A central inverter converts DC electricity from many solar strings into AC electricity through one large unit, often rated in megawatts. String inverters divide the same job across many smaller units.
The main operational difference is what happens when one inverter fails. A central inverter failure can take an entire section of the plant offline. A string inverter failure affects a much smaller share of total capacity.
Central inverter systems usually have a lower upfront cost, while string inverter systems spread operational risk across more units. But over the life of a solar plant, the inverter type is only part of the equation. How quickly faults are detected, diagnosed and repaired has a major effect on actual downtime.
This matters because inverter shutdowns are a significant source of avoidable solar losses. The 2026 Solar Risk Assessment found that inverter shutdowns accounted for 28% of recoverable performance risk across 6.5 GW of solar assets.
This guide compares central and string inverter designs from an O&M perspective. It explains how each design affects downtime, what happens when an inverter fails, how replacement planning differs, and how operators can reduce inverter-related losses with either system.
What is a central inverter?
A central inverter is a large inverter that converts electricity for a significant section of a solar plant.
Solar modules generate direct current (DC) electricity. Modules are connected into strings, and multiple strings feed their electricity through combiner boxes toward the central inverter.
The inverter then converts that DC electricity into alternating current (AC), which can be supplied to the grid.
At utility scale, a single central inverter can handle hundreds of kilowatts to several megawatts. This means one unit may serve an entire block of the plant.
A string inverter performs the same conversion but distributes the work across many smaller units.
Instead of sending electricity from a large number of strings to one central machine, groups of strings connect to separate inverters installed throughout the array. A large utility-scale plant may therefore use hundreds of string inverters rather than a relatively small number of central units.
The difference is not simply the size of the equipment. It changes how failures affect the plant.
If one central inverter fails, a large block can stop producing.
If one string inverter fails, only the strings connected to that unit stop producing. The rest of the plant can continue operating.
Central designs still lead the US utility-scale market, according to PV Tech Research. Globally, however, string inverters represented more than 70% of inverter manufacturing capacity in 2024.
String technology is also gaining ground in US projects of roughly 10 to 50 MW.
How do central and string inverters compare?
The basic trade-off is between equipment concentration and failure impact.
Central systems use fewer, larger units. String systems distribute the same conversion capacity across many smaller units.
That difference affects not only upfront cost, but also maintenance, spare-parts planning, monitoring and the amount of production lost when something fails.
| Factor | Central inverter | String inverter |
| Unit size | Hundreds of kW to several MW per unit | Typically up to about 350 kW per unit |
| Upfront cost | Usually lower per watt | Usually higher per watt |
| Impact of one failure | A whole block can go offline | Only a smaller share of the plant stops |
| Repair | May require specialist technicians and heavy equipment | A spare unit can often be swapped by site staff |
| Spares | Fewer but larger and more expensive parts | Whole spare units can be practical to keep on site |
| Monitoring detail | Faults appear at block level unless strings are monitored separately | Each inverter reports on its own group of strings |
Neither design is better in every category.
Central systems reduce the total number of inverters that need to be installed and managed. But they also concentrate more production behind each machine.
String systems spread that production across more equipment. One failure has less impact, but operators have many more individual units and alarms to manage.
For O&M teams, this means the important question is not simply which inverter fails less often?
It is how much production is lost when something fails, and how quickly can that production be restored?
Why do inverters matter so much to solar O&M?
Inverters sit at a critical point in the plant's electrical system.
The modules may still be producing DC electricity, but if the inverter serving them is offline, that electricity cannot be converted into AC power and exported normally.
That makes inverter availability directly connected to plant revenue.
The 2026 Solar Risk Assessment from kWh Analytics found that inverter shutdowns accounted for 28% of recoverable solar performance risk across 6.5 GW of global assets.
In other words, inverter outages represent a significant share of the production losses that operators may be able to prevent or recover.
Inverters also matter from a safety perspective.
According to pv magazine USA, the same assessment found that inverters were associated with 44% of all PV fires.
It also reported that 73% of inverter-driven brushfires involved equipment from a single manufacturer.
This makes inverter selection and condition monitoring relevant to more than energy yield. They are also part of the plant's safety and risk-management strategy.
What does an inverter failure cost under each design?
The main difference is the amount of capacity affected by each failure.
When a central inverter fails, a large section of the plant can stop producing at once.
When a string inverter fails, the immediate production loss is smaller because only the strings connected to that unit are affected.
That does not automatically mean string inverter systems lose less energy over their entire operating life. A string-based plant contains many more inverter units, which means there are also more individual components that can fail.
The more useful comparison is therefore not simply how many inverter failures occur.
It is how much energy the plant loses because of those failures over time.
NREL, now the National Laboratory of the Rockies, examined this question in a 2024 study of availability across the US PV fleet.
The study covered 8.5 GW of capacity across more than 2,200 PV systems.
It found that systems using inverters below 250 kW had median energy availability of approximately 99% to 100%.
Systems using larger inverters between 250 kW and 4 MW had somewhat lower median availability, at approximately 97% to 99%.
A difference of one or two percentage points may look small. But availability is measured in terms of energy, so each percentage point represents roughly 1% of expected annual production.
For a utility-scale plant, that difference can become significant.
The size of the outage is only part of the reason. Repair time also matters.
According to PV Tech, site staff can often replace a failed string inverter with a spare within hours.
A central inverter can be more complicated to repair. Depending on the failure, the work may require specialist engineers, replacement components and heavy equipment.
While the repair is being arranged, the entire block served by that inverter may remain offline.
This does not mean central inverter systems necessarily have poor availability. It means their O&M strategy has to account for the larger consequences of each outage.
Critical spare parts, manufacturer service agreements and response times become especially important.
Which design fits which site?
The right choice depends partly on the inverter technology, but it also depends on how the plant will be operated when something fails.
Consider a plant located close to a service hub.
If the site has a manufacturer service agreement, specialist technicians nearby and the required spare parts available, a central inverter failure may be resolved quickly. In that case, the larger outage associated with the failure may be manageable.
A remote plant creates a different situation.
If a specialist technician has to travel a full day before work can even begin, every hour of that delay means an entire central inverter block may remain offline.
At a site like this, string inverters may offer an operational advantage because local staff can potentially replace individual units without waiting for specialist support.
Monitoring also changes the equation.
A central inverter system without string-level monitoring can hide smaller problems. Individual strings or inputs may underperform without being immediately obvious at the inverter level.
A string inverter system creates the opposite challenge. Because there are many more inverter units, operators can receive a much larger number of individual alerts.
If those alarms are not filtered and prioritized properly, a real failure can disappear inside a long list of lower-priority notifications.
So both designs require good monitoring, but for different reasons.
Central systems need enough detail to reveal problems below the block level. String systems need enough intelligence to identify which alarms actually matter.
When do solar inverters need replacing?
Solar inverters should be expected to need repair or replacement during the operating life of a utility-scale plant.
The plant itself may operate for around 30 years or longer, while inverter components may need intervention before the rest of the plant reaches the end of its life.
NREL's 2024 life cycle assessment of utility-scale PV assumes a 30-year plant life.
Within that period, the assessment assumes that 10% of the inverter and transformer, by weight, is replaced every 10 years.
The same NREL report also cites another study that assumed a full inverter replacement after 17 years.
These figures should not be treated as a fixed replacement schedule for every solar plant. Actual replacement timing depends on the inverter model, site conditions, operating history and equipment condition.
The important point for asset owners is that inverter replacement should be planned before equipment reaches the point of failure.
That means tracking the failure history of each unit, maintaining accurate spare-parts records and reviewing equipment condition as warranties approach their end.
Operators can then decide whether equipment should be repaired, refurbished or replaced.
The planning process also differs between central and string systems.
Replacing a central inverter can be a significant project. Large equipment may have long lead times, and replacement can require specialist labor and lifting equipment. Budgeting and procurement may therefore need to begin well before the existing unit reaches the end of its expected service period.
String inverter replacement is more distributed.
Instead of replacing one large machine at once, operators can often replace individual units as they fail or reach the point where replacement makes more economic sense than continued repair.
How to reduce inverter downtime with either design
Regardless of inverter type, downtime falls when operators can detect faults early, understand their impact and restore production quickly.
Six practices are especially important.
- Monitor at the right level.
Each inverter should be monitored individually. For central inverter systems, operators should also monitor strings or combiner inputs where possible. This makes it easier to identify underperforming inputs before the problem develops into a larger outage. - Separate real faults from alarm noise.
Not every alert deserves the same response. Alarms should be categorized by severity and operational impact so teams can identify which problem needs attention first. - Set response targets according to outage size.
A central inverter failure removes much more production than a single string inverter failure. Response targets should reflect that difference. The more output being lost every hour, the faster the required response should be. - Keep the right spare parts available.
String inverter plants can often keep complete spare units on site. Central inverter plants may need critical components such as fans, boards and contactors available so repairs are not delayed by procurement. - Inspect equipment for overheating.
Thermal inspections of inverters, combiner boxes and electrical connections can identify abnormal heat before it develops into a shutdown or fire. - Document every repair.
Operators should record the original fault, the component that failed, what was replaced and how long it took to restore production. Over time, these records reveal repeat failures and provide evidence for warranty claims and replacement decisions.
These practices move inverter maintenance away from waiting for equipment to fail and toward condition-based operations.
We explain that broader shift in our guide to reactive vs. predictive maintenance.
It also depends on having enough operational visibility to locate underperformance quickly. Our guide to solar performance monitoring covers that monitoring layer in more detail.
How Areg AI handles inverter faults
Reducing inverter downtime requires more than detecting an alarm.
The complete process is:
detect the problem → identify the affected equipment → determine its priority → dispatch the work → complete the repair → record what happened.
Areg AI connects these stages in one operating system.
Solar SCADA connects inverters with other plant equipment, including strings, trackers, meters and substation equipment.
Its AI-powered alert classification helps surface actionable anomalies while reducing alarm noise. Each alarm is categorized by severity and mapped to the relevant device on the plant's digital twin.
Once a problem is identified, the system can automatically create a task and assign it to a field crew or robot.
Physical inspection adds another layer of information.
SOBOT, Areg AI's ground inspection robot, includes inverters and combiner boxes in its thermal and visual inspections. These inspections can identify abnormal heat and visible equipment problems before they develop into larger failures.
Operations Management handles the follow-through by supporting automated work-order generation and predictive maintenance insights.
Solar SCADA's warranty and claim management also keeps a record of spare-parts history.
This connects each repair to the equipment's longer operating history. Instead of treating every inverter fault as an isolated event, operators can see which units fail repeatedly, which components have already been replaced and what information may be needed for a future warranty claim or replacement decision.
To see how Areg AI connects inverter alarms, equipment inspections and repair workflows on one platform, explore Solar SCADA or book a demo.
For a deeper look at the monitoring infrastructure behind this process, read our guide to solar SCADA systems.
FAQ
What is a central inverter in a solar plant?
A central inverter is a large unit that converts DC electricity from many solar strings into AC electricity for the grid.
At utility scale, one central inverter can serve an entire block of the plant and may be rated from hundreds of kilowatts to several megawatts.
Is a string inverter or a central inverter better for utility-scale solar?
Neither design is better in every situation.
Central inverters generally offer a lower upfront cost and still lead the US utility-scale market. String inverters spread conversion capacity across more units, so a single failure affects less plant output and an individual unit can often be replaced more easily.
The operational trade-off depends on factors such as site location, service access, spare-parts strategy and monitoring.
Do central inverters cause more downtime?
A central inverter failure generally causes a larger outage because one unit serves more plant capacity.
NREL's 2024 fleet study found median availability of 97% to 99% for systems using inverters between 250 kW and 4 MW. Systems using inverters below 250 kW had median availability of approximately 99% to 100%.
This does not mean every central inverter plant will have lower availability. Repair speed, spare parts, monitoring and service access also affect how much production is ultimately lost.
How often do solar inverters need to be replaced?
There is no single replacement interval that applies to every inverter.
NREL's 2024 life cycle assessment assumes that 10% of inverter and transformer equipment, by weight, is replaced every 10 years during a 30-year plant life. The report also cites another study that assumed full inverter replacement after 17 years.
Actual replacement timing depends on the equipment, site conditions and failure history, so owners should plan for inverter repair and replacement as part of the plant's long-term O&M budget.