More PV for my pension?

michaels

So in June we had a 4kwh system installed on our 254 degree roof with an estimated return with FIT of about 7.2%

I am now thinking that my pension returns about 2% in real terms so perhaps I should divert more money from pension into more solar.

So we have a big enough roof facing 76 degrees (16 degrees N of E), 35 degree pitch to fit up to another 6kwh.

Can any one do the maths based on the current FIT and say a 6kwh additional installation costing 6k, factoring in the loss of FIT on my existing input and that we will probably end up exporting 80-90% of the new output? :rotfl:

Thanks

Martyn1981

Hiya. There won't be any loss on your current system, but the new system would be rated at 4-10kWp, since it will be the sum of all your PV.

The only potential loss, would be if the two systems shared an inverter and TGM, in that case, generation would be apportioned by size (not orientation), so you could see some of your better roof gen being valued at the poorer rooves FiT rate. However, given the rooves are so similar, and the FiT rates are close(ish), I wouldn't be too concerned.

Have a look at section 10 of the FAQs for more info, especially the issues of getting permission for a potential export of more than 3.68kW.

Assuming the East roof generates around 700kWh/kWp? Then FiT and export only on 6kWp would be:

4,200 @ 13.65p (11.22 +4.85/2) = £573

there would also be extra leccy savings particularly in the morning. When I added my WNW, my savings went up from around £140 to £180 .... just a thought.

However, this all assumes you can get permission. To optimise the system, with a shared inverter, you'd probably want about 5kW (maybe 6kW) so you'll need to see what the DNO says.

Also, check their workday turnaround time, if it's 45 days (or so) then you won't be guaranteed to get it done before the government does ..... whatever the hell the govt is going to do.

Mart.

michaels

Thanks Mart

Is the DNO the installer? Last time I think I had mine fitted within 10 working days of first contacting the installer, ready to go on 28th June (yes a Sunday) to beat the FIT change.

EricMears

michaels wrote: »

Thanks Mart

Is the DNO the installer? Last time I think I had mine fitted within 10 working days of first contacting the installer, ready to go on 28th June (yes a Sunday) to beat the FIT change.

DNO is the District Network Operator (that you may still think of as the local electricity board).

Getting permission for a 4kWp installation is usually pretty straightforward (esp if capped at 3.68 kWp); going above that might be more problematic.


Martyn is right to warn you of the possible problems with sharing an inverter &/or generation meter. However, it's extremely unlikely that your existing 4kWp system has an inverter that could cope with an extra 6kWp and you just need to make sure that your installer doesn't try to save £25 or so by putting the extra feed through the same meter.

michaels

EricMears wrote: »

DNO is the District Network Operator (that you may still think of as the local electricity board).

Is that UK Power Networks?

EricMears

michaels wrote: »

Is that UK Power Networks?

Very likely - UKPN cover London, the South East and the East of England - but there are half a dozen others it might be if you live elsewhere.

michaels

My maths says a 6k install paying 572 for 20 years returns 7.1% - what am I doing wrong, surely it can't be that high?

michaels

Martyn1981 wrote: »

Hiya. There won't be any loss on your current system, but the new system would be rated at 4-10kWp, since it will be the sum of all your PV.

The only potential loss, would be if the two systems shared an inverter and TGM, in that case, generation would be apportioned by size (not orientation), so you could see some of your better roof gen being valued at the poorer rooves FiT rate. However, given the rooves are so similar, and the FiT rates are close(ish), I wouldn't be too concerned.

Have a look at section 10 of the FAQs for more info, especially the issues of getting permission for a potential export of more than 3.68kW.

Assuming the East roof generates around 700kWh/kWp? Then FiT and export only on 6kWp would be:

4,200 @ 13.65p (11.22 +4.85/2) = £573

there would also be extra leccy savings particularly in the morning. When I added my WNW, my savings went up from around £140 to £180 .... just a thought.

However, this all assumes you can get permission. To optimise the system, with a shared inverter, you'd probably want about 5kW (maybe 6kW) so you'll need to see what the DNO says.

Also, check their workday turnaround time, if it's 45 days (or so) then you won't be guaranteed to get it done before the government does ..... whatever the hell the govt is going to do.

Mart.

Are you 1 or 3 phase supply. Did your DNO actually have to do anyhting for your install? How long did it take. G59/2 - only 92 pages in the guide....

Martyn1981

michaels wrote: »

Are you 1 or 3 phase supply. Did your DNO actually have to do anyhting for your install? How long did it take. G59/2 - only 92 pages in the guide....

Hi, I'm single phase. But 3 phase typically allows 3x the export without prior permission (11.04kW) but you'd need to check.

Obviously the supply cable can cope with more than 3.68kW, since most are rated at 80A or 100A, which is around 18kW to 23kW. However, what the DNO's are concerned about is the amount of leccy being 'pumped' backwards, and the ability of your street transformer, and the small local substation to cope with the total export of all SSEG's in the area (small scale electricity generators).

So all systems have to be registered with the DNO. In the case of 3.68kW (or less) inverters, they are notified after the install, but for anything that could (even if only theoretically) export more than 3.68kW you need to get prior permission.

For the 2kWp WNW extension, I asked nicely, they checked my house in summer 2012, noted that the street had been upgraded to individual supplies in Mch, and OK'd me for 5.9kW. The reason for 5.9kW is that I had to send them the certification documents for each of the three inverters, so they could check they were UK approved. They then added them together, and approved that as a theoretical max. I have asked, and they've answered that they simply don't care if I add more panels, only if I change the inverters for 1 (or more) that total more than 5.9kW.

Hope this makes sense!

Your best bet would be to ring them and ask, you may get a donut, or someone who knows exactly what they are talking about. Ask if it's worth 'asking' officially, which your installer will have to do. Get a feel for what might be allowed, eg only 3.68, or 5 or 6. From there you can estimate what could be installed split across the rooves. I'd link both systems through a single inverter, otherwise you'll be asking to add a huge amount of extra kW.

I genuinely doubt that a 6:4kWp split across E/W rooves would loose much to capping if you could get a 5kW inverter, but 6kW probably better.

SolarEdge also have inverters (I think) that can cap based on export (rather than generation), which might be accepted by the DNO, but you'll need to research. They are also launching the storage system in conjunction with Tesla, but this'll be pretty expensive at this point in time, and again, you'll need to see if this has some sort of export capping package, that might (just might) be accepted by the DNO in lieu of a generation cap.

Almost certain, that none of that will make any sense, I've even lost myself on that one.

Mart.

Martyn1981

Martyn1981 wrote: »

SolarEdge also have inverters (I think) that can cap based on export (rather than generation), which might be accepted by the DNO, but you'll need to research. They are also launching the storage system in conjunction with Tesla, but this'll be pretty expensive at this point in time, and again, you'll need to see if this has some sort of export capping package, that might (just might) be accepted by the DNO in lieu of a generation cap.

Almost certain, that none of that will make any sense, I've even lost myself on that one.

Mart.

Quick explanation. When we talk about capping an inverter to 3.68kW to meet DNO rules, we are referring to a rather crude method, which simply prevents the inverter producing more than 3.68kW.

There are systems, newish, and maybe approved by some DNO's (but early days), that monitor export, and prevent it exceeding 3.68kW. This is a far more intelligent idea, as it takes into account domestic consumption, water heating, battery storage etc etc, before capping generation.

Probably shouldn't have mentioned this, as it might be too late to even consider this route, or possibly a red herring at this stage, since the PV and DNO relationship is still evolving.

Mart.

Ectophile

In case anyone's wondering where the rather obscure figure of 3.68kW comes from, it's exactly 16 amps at 230V.