How to choose a solar inverter

Inverters differ by what they are wired to. An on-grid, or grid-tied, inverter converts solar power for use and export but does not run when the grid is down. An off-grid inverter runs from panels and batteries with no grid connection. A hybrid inverter does both: it works with the grid and manages a battery, which is why it is the usual choice where supply is interrupted.

The type decides everything downstream: whether you need a battery at all, whether export metering is relevant, and what happens during an outage. Settle it before comparing models.

An inverter's rated power is the continuous output it can supply. Sizing starts from the loads you intend to run at the same time, including the surge that motors draw when they start: pumps, compressors and air conditioners pull several times their running current for a moment, and an inverter that cannot supply that surge will trip even though its rated figure looks sufficient.

Panel capacity is a separate limit. Each inverter states a maximum PV input power and a maximum PV input voltage, and a string that exceeds either, particularly on a cold, bright morning, when panel voltage is highest, is outside the design envelope regardless of how well the annual numbers work out.

The IP code describes what the enclosure keeps out: the first digit solids, the second water. IP21 is protection against fingers and dripping water, which suits a sheltered indoor position. IP65 is dust-tight and protected against water jets, which is what allows an outdoor wall or rooftop mounting without building an enclosure for it.

The rating belongs to a specific model, not to a brand or a series name, and the installation still has to respect the manufacturer's clearance, shading and ventilation requirements. Heat shortens the life of power electronics whatever the enclosure is rated at.

A hybrid inverter works with batteries inside its battery-voltage window that also communicate over a protocol it supports. Chemistry matters for lifetime and depth of discharge: lithium iron phosphate, usually written LiFePO₄, and lead-acid tubular cells behave differently and are not interchangeable in a design.

Compatibility is a pairing question, model to model. A battery that works with one inverter in a range does not automatically work with another.

A datasheet gives you the figures to compare. An installation manual tells you what the installer is required to do, and reveals requirements that affect cost. A warranty document states the term, what it covers, who honours it and what voids it: a headline number of years means little without those conditions in writing.

Certification is checkable. A certificate carries a standard, an issuing body, a certificate number, the products it covers and its dates, and reputable issuers publish a register you can search by number. A logo on a page is not a certificate.

Support is a location question before it is a promise. Ask for the addresses of the service points that would handle your unit, what the process is when something fails, and who pays for transport of a heavy unit during the warranty period.

Firmware matters over a long ownership: ask whether updates are published, how they are applied, and whether an installer or the owner can apply them.

Grid-connected equipment has to satisfy the rules of the utility it connects to, and net-metering arrangements have their own approval process and equipment requirements. These are set by your utility and regulator, not by the equipment seller, and they change.

Verify the current requirements with your own utility and confirm in writing that the equipment you are buying meets them.