Hello, as it is an electronic project, using gpio and some electronic components will do the trick despite your requirements of php html etc.
I'll use an arduino (preferably uno or nano to make it small and power efficient) and make it create a switchable high frequency sound through out a speaker. But I don't understand whether you want it solar powered or AC powered? AC comes standard with a standart 9/12V adapter so if we use any solar panels, they also provide a 12V output, so what do you want us to do for it? Please pm me back if you want to collaborate, thanks.