[dredmorbius]

Many years ago (and possibly still today) there were firms offering refrigerator-cleaning services. Brushing off the condenser (external) coils.

Yes, that may save you a bit of energy. No, not that much, and overall the financial savings are a small fraction of the service's charge.

A friend worked in energy conservation at the time and actually studied the impact of cleaning coils on refrigerators as part of a recycling programme (so: measuring pre- and post-cleaning power consumption on units which had been in use, most for quite some time). The net results, over hundreds (if not more) units: to little difference to detect statistically.

If you're doing the work yourself or don't have to pay for it: possibly worthwhile for peace of mind if nothing else. Paying someone else? No.

I suspect a similar situation for solar panels.