My installer has quoted 8.91 kW of panels with a 7.3kW inverter. Will I lose energy?

Short answer: Despite the solar inverter being smaller than the solar panel array, you'll lose bugger all energy over a year compared with having a bigger inverter. This is good design.

Long answer: The Clean Energy Council guidelines allow a solar panel array 33% larger than the inverter rating. In this case your array is 22% larger. So all good there.

At this point I usually get the question: "But Finn! If my solar panel array is 8.91kW and my inverter is 7.3kW the inverter will clip the power output to the panels and I'll lose energy. It's just common sense!"

To which my answer is: "Look I know this sounds counterintuitive, but despite a bit of clipping going on on perfect solar days, you'll lose bugger all energy over a year. It comes down to the inverter working harder (where it is more efficient) and the clipping being very infrequent."

The best way for me to prove this is to do the calculations before your eyes:

Let's fire up a great website/calculator called PVWatts:

The questioner is in Sydney:

I put in the solar panel array size as 8.91kW. It is roof mounted, North facing and 22º from horizontal. Critically, in the 'Advanced Parameters', I put the DC->AC Ratio as 1.22 because the array is 22% bigger than the inverter:

The results: it should generate about 12,342 kWh/Year:

Now I do the same calculation with a DC->AC ratio of 1.0, to reflect an inverter the same size as the 8.91kW array, and I get these results:

12,329 kWh/Year, 13kWh less over 1 year. Bugger all.