Solar PV + Battery quotes

Martyn1981

Hiya. Interesting problem.
I doubt the DNO will revise that decision, it's pretty good (I've got 5.9kW). They need to review the number of connections linked to you, and the ability to absorb that export, so I suspect that's the number you need to work with.
You could go bigger with batts, though in the better 6 months you may find that any batt will just be full after a few days in Spring, so there is nowhere for any more excess to go as you probably won't be using much of it at night, and daytime will be covered directly by the PV.
10.5kWp probably means 8kW generation for most of the day in the summer, so you may need to accept capping or find ways to absorb more, such as the water diversion, BEV(s) etc, but I think you will quickly run out of room/uses. For the poorer 6 months you should be OK, especially if you add a small ASHP say 3.5kW, drawing around 700W.

Coastalwatch

Hi CT, have to agree with all that Mart has said above. He certainly pointed me in the right direction from day one.

As previously mentioned we've an 8.85 system with a 6k inverter which caps the system at just that. Unfortunately not the 5.6 kW you require, plus I believe the max a 6kW inverter can tolerate is 9.2 kW!

When looking into limiting the output further on our system in order to make us eligible for taking part in a V2G trial I discovered that with a system incorporating Solaredge then a Modbus can be employed and the output capped down to 4kW.  Because this involved an additional fee plus capping our system to the lower figure just didn't make financial sense so didn't progress further with it, but just might show there is a means available to comply with the DNO.

The larger system really assists in the darker months when output is limited and we don't regret for one minute going with it.

Good luck with what ever option you decide to go with.

Solarchaser

Hi cool techie I would say crack on as you are. 

As the solaredge inverter should have the capacity  (no pun intended) to limit export.
https://www.solaredge.com/uk/solutions/feed-in-limitation-and-metering-solution

If the installers selected inverter cannot do this, then I'd suggest you lean on them to provide this, as at the end of the day its their proposal to you, so in my opinion, they should be providing the solutions. 
And they should be liaising with the dno to ensure this is an agreeable solution.

This would work by only limiting solar production when the export is above your limit, meaning batteries are full, water diverter(s) are full (well water tank(s) are at max temp) and cars fully charged.... in truth some of those may not be true, but you are still exporting too much due to having such a large array, which is a good thing, not a bad thing.

To explore the alternative,  you would likely need 3 or more inverters and around 20 batteries.... thats just no-where near viable, and I'm still not sure dno would be happy tbh.

So in short, id suggest you lean on the installer to resolve this with the dno.
After all you are paying them several thousand pounds of profit for this installation. 

cool_techie

@Martyn1981 , @Solarchaser, 

Kind of confused here.

The installer has suggested, going ahead with the install, since the remaining electricity would be used up by me. Should i be asking for an additional battery?

Thanks. CT

Martyn1981

Hiya. I think the question is too difficult, as there are so many moving parts. I honestly think that in the best 6 months you will have more generation than you can use, and therefore nightime consumption will be quite low, so any batt, any size, will just fill up. For instance, let's say you draw 2kWh overnight, then a battery of 2kWh will be enough. If it's 4kWh, then you'll start the day with 2kWh and just charge up 2 more. If the batt is 10kWh, then again, you'll use 2kWh, and so on. So the battery size is almost irrelevant, it's your demand/discharge that dictates value. Just as an example.
So for those months I think you will see capping despite your best efforts, after the hot water is hot, and the BEV(s) are charged.
But in the lower 6 months, not only will you generate less, so less capping, but with longer nights you will use more from the battery, so things flip around.
I'd suggest aiming for a battery size that makes the most economic sense for the winter, and accepting that you'll have to cap some generation during the day. You may even want to consider some clever battery management, and time of day leccy use, so you don't consume generation early/late when it's lower (and can be exported), but then try to fill your boots, when generation is exceeding the export limit, say from 10am to 3pm. Again, these are examples.
Only my opinion, but I think the packages you describe are great. With DNO limits (on all of us) dictating export, you will never get the system to be perfect, so aim for best fit.

Last thought. Presumably you can add more batts later on? If so, then once you have experience of the system and where the 'problems' are, you can then try to polish it over the next few decades.

Solarchaser

So Mart is more eloquent in explanation,  what I would say is picture a lovely June morning, your 10kw+ array has heated your water tank to max, and your batteries are full by, let's say 1pm.
In the summer you use less leccy, but produce more.
So at 1pm all is full, but you are still generating 10kw+ which is over your allowed max.

Next day you have used some battery and some hot water, but again by 1pm everything is full again and you are exporting everything.
If the inverter is able to throttle back on export, then happy days, if not, im not sure how you get round the dno limit.
And furthermore I'm not sure who is responsible for the limit not being exceeded,  and by that I mean you, or the installer.

As a quick "for instance", in the summer my 17kwh of batteries will not be fully discharged overnight, ill still have maybe half left in the morning,  but by mid morning they are fully charged again, so after that everything is exporting. 

So if the installer is saying go ahead,  then I guess the installer would need to prove to the dno that you won't go above your limit??? 

Definitely you want the biggest array you can get, as in these winter months that extra kwp can give you a helpful few kwh's to keep the winter bills down.
Again as a quick "for instance" my array made a combined 10kwh on Friday, but being winter we used more than 30kwh in the house (I had charged the batteries overnight on octopus go, so ended up exporting 1kwh) and so the batteries never seen much solar charging.

So in some ways it doesn't matter how many water tanks you have and how many batteries (unless we are being super silly), at some point you won't have consumed enough yesterday, to use all of your solar today.

Then again maybe the first question should have been to ask how much energy do you use in a year, if you have a family of 10 who love baths, I suppose its possible you could use all your solar in a huge hot water tank.... I know, im being a little silly, but im aware one user (Michaels i think) had said his house consumes 20kwh a day just in hot water.

If this is confusing,  just refers to Marts answer, the wife has interrupted my typing a couple of times and I kinda lost my train of thought.

EricMears

Solarchaser said:

So Mart is more eloquent in explanation,  what I would say is picture a lovely June morning, your 10kw+ array has heated your water tank to max, and your batteries are full by, let's say 1pm.
In the summer you use less leccy, but produce more.
So at 1pm all is full, but you are still generating 10kw+ which is over your allowed max.

Next day you have used some battery and some hot water, but again by 1pm everything is full again and you are exporting everything.
If the inverter is able to throttle back on export, then happy days, if not, im not sure how you get round the dno limit.
And furthermore I'm not sure who is responsible for the limit not being exceeded,  and by that I mean you, or the installer.

Surely if you've been allowed to have a solar array that exceeds your maximum allowable export rate the inverter should just shut down (or at least switch some panels off) as the limit is approached ?  If the installer has said OK to go ahead they have either put such arrangements in place or would become responsible for any breach.

Martyn1981

EricMears said:

Solarchaser said:

So Mart is more eloquent in explanation,  what I would say is picture a lovely June morning, your 10kw+ array has heated your water tank to max, and your batteries are full by, let's say 1pm.
In the summer you use less leccy, but produce more.
So at 1pm all is full, but you are still generating 10kw+ which is over your allowed max.

Next day you have used some battery and some hot water, but again by 1pm everything is full again and you are exporting everything.
If the inverter is able to throttle back on export, then happy days, if not, im not sure how you get round the dno limit.
And furthermore I'm not sure who is responsible for the limit not being exceeded,  and by that I mean you, or the installer.

Surely if you've been allowed to have a solar array that exceeds your maximum allowable export rate the inverter should just shut down (or at least switch some panels off) as the limit is approached ?  If the installer has said OK to go ahead they have either put such arrangements in place or would become responsible for any breach.

Yep. As I understand it, when a limit is reached*, the inverter will then use the MPPT to select a 'not' maximum power point to track, and thus reduce the power output of the system.
*Old school was the inverter having a cap as agreed by the DNO, but some now have clever export limits (instead of generation limits), which mean the inverter can exceed the DNO cap, so long as the export doesn't exceed it, so household consumption can be included in the generation too. I believe these export systems are being deployed, but I just don't know much about them.

Solarchaser

EricMears said:

Solarchaser said:

So Mart is more eloquent in explanation,  what I would say is picture a lovely June morning, your 10kw+ array has heated your water tank to max, and your batteries are full by, let's say 1pm.
In the summer you use less leccy, but produce more.
So at 1pm all is full, but you are still generating 10kw+ which is over your allowed max.

Next day you have used some battery and some hot water, but again by 1pm everything is full again and you are exporting everything.
If the inverter is able to throttle back on export, then happy days, if not, im not sure how you get round the dno limit.
And furthermore I'm not sure who is responsible for the limit not being exceeded,  and by that I mean you, or the installer.

Surely if you've been allowed to have a solar array that exceeds your maximum allowable export rate the inverter should just shut down (or at least switch some panels off) as the limit is approached ?  If the installer has said OK to go ahead they have either put such arrangements in place or would become responsible for any breach.

Yeah thats what I alluded to above with the inverter capping output, and I believe as Martyn said the mppt moves to a less than optimal point where it reduces output.

I guess I went the long way around asking CT if the installer had confirmed the inverter would export limit, because going by the reply from CT it kinda seemed like installer just said "it will be reet,  you will use it all".

And I assume that the installer would be responsible, but call me cynical, I would also be wary of the installer saying "yeah just sign here, all is fine".

See the other thing is, I dont recall reading anything saying dno's were happy with the export capping inverters, last I read the only acceptable way to cap output was to fit a device costing around a grand.... can't remember what it was called, 4 letters, Lisa or Rita or something. 
*edit. Its called an Emma

Yep I've definitely went round the houses rather than just ask CT if the installer said the inverter would limit output.

So CoolTechie, did the installer say the  inverter would limit export?

Solarchaser

Actually having read Coastalwatch 's contributions again, it seems that there is a president for the dno accepting inverter capping, so looks like it will all be grand, and I'm waffling on about nothing.