String Inverter Brands Comparison: How to Compare Inverter Offers for a C&I Plant Without a Brand Ranking

To compare string inverter offers for a commercial or industrial plant, line every bidder up on the same ten points rather than on brand: AC rating and DC/AC ratio, MPPT inputs, temperature derating, grid-protection settings, test certificates, warranty terms, service response, monitoring access and the replacement price when the warranty ends. The brand follows from those answers. It cannot replace them.

What should you compare first?

A brand ranking looks helpful and fails in practice. The same unit performs differently on a hot metal shed in a dust belt and on an RCC roof in a cooler town, and the best unit on paper is useless if the nearest trained engineer is two days away. So we do not rank brands here. We give you the table to fill in, one column per bidder.

Which datasheet numbers are easy to misread?

Three numbers mislead buyers more than any others. The first is peak efficiency. A figure quoted at the best operating point tells you little about a morning, afternoon or cloudy hour; ask for weighted efficiency. The second is the DC/AC ratio: it is a design choice, not a quality mark, and the useful question is how much energy is clipped on your array over a year. The third is the temperature at which full output is held. Two inverters with the same nameplate can deliver different energy on the same hot afternoon, and the difference shows up in the generation report.

Also check the rating basis. Some offers state kW AC, some kVA, and some give the DC capacity of the array and leave the AC rating implicit. Convert everything to AC kW before you compare prices per kW.

What does the grid operator require of any inverter?

Requirements come from the state regulator and the DISCOM, so they vary, but they follow the Central Electricity Authority's technical standards for distributed generation. As one worked example, the Joint Electricity Regulatory Commission's rules for Goa and the Union Territories set out these inverter conditions in an annexure:

• Efficiency and measurement to IEC or IS 61683, and environmental testing to IEC 60068-2 or the equivalent BIS standard.
• Continuous supervision of grid conditions, with disconnection on grid failure, under-voltage or over-voltage.
• An operating voltage window of 80% to 110% of nominal, with the plant isolating itself from the grid after a two-second clearing time beyond it.
• Harmonics to IEEE 519, with individual harmonics under 3% and total distortion under 5%.
• A grid frequency synchronisation device, with synchronisation causing no voltage fluctuation greater than 5% at the connection point.
• Protection against islanding, and a separate backup wiring arrangement with isolation switches where a battery is connected.

Other states set their own details, and those numbers should be read from the regulation that applies to your site. The point for buyers is that every bidder should be able to show, on paper, how their unit meets the same list. If one cannot, that is information.

String or central: what changes in the offer?

String inverters suit roofs with several orientations, mixed shading or many small sections, because each input tracks its own strings and a single failure takes out only a fraction of the plant. Central inverters can make sense on a large, uniform array where one machine serves a block, but they bring longer DC runs, a dedicated enclosure and a larger single point of failure. Our page on string and central solar inverters sets out how we select between them for a given array. The size pages show how this plays out at different scales: our 100 kW page describes two to four string units, while the 1 MW page discusses where architectures change.

When you compare offers across the two types, compare installed cost including cabling, enclosures and civil work, and compare the loss from one failure. Ask each bidder: if one unit trips for a week, what share of generation do I lose, and how fast will you replace it?

How should you read the commercial terms?

Put the commercial terms side by side the way you put the technical ones. Warranty length is only the headline. What matters is the remedy (replacement or repair), who pays freight and site labour, how quickly a replacement arrives, whether warranty continues if the plant is monitored by a third-party platform, and how much the extension costs. Ask for a named service contact and a written response time. If the offer says "equivalent make" in the bill of quantities, insist on the datasheet and your approval before any substitution, because that single phrase can undo a careful comparison.

How Secured Engineers helps

We design the plant in-house, select inverters to the array and the DISCOM's connection standard, and commission them with the protection settings recorded for the inspection. Approvals including DISCOM net-metering are prepared in-house, and MEPF and solar can sit under one contract. We work from offices in Noida (Delhi NCR) and Ludhiana, across 535+ projects in 18+ states, with 89.77% repeat clients. We have no brand to push in this article and will review any set of offers on the same table.

If you already have two or three inverter offers, send them to us and we will put them on one comparison sheet and tell you what each is silent about. Start from the solar EPC service page, then reach us on WhatsApp, call +91 70099 85817, or ask for a free proposal.