Hi Michael,
Descriptions I've seen of noctule mention fast, high and direct flight. This one was flying almost casually, looping around the same area for several minutes hunting insects. Is that inconsistent with noctule?
I'm not a bat expert, but I made a very similar observation to yours earlier this year, seeing a bat circling over the street, houses and gardens, and finally an adjacen meadow, in broad daylight at 2 pm. I had a good impression of its size, and came to the conclusion it was indeed a noctule.
Unfortunately, I had forgotten the camera battery in the charger, so I have no good photo! :-(
I talked to a bat expert about this, and he said that it is not uncommon to see bats hunting in daylight if the nights are cold, which makes it hard for them to find insects. He also mentioned that sparrowhawks pose a threat to bats in daylight ...
Previously, I have seen noctules hunting in the evening several times, and they were generally circling most of the time. In one case, noctules and a couple of Barn Swallows were flying very similar "patterns" fairly high up on a summer evening, obviously "working" the same swarm of insects.
I'd speculate noctules might generally fly at the same height as Barn Swallows under similar conditions if they tend to hunt the same prey.
Regards,
Henning