Hi Simone,
BTW, very nice watch...
I was ready to recommend you to contact the owner of http://www.soluhr.com website, since he is the ultimate source on vintage solar watches.
But, unfortunately, I've seen that the site is down now...
Anyway, I have some very early digital LCD solar watches,thus I may say (without being an expert in the field!) that your watch combines a quite early solar cells design and some late 70's on-the-face buttons, with a LCD specific to the very late 70s-early 80s watch LCDs.
Thus, according with my somehow limited knowledge - at least compared with the owner of soluhr.com - I will date your watch as being 1978-1982.
HOW DO YOU KNOW THAT IT IS A 1979 watch??? . Because I am really curious!
I know this is not much, but I hope that it may help
Regards,