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Hi all,

I've had a reply from our DNO, Western Power, regarding adding more solar/batteries. We already have a 4kW array from 7 years ago, for which we receive FiT payments, so plan to leave that system alone so we don't affect the payments. Their reply in regards to a query from our electrician installer is:-

Hi xxx,

I’ve run the study here and unfortunately here you could only install g98 or g99 FastTrack level generation (a total of 7.4kW limited down to 3.68 for export) without LV and transformer upgrades.

If you’d like to move forward on that basis let me know.

So, unfortunately it seems like we can only add batteries via G99 fast track, but the battery inverter needs to be limited to zero export so that 3.68kW is not exceeded. This will be satisfied as long as a battery inverter we choose has G100 compliancy and is on the ENA register, is that correct?

I'm hoping to get some Pylontech batteries, US3000C's, and add a AC coupled Luxpower Squirrel inverter if I can get hold of one, if not then Solis/Sofar AC inverter will do the job, but Lux seemed better due to being able to charge/discharge up to 3.6kW rather than 3kW from the others. From my research any of these will be good to satisfy the DNO I think, or will the DNO need a specific export limitation device added to ensure 3.68kW export is never exceeded?

Then the next issue is adding extra solar PV panels,? We're looking to add 2.5-3kW roughly. The only way I can see to do this is to directly couple new solar to the Pylontech batteries via their own battery charge controller? I assuming the Pylontech batteries will work fine with both a AC coupled Lux inverter and then a Victron? charge controller connected to them?

Would the only other way to add extra solar PV be a hybrid inverter, with both new solar and batteries connected up to it, but then this wouldn't benefit from the existing 4kW array being able to charge the batteries which kind of defeats the point of getting the batteries in the first place for us.

Any advice/comments appreciated. I dont think our electrician/solar installer will have connected up a system like this before with panels directly charging these batteries so would like to get things straight in my head to help persuade him, as I think he wants to use a Puredrive/Huawei system due to having installed them before, although I'm not sure yet how he would plan on adding extra new PV to those.

Thanks.

Sounds like a plan. A G100 certified battery inverter would ensure you never export more than 3.6kW.

You can couple as much solar as you like to your batteries and the DNO isn’t involved. A few people on here have done that.

Another option for summer when you’re generating more than you can use/store is an off-grid inverter for your hot-tub or granny EV charger. This again would be none of the DNO’s business…

Right now you cannot be picky about battery model! US2000, US3000, US5000 you have to buy what you can find! (Although my back is in spasm just thinking about the US5000).

Having a look this morning and found this. What a chancer!
https://www.ebay.co.uk/itm/185416765273 ... 7Ciid%3A10

Bargaintastic! Shame I'll have to pass right now.

As an alternative to a DC coupled new solar array to the batteries, would it be possible to install the solar PV as normal, and then use something like - https://www.itstechnologies.shop/collec ... tracker-dc this Solis inverter which has export management built in, so as long as you use it with its CT clamp, you set it to the export limit of 3.68kW and it will shut down and the DNO limit of 3.68kW export wont be exceeded?

I can't see or understand why this wouldn't be ok, but the sentence in the DNO's reply above about 'a total of 7.4kW limited down to 3.68kW' seems to imply for some reason that its 3.68kW from the existing solar inverter we already have, and then new 3.68kW from the new batteries inverter, so another inverter for the solar PV, even if limited so as not to exceed a total of 3.68kW export, wont be accepted for some reason? Am I understanding this correctly? Anyone know why if so and whats the point of the 7.4kW value, surely that could be any number as long as the export limit is imposed? And any chance to persuade the DNO to accept any amount of installed generation, as long as the export is limited to 13A overall?

I dont know the answer but i do wonder how you can detect total export from 2 sources batt and PV with only one CT clamp if that is what you are proposing.

I think the DNO is perhaps thinking what happens when the batts are full and both your systems inverters could be exporting what are you going to do ?
OK totally switch off the new system.

What are you going to do when both systems are exporting say 2.5kw ea. OK cut off the new system and loose the export tariff if applicable. I can envisge a lot of on/off switching of the new inverter from loads and clouds. In fact it could almost get itself in a loop. The old system exporting 3.5kw so the new system switches on but then immediately switches off for exceeding the 3.68kw.

I am confused and cannot help thinking just do what you wish and tell nobody. Just do not touch the FIT system.

The CT clamp for the Solis export detection goes around the incoming grid mains cable. So it doesn't know if the export is coming from solar array 1/2/3? or batteries, all it knows it the value, and if you set it to 3.68kW, then if export goes above that, it scales back/turns off. I don't know if it would fully turn off, or just reduce its output so as to not exceed the 3.68kW. Like you say, if its a full on/off as a result, it would be doing a lot of short cycling on/off which I cant imagine is great, and I imagine it can scale.

The only downside to a sep system charging your batteries via a charge controller is that if the stack gets up to 100% then the 2nd system will switch off while the fit system will just export to grid.

I deliberately keep my stack quite low to give it a couple of hours charging headroom. Stack size Is important as is other stores of energy so you can have enough in the tank even quite depleted to get you to your next tou charge window if you mistimed something or the weather changed.

It works well for me.

But if the battery stack is up to 100%, and you had the separate new PV system on its own inverter not a charge controller, all it would be doing is exporting to grid anyway? So whether it's via a charge controller and hence turned off at stack=100%, or via its own inverter and exporting at stack=100%, it doesnt make a difference does it to your utilisation of the new PV generation, you wont be losing anything in either situation would you?

pudding wrote: ↑Mon May 16, 2022 10:20 am But if the battery stack is up to 100%, and you had the separate new PV system on its own inverter not a charge controller, all it would be doing is exporting to grid anyway? So whether it's via a charge controller and hence turned off at stack=100%, or via its own inverter and exporting at stack=100%, it doesnt make a difference does it to your utilisation of the new PV generation, you wont be losing anything in either situation would you?

Yep, I would then be looking at another export payment for the second system if that were even possible or going with the charge controller, less cost and less hassle. I am not at core altruistic. I see no attraction in giving power to the grid and not being paid.
Horses for courses.

Just noticed that you are solar pv only with a grid tied inverter. No batteries or hybrid inverter existing within the approved fit system? Different story then. Looks like it's an approved hybrid set to zero export and batteries then. Can you source an approved hybrid that also doubles as an inverter?

In what way?

From my viewpoint, I can't really see it making a difference connecting new solar PV via a charge controller or inverter in terms of using what it generates.

In the case where the batteries are full and house requires power, over what the existing 4kw array can provide, if the new solar is connected via a charge controller, then it can't provide the extra directly, and the batteries will, with the new PV then charging the batteries as they are used. OR, new solar via an inverter would provide that extra power directly and the batteries stay at 100%. End result should be the same in each case shouldn't it, approximately? Just it's simpler and cheaper with the charge controller.