Why is Tasmanian wholesale electricity price the highest in the NEM?

My chart of 10 day smoothed daily AEMO prices shows that Tasmania has been the NEM price pusher for over a month now and was also near the top of the price skein through much of 2017.
My attention was guided to Tasmania by seeing our PM on TV news offering Commonwealth largesse in Hobart and he mentioned Tasmanian renewable energy and the “Battery of the Nation” project that he seems smitten by. Note there is a State election looming and the Liberal Govt is behind in polls. “Battery of the Nation” seems to be a scheme for the State to bludge more money out of Canberra to increase wind power, pumped hydro and general hydro. Facts are Tasmania is a large importer of power now with average net imports of 5,761 MWhrs per day which is ~23% of demand (see figures in Table for Mar and Apr 2017).

So a fiscally sensible Fed. Govt. would say to Tasmania – look you are big importers of electricity now so you are far from being the “Battery of the Nation” in fact you are one of the “bludgers of the Nation”. Contact us again when you develop your own projects and your electricity supply situation is near import/export neutral.
I am trying to get data for all 2017. Does anybody have costings for the “Battery of the Nation” boondoggle which is probably on a par with Snowy 2.0 in the $5 to 10Bn range of extra Commonwealth debt.