Inverters & equipment

Central inverter vs string inverter cost tool

Enter your system size and cost assumptions for each approach. Get total upfront cost, estimated production benefit, and payback period for string inverters over a central inverter.

Your numbers

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 System size
Total array size for the commercial-scale system being compared.
Expected annual AC output for the system as designed.
3 Central inverter option
Central inverters typically run lower per watt than string inverters.
One large unit typically means simpler, faster install labor.
4 String inverter option
Combined string inverter cost typically runs higher per watt than central.
Used to estimate how many units the system requires.
More units generally means more mounting and wiring labor.
Estimated annual production string inverters recover from shading or mismatch a central inverter would lose. 0% for uniform, unshaded arrays.
5 Analysis
Rate used to value the recovered production.
Time period for the net benefit calculation.

How it works

Three steps to your comparison

Step 1

Get quotes for both approaches

Ask your installer or supplier for per-watt equipment pricing and installed labor estimates for both a central inverter and an equivalent string inverter setup, so you're comparing real numbers rather than rules of thumb.

Step 2

Estimate the shading and mismatch on your site

A uniform, unshaded ground-mount array might see close to 0% recovery benefit from string-level MPPT, while a rooftop with multiple orientations or partial tree shading could see several percent. The inverter efficiency curve comparison tool can help separately quantify efficiency-driven differences between specific models.

Step 3

Weigh payback against non-financial factors

A short payback period makes string inverters an easy call, but even with a longer payback, factor in redundancy against equipment failure and confirm warranty terms with the inverter warranty value calculator before deciding.

Understanding central vs string inverter costs

Why the upfront cost usually favors central inverters

A single large central inverter benefits from economies of scale in manufacturing and typically has a lower dollar-per-watt equipment cost than an equivalent capacity split across several smaller string inverters. Installation labor often follows the same pattern, since mounting and wiring one large unit is generally simpler than repeating that work across multiple string inverter locations. On paper, central inverters usually look cheaper before you factor in production differences, though if you're financing either option, the loan payment calculator can translate that upfront gap into a monthly-payment difference worth weighing too.

Why string inverters can still come out ahead

The upfront cost gap doesn't tell the whole story. A central inverter has a single maximum power point tracker (MPPT) for the entire array, so if part of the array underperforms, whether from partial shading, a different roof orientation, or module mismatch, the whole array's output gets pulled down to match the weakest section. String inverters, with independent MPPT per unit, let each section perform closer to its own potential. On arrays with any real-world non-uniformity, that recovered production can be worth more over time than the extra upfront cost, which is what the payback period in this tool estimates. NREL's PVWatts calculator offers a closer, more technical look at how mismatch and MPPT tracking actually affect production.

Why site conditions decide which option wins

There's no universal right answer between the two approaches; it depends heavily on the specific site. A large, open, single-orientation ground-mount array with no shading has little mismatch loss for string-level MPPT to recover, which tends to favor the lower-cost central inverter. A rooftop system with multiple sections facing different directions, or any meaningful shading from trees, chimneys, or adjacent structures, tends to favor string inverters, since there's real mismatch loss on the table to recover. The Department of Energy's inverter and grid-services guide covers this tradeoff from a broader systems perspective.

Why redundancy is worth considering separately

Beyond the cost and production math in this tool, a central inverter represents a single point of failure. If it goes down, the array's entire output stops until it's repaired or replaced, which can mean weeks of lost production for a large system. A string inverter failure typically only takes out the strings connected to that one unit, so the rest of the array keeps producing. This calculator focuses on cost and energy value, but that reliability difference is worth pricing out with the inverter failure repair cost estimator, and alongside the inverter count for large array calculator when planning a commercial-scale system.

What this tool doesn't cover

This calculator uses simplified per-watt and per-unit cost assumptions rather than a detailed bill of materials, and the mismatch recovery percentage is an estimate you supply based on your site's shading and orientation profile, not a guaranteed figure. It also doesn't factor in ongoing maintenance costs, monitoring capability differences, warranty length (covered by the inverter warranty value calculator), or the inverter-specific efficiency comparison covered by the inverter efficiency curve comparison tool. Use this as a starting point for the cost conversation with your installer, not a final decision on its own.

Questions

Frequently asked

String inverters typically run 40-60% more per watt than a central inverter for the same total capacity. A central inverter is a single large unit converting DC to AC for the entire array; string inverters are multiple smaller units, each with independent MPPT that can capture more energy from arrays with shading or roof segmentation.

String inverters have a higher combined dollar-per-watt cost and more installation labor since there are more units to mount and wire, but on arrays with any partial shading, multiple roof orientations, or module mismatch, the independent MPPT on each string can recover production a central inverter's single MPPT would lose. Whether that recovered energy outweighs the extra upfront cost depends on the specific site.

Central inverters tend to make the most sense on large, uniform arrays with a single orientation and no significant shading, like open-field ground-mount systems, where there's little mismatch loss for string-level MPPT to recover in the first place. In that scenario, the lower upfront cost of a central inverter rarely gets offset by a meaningful production gain from switching to string inverters.

This calculator focuses on upfront cost and production value, not failure risk directly, but it's worth factoring in separately. A central inverter failure can take the entire array offline until repaired, while a single string inverter failure typically only affects the strings connected to that unit, leaving the rest of the array producing.

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