I’m guessing all energy is provided from the 12 roof PVs as they are quoting zero carbon.
For a family home, during winter when there is little light and increased usage (heat, ight?) I'd be surprised. More likely that they select an "ethical" energy supplier that only supplies from renewable sources?
Just checked and looks like heating and hot water is centrally produced:
Built-in innovation delivers exceptional economy with energy efficient appliances fitted as standard. Homes at Elmsbrook use on average 31% less electricity than the average Bicester home. Heating and hot water will come from the district’s Heat and Power system, so no more worries about boilers, while each house has rooftop solar panels, collectively generating enough electricity to power 528 typical UK homes.
More info at: https://www.fabrica.co.uk/content/doclib/51.pdf#zoom=100
Elmsbrook is the only true zero-carbon community of this scale in the UK. All homes at Elmsbrook, of which there will be 393 across four phases, are carbon neutral. With the first two phases complete, we are now launching the final phases of this ambitious project
And: Energy Minister unveils new energy centre at Elmsbrook, NW – Growing Bicester
The CHP plant, which supplies heat and hot water to all homes through a district heating system that harnesses waste heat from electrical generation exported to the grid, helps minimise energy consumption and prevents the need for a separate boiler in each home.
Regarding electricity, looks like they are generating more than enough from the EVs (as stated above). They are stating true zero carbon so the heating is either from over production from the houses EV, they have additional EVs or they are buying in green energy I guess.
Solar roof tiles have been around for years, we built our extension in 2004 and soon afterwards I discovered Marley did a solar tile, but the roof was already fitted so too late.
Https://www.jewson.co.uk/media/202979/solar_century_pv.pdf
We've had a 4Kw PV system fitted since December 2015, and it certainly doesn't provide enough electricity for us, I doubt even if we had battery storage it would either.. Pay back is looking more like eight years than the six we were told. Most of our lighting is Led, and we don't leave lights on in rooms if we're re not in there, of course there is a server running 24/7, lots of equipment in standby as well. One wonders if these test houses take into account how the average person lives
A lot of our heat goes straight out the windowsas the wife insists on having bedroom windows open, not wide but enough to lose heat, this is where I can see whole house ventilation and heat recovery systems will really pay off, but the house does need to be airtight. I wonder just how many years it will stay airtight for though.