Free solar panel discussion

cathd6

I fully admit to and apologise for my heavily-disguised ambiguity, but not for the fact that I have saved a packet of money (to avoid ambiguity, let 100 units of "packet" = 1 "shedload")

zeupater

cathd6 wrote: »

.... Our electricity bill for the first quarter post-installation as compared with the last bill covering the pre-installation period was significantly reduced (and Zeupater has shown above how this is plausibly likely to have been equivalent to circa £100 from the panels - FYI he (I assume) is correct and we don't choose our electricity provider solely because they are offering the cheapest tariff for 3 months)

2) £100 worth of electricity (which is a statistically useless figure on its own, if you're not talking in general terms) IS a significant carbon saving. £400 over a year, which I'm expecting to hit, is also significant.

Hi Cathd6 / All

Firstly, I must catagorically assure everyone that I have not at all shown any figures which would at all support a saving of £100 for the three month period Dec'10 to Feb'11. The calculations provided would only show that it is possible to generate the claimed 2253kWh in the 6 month period Dec'10 to May'11 by a theoretical 4kWp south facing array in Wembury and demonstrate that the following split would be likely ....

Dec-Feb ... 529kWh
Mar-May ... 1724kWh

... therefore to achieve a saving of £100 in the period Dec-Feb would need the tier 2 electricity cost to be in the region of 18.9p/kWh and ALL of the generated energy would need to be self consumed. Looking at a more realistic energy price of 10p/kWh and still using ALL of the genererated energy in-house, the system would have needed to outperform the 'flexed' figures by +89%, which is totally implausible .... in case this has not been understood ... I repeat, totally implausible.

I have also attempted to demonstrate how it's possible to apply short-term actual weather data to pv generation forecasts based on long term averaged data and how this can explain how a month such as December'10 could possibly outperform a nominally better month, such as Feb'11.

I do hope that Cathd6's system performs well, however, my strong belief is that it has not performed as well as the claimed £100 of imported electricity savings for it's first three months, and that a £400 saving is almost impossible over a full 12 month period, unless there was a huge and continuous base load. However, I would agree (and have shown) that the 2253kWh of production through to the end of May is likely a genuine figure. It will be interesting to see what the electricity bill savings are for the next few quarters .....

HTH
Z

zeupater

Cardew wrote: »

.... and the important claim on a Free solar panel thread has not been backed up by zeupater ....

I agree ...... my figures do not in anyway support the claimed £100 saving on imported energy (Dec'10-Feb'11) .... see previous post for details.

HTH
Z

cathd6

Then I owe you an apology because I entirely misunderstood your last post. The mystery lives on. For my own curiosity, I'm going to have to compare the bill against the generation. I guess it's altogether possible that having an extra 4 people in the house over Christmas meant more people to turn the lights off... or something
Re £400, it's just based on 50% use of the power we've generated over 6 months x 2, with our first quarter's bill in mind as a check.
That's under £400, but based on an average year the next 6 months should perform better than this half.

lardconcepts

I got sucked into this thread by accident and almost lost the will to live after going back about 10 pages. A lot of the pro-panel arguments here seem to be almost straight from the same hymn sheet as solar salesmen from events I have been to recently.
The same level of interest in answering specific questions or providing evidence, too.

It seems very hard to make any sort of saving from PV especially rent a roof, unless you never go out and literally live your life around the possibility of the sun shining at certain times. If it's money you want to save on your electricity, I have posted below some ACTUAL figures from switching my electricity plan, and unlike some pro-panel posters, I am happy to post actual copies of my bill minus name and address of course.
If you also google for the lifecycle of a "day" of electricity production, you will find that the overall carbon saving from using off-peak electricity is actually greater than PV: http://www.thedailygreen.com/going-green/community-tips/off-peak-electricity

It seems to me there is an obsession that any carbon reducing idea has to be expensive and inneficient when often the opposite is true.
For example my standard diesel engined ecomotive does more mpg, produces less carbon emissions and costs half the price of a Prius.

Also A US research company has made an attempt to analyse the carbon dioxide emissions from the Prius over its lifetime, from the mining of raw materials to the eventual destruction of the used car.

They came up with an even more eye-catching line: a Prius is even more damaging than the vast, gas-guzzling Hummer - the very symbol of wasteful driving.

If often helps to look a bit beyond the glitzy new tech pushed by salesmen. You may be surprised at what you find.

Actual electricity bill, standard tariff: 01/04/10 to 29/04/10
405 standard units * 11.223 = £45.78
29 days * 12.23 = £3.54
Total ex: vat £49.02

Actual electricity bill, twinheat A: 15/04/11 to 10/05/11
peak 156 * 14.015 = £21.86
off-peak 228 * 6.311 = £14.39
(total units: 384)
standing charge 26 days * 16.95p £4.41
Total ex vat: £40.66

So in fact we used a lot MORE electricity than this time last year and we're still saving over tenner a month (26 vs 29 days)

If we assume identical use: 228/26 * 29 = 428
428 * 11.223 = £48.02
29 days * 12.23 = £3.54
Total ex: vat £51.56

So let's say a £10.90 saving per month, the meter cost £50 to swap, after 5 months we're at break-even and every year after, we're saving about £130 with absolutely zero change of lifestyle or risk or maintenance. In fact, we should be rewarded for being greener because balancing load and using more off-peak is better, which is why it's cheaper .

zeupater

cathd6 wrote: »

Then I owe you an apology because I entirely misunderstood your last post. The mystery lives on. For my own curiosity, I'm going to have to compare the bill against the generation. I guess it's altogether possible that having an extra 4 people in the house over Christmas meant more people to turn the lights off... or something
Re £400, it's just based on 50% use of the power we've generated over 6 months x 2, with our first quarter's bill in mind as a check.
That's under £400, but based on an average year the next 6 months should perform better than this half.

Hi

I follow your logic on the £400. Your 2253kWh of generation at a tier 2 rate of 8.9p/kWh would be £200 for 6 months, therefore double that to £400 for 12 months. However, there are possibly two major logic errors contained in the assumptions ......

Firstly, the 2253kWh for six months cannot realistically be considered to be a winter quarter of 2253/2 and a spring quarter of 2253/2 as the number of daylight hours available have a significant influence on the generation, that's effectively what everyone is saying.

The second issue is the £400 imported energy saving. In order to achieve this you would need to use all of the generated energy yourself.

With a 4kWp system generating an exceptional 2253kWh over 6 months, the likely savings which most with owned systems would see as being realistic would likely be .....

FiT on 2253kWh @ 43.3p/kWh = £975.55
Assumed Export on 1126kWp(2253/2) @ 3.1p/kWh = £34.91
Average (optimistic) of somewhere around 3.5kWh/Day in house consumption @ 10p = £63.88

So total revenue & savings from an owned system producing 2253kWh over six months is estimated at £1074.34(975.55+34.91+63.88), with a rent-a-roof system saving estimated as being £63.88 .... however the following six months of sunshine is unlikely to guarantee that a system will always perform as well .....

HTH
Z

Cardew

cathd6 wrote: »

Then I owe you an apology because I entirely misunderstood your last post. The mystery lives on. For my own curiosity, I'm going to have to compare the bill against the generation. I guess it's altogether possible that having an extra 4 people in the house over Christmas meant more people to turn the lights off... or something
Re £400, it's just based on 50% use of the power we've generated over 6 months x 2, with our first quarter's bill in mind as a check.
That's under £400, but based on an average year the next 6 months should perform better than this half.

cathd6,
Whilst my posts are doubtless abrasive, this really is an important issue in the context of this thread - i.e. the 'rent a roof' systems.


If you are collecting FITs then they provide the main financial incentive, and the savings on electricity bills very much a secondary consideration.


There is plenty of evidence that some 'rent a roof' companies have resorted to the tactics of double glazing salesmen of yesteryear. They are making outrageous claims of potential savings; and by the evidence on here, having considerable success.

e.g. Charging a deposit, then £500 to have the panels fitted, £5 a month maintenance coupled with restrictive conditions in a legally binding 25 year agreement.


All of the evidence indicates that if people save £100 a year from their Rent a Roof panels they will have done well; many will save much less.

People seem unaware that using an immersion heater might 'use up' some of the electricity, however savings can only be costed at gas prices per kWh or off-peak electricity(if you heat water by that method).

Indeed, as explained else where in this forum, using an immersion heater to soak up PV generated electriocity is very likely to result in an increase in expenditure and not a saving.

On a money saving forum like this it is surely important that prospective clients of these 'Rent a Roof' firms who visit MSE for advice are aware of realistic potential savings.

semsley_2

Just a thought but could additional electricity savings be made from solar panels by switching from say gas central heating to electric night storage heaters switched on during the day (when electricity is generated by panels) and off to generate the heat during evenings?

angeltoad

We were assessed by Nationwide who siad they were the sister company to a Shade Greener (who refused us free ones cos roof oo small). they then said they can get just 6 panels on our south aspect roof and were willing to put them on the side roof too even hough it faces East .
I was wondering if this is really cost effecive or if hey are making money from the panel installation. Does the FiT only work well if you can generate 3 or 4 watts? He said it works on daylight not sunlight when he was talking abou uilising the side roof. ?
anyone with a smaller roof got any fedback?

John_Pierpoint

This is confusing.
Are you getting "free panels" in exchange for the installer getting to keep the Feed in Tariff (FiT) subsidy?
or
Are you being asked to pay for the TWO installations?