Renewables: "talking 'bout my generation"

sly_dog_jonah

jkpaul wrote: »

Thanks Eric, that's an interesting summary. In order to compare it to our situation it would be useful to know what your average annual usage in terms of units was pre-Solar PV ... I ask because given the problems we've had with a dodgy import meter I'm very interested in what electricity usage / import savings people are seeing.

Currently I've been offered a nominal credit of 6 units per day (Feb - July) for the fact we've been overcharged due to the exported electricity being added onto our import readings. :mad:

I've rejected this, asking for them to interrogate the meter and get the actual figures from it. :wall:

That's a derisory offer. You have a large PV system so probably export the majority of the generation even if you are able to utilise some of it during the day. At the very least they should estimate the export at 50% of your generation and therefore subtract that off your import readings. Do you have historical readings to go by, i.e. before you had the solar installed? Our import is down 25-50% depending on the time of year, around 35% is probably about average so far. What is your average generation over the same period?

EricMears

jkpaul wrote: »

Thanks Eric, that's an interesting summary. In order to compare it to our situation it would be useful to know what your average annual usage in terms of units was pre-Solar PV ...

Not an easy figure to supply but :-

31 July 09 (Act) - 20 Aug 10 (Est) 5815 day units 3609 night ones

16 Aug 11 - 15 Aug 12 (both act) 2566 day units 1484 night
Not only is the 09/10 period 3 weeks longer, the final reading was an estimate and I can't remember offhand in which direction they were wrong let alone how much !

FWIW, E.on on the Aug 2010 bill were forecasting that I'd use 8850 units in the following year - but I switched to Npower almost immediately then to Scottish Power last year both of which companies were doing online billing (hence my not having access to the 10/11 figures).

My apparent saving of >5000 units can't possibly be accurate of course - it's actually a lot more than I generated and it would have been something of a miracle if I'd managed to use 100% of the generated power never mind 150%

There is however no possibility that my import meter has been running backwards - we have carefully checked for that. Can only assume that 'usage-awareness' is the significant factor.

legoman62

8.98kWh today
Peaked at 2.4kWh around12.30:D
Then the rain came:(

jkpaul

sly_dog_jonah wrote: »

That's a derisory offer. You have a large PV system so probably export the majority of the generation even if you are able to utilise some of it during the day. At the very least they should estimate the export at 50% of your generation and therefore subtract that off your import readings. Do you have historical readings to go by, i.e. before you had the solar installed? Our import is down 25-50% depending on the time of year, around 35% is probably about average so far. What is your average generation over the same period?

Thanks SDJ, I appreciate your support.
We do have some historical readings but of course they are not as detailed as those taken since we installed Solar PV.

In previous years we've used around 6250 units - around 17 units per day.

Since the installation (Nov 2012) we've apparently used an average 18 units per day (4772 units, 266 days).

This figure includes the exported unused units during the sunny days and does not show the reduction in daytime electricity import which we know is there but cannot quantify.

Our average generation is 10.5 units per day.

I agree with your figures - I even said to them that I'd accept a figure of 9 units per day credit but they rejected that!

So now I'm pursuing a complaint (4 weeks in so far) and although I've found out a lot more in that time, they don't seem to have learnt much. The first proposal from the complaints (feedback) team was to suggest I might want to go back to my previous supplier, E.ON, "because as a large supplier they'll probably have a system for dealing with this situation"! :rotfl:

"We won't charge you the early departure fee for leaving in the middle of the contract ... " :T :j :beer: :A

You can imagine the stunned silence at my end of the phone!

I am not trying to be greedy - I don't want a generous offer (well, OK, perhaps a little) - I just want an accurate one. Given that data is in the meter, it seems crazy to accept a low guesstimate!

We continue!

Oscargrouch

jkpaul wrote: »

You can imagine the stunned silence at my end of the phone!

I am not trying to be greedy - I don't want a generous offer (well, OK, perhaps a little) - I just want an accurate one. Given that data is in the meter, it seems crazy to accept a low guesstimate!

We continue!

And continue, so you should. Erics shown savings on import gives a good idea of what can be done when you have Solar and Savvy. Quote data like that to them, that's better than a bad guesstimate..Go for It ! :j

EricMears

Oscargrouch wrote: »

And continue, so you should. Erics shown savings on import gives a good idea of what can be done when you have Solar and Savvy. Quote data like that to them, that's better than a bad guesstimate..Go for It !

Whilst anyone is more than welcome to use any of my data (suitably anonymised of course) I'd hate to claim that my apparent import savings are accurate.

I'd like to think that I'd been able to use (say) 75% of my own generation - but with total generation of only 3550 kWh a saving of 5000+ kWh obviously depends on other factors. Delighted as I am with the experience, I really can't think how I've done it.

A major saving will have occurred when our son went up to uni - but that was in Oct 2009 so my 'base period' already includes that saving. I think the new fridge-freezer happened after the base period but really don't believe that could have saved anything like the 10kWh /day I'm looking for. Apart from those, everything else seems the same.

I'm inclined to suspect I might have some sort of meter error - but it's not the obvious 'meter running backwards' fault so I'm more inclined to believe the meter is working correctly now but could have had a temporary fault a few years ago so don't feel the need to advise my supplier (who wasn't my supplier then) of the situation.

Ferdy147

EricMears wrote: »

We started generating Tuesday 16th. August 2011 at 13:45

2012 is of course a leap year so I’m working things out today – 365 days later. I guess if I wanted to be really accurate, I ought to add on a quarter of whatever we generate between now and same time tomorrow (but I won’t bother).

TGM reading at 13:45 today was 3550 kWh. (which compares very well with the inverter reading of 3544. I can live with a 0.17% error ).

Total FIT claims will be £1633.69 (that includes the effect of the April 1st price rise) which represents a 13.07% ROI


Imported electricity savings are a bit harder to estimate. Compared with July 2009-10 (last year for which comparable figures are available), we appear to have saved 3249 daytime units (say £325) and 2125 night ones (say £105) - a total of £430.

Probably not true to claim all of that as SP contribution. I have of course become more aware of power usage since then and we've also replaced an old fridge/freezer with a modern (& hopefully more efficient) one, but if it were true, ROI increases to 16.5%

Thanks for that....we have a 3.92kw system and are hoping for generation figures similar to yours. Ours was installed in Feb so we still have just under 6 months to go to get to the 1 year mark. The good months are almost gone.....

sly_dog_jonah

jkpaul wrote: »

Thanks SDJ, I appreciate your support.
We do have some historical readings but of course they are not as detailed as those taken since we installed Solar PV.

In previous years we've used around 6250 units - around 17 units per day.

Since the installation (Nov 2012) we've apparently used an average 18 units per day (4772 units, 266 days).

This figure includes the exported unused units during the sunny days and does not show the reduction in daytime electricity import which we know is there but cannot quantify.

Our average generation is 10.5 units per day.

I agree with your figures - I even said to them that I'd accept a figure of 9 units per day credit but they rejected that!

So now I'm pursuing a complaint (4 weeks in so far) and although I've found out a lot more in that time, they don't seem to have learnt much. The first proposal from the complaints (feedback) team was to suggest I might want to go back to my previous supplier, E.ON, "because as a large supplier they'll probably have a system for dealing with this situation"! :rotfl:

"We won't charge you the early departure fee for leaving in the middle of the contract ... " :T :j :beer: :A

You can imagine the stunned silence at my end of the phone!

I am not trying to be greedy - I don't want a generous offer (well, OK, perhaps a little) - I just want an accurate one. Given that data is in the meter, it seems crazy to accept a low guesstimate!

We continue!

Hi jkpaul,

I've done some calculations based on your previous consumption per day, your generation per day and your (import+export) per day which your meter has been incorrectly adding together.

The calculations are based on the important assumption that your household consumption of electricity has not changed since you had the PV installed. In other words, you haven't started consuming more electricity in the household, and you haven't reduced it either. The important note is that I'm referring to consumption (i.e. what your appliances, lights used), not import, generation or export. Since this assumption is what electricity companies rely on to estimate customer usage, they should be OK with that.

Lets define some variables:
C = your consumption per day in the house, both before and after PV was installed. This you said was 17kWh/day, before so we assume the same after installation.
G = Generation/day = 10.5kWh/day
E = Export/day, unknown
I = Import/day, unknown

Since your meter adds I and E together, we know that:
E + I = 18kWh/day
...which is what the meter is currently recording since the PV was installed.

But we also know that your consumption will exactly equal what you import plus what you generate minus what you export (since power can just vanish!):
C = I + G - E = 17kWh (if the assumption about consumption before/after installation is valid)

So adding in the G which you know to be 10.5, we can rearrange to:
I-E = 17-10.5 = 6.5kWh/day

but we also know from above that:
I+E = 18kWh/day

Therefore we can solve the simultaneous equations to show that:
I = 12.25kWh
and
E = 5.75kWh

So in other words, your meter has been over-reading by 5.75kWh/day on average, and should be recording 12.25kWh per day. This means you are exporting on average 54% of your generation, which seems reasonable.

Therefore on this basis, the offer from your company of a credit of 9kWh/day is very generous: I eat my words from last night, but I didn't have all the facts in my defence.

If the assumption is wrong, and your consumption of electricity has decreased for example due to replacing old appliances with more efficient ones, say by 2kWh/day then the import reading should be lower (11.25kWh/day) and the export amount would be higher (6.75kWh/day).

On the other hand, if you are consuming more electricity since having the PV installed (eg heating water with an immersion whereas before you used another fuel) then the import reading would be higher and the export would be lower.

In fact, their offer of 9kWh/day credit is effectively saying E=9kWh. Punching the numbers into the formulas means that consumption would have had to drop to 10.5kWh/day from the previous 17kWh/day (a drop of 40%), and that you would have been using only 14% of your generated electricity and exporting 86%. All in all, its a very good offer (but you did mention its only for some of the period since installation, because you switched suppliers?).
Hope that helps, and good luck :beer:
PS Hope you've got the new meter installed now!

Martyn1981

EricMears wrote: »

I think the new fridge-freezer happened after the base period but really don't believe that could have saved anything like the 10kWh /day I'm looking for. Apart from those, everything else seems the same.

Hiya Eric, not an electrician, so a little out of my comfort zone, but could the old fridge freezer have been slightly faulty, and been running most of the time, rather than cycling. This could account for quite a sizeable amount of leccy.

Other than that, it might be down to awareness, but as you say, those are huge savings, so you were either 'unaware' before, or are now the poster child for PV educational side-effects - I bow down to you sir.

Mart.

zeupater

EricMears wrote: »

Whilst anyone is more than welcome to use any of my data (suitably anonymised of course) I'd hate to claim that my apparent import savings are accurate.

I'd like to think that I'd been able to use (say) 75% of my own generation - but with total generation of only 3550 kWh a saving of 5000+ kWh obviously depends on other factors. Delighted as I am with the experience, I really can't think how I've done it.

A major saving will have occurred when our son went up to uni - but that was in Oct 2009 so my 'base period' already includes that saving. I think the new fridge-freezer happened after the base period but really don't believe that could have saved anything like the 10kWh /day I'm looking for. Apart from those, everything else seems the same.

I'm inclined to suspect I might have some sort of meter error - but it's not the obvious 'meter running backwards' fault so I'm more inclined to believe the meter is working correctly now but could have had a temporary fault a few years ago so don't feel the need to advise my supplier (who wasn't my supplier then) of the situation.

Hi

What do use your nighttime electricity for ? ... that's probably the best place to start .... HW or HW & heating, morning/evening electric showers ? .... any changes in your usage patterns ... draughtproofing, insulation, cylinder jackets ...

On a direct comparison you've also accidentally & unfortunately chosen the wrong two years to compare ... winter 2010/11 was uncommonly cold and winter 2011/12 was uncommonly mild ....

To put into perspective, we used the same amount of logs last winter as we did the year before and usually top-up with gas heating when the log-burner can't cope .... Dec'10+Jan'11 gas consumption was over 4400kWh whilst over the same period the following winter only around 400kWh was used... a year-on-year difference of 4000kWh over 2 months which should be a consistant figure even is we didn't have the log-burner ... I know a number of people who topped up their heating with electric fan-heaters for long periods when the temperatures here didn't rise above -15C even at midday during Dec'10 ...... definately something to consider ...

HTH
Z