Green Building Forum - Extra or missing 40% Feed in tariff for PV

Extra or missing 40% Feed in tariff for PV

James Norton — Mon, 10 Oct 2011 13:53:00 +0100

Recently at a meeting where it was suggested that there is some sort of registration that means that you could be 40% better or worse off if not done correctly... (but offered no more info...)

I advised at the time that the key thing was fully above board MCS certification etc and that there could be minor advantages in choosing one supplier over another but that I would look into it...

Any thoughts...?

J

Extra or missing 40% Feed in tariff for PV

ted — Mon, 10 Oct 2011 13:54:54 +0100

Sounds like BS to me.

Extra or missing 40% Feed in tariff for PV

James Norton — Mon, 10 Oct 2011 14:01:51 +0100

All I wondered was whether different suppliers might be paying more or less on the export tariff...?

..perhaps 40% compared to the others but surely not 40% of the total revenue...?

Unless there is some other overlapping funding...?

J

(but my 1st instinct is to agree with you...)

Extra or missing 40% Feed in tariff for PV

ted — Mon, 10 Oct 2011 14:17:40 +0100

Perhaps they were talking about registration of export meters.

If you are on deeming at 50% when you are actually exporting 90% then, yes, you would be losing "40%" of the potential export income by failing to have an export meter. And different suppliers do handle export meter installation and registration with differing degrees of urgency, so choosing one supplier over another could make a difference. But it would be quite small in the overall scheme of things.

Extra or missing 40% Feed in tariff for PV

renewablejohn — Mon, 10 Oct 2011 14:19:01 +0100

Could this be something to do with oversizing your system. Put a 4kw controller in with 6kw of panels. when sunny dump the 2kw excess but on cloudy days still export your 4kw output. ( round figures used not DNO limits)

Extra or missing 40% Feed in tariff for PV

James Norton — Mon, 10 Oct 2011 14:59:39 +0100

Ted,

That was my thought,

John,

Now definitely something administrative...

J

Extra or missing 40% Feed in tariff for PV

Jeff B — Mon, 10 Oct 2011 15:26:03 +0100

Posted By: renewablejohnCould this be something to do with oversizing your system. Put a 4kw controller in with 6kw of panels. when sunny dump the 2kw excess but on cloudy days still export your 4kw output. ( round figures used not DNO limits)

Renewablejohn: That is an interesting concept. Are there any such systems in operation do you know, or is this just an idea on your part?

Extra or missing 40% Feed in tariff for PV

DamonHD — Mon, 10 Oct 2011 16:08:02 +0100

My system is slightly oversized, ie: 5.2kWp panels with 4.1kWp (continuous) rated inverters (4.5kWp in bursts).

Rgds

Damon

Extra or missing 40% Feed in tariff for PV

renewablejohn — Mon, 10 Oct 2011 16:08:07 +0100

Just thought it was standard practice until somebody tells me it is illegal.

Extra or missing 40% Feed in tariff for PV

DamonHD — Mon, 10 Oct 2011 16:15:18 +0100

It's not good to go *way* over spec since it may throw away to much potential generation on the best days and may even damage the inverter. Some oversizing should result from comprehensive modelling I think.

Rgds

Damon

Extra or missing 40% Feed in tariff for PV

ted — Mon, 10 Oct 2011 16:41:25 +0100

UK guideline is to size the inverter at 80% of the panels kWp. And many manufacturers are now producing inverters that can be 'capped' at 16A output (3.68 kW) in order to meet the stricter DNOs G83 requirements.

Extra or missing 40% Feed in tariff for PV

Gavin_A — Tue, 11 Oct 2011 23:41:40 +0100

probably related to installers accidentally registering systems as stand alone, which is easily enough done due to it being the first option in the list IIRC, which is daft given that it accounts for less than 1% of all installations.

easy enough corrected as well mind, providing it's spotted before it goes off and gets processed by the supply company. I've no idea what happens if it's not caught until after it's fully registered, but I can imagine it would be a pain to sort out.

Extra or missing 40% Feed in tariff for PV

James Norton — Wed, 12 Oct 2011 09:07:33 +0100

Posted By: Gavin_Aprobably related to installers accidentally registering systems as stand alone,

...stand alone...?

J

Extra or missing 40% Feed in tariff for PV

Nick Parsons — Wed, 12 Oct 2011 09:13:38 +0100

Off-grid.

Extra or missing 40% Feed in tariff for PV

renewablejohn — Wed, 12 Oct 2011 09:22:15 +0100

Posted By: DamonHDIt's not good to go *way* over spec since it may throw away to much potential generation on the best days and may even damage the inverter. Some oversizing should result from comprehensive modelling I think.

Rgds

Damon

What if you put some super capacitors in parallel to even out the generation by discharging during cloudy periods

Extra or missing 40% Feed in tariff for PV

DamonHD — Wed, 12 Oct 2011 09:29:30 +0100

Worse in many regards I suspect.

For a start they wouldn't help when you have sustained clear skies and bright sunshine when you'd be losing potential generation. Carrying energy for more than a few seconds (eg until after the sun starts to go down) would require *huge* supercaps. Fill your loft, empty your wallet. The whole point of most grid-tie is to avoid needing expensive storage while getting the energy used effectively.

Secondly I suspect that many inverters rely on the 'constant current' nature of PV to protect inputs components from damage, and a supercap wrongly placed could blow that assumption out of the water with huge current surges. (There are often small electrolytics on the inputs for some smoothing though I suspect.)

Thirdly, supercaps do not naturally enjoy the high voltages typical of a grid-tie PV array, so an elaborate charge-balancing mechanism might be needed; complex and possibly leading to energy losses in its own right.

But that's only a WAG or three.

Rgds

Damon

Extra or missing 40% Feed in tariff for PV

ted — Wed, 12 Oct 2011 09:33:59 +0100

"Stand alone" for FiTs means directly connected to the grid, not via a dwelling.

But the FiT for this is currently 8.5p rather than the 43.3p for a â‰¤4kW dwelling so doesn't account for a 40% difference. More like 500%.

Extra or missing 40% Feed in tariff for PV

James Norton — Wed, 12 Oct 2011 09:48:25 +0100

Posted By: ted"Stand alone" for FiTs means directly connected to the grid, not via a dwelling.

I think this is where it might come from (the 40% could well be a red herring). The array in question is on one block of 2 blocks of 5 apartments and is connected to the landlords supply...

Is there any way around this for example connecting to one of the ten apartments (perhaps one that was being rented rather than sold...?

J

Extra or missing 40% Feed in tariff for PV

GBP-Keith — Wed, 12 Oct 2011 12:19:26 +0100

James, why don't you contact the person (who told you this) at the meeting you were at and get them to qualify their comment. Was it in a presentation or just off the cuff during tea break?

Extra or missing 40% Feed in tariff for PV

GBP-Keith — Wed, 12 Oct 2011 12:34:51 +0100

Posted By: tedPerhaps they were talking about registration of export meters.

If you are on deeming at 50% when you are actually exporting 90% then, yes, you would be losing "40%" of the potential export income by failing to have an export meter. And different suppliers do handle export meter installation and registration with differing degrees of urgency, so choosing one supplier over another could make a difference. But it would be quite small in the overall scheme of things.

I was quoted Â£2000 for an export meter by EON and frankly they would have still probably refused to install one if I had paid up. They are only interested in paying the 50% of generation for domestic pvs because i don't think they have 'the machinery' for dealing with oddballs!

I briefly looked into a 50kW system on the ground but due to a number of factors (not least cost and uncertainty of the economic climate) I plumped for an 8.9kW system (I wanted 9.9 but my shed was not big enough).

The most significant worry about this was the fact that I have had to stump up over Â£4000 for Western Power to change out their transformer. Locally (west wales) they seem to be forcing anyone who wants over 3.6kW system to do this.

I toyed with trying to keep the whole generation offgrid but it would have cost me about Â£7000 more in inverters (namely a Sunny Island) and my installer worked long and hard to convince me that my generation potential would be way less if I stayed off the grid with this particular array.

Extra or missing 40% Feed in tariff for PV

GBP-Keith — Wed, 12 Oct 2011 12:39:57 +0100

Posted By: tedUK guideline is to size the inverter at 80% of the panels kWp. And many manufacturers are now producing inverters that can be 'capped' at 16A output (3.68 kW) in order to meet the stricter DNOs G83 requirements.

I'm pretty sure that my installer is oversizing the inverters that he is using on my system. I'll check with him. I might have thought it was unwise to install inverters that are sized below the full potential of the panels. My experiences with pvs indicate that they can easily exceed their rated output. I have also been hearing stories of failed (or certainly in need of attention) grid tied inverters.

Ted. Is the capping that you refer to above being introduced so that systems can be installed without the need to change transformers?

Extra or missing 40% Feed in tariff for PV

jamesingram — Wed, 12 Oct 2011 12:46:16 +0100

Supplier such as SMA suggest inverter size 90-110% of array size
capping is to make installs fall into G83/1-1 requirement, which only require installer to inform DNO post installation
so much simpler all round

Extra or missing 40% Feed in tariff for PV

James Norton — Wed, 12 Oct 2011 13:10:40 +0100

Posted By: GBP-KeithJames, why don't you contact the person (who told you this) at the meeting you were at and get them to qualify their comment. Was it in a presentation or just off the cuff during tea break?

I tried but what I've described is about the best he had. I got the impression that what my colleague heard was...

"....blah blah blah... environment.... blah blah... hippy stuff.... ...blah.. blah... PV... ...blah... blah... lost some money by filling out the wrong form...!!! ...blah blah..."

J

Extra or missing 40% Feed in tariff for PV

ted — Wed, 12 Oct 2011 13:44:45 +0100

If it is on a building then there is no reason for it to be on the 'stand-alone' tariff.

The definition is "not attached to a building and not wired to provide electricity to an occupied building".

Note the 'and'. This means that for the 'stand-alone' tariff to apply the system must be both:

a) not attached to a building
and
b) not wired to provide electricity to an occupied building

If either part a or b is not true then the whole is not true. And I would have thought that just being connected to the landlords supply would be enough anyway. The 'stand-alone' category was really created to handle solar farms where 100% of the generation goes directly to the grid for use elsewhere.