A very tight fit on hipped roof

Mixture of panel types on a very tight site

9 Aug: This roof is on a house of Richard's Mum, an ex-West Bridgford resident, now living further south - this photo was sent to me as a good example of doing almost everything.
    The house has 1.5 kW of PV installed, which is very good considering the tight fit. If we had this house as an enquiry to Rushcliffe Solar, we would have advised against it - with the modest level of detail we would get from Googlemaps, with the problem of the hip tiles and the roofight, (leaving at best room for only 8 panels) would have made us assume it was too difficult to fit. However, it shows that if you get an installer to do a close-up dimensional survey, and apply a bit of determination, you can achieve the near impossible using an ingenious fit of rails and panels.
    We noticed that the geometry of the panels on Richard's house have been rotated to make it fit.
    Normally, you would make more use of the upper part near the ridge, but this is already occupied by 3 solar thermal panels.

In addition to this PV installation, the house has the three solar panels for water preheating. They also have a wood burning stove for room heating - although this is just room heating (does not have back boiler pipes).
Hence, for this house, very low running costs overall.
  I am trying to find out more about it - two questions:  is the main background heating still requiring a Gas boiler, and is there a chance for an Air source Heatpump to replace the old boiler?
  It is good to see that they have 200 litres of Rainwater capture, for irrigating the garden.