"If you are of the opinion you can afford 28.6 m^2 of PV without taking out a 2nd mortgage on your home then go for it"
You need to spend less time with theory and more with real examples. Those 28.6 m^2 of panels you say require a 2nd mortgage is actually the panels I bought for my house, the whole system cost less than most brand new cars and with the FIT subsidy has a pay back of less than 10 years and will run for 25+.
So using my system lets go for a real world example instead of your theory
- 22 x 180Watt Sharp panels (each panel having dimensions 1m x 1.3m), so 3.96kWp
- 1 x SMA SunnyBoy 4000HF inverter
- Installation, wiring etc
- Sunny Beam display (a little gadget to tell me current power output, daily money made etc, just couldn't resist)
- My council being scumbags and wanting to make money out of me so insisting on their own inspections, fully chargeable of course (despite installer being competent body scheme, MCS certified etc), making me get structural engineer roof loadings -> councils in Devon don't try to extract money in this way and just let you get on with it.
Total cost: just under £14,000
According to pvgis (and I have checked those figures against other systems that have been running for a full year and they seem close), I'll generate > 3300 kWh. Since 1st April it's been 43.3p / kWh and without an export meter you get an assumed 50% exported at 3.1p / kWh. So that's 44.85 p / kWh which give me a FIT payment of £1480 a year index linked for the next 25 years (went up 4.8% this year).
Since install in March I have generated more than 1,400kWh.
If you can't afford 14k then do get a loan over 10 years, it'll payback the interest on the loan and you'll have 15 years of no loan and money coming in. Or get a smaller system, I went for the sweet spot of 4kWp, if you go over that then the tariff drops so you need to go over 4kWp by a significant amount.