Free solar panel discussion

Nang

grahamc2003 wrote: »

I think where Nang is going badly wrong is trying to compare bills from last year with this year to estimate the savings due to PV. There are just so many other variables that such a comparison, as you state, is nonsense.

So in summary

From the 2 suggested methods of measuring this:-

1. Export meter:- Provides benefits without before and after comparisons and throws in the concept of free electricity, in the after component of the comparison. Hmmm not very conclusive me thinks.

2. Compare last years to this years doesn't work cos there are two many other variables.

To conclude:-

Bad news for anyone who trying to work how much they will reduce their elect bill by, by renting out there roof for 25 years.

Good news for dodgy companies who like to make claims like "this will make a saving of 40%" of your yearly electricity bill.

Cant see how this is good news for folk who want to workout if its a good idea to get on the free scheme.

Nang

Cardew wrote: »

Mmmm

Even allowing for his wording, I can't agree that this quote means what you are assuming!



The whole point of that quote was that people are going to save 9p for each kWh utilised in the house(instead of 3p) and then savings on gas 'too'.

Indeed people will save 9p for each kWh used for consumption that would be otherwise drawn from the mains. e.g.if a fridge/freezer draws 0.15kW and might use say 0.5kWh during daylight hours. It is reasonable to think that, on many days in the year, that will be a straight saving. However some days even that consumption won't be covered.(someone just reported that his system generated 8kWh one day and 0.1kWh the next day.)

Yes but you are not going to switch on the appliance to save that gas unless you know the power is actually available, i.e its sunny and the sun is high.

So I cant see how your point about xkw hour generated on one day and y generated on the next day is relevant here.

Cardew

Nang wrote: »

Yes but you are not going to switch on the appliance to save that gas unless you know the power is actually available, i.e its sunny and the sun is high.

So I cant see how your point about xkw hour generated on one day and y generated on the next day is relevant here.

Andy,
When you came on this website you hadn't even included any savings from generated power consumed in the house - on the grounds it was 'small potatoes'. Now you seem to be splitting hairs and advancing reasons why estimates(note -estimates) might be inaccurate.

An export meter will enable you calculate exactly how much you have used it the house. If you wish to surmise some of that consumed electricity will be nugatory - so be it.

There are loads of case studies that show that a reasonable estimate for household consumption is 500kWh to 1,000kWh per year. Even if you managed to your satisfaction to calculate your consumption down to the nearest microwatt, it wouldn't be more than a rough guide for others. Don't forget also that the price people pay for electricity varies widely.

The relevance of the xkWh and ykWh is simply to make the point that output varies tremendously day to day. As you need your fridge/freezer running(the example I gave) it will use the PV generated output on the majority of days, but some days the PV output will be insufficient and power just for that appliance will be drawn from the mains.

Frankly the 'use the immersion heater instead of gas' is a non-starter for most people. Many systems are not big enough and it is rare that even large PV systems like yours generate the 3kW plus the 'background' load.

Nang

Cardew wrote: »

Andy,
When you came on this website you hadn't even included any savings from generated power consumed in the house - on the grounds it was 'small potatoes'. Now you seem to be splitting hairs and advancing reasons why estimates(note -estimates) might be inaccurate.

An export meter will enable you calculate exactly how much you have used it the house. If you wish to surmise some of that consumed electricity will be nugatory - so be it.

There are loads of case studies that show that a reasonable estimate for household consumption is 500kWh to 1,000kWh per year. Even if you managed to your satisfaction to calculate your consumption down to the nearest microwatt, it wouldn't be more than a rough guide for others. Don't forget also that the price people pay for electricity varies widely.

The relevance of the xkWh and ykWh is simply to make the point that output varies tremendously day to day. As you need your fridge/freezer running(the example I gave) it will use the PV generated output on the majority of days, but some days the PV output will be insufficient and power just for that appliance will be drawn from the mains.

Frankly the 'use the immersion heater instead of gas' is a non-starter for most people. Many systems are not big enough and it is rare that even large PV systems like yours generate the 3kW plus the 'background' load.

Yes, I think it is small potatoes compared to fits.

But lets not forget that for the chaps going for the free systems its there sole reason for doing it (and when you think about it the main point of this discussion).

And FYI the system on a sunny day even in mid November will make most of, if not all of that 3 KW for the immersion, so that most of the year.

grahamc2003

Nang wrote: »

So in summary

From the 2 suggested methods of measuring this:-

1. Export meter:- Provides benefits without before and after comparisons and throws in the concept of free electricity, in the after component of the comparison. Hmmm not very conclusive me thinks.

2. Compare last years to this years doesn't work cos there are two many other variables.

To conclude:-

Bad news for anyone who trying to work how much they will reduce their elect bill by, by renting out there roof for 25 years.

Good news for dodgy companies who like to make claims like "this will make a saving of 40%" of your yearly electricity bill.

Cant see how this is good news for folk who want to workout if its a good idea to get on the free scheme.

Nang - you are well and truly mixing up two disticnt things here. The two things you are mixing up are
1 - whether comparing last years bills to this years bills is a good method of seeing how much pv has saved you and
2 - whether comparing last years bills to this years is a good method for proving you haven't saved anything like 40% of your bills due to pv.

I thought you were saying 1. (and reading back through your posts I'm now certain you were). Case 1 is nonsense.

If you were somehow trying to imply 2 - then I'd agree, measuring last years and this years consumption will give a very good indication that the 40% claim is rot (and cruel in fact).

It comes down to the resolution, or error, in the measurements. The other variables which make 1 impossible are not sufficiently great to make 2 meaningless.

I must say, your posts do take quite a bit of deciphering sometimes - try to put youself in the position of your readers when you make a post which, at this level, is tallking about quite specific fine details. (an example in a previous post was the word 'too' which was very ambiguous, just as the word 'this' in your first sentence.

But your aim (which I think is sound) of trying to estimate realistically the savings due to pv is very difficult to do. We can certainly see in retorspect the number of kwh of pv used (but that only if you have an export meter, which I think most don't, knowledge being power and all that), but translating that into cash savings, even in retrospect, is impossible to calculate, and can only be estimated. So yes, these uncertainties (which in general buyers/renters of pv panels don't really want to know anyway - just look at the reaction when estimates using methods of real merit are used) play into the hands of pv salesmen. I'm sure most are happiest when the have their free pv system installed with a totally misplaced confidence that they are saving 40% of their bills, rather than knowing that they are only saving something I'd estimate as typically £40-£80 (lowered from the previous estimates posted by reliable posters due to the issues you have raised).

grahamc2003

Cardew wrote: »

Frankly the 'use the immersion heater instead of gas' is a non-starter for most people. Many systems are not big enough and it is rare that even large PV systems like yours generate the 3kW plus the 'background' load.

But not as daft as the suggestion to rewire your house so the pv drives storage heaters, as has been suggested! Fun here isn't it!

grahamc2003

Ok, I'll admit in advance I'm a bit of an anorak. Anyhow my consumption in my all electric house, on a day, week and month basis is

Sat 20-11-2010 53.07kwh (gulp!)
Sat 21-11-2009 26.40kwh

Week ending sun 14 nov 2010 306.52kwh
Week ending sun 15 nov 2009 271.48kwh

October 2010 814.76kwh
October 2009 611.31kwh

Nothing much has changed between last year and this. The consumption is probably due to different weather over the two years. I'm not sure of the accuracy of the Owl meter I've taken the readings from, but I sus[pect it's accurate enough for this purpose.

Nang

grahamc2003 wrote: »

Nang - you are well and truly mixing up two disticnt things here. The two things you are mixing up are
1 - whether comparing last years bills to this years bills is a good method of seeing how much pv has saved you and
2 - whether comparing last years bills to this years is a good method for proving you haven't saved anything like 40% of your bills due to pv.

I thought you were saying 1. (and reading back through your posts I'm now certain you were). Case 1 is nonsense.

If you were somehow trying to imply 2 - then I'd agree, measuring last years and this years consumption will give a very good indication that the 40% claim is rot (and cruel in fact).

It comes down to the resolution, or error, in the measurements. The other variables which make 1 impossible are not sufficiently great to make 2 meaningless.

I must say, your posts do take quite a bit of deciphering sometimes - try to put youself in the position of your readers when you make a post which, at this level, is tallking about quite specific fine details. (an example in a previous post was the word 'too' which was very ambiguous, just as the word 'this' in your first sentence.

But your aim (which I think is sound) of trying to estimate realistically the savings due to pv is very difficult to do. We can certainly see in retorspect the number of kwh of pv used (but that only if you have an export meter, which I think most don't, knowledge being power and all that), but translating that into cash savings, even in retrospect, is impossible to calculate, and can only be estimated. So yes, these uncertainties (which in general buyers/renters of pv panels don't really want to know anyway - just look at the reaction when estimates using methods of real merit are used) play into the hands of pv salesmen. I'm sure most are happiest when the have their free pv system installed with a totally misplaced confidence that they are saving 40% of their bills, rather than knowing that they are only saving something I'd estimate as typically £40-£80 (lowered from the previous estimates posted by reliable posters due to the issues you have raised).

First of all, apologies for the lack of clarity in my posts, I will try and proof read for a bit longer.

When I first made the original post I believed you could get a figure by making yearly comparisons.

After having this debate on the forum, I have come to the conclusion, that you cant really reliably measure these savings.

I think this is very bad because it will give some unscrupulousness companies the opportunity to take advantage.

I was also hoping to publish some figures on my blog for the saving side of the equation, to try and inform the potential free panel customers.

But I am not convinced now that this is even possible.

Andy..

Cardew

Nang wrote: »

But lets not forget that for the chaps going for the free systems its there sole reason for doing it (and when you think about it the main point of this discussion).

That of course is what myself and others have been 'preaching' ever since the 'rent a roof' schemes were introduced. We have posted many times about the probability of PV generated power used in the house being much lower than people hope.

The problem is that in many cases you are unlikely to get objective posts from people who have taken the plunge and rented their roof.

This is a good example for someone who has paid £500 for the privilege of renting his roof for installation of a 2.8kWp system:

I recently had this company install my solar photovoltaic system in Redditch and i deem them as very commendable. I am noticing savings of around £15-£20 per month on my electricity as well as sending 20 ish units per day back to the national grid. On my workings i calculate that to be 60p a day working out at around £180 per year plus a deduction of £180 - £240 per year of my electricity bill. All in all a sound £500 investment as my money will easily be re-couped within 24 months and then the next 23 years will be profitable. If i decide to leave the house hte agreement stays but surely that is a good selling point?

Any questions or advice would be more than welcome?

Willing to offer advice as well - about a system that appears to be producing about 7,000kWh a year.

The problem is that he believes(or wants to believe) his figures are reasonable, and other people will believe him.

A house is advertised for sale with an ASG(3.3kWp) system on the roof and the blurb talks about £400 a year savings.

Contrast that with mcifi5 who has had a system for over 2 years, has a wife and 2 children at home all day, and uses about 500kWh a year.

Nang

grahamc2003 wrote: »

But not as daft as the suggestion to rewire your house so the pv drives storage heaters, as has been suggested! Fun here isn't it!

Graham

Apologies for potentially reopening a can of worms here, but what about if:-

When they installed the system, they installed a relay that only switched on the immersion heater when there was enough PV power available for it. Would this not save money for the home owner? As you would be generating hot water through the cheap / free, elect and not by burning the gas.

I also considered there might be an additional reliability benefit (for sunny period) as the panels have no moving parts.

I have had nothing but bad experiences with combi boilers, they seem to be unbelievably unreliable, perhaps even more so than the British weather

In fact, I'm currently sitting in the cold, as our combi boiler has broken down, despite only being one year old.:(