Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.
I'm sure someone on the forum must have this situation so..
What happens if you have Solar PV on a house that has an old mechanical meter, one that runs backwards when you are exporting? Presumably your bill reduces at your unit rate (eg around 14p/kwH) in addition to you getting 3p/kWH for what you export?
Is there a problem if two consecutive meter readings imply negative consumption (perhaps due to you taking a long holiday in summer)? Then what happens? Do they insist you have made a mistake or demand you fit a modern digital meter?
You have to tell them that you have a PV installation and they then have to change your meter. Failing to tell your energy supplier that you've fitted PV, and that your meter is running backwards, is probably against their terms and may well be seen as an attempt at fraud.
It's only very old meters that will run backwards, I believe, as the supply companies rolled out ratchet-equipped mechanical meters around 20 years ago, to prevent the reverse auto transformer fraud technique. Later digital meters automatically incorporated a reverse flow detection circuit, that causes the display to indicate when the meter is being driven backwards. This error display may also trigger a fraud alert from a meter reader, and is another reason for making sure your supplier knows your have a grid tie PV installation.
There cannot be many of the old mechanical meters left, they have to upgrade them every 20 years. Does anyone have one of the old coin operated gas meters that could accept a a piece of ice shaped like a 50p, or is that just an urban legend?
When I first got the PV system installed a year ago my old meter ran backwards. I told my supplier and they took three months to come and fit a new digital import/export meter.
As they could not work out what to charge me for import during that time they tried to add all I generated until the day of the new meter install to the then old meter reading and use that as the base to charge me for i.e I would have ended up paying for all I generated and exported as well as what was actually imported. As I kept daily records of all my meters I managed to work out a compromise, but it took until October to get actually resolved.
My parents have a mechanical meter that runs backwards, they have told their provider twice that the meter needs changing but nothing has been done one year on
When I first had PV in my supplier had the DNO come and swap out our ancient model that would probably have burst into flames had it been driven backwards. The DNO regaled me with his view about how PV was a waste of money and a rip-off, and how AGW was a con, etc, and proceeded to fit a new mechanical meter ... that ran backwards the moment the PV was actually connected up.
So it stayed until I persuaded the supplier to spend money on an import/export pair so that I could actually measure consumption accurately. (Cue more whining from new DNO engineer about how I hadn't left enough space on 'their' panel in the consumer unit, etc, even though they had been supplied with dimensions, etc, and could have got it right at fitted at ratched meter as requested the first bloody time...) Turns out that the supplier simply wasn't getting charged for the phantom 'leccy when the meter was going backwards, so didn't feel the need to charge me for it even though I'd carefully estimated usage for them.
On another property I have put solar on, the meter goes backwards, I've told the (same) supplier, and they have not felt the need to send out the DNO yet it seems... (Mind you, I've not had a penny of FiTs out of that install yet, grrrrrrr.)
<blockquote><cite>Posted By: SteamyTea</cite>There cannot be many of the old mechanical meters left, they have to upgrade them every 20 years.</blockquote> lol - I see a fair few of them, and we've got one that's not been touched for at least 34 years and I'd hazard a guess that it's been in place since the 60's or earlier.
Books 
