Commercial Solar Inverters: String, Central, Optimisers or Microinverters?

Updated 20 October 2026 · SEO Dons Editorial

What does the inverter do in a commercial PV system?

The inverter converts the DC output of the modules into AC power the building can use, tracks the operating point that gets the most energy from each group of modules, and is usually the main source of monitoring data. RC62, the joint fire safety code for PV used by insurers, calls the inverter the core of a PV system, converting DC to AC and generally providing monitoring data on DC and AC performance.

It is also the hardest-working component on site. RC62 states that at peak operation the conversion is around 97% efficient, with the losses turned into heat, and identifies the IGBT (insulated-gate bipolar transistor) board as the most likely critical point of failure. It also expects that the inverter will need replacement during the life of a PV system, so inverter choice is as much about service, spares and replacement as about headline efficiency.

RC62 lists four ways to arrange the DC-to-AC conversion: module-based microinverters, DC string inverters, power optimisers working with inverters, and larger centralised inverters. How the choice fits into a full specification is covered in our commercial PV systems guide.

When do string inverters make sense?

A string inverter takes several series-connected strings of modules, tracks them through its maximum power point inputs, and converts them to three-phase AC near the array or in a plant room. A commercial roof is normally split across several string inverters, so a single fault takes out only part of the generation while the other units keep running.

String designs suit roofs with a few consistent orientations and little shading. Their weak points are on the DC side. The BRE study of PV fires carried out for the government found that DC isolators presented the greatest fire risk in its incident database, with approximately 30% of recorded incidents caused by malfunctions in that component. RC62 now advises eliminating separate DC isolators wherever possible, noting that many inverters have integrated isolators.

When is a central inverter the better choice?

Central inverters concentrate conversion in one or a few large units, fed by combiner boxes that gather many strings. RC62 describes combiner boxes that merge the inputs of up to 40 strings (400 A) into one DC cable pair, and warns that they are more susceptible to fire risk than other components because of their many screw terminations and high DC currents.

The design case for a central inverter is a very large, uniform array, often one connected at high voltage. RC62 notes that larger PV systems are often connected to the grid at HV or EHV, needing additional transformers, isolation and switchgear, and that transformers operate at maximum duty in peak sunshine. The trade-offs are concentrated risk (one fault can stop a large share of output), longer DC cable runs, and the need for a spares and service plan for a single large unit. On a commercial rooftop, where the building limits the array size, several string inverters usually give more flexibility.

What do optimisers and microinverters add?

Module-level power electronics (MLPE) move part of the conversion onto the roof. RC62 defines them as devices for DC-DC or DC-AC conversion at the module level, which can limit DC voltages close to the modules in the event of a fault. Optimisers condition each module's output before it reaches a string inverter; microinverters convert each module's output to AC directly.

Three situations favour MLPE on a commercial roof:

Shading and mixed orientations: rooflights, parapets, plant and split roof planes mismatch the modules in a string; module-level tracking confines the loss to the affected modules.
Fire-safety voltage limits: RC62 explains that low voltage means not exceeding 1500 V DC between conductors, or 900 V DC between conductors and earth. If a design cannot be classified as low voltage, additional fire protection must be built in, and module-level electronics that switch to extra-low voltage when the AC supply is disconnected are one of the measures RC62 names.
Module-level visibility: a fault on one module shows up in the monitoring instead of disappearing into a string average.

The price is more electronics and more connections on the roof. RC62 notes that each MLPE manufacturer has particular procedures, requirements and methodologies for testing, so commissioning and maintenance must follow the maker's method, and whoever maintains the system needs to know the product.

How should the DC:AC ratio be set, and what is clipping?

The DC:AC ratio compares the array's rated DC power with the inverter's rated AC output. A ratio above 1 is normal practice: as a study presented through Sandia National Laboratories' PV Performance Modeling Collaborative puts it, nominal inverter capacities are commonly less than the sum of the PV panels in order to reduce the cost of the installation. When the array briefly produces more than the inverter can convert, that excess is lost, or clipped.

How much energy is clipped depends on the site's climate, the roof orientation and the ratio chosen, so the right figure is site-specific. Three checks keep it honest:

Stay inside the maker's limits. The inverter datasheet sets the maximum DC input voltage, current and array power it accepts, and the design must sit inside them.
Ask for the clipping loss. A yield report should state the modelled annual energy lost to inverter clipping, not just the ratio.
Check the model's time step. The same Sandia-hosted study explains that the inverter clips power instantaneously, so calculations that clip hour-averaged DC power overestimate AC output, an error it expects to grow with higher DC:AC ratios and more variable sunshine. Under broken UK cloud, ask whether the model uses sub-hourly data or applies a correction.

How the array itself is sized against demand is covered in sizing a commercial solar PV system.

How efficient are inverters, and how long do they last?

With peak conversion around 97% according to RC62, differences between quality inverters matter less than how well each unit is installed and cooled. RC62 notes that typically around 3% of throughput is lost as heat, that inverters can produce significant heat in normal operation, and that obstructions and stored materials must not reduce their ventilation.

Life expectancy is the bigger financial question. RC62 expects a PV system to have a design life of 30 to 35 years, and says the design should minimise the risk of product failure over that design life, not the warranty period alone. Because it also expects inverters to need replacement during a system's life, a sound financial model includes at least one inverter replacement, and a proposal should state the inverter warranty term and what extending it would involve. Our guide to payback, ROI and IRR shows where that cost sits in the numbers.

What about grid compliance and monitoring?

Generation equipment connected in parallel with the network, including energy storage, has to meet ENA Engineering Recommendation G98 or G99 as applicable, and type-tested equipment makes that simpler. The Energy Networks Association hosts a verification report register where manufacturers of type-tested generating units upload documentation showing they meet the requirements, and the resulting reference number can be quoted on application forms. The connection application itself is a matter for the network operator's own process.

Day to day, the inverter's monitoring is where its quality shows. RC62 notes that many PV systems have monitoring that reports everything from kWh generation to AC and DC string or module parameters, insulation resistance and event records, and that good telemetry gives insight into performance changes that may signal a problem. When comparing inverters, check whether the platform reports at string or module level, how alarms reach the site, and whether data can be exported to an independent system. The commercial PV systems page explains what a full specification should list, and you can request quotes through the site's enquiry form.

Sources

RC62: Recommendations for fire safety with PV panel installations, version 2 (2023), RISCAuthority and MCS, published by the Fire Protection Association, checked 20 October 2026
Fire and Solar PV Systems: Investigations and Evidence, issue 2.9, BRE National Solar Centre for BEIS, via GOV.UK, checked 20 October 2026
The Effect of Short-Term Inverter Saturation on PV Performance Modeling, Allen, Hobbs and Bolen, hosted by Sandia National Laboratories' PV Performance Modeling Collaborative, checked 20 October 2026
EREC G98 and G99 frequently asked questions, Electricity North West, checked 20 October 2026
Export Limitation, National Grid Electricity Distribution, checked 20 October 2026

Common questions

Should a commercial roof use one large inverter or several smaller ones?

It depends on scale and layout. Several string inverters spread the risk, so one failure stops only part of the output, while a central inverter can suit a very large, uniform array, particularly one connected at high voltage, provided spares and service are planned.

Do optimisers make a commercial PV system safer?

They can help. RC62 describes module-level electronics as able to limit DC voltages close to the modules in the event of a fault, and lists them as one way to meet low-voltage requirements. They add components to the roof, so correct installation and maker-specific testing still matter.

Where should commercial inverters be installed?

Somewhere ventilated, accessible and protected. RC62 says the location of inverters and other electrical equipment needs careful consideration, that stored materials must not block their ventilation, and that automatic fire detection should cover indoor areas where they are installed.

Does inverter choice affect an export-limited grid connection?

Yes. Where a site has an export limit, the limitation scheme works by restricting generation or storage output, or increasing on-site demand, so the inverters must accept that control signal and respond reliably.