Generally you don't need to bother cleaning your solar panels. Unless you're up there spinning tyres and shooting exhaust particulates at them!
If you're in a dust-prone area, under fig trees, are regularly visited by pigeons or have horizontal panels, then you'd need to clean them more regularly.
Otherwise, it only makes about 5% difference to your production on average if you clean every day. Once a year is probably worth it if you enjoy doing it yourself. Not really worth paying someone for it though.