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Suspiciously high and random solar water/pv claims at an Enviro Home showhouse.

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Posted by Jonathan on September 7, 2006, 11:26 pm
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.

12-40% from solar PV, 7-25% savings from hot water depending which sign you

So I grabbed my camera and blogged it:


Feel free to correct me or post comments in the blog, too. But for a
"showhome", I see a lot of inconsistencies...

Posted by Anthony Matonak on September 8, 2006, 3:40 am
Jonathan wrote:

They're not really inconsistencies.

: 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.


Posted by Christian McArdle on September 8, 2006, 2:25 pm
Alternatively, the 13% refers to carbon emissions and the 25% refers to gas.
There are also carbon emissions from electricity, so it makes complete
sense. You could completely eliminate the gas consumption of the house and
still only halve the carbon emissions, as the house still uses electricity,
which is unaffected.


Posted by Jonathan on September 8, 2006, 4:17 pm
Well, the most high efficiency tile they make needs 8m per kiloWatt, peak.

So you'd need 24m of roofspace for your 3kW, and as the house I saw, in the
middle of a hot sunny day, was making about 450W of non-storable energy,
this is why I am skeptical about the 40%

Posted by Christian McArdle on September 8, 2006, 4:24 pm
That sounds perfectly reasonable. I'm surprised you can get so much from a
small area.

450W would usually easily cover my electrical usage. Wouldn't help at night,
or for brief peak usage when the washing machine element fires. It would,
however, cover my lighting and electrical goods.


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