String, Micro or Optimizer: Choosing an Inverter

What does an inverter do?

Panels make direct current. Your house and the grid use alternating current. The inverter converts one to the other, matches the grid's frequency and voltage, and shuts down if the grid fails. It is also the part with the most electronics, and it is usually the first component to need replacing, so its type affects long-term cost as well as day-one performance.

How does a string inverter work?

Panels are wired in series into strings, and one central inverter handles each string or several. The design is simple, proven and generally the lowest cost per watt. The drawback is that a string behaves like a chain of water hoses: if one panel is shaded or damaged, current through the whole string drops. On a clean, south-facing roof with no shade this barely matters. On a roof with a chimney, a dormer or trees, it can cost a meaningful share of annual output.

Strings need panels with the same orientation and tilt, or separate strings for each plane. If the system has panels on both east and west roofs, a string inverter with two inputs can handle it.

What are microinverters and optimizers?

A microinverter is a small inverter mounted under each panel. Every panel operates independently, so shade on one affects only that one, and panels on different roof faces can mix. There is no high-voltage direct current running across the roof, which some installers prefer for safety. The costs are a higher price per watt, more units on the roof, and a larger number of parts that could fail, though each failure is small.

A power optimizer is a device on each panel that adjusts its voltage so shade or mismatch does not drag the string, while a central inverter does the final conversion. It is a middle path on cost and gives panel-level data.

Cost is where the gap shows. Roughly speaking, a string setup is the baseline, optimizers add a moderate premium, and microinverters add somewhat more, though the differences shift with market conditions and system size. Ask each bidder to price the same panel set with each option, so you see the gap on your own roof and not on a brochure. The cheapest bid with the wrong inverter for your shade may cost more in lost energy than it saves.

Which suits which roof?

• Simple, unshaded, single-plane roof: a string inverter is usually the economical choice.
• Partial shade, multiple roof faces or panels of different ages: microinverters or optimizers are more forgiving.
• Plans to add panels later: microinverters make expansion easier, while a string inverter must be sized with headroom.
• Battery backup in mind: check which inverter models support it before deciding, as covered in solar in a power outage.

Snow is a factor in Canada. Panels with a partial snow cover on the lower edge behave much like shaded ones, and the way each type responds differs. Read about the winter picture in solar panels in winter.

What about monitoring, warranty and lifespan?

Microinverters and optimizers report production per panel, which makes a failed or shaded panel easy to spot. String systems report at the inverter and may show less detail. Learn how to use this data in solar system monitoring.

Inverter warranties are commonly shorter than panel warranties. String inverters often carry a shorter warranty and may be replaced once during a panel's life, while microinverters are often sold with longer terms. Always confirm the length in writing and what the warranty covers for labour; the warranty guide explains the clauses.

The heat-focused system at Drake Landing, shown in solar collection, used thermal collectors with no inverter at all, which is one reason hot-water and space-heating collectors are simple devices by comparison.

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