What subject is the dissertation on? The modelling done so far sounds very simplistic compared to what I would have expected.
One thing which would be potentially very interesting for modelling payback is to look at real-life data for historic PV output - this is available to download from
https://www.solar.sheffield.ac.uk/pvlive/ and if you have a model for domestic energy use in 15 minute increments you could match these up to see whether energy is likely to be consumed locally or exported. Once you've done that it's straightforward to introduce a model for a battery, Smart Grid Ready heat pump, etc.
In the same way wind power data for the whole of the UK is available to download - quite a few sites have it, I tend to use
http://www.gridwatch.templar.co.uk . More care needs to be taken here to work out capacity factors since unlike PVLive the total installed wind fleet isn't listed in the same data set, but it should be possible. That will then essentially give you a power curve for a notional "national average" wind turbine, which you can then adjust for a domestic one which I suspect will tend to have higher cut in/cut out speeds.
The other thing to watch out for is maintenance costs, cost of capital, etc. - PV is pretty much maintenance free unless an inverter dies, but the same is emphatically not true for wind as you need to keep an eye on bearings, etc. Any financial calculations should really include this too.
