.....Bill
On a new property I'd go for 70* or vertical panels. My current house has a number of shortcomings for RE.
I hear what you say about 'clumpy' and my own measurements (by proxy, from my pilot PV system) suggests that 7 days' storage would be needed to carry through those.
Now a 7-day store in the house, or seasonal thermal store to cover the 33% you said still had to come from oil, is not totally impossible at all.
That actually gives me a sensible target to shoot for!
Rgds
Damon[ Parent ]
Further thoughts... Thanks again for your data point.
My plans are a mixture of theory (what might be possible in order to go zero or negative carbon), and more practical (what I might do at my current tiny house or if we move to somewhere close by larger).
Your 67% figure is quite interesting, ie 2/3rd of year-round DHW and CH from solar thermal, with the balance from another fuel source.
If I aimed for that with solar thermal with protection from overheating, then I could in principle (though expensively) make up some of the gap with solar PV and a plain ground-source heat-pump and/or a more moderate thermal store than I was planning before (eg 20kl rather than 60kl). A good CoP on the heat-pump might compensate for much of the relative inefficiency of PV compared to thermal for energy capture.
And the big potential advantage of solar PV is that I can safely just not use any excess, eg in summer, or even export it to the grid. Overheat is not an issue.
I'm trying to work through making some of these ideas a bit more practical on this page:
http://www.earth.org.uk/towards-a-LZC-home.html
though please bear with me since I'm still mid-thought, so maybe check by later today.
Yes, at this house DHW (and cooking) gas use is ~10kWh/day, and CH (central/space heating) load for half the year is approx an additional 20kWh/day (and zero the rest of the time).
So total year-round DHW/CH demand is approx 7.3MWh/year.
But under the scheme that I've outlined here:
the heat-pump would only need to be working flat-out to supply all the CH needs in mid-winter, as solar thermal would be contributing some or all DHW/CH needs at other times.
We can of course work on reducing the CH demand by increasing insulation, etc, and that will make GSHP more plausible.
I am assuming that if we move to a new place we can keep DHW/CH demand similar or even lower.
For the current house it's probably hopeless, but I can tell you that PVGIS (http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php) suggests: 886Wh/m^2/day at about our roof pitch (36*) and 944Wh/m^2/day on a vertical surface in December south-facing, with year round averages of 3100Wh/m^2/day and 2180Wh/m^2/day.
I think that those numbers are roughly halved on east- and west- facing pitches, though tubular collectors may do better than that suggests because of their profile.
I don't know our exact roof pitch, but by eye 36* isn't far off.
The north-south ridge of the roof is roughly 5m long and the house front to back (ie east to west) is about 8m.
Interesting. Thanks for that.
I think the situation is not at all good for this house for real RE.
Really time to look for a better place I think... B^>
Thanks!
I'm proposing a tank of up to 60,000l which would hold all our winter DHW/CH heat, though a mixed scheme might get away with 20,000l. And the surrounding soil would be good to use except that we might (I don't know) have relatively fast-moving groundwater not very far down from two nearby rivers.
http://www.earth.org.uk/milk-tanker-thermal-store.html
My current house isn't really good for either scheme, unfortunately... So as we're looking to move anyway, it's an opportunity to find a more suitable location for RE too.
I earn most of my living from one of the big US investment banks (announced its results yesterday). Everyone was glum, since they did bonuses the same day, but no one's jumping off the roof. I expect a little more market turbulence, but I think my contract is safe for now for example, and we have money in the bank, and no debt other than our mortgage.
Anyway, that means that I need to stay within commuting distance of London, and even finding land to build on looks tough.
So we're looking for the best existing property we can: one bedroom more than we have now, a bigger garden (for playing in and burying a thermal store!), a nice place to live, good doctors and schools for our daughter (turned 2 today!), easy commute to London by public transport (possibly with the assistance of a small electric car), and of course a nice south facing unshaded aspect (eg on the roof) for solar thermal/PV...
From where I do most of my work in Canary Wharf over to the east of London, 30 miles or less could get you into relatively open space. It's certainly a line of investigation for me.
