I admit I took 'liberties' when using the Double Glazing line.... but it would appear that I'm not alone in my suspicions or reasoning behind the whole scheme. Here's a quote from another forum that was discussing the situation: (my bolding)
...it identifies a crucial aspect I, so far, hadn't considered. Which then begs the question - if Sunamp aren't taking subsidies directly then is their deliberate targeting of people already using them their basic business model? According to the post I quoted, Sunamp could be guilty of misleading people into using their savings from FiTs by directing the energy from the grid to their heat storage system.The whole situation gets on my nerves, it would be far more efficient to just export the electricity to the grid (which is what the Feed-In Tariff is supposed to compensate you for) and use gas (or solar hot water panels) to heat the water; as usual a crap subsidy system creates perverse incentives. I don't blame anyone for minimising their own bills if they can legally do so, I would do the same, but as someone who doesn't have solar PV and can't install it because this house is in a conservation area, it winds me up that the government are paying people for electricity that they are using themselves!
Clever.
If your CEO is to be congratulated on one thing it's identifying a way to tap into other people receipt of FiTs payment. Not sure which I despise the most - those taking advantage of the taxpayer subsidising solar or a third party that's realised they could do the same but not receive the flak otherwise associated with it.....
Comments report typical systems costing £1,700 to £2,200 depending on source (+VAT). As an upfront cost to be recouped on an annual saving of the £43 that you actually agree to you're talking a 40-50 year repayment schedule
Just as well the system has been tested to a 50 year lifespan.... 
Sunamp themselves report a repayment time of around 7-8 years - no doubt using the 'best possible scenario' of which I'm not party to. Is the figure they quote based on savings from the Sunamp system or from the subsidised solar systems people already have?
If you trawl the web and see other peoples comments (no reviews that I have come across though) you'll find pretty much the same comments and criticisms we've identified in this thread.
But if such a storage system could be used to store heat that could then be reconverted to electricity then you'd fighting me off with a shitty stick to prevent me buying one!
As it is, you're just waving the shitty stick at the taxpayer (albeit behind their backs).
No offence....