I've just wired in a 1kw grid tie inverter, feeding the power from solar panels into the mains grid, ( in Thailand , so no rules or regulations). There are some problems I've noticed. Toaster buzzes , but works. Induction cooker won't work, lights come on , fan works but no heat delivered, when grid tie switched off, works fine again. Soldering iron ( temperature controlled) won't heat up fully. This seems to indicate the grid tie inverter is not pure sine wave. What can be done? Would a power line filter help?