Everyone asks how many panels they're getting. Almost nobody asks about the inverter, yet it sets the ceiling on what your system can deliver, decides whether you can add a battery cheaply later, and is the component most likely to need replacing first. Ten minutes understanding it will make you a sharper buyer.
Panels and inverters are rated differently, on purpose
Your panels are rated in kWp, the peak output under ideal test conditions. Your inverter is rated in kW, the maximum AC power it can actually push into your home or the grid. These two numbers are usually different, and that's deliberate. A typical quote might pair 5.2kWp of panels with a 4kW or 5kW inverter.
Panels almost never hit their rated peak in Britain. Cloud, heat (panels lose efficiency when hot), pitch and orientation all shave the real output. Pairing panels with a slightly smaller inverter, known as oversizing the array, means the inverter spends more of the day in its efficient operating range instead of idling at low load. An array-to-inverter ratio of around 1.2 to 1.3 is normal and sensible.
Clipping: the trade-off in plain numbers
When the panels do briefly produce more DC power than the inverter can convert, the excess is simply not generated. That's called clipping. On a 5.2kWp array with a 4kW inverter you'll see flat-topped generation curves around midday on the best dozen or two days of the year.
It looks alarming on the graph and costs surprisingly little in practice, typically 1 to 3 percent of annual generation for a sensibly oversized system. The savings on the smaller inverter usually outweigh the loss. Where clipping does get expensive is on aggressive ratios above about 1.4, or on east-west roofs where the installer hasn't modelled the two orientations properly. Ask your installer what annual clipping loss their design tool predicts; a good one will know the number.
The 3.68kW question
There's a regulatory wrinkle that shapes inverter choice in the UK: 3.68kW per phase is the most a system can export without advance permission from your local network operator (the G98 limit, explained in our DNO guide). Above that, the installer needs G99 approval before the install, which adds weeks.
This is why so many quotes specify a 3.68kW inverter even under a bigger array. Sometimes that's the right engineering call. Sometimes it's the installer optimising for their schedule rather than your generation. If you're being offered a 6kWp array on a 3.68kW inverter, ask whether a G99 application or an export-limited larger inverter was considered, and what the predicted difference in annual output is. Make them show their working.
String, hybrid or micro: which type you actually need
A string inverter is the standard choice: one box on a wall, all panels wired through it. Cheapest and proven, but the whole string performs like its weakest panel, which matters on shaded roofs. Microinverters put a small inverter behind each panel so every panel performs independently. They cost more and make sense for complicated or partially shaded roofs. Power optimisers are the halfway house, giving per-panel optimisation while keeping one central inverter.
A hybrid inverter manages both panels and a battery in one unit. If there is any chance you'll add a battery within a few years, specifying a hybrid inverter now is one of the cheapest favours you can do your future self, because it avoids buying a second inverter or replacing the first one when the battery arrives.
What to check on your quote
Look for the inverter brand, model and rated kW, not just the panel specification. Check the warranty: 10 years is reasonable, 12 or more is good, and 5 should prompt a question, because inverters work hard and are the most common component to fail in years 10 to 15.
Then sanity-check three things: the array-to-inverter ratio (roughly 1.1 to 1.3 is the comfortable zone), whether the export arrangement is G98 or G99, and whether the inverter is hybrid if a battery is anywhere in your plans. Those three questions cover most of what separates a thoughtful design from a copy-paste one.