Solar panel IBI discount

Part of the justification for the cash outlay on solar panels was the availability of a 50% reduction on IBI for 3 years.
Our application was submitted in February, and after waiting 9 months I have just received the rejection.
Apparently you must install at least 5kw of capacity for every 100 square metres of build (including swimming pool).
I would suggest that most houses of 100 sq.m. would have difficulty in finding sufficient suitable roof space for the 12 large panels needed.
A house of 150 sq.m. would need to generate 7.5 kw which is probably more current than most domestic cabling would allow.
It seems the number of properties that could qualify for this deduction is going to be very small.
While the sales person at Iberdrola was keen to point out the potential discount and also the possibility of an income tax rebate, there was no mention of how unlikely you would be to receive it.
As ever, Buyer Beware!

And if your house was built illegally but is now legal you will get nothing.