In the past photovoltaic generation was very expensive thanks to the cost of the high tech semiconductor factories needed to make the collectors. Now mass production has brought costs down to a level where PV makes economic sense.
In PHPP solar PV is now modelled but does not show as a contribution to primary energy – the rationale is that PV systems are connected to the grid, and electricity not used in the house is exported for use elsewhere and there is no direct relationship with the energy used in the dwelling. Also historically the generous subsidies for PV and resultant trend for PV to be installed by third parties as a financial investment has led to the view that PV is not tied to a particular building in the same way as solar thermal.
The new Passivhaus plus energy standard includes PV generation, but retains the same Passivhaus building efficiency levels as the standard Passivhaus.
Standard domestic tariffs don’t meter export of electricity so it is in the householder’s interest to use as much as possible of their PV generation. Immersion heater controllers are available which divert any surplus power to an immersion heater, providing effectively a cheap solar hot water system. This isn’t accounted for in PHPP or Passivhaus certification and the view is that this electricity could be exported and used elsewhere, so it isn’t really free.