So now I have a solar PV system how do I make the most of it???

zeupater

Golauhaul wrote: »

Hello,

I've just joined. Our PV system was installed yesterday. I'm puzzled by the maths, and would be most grateful for enlightenment!

1. I believe that I will in due course be paid under a FiT for 50% of my generated electricity (as recorded by my generation meter). That's at about 43p / KWh. Great.

2. If I generate more than I consume, I see that my analogue old consumption meter goes backwards. That will reduce my electricity bill by about 13p / KWh. In summer, this may be the outcome notwithstanding night consumption.

3. If I consume more than I generate, such that my consumption meter increases its reading, I will have the usual bill, for which units are charged at about 13p.

Now what I don't understand is how it is beneficial to use during the day as much as I can of "my" electricity: Look at these examples:

Example 1: During day I generate 10KW; use none; during night I generate none; use 10KW:

Generation = 10KW of which 50% deemed exported at 43p KWH = +£2.15; Consumption meter reverses during day by 10KW, saving 10 x 13p = £1.30;
Consumption at night = 10KWh @ 13p = -£1.30. Balance = +£2.15.

Example 2: During day I generate 10KW; use 10; during night I generate none; use 0.

Generation = 10KW of which 50% deemed exported at 43p KWH = +£2.15; Consumption meter does not move during day.
Consumption at night = 0. Balance = +£2.15.

Same result.

How does it pay to use by day? Where am I going wrong? !!

Hi & welcome to the forum .....

It's your logic around the FiT payment and deeming which is wrong.

Assuming that your system falls within the 4kWp FiT banding you will be paid 43.3p/kWh for all energy you generate, whether you use it yourself or not, and in addition to this, assuming you don't have an export meter, you will be paid 3.1p/kWh on a deemed 50% of the total generation, so effectively a payment of 44.85p/kWh generated. It is only the 3.1p export payment which is deemed to be 50%.

HTH
Z

John_Pierpoint

If you actually manage to report negative consumption of electricity during the summer, you will have problems getting as negative bill.
I was in this position last year - nothing to do with FiT's but someone had messed up the records and I was being charged for someone else's meter.
I would also expect that a negative reading would get your "faulty" meter replaced with something that could not go backwards - or even worse something that counts the electricity units which ever way they are going:eek:

Here is an interesting example of a meter that always goes forwards, even when exporting electricity.
https://forums.moneysavingexpert.com/discussion/3191844

Golauhaul

Thanks, Zeupater, for clarifying the 50% point.

Nevertheless, revising my examples accordingly, I seem to come to the same result:

Example 1: During day I generate 10KW; use none; during night I generate none; use 10KW:

Generation = 10KW for which paid at 43p KWH = +£4.30; Also deemed 50% export (5KW) for which paid @ 3p/KW = +15p; Consumption meter reverses during day by 10KW, saving 10 x 13p (the cost of each unit sold to me by the Board) = +£1.30;
Consumption at night = 10KWh @ 13p = -£1.30.

Balance = (£4.30 + 15p + £1.30 - £1.30) = +£4.45

Example 2: During day I generate 10KW; use all 10KW; during night I generate none; use 0.

Generation = 10KW for which paid at 43p KWH = +£4.30; Also deemed 50% export (5KW) for which paid 3p/KW = +15p; Consumption meter does not move during day.
Consumption at night = 0.

Balance = (£4.30 +15p) = +£4.45

Same result. Never was too good at sums - but where's the mistake?

furndire

Golauhaul - your figures work because your meter goes backwards - this time of year, as John_Pierpoint says, you will very quickly be in negative consumption of electricity. Make sure your Electricity supplier is aware of the meter going backwards - if you can, record the phone call - the onus is then up to them to make sure your meter is working correctly.
Our Electric suppliers have just done the 1/2 yearly meter read - are others doing the same.

Golauhaul

Thanks, Furndire. You're right. I can now see that the difference is caused by the saving caused by the consumption meter going backwards when I am generating more than I am consuming. Remove that element, and I see that it makes sense to use as much as possible of "my" generated electricity during the day.

At the risk of prolonging this unduly, may I ask why you think I should draw to the attention of my electricity provider the fact that their meter runs backwards when I generate more than I consume (such that in effect I get a triple payment: for generating; for exporting; and for reduced readings on the consumption meter)? I admit it seems a bit dishonest, but is it? What's the advantage of telling them?

furndire

You then are showing that you are not dishonest - I agree its not dishonest, but to me it would be covering my back - you've told them, its now their problem, if they don't chose to do anything about it, (chances are they won't judging by what has happened to others) they can't come back & say you didn't let them know.

zeupater

Golauhaul wrote: »

Thanks, Zeupater, for clarifying the 50% point.

Nevertheless, revising my examples accordingly, I seem to come to the same result:

Example 1: During day I generate 10KW; use none; during night I generate none; use 10KW:

Generation = 10KW for which paid at 43p KWH = +£4.30; Also deemed 50% export (5KW) for which paid @ 3p/KW = +15p; Consumption meter reverses during day by 10KW, saving 10 x 13p (the cost of each unit sold to me by the Board) = +£1.30;
Consumption at night = 10KWh @ 13p = -£1.30.

Balance = (£4.30 + 15p + £1.30 - £1.30) = +£4.45

Example 2: During day I generate 10KW; use all 10KW; during night I generate none; use 0.

Generation = 10KW for which paid at 43p KWH = +£4.30; Also deemed 50% export (5KW) for which paid 3p/KW = +15p; Consumption meter does not move during day.
Consumption at night = 0.

Balance = (£4.30 +15p) = +£4.45

Same result. Never was too good at sums - but where's the mistake?

Hi

The problem is not the sums, just the logic ..... for example, your example 2 does not reflect the daytime saving for using all of the generated electricity in house ..... using your figures thats 10kWh at 13p, so £1.30 of extra savings missing .....

HTH
Z

Golauhaul

Ah! I wonder if I could press you to show me the calculations as they should be, please?

But my principal question - rapidly becoming an obsession! - is to ask someone to show me why (given that my meter goes backwards for units generated) it is best to use electricity when being generated, as opposed to when we might prefer to use it e.g. at night.

Very many thanks.

furndire

In your situation, I tend to agree with you, as least when you are using it at night, you know you have a known amount of KW to use - so are not relying on daytime production which can dip at anytime - ie that great big cloud that knocks you monitor down to zero.

grahamc2003

Golauhaul wrote: »

Ah! I wonder if I could press you to show me the calculations as they should be, please?

But my principal question - rapidly becoming an obsession! - is to ask someone to show me why (given that my meter goes backwards for units generated) it is best to use electricity when being generated, as opposed to when we might prefer to use it e.g. at night.

Very many thanks.

If your meter goes backwards, then it makes no odds whatsoever when you use your electricity.

But firstly check your meter actually lowers the readings rather than just sending the wheeel in reverse - some meters have the wheel going backwat=rds, but a ratchet stops the readings from going down, i.e. those don't credit your usage.

Also, the supplier will likely order a meter change as soon as they find out, and at that time, yo'll have to alter your strategy, and it will matter (a little) when you use your electricity - you can then play 'match usage to generation' which is a very difficult game to play, although most people seem to think it's easy.

I'm not sure what your agreement is with your supplier, but it may be against the agreement to ever drive the meter backwards - not sure whether they have any comeback if you do and don't inform them