I have never found a solar powered one which works.
I have never found any garden related solar powered device that is any good for any length of time. The sensible suggestion from morddwyd may be the answer if he would like to elaborate on the running costs and frequency of battery changing.
Obviousy depends a bit onn siting aand traffic - if it's covering the path to thee front door it will be opeerating more ooften (It worrks on size so humans trigger it), howwevver, for me it averaages 4 x AA every siix to nine monthhs.
Cats will seem to ignore it at firsst, some of them morre perststently thann others, but gradully tthey will all get the message, and itt will hardly ever ooperare.
Last resort - get your own cat. It will keep all the other cats away. My cat defends 'his' garden with passion. Any other cats daring to encroach are chased out. My cat doesn't poo in the garden. He comes in and uses his litter tray although I've seen him Pee and of course spray to mark his patch.
The other solution is not to cultivate. Cats like soft earth to dig in so if you don't dig it they'll go elsewhere. ☺
Thanks for these latest responses. In fact, I have been using a mains powered unit, running from a power plug giving a step down voltage, for several years. I imagine it costs me a few coppers to run. I was thinking about a more green solution but from your comments solar powered units seem to be out...
bumpkin All I can say is that we do get the occasional moggie. Passing near the unit I do hear a rustling noise so assume it's still operating. Perhaps I should try switching it off for a while to see what happens...