll complicate system design. In practice they don't. You design the string to the inverter exactly as you do now, using the panel datasheet. Then you add three quick checks to make sure every panel sits inside the optimiser's limits, and one rule about gateways.

The four rules

• One optimiser per panel.
• One GT gateway per string, up to 30 optimisers.
• Every panel within the optimiser's input limits (below).
• A certified inverter. Archai is certified with Solis and with Fox ESS single-phase inverters. If you're using anything else, ask us before quoting.

The optimiser limits

For the Archai iOPT 800W, the numbers that matter at the design stage are:

• Max input power: 800 W
• Max input voltage: 70 V (check against the panel's Voc)
• Max input short-circuit current: 23 A (check against the panel's Isc)
• MPPT range: 12–60 V
• Max system voltage: 1500 V

Most residential and light-commercial panels on the UK market today sit comfortably inside these. The ones to look at twice are very high-current modules, so always check Isc on the datasheet.

Worked example: one string on a Fox ESS hybrid

The job: 14 × 450 W panels with Voc 49.5 V and Isc 13.9 A, wired as a single string on a Fox ESS single-phase hybrid.

Check each panel against the optimiser:

• Power: 450 W against 800 W max. ✓
• Voltage: 49.5 V against 70 V max. ✓
• Current: 13.9 A against 23 A max. ✓
• Inverter: Fox ESS single-phase, certified. ✓

Bill of materials: 14 × iOPT 800W and 1 × GT gateway.

That's it. The inverter-side design (string voltage window, MPPT inputs, DC isolation) is the same as without optimisers.

Two strings? Two gateways

Now take 22 × 430 W panels split across two strings of 11 on a Solis inverter. Each string needs its own GT, so the order is 22 × iOPT 800W and 2 × GT. Each string has 11 optimisers, well under the 30 limit.

Then a quick test: 18 panels on one string is 18 × iOPT 800W and 1 × GT. Not nine optimisers, and not one GT per panel.

When to call us first

Send us the design before you quote if any of these apply:

• a very long string, close to the 30-optimiser limit
• mixed panel models on the same string
• an inverter brand or model you haven't used with Archai before
• a panel with Isc close to 23 A

We'll check it and come back quickly. And if you'd like to practise, the free Archai installer course has a design module with an exercise and a short quiz.