If you want a rewording that's closer to my original meaning, it'd be more like "I bet these were made with a cold climate, like that in the northern USA, in mind. They'd lose 10-20% efficiency in summer where I live."

Edit: Although that may not be a terrible thing, if they're overprovisioned compared with the inverter's maximum output so as to keep the inverter at full power for a larger proportion of the time. Depending on climate, you could probably balance out losses due to summer heat with losses due to reduced winter daylight, at least to a degree, giving more reliable year-round power.