Considering more solar and a battery

Screwdriva

Reed_Richards said:

Screwdriva said:

I would and have expanded my system to the maximum with no regrets. Hard to say for certain but the installers I use have had great success with PW3 DNO approvals. 

But I presume all these installers are in much the same area?  My impression is that different DNOs, and probably considering different locales, can take quite different views.  Is there any database you can look up to find out what others in your neighbourhood have been allowed to install?    

Incorrect. I do my best to help individuals across England & Wales and have similar (albeit very recent) results across all DNOs (except South Devon, where the grid infrastructure limits export limits for some reason). Another great example is the 2024 approval for 16kW system (1 X 10kW + 1 X 6kW SolarEdge inverter) in Colchester. Both inverters connect to an GE All in One battery and 44 Eurener bifacial panels. 

UKPN is the best of them all. When I met with Tesla Solar, they shared they  had invested resources in educating utility companies on the benefits of their systems and it is paying dividend for them. 

NedS

Martyn1981 said:

Hi Ned, not important, just pondering, but are you still planning on dropping the Fox inverter and putting both strings through the PW3, or going to see what the DNO say, and work from there?

I assume that the PW3 could grab the export from the Fox (actually export from the house) and put it in the battery, along with the direct PV generation on its DC side. But there would then be DC to AC to DC losses.

Still thinking out loud, I suppose you must be removing the Fox inverter, or the DNO will add all the PV together .....just curious as this is an unusual query/decision, but one I can see happening more and more in the future as folk upgrade/revise existing systems.

@Martyn1981 Yes, I have options.

We already have a Fox ESS 3.0kW inverter with exiting solar array.

We are adding a further 3.56kWp and Tesla PW3 with 11.04kW output rating.

My preferred (although I'm happy to be persuaded otherwise if anyone has a clear argument to the contrary) solution is to disconnect the existing inverter and wire that solar PV string into the PW3 (DC coupled).

If I leave the existing Fox inverter, then I'd be requesting DNO permission for the existing 3.0kW plus an additional 11.04kW for the newly added PW3 (with newly added 3.56kWp added to the DC side), so I'd need a total of 14.04kW, or I would have to limit the PW3 output.

If I remove the existing Fox inverter and put both the existing solar array and new solar array (7.2kWp in total) into the PW3, then because they are DC coupled, I only need export limit for the PW3, so 11.04kW max.

There are pro's and con's for leaving half the solar AC coupled, but mostly I'd prefer it DC coupled to maximise our allowable peak discharge rate from the battery. If the DNO were to only give me 6.68kW, if 3.0kW solar is still AC coupled, I would be limited to 3.68kW discharge from the PW3 which may not be enough to always power the home when multiple appliances are turned on. Having all of the solar DC coupled gives me the full DNO permitted limit, up to the capability of the battery (11.04kW)

NedS

When I was initially discussing with the installer, who has experience with DNO applications in my neighbourhood (they have done a few properties just around the corner), I asked how much they thought the DNO might offer, and they immediately replied 6kW so I'm assuming that is what other local residents were offered. Maybe they had less solar though (6kWp), as that is the driving force behind wanting 7kW DNO export.

greenbee

I've just had DNO approval for an additional 5kW export, taking my total up to 10kW, so am going to go ahead with the installation (we've been given a commissioning deadline of early May). I'm only a couple of miles from an interconnector, and surrounded by solar and wind farms, so I suspect that my installation is inconsequential compared to what else they have going on! 

NedS

We've just had the DNO offer back, and it's not good news.

They will allow the increased solar (to 7.2kWp) and the PW3 can be installed with the inverter set to 8kW (great, no clipping in summer), but they have limited export to only 1kW.

With such a low export limitation, there is no way we will be able to use/store/export the generation for much of the year. We will actually be worse off in summer as we already generate twice what we use each day and export 2/3rd of it. We really need to be able to export a decent amount in summer to make the numbers remotely stack up, but with a 1kW export limit, our bills will increase in summer as there's no way we can use, store or export 7.2kWp of generation from our unshaded south facing roof. I'm really keen to maximise the solar installation to benefit the winter months where we can store/use everything we generate for the ASHP.

I've asked the installer to go back to the DNO and see if they will trade some generation capacity for a higher export limit, but I'm not hopeful.

Alternatively, I wonder if I can add a PW3 to my existing solar (replacing existing inverter) with the inverter settings limited to 3.68kW under G98 without requiring prior approval? Edit - apparently a PW3 limited to 3.68kW can be installed under G98, but home backup requires a G99 application regardless, so that's not a great option either (having to pay for a Gateway but then unable to use it's most useful feature)

Martyn1981

Wow, that's a shock. Is there any chance it's 1kW 'more', so 4.68kW export limit (3.68 + 1)?  4.68kW export, with a DC side battery will work, I think.

I've got 6.725kWp ESE + SSW going through a 3.68kW AC limit, but the DC battery acts as a buffer, so I'm not getting any clipping, so long as I empty out enough of the battery early, so it can 'catch' the extra, whilst exporting the 3.68kW limit.

For instance, today I started exporting at 5.30am, with the battery level falling till around 9am when generation started to exceed 3.68kW. At that point the amount above 3.68kW started to charge up the battery, and the trick is to make sure the battery isn't full till about 4pm*, at which point generation has fallen back down to ~3.68kW.

Hope that makes sense, and the times will of course differ based on system size and orientation.


*Actually slightly more complicated for me, as I have a 2kWp WNW system, and as that generation rises, I've noticed the other system dials down 'throughput' below 3.68kW, as it's apparently limiting actual household export to 3.68kW, something I didn't know it would do.

Screwdriva

NedS said:

Alternatively, I wonder if I can add a PW3 to my existing solar (replacing existing inverter) with the inverter settings limited to 3.68kW under G98 without requiring prior approval? Edit - apparently a PW3 limited to 3.68kW can be installed under G98, but home backup requires a G99 application regardless, so that's not a great option either (having to pay for a Gateway but then unable to use it's most useful feature)

Technically, yes this is possible as you are not exporting any additional amount to the grid (theoretically, you could replace a 5kW SolarEdge inverter with a Fronius unit without informing the DNO. Same goes for panels too). Your installer could even re-apply for a G98 (good hygiene) and receive it automatically! 

As a worst case scenario, you are able to install the PW3 as a battery inverter only i.e. no gateway. You'll save ~£500 (~£7K installed),but will need the Tesla remote meter to manage the system. But I don't think you are there yet...

As shared previously, I believe you are well positioned to challenge the DNO via your installer to preserve your G98 allowance (which is the minimum allocation to all) via a G99 application. I have yet to see a single instance of them not accepting this when legal notices are issued. Your home insurance legal cover (assuming you have it) should be able to issue a "letter before action" to the DNO's legal team at no cost to you. Ask me how I know this  

Qyburn

NedS said:

I've asked the installer to go back to the DNO and see if they will trade some generation capacity for a higher export limit, but I'm not hopeful.

It may be just terminology but the DNO has no interest in generation capacity. They are only interested in the AC side which would be the output from the inverter(s) including the inverter in an AC-coupled battery.

If you have compliant export limitation in place then the DNO is likely to set two limits, export, and total system size. Their interest in the total is because export limit is imperfect so they need to assess the effect if your total power was exported. SSEN told me they looked for less than 1.3% voltage rise due to export, and no more than 2.3% from total. Noting that in my case they didn't assess network impact, only my connection.

 Based on that your "total system" size would be 14kW if the PW3 was unlimited, and that would be the case even if you had it set to disallow export.

 Since you already have the 3kW inverter, presumably with no limit, are you sure the DNO are not offering a 4kW export total?

NedS

Thanks all for the advice.

The installer have informed me the offer is for 1kW total export. I can certainly call the DNO to confirm this if folks think this is likely incorrect.

Martyn1981

NedS said:

Thanks all for the advice.

The installer have informed me the offer is for 1kW total export. I can certainly call the DNO to confirm this if folks think this is likely incorrect.

Thanks for the update. Does sound odd to me, I don't think I've ever heard of such a low figure before, especially as you already have 3.68kW (is that right?)

Are they actually suggesting they would be minded to reduce your limit. I hope something is being missed in translation here.