Why I can’t make any economic sense out of the Victorian Government Battery Subsidy

If I buy this battery and the government pays for half of it after 15 years I have $2,985 in my pocket but I paid $4,838 so I am still well behind. If I had to borrow the money, then I am even worse off because I have been paying interest all the way along. If instead, I put the money into my house mortgage and assume an interest rate of 4.5% then the internal rate of return is 4.28%. I now have AUD$7,885.94 in my pocket (the saved interest and the original money I have paid off my loan)