I'm in Wales so don't know if it's the same, but they don't care if you connect to a utility or not. When it comes to signing off they will expect an electrical certificate though so you may still need to have the pv / batteries signed off by a sparky.
If you were running a generator then the noise might be an issue, and solar alone won't give you much power in midwinter, but the only other issue might be the heat source for the house and energy performance cert - depending on when planning was granted, new-builds will need to meet a certain level of energy efficiency and may be restricted on types of fuel: for example, my house (still a work in progress) was required to have either an heat-pump (air source or otherwise) or 4kw of PV for the minimum requirements with standard insulation; as it happens I've put more insulation in than required, already have 5kw PV and hydroelectric, and will have an ASHP too.
Your friend will need a lot of pv to run an ASHP, but if they’re going for passivehause then that might not be an issue.