A solar array produces direct current. The grid runs on alternating current. Something has to convert one to the other, and there are two architectures for doing it.
A string inverter takes the whole array, wired in series, and converts it in one box, usually in a loft or a garage. Microinverters put a small converter behind each panel, so what leaves the roof is already alternating current. DC optimisers are a third arrangement: per-module electronics that condition the DC before sending it to a single central inverter, which puts them between the two in both behaviour and price.
What per-module conversion actually fixes
Panels in a series string share a current. The string is therefore limited by its weakest member, and modules are never identical. They differ from the factory within their power tolerance, they age at slightly different rates, and they get shaded at different times of day.
With one central inverter, the array has one maximum power point for the whole string, and that operating point is a compromise across every module in it. With per-module electronics each panel runs at its own optimum, so a weak module underperforms on its own rather than pulling its neighbours toward it.
How much that is worth depends entirely on how uneven the array is.
| Roof | Value of per-module conversion |
|---|---|
| Single plane, one orientation, no shading | Marginal. Mismatch between new modules is small |
| Two or more orientations | Substantial. A single string cannot optimise for both at once |
| Chimney, flue or aerial shading part of the day | Substantial. Contains the loss to the shaded module |
| Tree shading that will worsen over the years | Substantial, and increasing over the system life |
| Array likely to be extended later | Useful. New modules can be added without matching the existing string |
On the first row the case for microinverters rests on warranty and monitoring rather than on yield.
It is worth being precise about the shading claim, because it is regularly overstated. Per-module electronics do not recover the output of shaded cells. Bypass diodes inside the module have already limited that loss to roughly a third of the module. What per-module conversion prevents is the shaded module influencing the operating point of the rest of the string, and the case where a central inverter tracks the wrong peak on a distorted curve. The mechanism is set out in do solar panels work in shade.
The warranty difference, which usually decides it
Panels are warranted for 25 years and routinely run longer. Inverters are electronics with capacitors and switching components, and they are not warranted for anything like that.
String inverter warranties commonly run 10 to 12 years, with paid extensions available. Microinverter warranties commonly run 25 years, matching the modules. That gap is the real decision, because it determines whether a replacement happens inside the life of the system.
Work it out with your own numbers rather than a generic figure. The replacement cost is the inverter plus the labour, and for a string inverter in an accessible loft that is a straightforward visit. For microinverters it is a roof job with scaffolding, which is why the failure rate matters more than the unit price: replacing one microinverter is a small part but an expensive access.
Set the day-one premium against the cost of one string inverter replacement, discounted back to today, and the comparison becomes a number rather than an argument. That arithmetic is also the reason the two architectures can both be correct for different households.
The rest of the trade
| String inverter | Microinverters | |
|---|---|---|
| Day-one cost | Lower | Higher |
| Typical warranty | 10 to 12 years, extensions sold | Commonly 25 years |
| Replacement access | Indoor, one unit | On the roof, per unit |
| Uneven or multi-orientation roof | Compromised by a single operating point | Each module optimised separately |
| Monitoring granularity | Whole string | Per module |
| Single point of failure | Yes. Inverter down means array down | No. One unit down means one panel down |
| DC voltage on the roof | High DC across the array | Only the module voltage; AC beyond that |
| Battery pairing | Often simpler, especially DC-coupled | Usually AC-coupled, which adds a conversion step |
Two rows deserve expansion.
Monitoring granularity sounds like a convenience feature and is worth more than that. Per-module data is how a dirty panel, a failing module or an inverter tracking the wrong peak gets noticed. With string-level monitoring the array reports one number, and a module that has quietly stopped contributing is inside the noise.
Battery pairing matters if storage is planned. A DC-coupled battery on a hybrid string inverter stores solar generation without converting it to AC and back, which avoids a round trip. Microinverter installations generally pair with AC-coupled storage, which is simpler to retrofit and loses a little efficiency to the extra conversion. If a battery is likely, decide the inverter architecture with that in mind rather than afterwards.
Where each one actually wins
A string inverter is the right answer on a simple, unshaded, single-orientation roof where the budget is doing real work, and particularly where a DC-coupled battery is planned. The efficiency advantage of per-module electronics on that roof is small, and the money is better spent on more panels.
Microinverters are the right answer on a complicated roof, on an array that will be extended, where the owner wants per-module visibility, or where avoiding a mid-life roof job is worth paying for. They are also the more forgiving choice when nobody is certain how the array will behave, because the failure modes are contained.
What should not decide it is a quote that presents one architecture as modern and the other as obsolete. Both are current, both are sold by serious manufacturers, and the correct choice is a property of the roof rather than of the technology. If a quote does not explain which features of your roof led to the choice, ask.
Warranty durations are the terms commonly published by manufacturers at the time of writing and vary by product and region. Read the specific warranty document for the units being quoted rather than relying on a typical figure. Checked 2026.