The key to maximising the potential saving, and to fully utilise any of the renewable technologies you mentioned, is proper insulating of the building to begin with.
So consider updating the insulation, floor, walls and roof if you can, and sealing around all the openings.
No one systems can do the work of the other, ie you need to combine a mixture to get the best possible solution.
Air source & pv panels offer the best solution for most existing buildings.
No matter what the output from your panels, or what time of day it is, the most cost-effective strategy is to use all the electricity they produce.
If you install an air source heat pump to power your heating and hot water, you get the perfect partner for your PV panels excess output.
Roughly speaking for every kw you generate will be multiplied into 3-5 times as much heat energy, which can be automatically be fed into your hot water tank.
Ground source heating works best with modern houses, where there's a need for under floor heating, and naturally the insulation levels are already higher.
You should also look at the Renewable Heat Incentive RHI.
A Government backed scheme for grants for renewable technologies for domestic use.
Domestic Renewable Heat Incentive | Ofgem
Renewable Heat Incentive | Energy Saving Trust