Jonathan wrote:
I nipped down to Reading to seen, amongst other things, the Enviro Home at
the St James Kennet Island development.

I noticed a couple of inconsistencies and figures I didn't recognise.

They're not really inconsistencies.

12-40% from solar PV, 7-25% savings from hot water depending which sign you
read....
....
http://www.digitaltoast.co.uk/enviro...saving-claims/

: This envirohome emits 70% less carbon than a typical UK terrace house.

They are saying that this home uses less energy than a typical UK
terrace house. Also, since the energy that it doesn't use would
come from carbon emitting sources then it must also, ultimately,
send less carbon into the air as well.

All the percentages on that sign are referring to the amount of
carbon emissions avoided by saving energy.

: Solar photovoltaic cells on the roof of this house collect the
: sun's energy and turn it into electricity. This unit provides the
: envirohome with about 30%-40% of it's electricity.

This is not all that high. A 3kW array could produce this much
electricity without breaking the bank, especially since it's
integrated into the roofing tiles.

: The Solar PV tiles on this roof will provide up to 40%
: of the annual electricity requirements of this house.

30% to 40% is within the 'up to 40%' so I don't see any major
discrepancy there. Sure, it's likely to be closer to 30% but
it's all estimates anyhow.

Now the solar hot water. 13% less carbon emissions than a comparable
home and 25% lower gas bills do not have to be incompatible figures.
I don't know how gas is billed but 25% lower bills may not mean 25%
less gas used.

Anthony