Grid connection limit?

Martyn1981

iotum wrote: »

Thanks Mart.

I'd be splitting it over 2 roofs. Can fit 10 panels SSE facing and rest can go on a WSW facing roof. So I reckon that would work quite well as it would spread the production curve out over the afternoon / evening.

The challenging bit seems to be getting solar installer sales people to understand oversizing. I've been told the limit is actually 4kw - not 3.6kw and that MCS won't let them go over the 4kw limit. They seem to think that if I wanted more than 4kw I'd need to have a higher wattage inverter and put a modbus meter on it to limit export. But the SolarEdge SE3680H can take well over 5kw according to the spec sheet.

Don't worry, loads of installers seem to throw around a casual 4kW as some sort of limit. Bit of background:

FiT's - used to have two small bands 0-4kWp & 4-10kWp (now just 0-10kWp). The Fit rate dropped for the larger system so it became a kind of limit as going for say 4.1kWp meant the whole install got the lower rate!

The DNO - 3.68kW rule (not a limit) that prior permission is needed for larger potential export.

UK roof sizes - based on the original panels (around 220Wp to 250p) meant about 16 panels was a natural limit for most rooves.

These 3 almost accidentally similar conditions sort of became an urban myth 'rule' at around 4kW or 4kWp.


As you say, two orientations means you can probably get away with about 5kWp and next to no capping (fingers crossed) on a 3.68kW capped inverter. If the installers have any concerns then they should be able to install a larger inverter but set it to 3,680W max when they install it, and still report the system to the DNO as 3.68kW, but you can always e-mail Solaredge and ask them for their opinion, just give the location, orientations and panel model (and numbers).

Can I just check, are your rooves only 90d apart, not 180d? Not saying you are wrong as roof designs differ, it's just that a 90d difference will mean that they peak closer together, but 5kWp is probably still OK, and even if they do better and you get some summer capping, it's not the end of the world.

pile-o-stone

I'm not sure I'd touch a solar installer who didn't know that the DNO limit is the 3.68kW AC electricity generated at the inverter rather than the xxxkW DC electricity generated at the panels.

There are lots of articles on the web that discuss oversizing panels for the inverter (i.e. fitting 5kw of panels onto a 3.68kw inverter). Here is a post from Australia, so the limits are different but the theory is the same. There will be more UK specific sites out there, but I really like the simple explanation in this one, plus the cartoon is great as it's me and every other solar enthusiast. The only thing missing is a wife stood next to the chap with a frown on her face

https://www.solarquotes.com.au/blog/oversizing-solar-arrays/

If you have sufficient roof space and could afford to fit the highest output panels (370w is the highest I've seen), then it may be worth applying to the DNO to go above the 3.68kw limit. For a single phase supply (this is what most UK homes have), you can install upto 10kw of solar (that's 10kw at the invertor not the panels themselves).

I applied to add a further 1.5kw to my existing 3.68kw array and the DNO approved it free of charge. A little later I had the idea of fitting a solar pergola to add a few more panels, but this time the DNO said it'd cost me £1500 to 'upgrade the grid' and then I'd be allowed the maximum generation of 10kw. It's not worth it in my case as I don't have the space available to install that much solar.

It's worth asking the question to the DNO, it might cost you a few hundred quid, or nothing at all (except for the £300 admin fee they now charge for the assessment).

iotum

Thanks Mart and pile-o-stone

Yes roofs are 90 degrees apart. House is a mirror image of an L shape with the bottom of it facing south ish -150 degrees. I've asked the installer for a new quote with 16x295w split 8 /8 and a 3.6kw SE inverter. If he comes back saying that would break MCS rules or similar then I'll look elsewhere.

Tempted to fit more but having to consider look of house and neighbours and budget. So might need to save up for the pergola idea. If I ever add batteries then might be a good time to add some.

Heedtheadvice

..........and just to query the retrofit idea to get more generation....
Does that not invalidate certification and any current FIT agreement?


I have though of augmenting my generation capability without measuring it/claiming FIT so that background consumption and early/late day generation (unmeasured) could be catered for getting nowhere near the DNO's limit....


...pending M's cheap battery prediction! :T

Martyn1981

Heedtheadvice wrote: »

...pending M's cheap battery prediction! :T

uummmm, yeah, about that - I'm getting less bullish, the problem seems to be that battery demand is ramping up faster than supply, so my hopes for falling prices soon, and cheap(ish) batts by say 2020/22 are diminishing.

Just heard that Nisan have increased the cost of a 24/30kWh battery pack for the Leaf from $5,500 to about $8,000 ...... that can't be good news!

I might have a quiet sulk, but Wifey will be happy.

Exiled_Tyke

Heedtheadvice wrote: »

..........and just to query the retrofit idea to get more generation....
Does that not invalidate certification and any current FIT agreement?


I have though of augmenting my generation capability without measuring it/claiming FIT so that background consumption and early/late day generation (unmeasured) could be catered for getting nowhere near the DNO's limit....


...pending M's cheap battery prediction! :T

Is there any need to export at all? Is it possible to have this set up so that it supplies the house when there is demand (and may be even a battery in time) but doesn't export that way no FIT (but there was none any way) and no breaking DNO limits?

iotum

"Extensions don't get any FITs, and FiT ends next Mch,"

Ok so seems fair that if you add more panels after the end of FIT then you don't get FIT for the extra panels. But how do you separate the electricity generated from the old panels and the new panels ? Doesn't it all go through the same meter ?

Martyn1981

iotum wrote: »

"Extensions don't get any FITs, and FiT ends next Mch,"

Ok so seems fair that if you add more panels after the end of FIT then you don't get FIT for the extra panels. But how do you separate the electricity generated from the old panels and the new panels ? Doesn't it all go through the same meter ?

Yes, so what you have to do is inform your FiT provider about the size of the extension so that they can apportion generation.

So if you had 4kWp and add 2kWp, then they will take your meter reading and pay you based on 2/3rds of the reading.

In the likelihood that you did the best roof(s) first, then you may find that the extension doesn't generate as much (per kWp) as the original, so you could lose out:

Say the 4kWp generates 4,000kWh pa, and the extension generates 1,500kWh pa, then you'd be paid 2/3 x 5,500kWh = 3,667kWh not 4,000kWh.

The FiT system is not exactly friendly these days, the government has sadly taken a very harsh approach to PV and on-shore wind, but at least they are pro off-shore wind.

Dave_Fowler

iotum wrote: »

"Extensions don't get any FITs, and FiT ends next Mch,"

Ok so seems fair that if you add more panels after the end of FIT then you don't get FIT for the extra panels. But how do you separate the electricity generated from the old panels and the new panels ? Doesn't it all go through the same meter ?

The simplest way is not to put the new panel's generation through the meter by keeping the two systems completely separate. If this can't be done the FIT payment is proportioned according to the size of the original and the new system.

Edit: Hi @Mart, beat me to it with a much more comprehensive reply

Dave F

Zarch

iotum wrote: »

"Extensions don't get any FITs, and FiT ends next Mch,"

Ok so seems fair that if you add more panels after the end of FIT then you don't get FIT for the extra panels. But how do you separate the electricity generated from the old panels and the new panels ? Doesn't it all go through the same meter ?

Just to be clear.

If you put the initial install in this week and then add the extra panels before March, you still won't get any FIT on them. There are no FIT benefits on any extension, even ones before March.

That initial install is a one time hit thing for FIT payments. Hence its really best to try and max out the initial install if funds allow as you'll get FIT on all of it.

In the same way that installing a full system post March with no FIT at all, adding extensions really isn't cost effective as it might take about 20 years to recoup the outlay. With no FIT in place you are solely relying on energy saving costs (ie you using the generated energy).

So if you already put in place 5kWh on the original install, then add say another 2kWh.... are you really going to use that extra 2kWh? You'd need a lot of appliances running at once to make use of 7kWh for example. Obviously EV or battery may change that later down the line?

Whereas with FIT in place on everything, you at least have a fighting chance (usually around 8/9 years depending on install costs) to get your outlay back from the larger install.

Hope that makes sense?