[Matty4]

I've had a bit more of a think about the numbers and came to the conclusion that if we took that money and invested it into a term deposit at current rates of 5% we would have earned ~$4500 in interest (less tax) over a 6 year period.

We currently see bills from $650-700 per qt and I'm looking at a 5kw system. If I could knock $500 per qt off that bill it will pay for itself in ~6.5years, effectively giving me a return on my investment of close enough to 17%!!!
Where else would you get that? And still have it earn more in the long term?

She's been convinced!!