Solar Panels - Energy Saving

Martyn1981

Just found this research from Loughborough.

It tickled me because they are using calculations based on a 3kWp system, and produced findings from unoccupied all day, through various stages, to occupied all day.

The reason I found it funny is purely coincidental, but the lowest consumption figure they suggest is 15%, and assuming (perhaps wrongly!) that a 3kWp system will generate 3,000kWh, then 15% is 450kWh.

So, 450kWh and up.

Edit: Also found some real figures from 3 houses on this site. M.

Mart.

zeupater

Martyn1981 wrote: »

Hiya Z. What are your thoughts on the study that finds only a 450kWh reduction when the control group is taken into account?

I can't argue with a genuine study if those are the findings, but I'm confused by the control groups significant savings within the comparison period.

Can you think what might have gone wrong, or is it us?

Mart.

Hi

Having just read the report, here's my considered opinion ... "what a load of rubbish".

The report compares three groups, those with pv, the total housing stock & a 'matched' group without pv with the same annual electricity consumption (5200kWh) as the pv group, selected specifically for comparison. The matched group is selected because .... (Introduction P4) 'Comparison with such a matched group was necessary because microgenerator households tend to have higher-than-average electricity consumption'... the report fails to fully describe either the selection methodology, the validation process or the source of the usage data ...

The report effectively says in table B3 that installing pv resulted in a mean reduction of 900kWh/year (17.3%) on properties within the pv set against 200kWh/year (4.8%) for the housing stock as a whole, whilst the 'comparison group' achieved 500kWh/year (9.7%) .... this is pretty odd really as the figures convey that this group has reduced their electricity consumption at almost exactly twice the rate of the national average (9.7/4.8) which should immediately ring alarm bells on the selection criteria ... note, the percentages just referenced are missing from the report and needed to be calculated, perhaps if someone had done the same and seen the ratio applied they'd have stopped & thought ....

Okay, the above is then weighted in a convoluted way within table B4. The 900kWh reduction in the pv set suddenly represents 15% (was 17.3%) which logically means that the average usage must have been adjusted to 6000kWh/year (900/0.15) ... and ... the 500kWh reduction in the 'comparison group' has also been represented as 6% (was 9.7%) which logically means that the average usage must have been adjusted to 8333kWh/year (500/0.06) ....

Herein lies the problem .... both of the datasets in question have usage of 5200kWh/year but the control set, whilst already having serious question-marks over the selection criteria has been further manipulated .... remember, the reason for selecting the matched group was stated to be ... 'Comparison with such a matched group was necessary because microgenerator households tend to have higher-than-average electricity consumption' ... so why now compare pv with a 'matched' group and deduce that there's a difference of 400kWh(900-500), then maintain that the difference is still 400kWh, but the usage must be moved to 6000kWh & 8333kWh to justify the difference ? ....

Obviously, concerning the 'matched group', there's both an initial selection criteria issue and it's been further manipulated in an illogical way .... the comparison must therefore be rebased. Due to the pv data being based on accurate readings (as described in the report), I have absolutely no idea why the 'known' dataset was manipulated at all - it shouldn't have been, but let's play their game, using their figures and correct their error through rebasing .... so 900kWh/year is rebased to 780kWh((900/6000)*5200) & 500kWh/year should be 312kWh ((500/8333)*5200), a difference of 468kWh/year(780-312), which is pretty close to the 450kWh/year which was referenced by the EST ...

.... However, here's the logic bomb - and it's fully supported by what the manipulation tells us .... the dataset with pv must logically have already taken efficiency measures which the 'matched group' hasn't. On a like-for-like basis, the 'matched group' is much further behind on the efficiency curve at the beginning of the period in question, obviously by 2333kWh (8333-6000) on average, so their average 500kWh/year of electrical efficiency reduction after 2 years still has 1833kWh (2333-500) of effort to go before the whole exercise becomes anywhere near valid .... of course, the report authors made a statement in the summary, but unfortunately missed the relevance of what they'd written - (Summary P12) "For example, earlier work by DECC found that microgenerator households were much more likely to have energy efficiency measures (such as wall insulation or double-glazing) installed, suggesting an increased level of energy awareness" ... :think: .. :wall:.. :whistle:

Oddly enough, back in 2011/13 (the period covered in this report), the members of this forum already with experience of pv used to provide guidance of a range of £80-£100 as being a likely pv saving when using £0.12 as the energy cost and that if saving 1000kWh/year any prospective buyer would be doing well .... oddly enough, that gives a range of 666 - 833kWh/year, with 1000kWh (£120) being reasonably good , which is entirely in line with the 900kWh/year saving which the flawed report starts with .... all of which brings us back to the beginning - the report is based on a flawed logic and as such is a load of rubbish ...

HTH
Z

Martyn1981

zeupater wrote: »

Hi

Having just read the report, here's my considered opinion ... "what a load of rubbish".

HTH
Z

Thanks Z. I have to admit I was thrown by the manipulation of consumption in the control group, and similarly thrown by the conclusions on the starting point of energy efficiency.

I can't see the EST changing their advice however, which is rather sad as it seems (to me) to seriously undervalue the leccy savings component of PV.

Given the dates of the installs, and the larger than average consumption, I'd have thought this comparison needs to be redone (properly) looking at installs in the last few years.

If the control groups continue to reduce demand by 500kWh pa, then all the better for them, as they must be heading for zero import by the end of the decade. :think:

Mart.

Martyn1981

zeupater wrote: »

all of which brings us back to the beginning - the report is based on a flawed logic and as such is a load of rubbish ...

HTH
Z

Been further pondering your conclusions and decided to fight fire with fire, or DECC report with DECC report.

According to page 7 of this report, average domestic leccy consumption reduced by 100kWh between 2011 and 2013 (4,200kWh down to 4,100kWh).

I suppose a higher use house of 5,000kWh (or so) might see a 20% greater reduction, but if the graph represents import (rather than consumption) then part of the fall should be allocated to PV too, probably balancing it out.

[Edit: Thinking about it, all you have to do is compare pre PV import to post PV import, then compare that to the drop in the national average import over that period. The PV would only affect the drop in year 1, and should have minimal impact on the national figures (1% or less), from year 2 onwards the PV would help to reduce the average, but not affect year on year reductions. That shouldn't be a difficult survey to carry out at all. M.]

Mart.

zeupater

Martyn1981 wrote: »

Been further pondering your conclusions ....

Hi

No need to ponder any further ... the report is simply a load of nonsense, rubbish, MBE or anything else you'd like to use .... furthermore, there's only two logical reasons for this being the case ...

(a) It's been compiled by intellectual lightweights.
(b) The primary driver is political.

... beyond that, considering the obvious fundamental flaws in the logic employed, it's really down to the authors to justify themselves and take appropriate corrective actions ...

HTH
Z