Inverter Sizing Calculator

How to size a solar inverter

The inverter converts your panels' DC electricity into the AC your home and the grid use, and it's one of the most important sizing decisions in a system. Size it too small and it "clips" the array's peak output, throwing away energy on the sunniest days; size it too large and you've overspent and the inverter runs inefficiently at low loads. The goal is a sensible match between your array's DC capacity and the inverter's AC rating — a ratio that deliberately leans slightly toward an oversized array.

The DC-to-AC ratio (inverter loading ratio)

It's standard practice to install more DC panel capacity than the inverter's AC rating — a 1.1 to 1.3 DC-to-AC ratio is common, sometimes higher. This sounds wasteful but isn't: panels rarely hit their rated output (only in perfect, cool, bright conditions), so a 5 kW inverter paired with around 6 kW of panels spends far more hours running near its efficient sweet spot, and the small amount of "clipping" lost on a handful of perfect midday peaks is more than repaid by stronger output across all the ordinary hours. The right ratio depends on your climate: cloudier, cooler places can push the ratio higher; very sunny, cool, high-output sites keep it lower to limit clipping.

String, micro, or hybrid?

• String inverters handle a whole array (or strings) centrally — cost-effective and simple for unshaded roofs.
• Microinverters sit under each panel, so shading or a weak panel doesn't drag down the rest, and they suit complex or multi-orientation roofs.
• Hybrid inverters add battery management, letting you store solar and provide backup — increasingly the default where storage is planned.

Whatever the type, the AC rating must comfortably cover your needs and respect the array's voltage and current limits (see our string sizing calculator for the voltage side).

Don't forget loads, for off-grid and hybrid

For grid-tied systems, the inverter is sized to the array. For off-grid and battery systems, it must also handle your largest simultaneous AC load, including the surge that motors, pumps, fridges and air-conditioners draw at start-up — often several times their running wattage for a moment. An inverter that's fine for steady loads can trip on a compressor's inrush, so size for the surge, not just the running total.

Inverter sizing mistakes to avoid

• Matching inverter exactly to array. A 1:1 ratio wastes the efficiency gains of slight DC oversizing.
• Massive oversizing. An inverter loafing at a fraction of its rating is inefficient and pricier than needed.
• Ignoring surge for off-grid. Startup inrush can exceed the inverter's limit and cause trips.
• Overlooking voltage limits. The array's string voltage must stay within the inverter's MPPT window.

Efficiency, standby draw and lifespan

An inverter's rating is only part of the story; how it behaves across real operating conditions matters just as much. Inverters are most efficient in the middle of their load range and least efficient at very low loads, which is part of why a wildly oversized inverter is a poor choice — it spends much of its day loafing inefficiently and drawing standby power even when little is being produced or used. Conversion efficiency for good modern units sits around 95–98%, but that figure sags at the extremes. Inverters also have a shorter lifespan than panels: where panels are warrantied for around 25 years, inverters typically last 10–15, so most systems need at least one inverter replacement over their life. That replacement is a real cost worth factoring into any payback or lifetime-savings estimate, and it's a reason not to over-specify an inverter you'll have to replace anyway before the panels retire. Sizing sensibly — neither clipping heavily nor loafing — gives the best efficiency and the best value over the system's life.

Frequently asked questions

As a starting point, an inverter rated around 75–90% of your array's DC watts (a DC-to-AC ratio of about 1.1–1.3) suits most grid-tied systems. So a 6 kW array often pairs with a 5 kW inverter. Enter your array size above for a tailored figure.

No — it's normal and usually beneficial. Because panels seldom reach rated output, a modestly oversized array keeps the inverter working efficiently for more of the day. Only a little energy is clipped at peak, and that's outweighed by the gains the rest of the time.

Clipping is when the array briefly produces more DC power than the inverter can convert, so the excess is lost. A small amount of clipping at midday peaks is acceptable and expected with a sensible DC-to-AC ratio; heavy clipping means the inverter is undersized.

For off-grid or hybrid systems the inverter must handle your peak simultaneous load and the surge from motors and compressors, which can dictate a larger rating than the array alone would suggest. A hybrid inverter also manages battery charging and backup.

Typically 10–15 years for a quality unit, against around 25 years for the panels. That means most systems need at least one inverter replacement during their life, which is a real cost to include in payback estimates. Microinverters often carry longer warranties but are replaced individually if one fails.

Modern inverters run at about 95–98% efficiency in their sweet spot, so the difference between good units is small — usually a percent or two of annual yield. Correct sizing (avoiding heavy clipping or chronic low-load operation) affects real-world output more than chasing the last fraction of rated efficiency.