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Author Topic: pv array size increase  (Read 4247 times)
AlanM
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« on: December 29, 2011, 02:57:47 PM »

Hi
quick question re the rules governing the increase in an array. I believe that the rules were/(still are?) that any addition carried out within 12 months of commissioning counts as the  first installation, and after 12 months it is a new installation.
 Is this still the case after the last couple of reviews?
Reason for asking is i could raise enough funds to do a small 2kw array soon, and then add another 2 when i have funds, before year end. It may not matter but if the government do another post consultation review, it would be as well to get a registration before they issue the results of the review.( cause more trouble.  )

Alan
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M
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« Reply #1 on: December 29, 2011, 03:03:25 PM »

Whilst the addition counts as the same installation within 1 year, I thought the whole new system was rated as at the amendment date? Or have I got that completely backwards?

Mart.
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Ivan
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« Reply #2 on: December 29, 2011, 04:50:40 PM »

I think Ted posted recently answering a similar question saying that our esteemed leaders have changed the rules on this one, to prevent you doing this.
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Ted
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« Reply #3 on: December 29, 2011, 05:38:51 PM »

Yes, the FiTs legislation was updated in October to remove the 12 month rule for extensions.  All installations now get paid at whatever the current rate is at the Eligibility Date for that part.
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M
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« Reply #4 on: December 29, 2011, 07:30:27 PM »

Sorry Ted but can I be lazy and get your thoughts on this then.

I've got 3.6kWp on my ESE roofs, installed in August.

I quickly became aware that I wouldn't generate any (significant) power after 4pm ish. Not a problem financially, the FITs I'll receive are very generous. However I'd love to produce some energy when cooking dinner 6ish and the sun is screaming in through the front glass, (not all year I appreciate) so...

Problems of shading on WNW roof from chimney and little roof over bay, but I should be able to put one row of panels across and between. 5 regular, or 6 slimmer panels.

Now I know this'll be expensive proportionately, and not a great investment, but happy to balance it out against the favourable returns on the other system.

Long story short, as this'll push me over 4kWp, possibly 5.1kWp, is this then possible now, without affecting the other system?

I'm actually happy to wait for cheaper prices, and even FITs free (the way it's going), but wondered if there were now any time constraints. Slight problem I don't have the money, but one problem at a time.

Thanks.

Mart.
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AlanM
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« Reply #5 on: December 29, 2011, 11:24:00 PM »

Ok, right back to the drawing board then,
thanks Ted
Alan
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Ivan
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« Reply #6 on: December 30, 2011, 12:29:41 AM »

I suspect there are a lot of grey areas - eg if you had 8kW - 4kW on the East Roof and 4kW on the West roof, both controlled (for argument's sake - not in reality for various technical reasons) by a changeover switch, so only 4kW could be connected to the inverter at a time - would that be a 4kW or 8kW system. My view is that it could be conceded as a 4kW tracking system. However, if you've got a 3.7kW system installed now, and plan to increase the size so that more than 3.7kW is connected simultaneously, then it falls outside the December 12th cut-off date.
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GavinA
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« Reply #7 on: December 30, 2011, 12:51:44 AM »

or using a 4000TL, which would limit the output to 4kW (or whatever it's set at) regardless of it having input from additional panels on a different roof.

it's all a bit of a minefield though, one in which I've not yet had to tread.
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M
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« Reply #8 on: December 30, 2011, 08:00:33 AM »

Only my thoughts and assumptions, but would welcome comments.

Current system ESE 3.6 (2.4 + 1.2), proposed addition WNW 1.5. Something about having PV, but not addressing the 6pm peak for some of the year seems wrong to me, so,

Give it 5 years;

FITs will probably be gone (or thereabouts),
Panel developments may bring some potential increase,
Inverter developments may bring some new choices,
Price will be less,
Save up money from current FITs income,
Very poor investment financially, due to orientation, but happy to absorb into already generous FITs income.
If there are no subsidies, then as long as the install is fully legal and compliant, there shouldn't be any approval issues.

One step at a time me thinks.

Mart.
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Ted
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« Reply #9 on: December 30, 2011, 11:23:54 AM »

The 43.3p rate isn't quite gone yet. There is still the Judicial Review (and maybe DECC's appeal) to be heard. So it may still apply to systems installed up to the end of March.

The Total Installed Capacity is the 4kW limit you don't want to go over as the (proposed) 21p would then drop to 16.8p but, as Gavin hints, there are other ways around this by limiting the total inverter output.
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Ivan
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« Reply #10 on: December 30, 2011, 01:15:25 PM »

I thought the FITs were very clearly linked to the rated output of the installed PV, not the rated output of the inverter (otherwise you could install 10kW on a 4kW inverter, and have almost constant 4kW output for a lot of the year).

We've heard of a few PV installations receiving site visits by MCS inspectors within 2days of submitting a generation meter reading above what MCS considers 'expected' for the installed capacity of the system.
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BruceB
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« Reply #11 on: December 30, 2011, 03:16:32 PM »

If you have a look at the legislation, the FIT band an installation sits in is determined by its Total Installed Capacity (TIC).  That has a statutory definition.  Simplifying, the TIC is the lower of the inverter output or the panel kWp installed times inverter efficiency.

So you could put 10kWp of panels on a 4kW inverter, but it would probably not be cost effective.  I have generally recommended 10% - 20% over-panelling compared to inverter output where people have the space and can afford it.  That is a cost effective way to get a good increase in output.  I have always reflected the expected increase in the forecast I put on the MCS certificates.

Overpanelling works particularly well with SE/SW combinations or E/W combinations, where full sunlight does not fall simultaneously on all panels.  For example, with an Aurora PVI-3.6-OUTD inverter, although the maximum output is 3.6kW nominal, each mppt can individually handle 3kW, so it is quite useful for assymetric loading.

Regards
Bruce
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GavinA
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« Reply #12 on: December 30, 2011, 04:16:09 PM »

it's all a bit of a minefield though, one in which I've not yet had to tread.
to be clear, this bit only refers to the addition of a second array to an already installed system.

We've done a fair number of systems with arrays that are significantly over 4kWp either on one or 2 roof faces but limited by the inverter to below 4kW AC output, and I'd generally agree with Bruce's 10-20% oversizing recommendations, though a bit more can be advisable on an east/west system eg upto 6kW of panels onto a 4000TL split at 3kWp per side would be fine.
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M
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« Reply #13 on: December 30, 2011, 05:11:26 PM »

Funny enough, only thinking about larger systems today when out for a stroll.

It struck me, that 4kWp is really just a pretend line, though of course it does have some important coincidences,
1. About the size of a large roof,
2. Similar to DNO ramifications,
3. FITs rules.

But if FITs ends in a few years (oh god do I know how contentious that point is), and if lets say prices drop to 5k in 5 years for a 4, then it may be a better investment to put two 3's on an E/W, possibly for about 6.5k? that way a domestic property gets some more economies of scale. Also opens up the argument that PV is only for south roofs.

I know this is all theoretical, but that would give a nice power supply all day, without a huge peak of export in the middle, and provide 1or2kW's around 6ish April to September(?). This might, and I'm only guessing might be a better financial investment (if no subsidy) than a southern 4. I know money shouldn't matter, but a good investment (savings on bills) is much easier to sell sometimes, than 'save the planet'.

I'm assuming a lot, mainly that the 4 or the 3+3 could use the same inverter, so only a little more work when on site. And higher consumption of approx 4,500 units (3+3), than of approx 3,800 units(4). Not greener, but possibly more economically acceptable.

Mart.
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