Considering more solar and a battery

NedS

Screwdriva said:

NedS said:

Given our annual usage of around 7000kWh, is doubling the solar array to 7.2kWp reasonable? I'm assuming it's pretty much a no brainer to fill our available south facing roof space? Are we likely to get DNO approval?

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. 

I've just been looking at Intelligent Octopus Flux, and although Tesla batteries are not compatible yet, this does look like the tariff of choice in summer for any large net exporters.

Does anyone have any information when Octopus expect to add Tesla compatibility to Intelligent Octopus Flux?

Martyn1981

Qyburn said:

Martyn1981 said:

I was pondering this part: can the PW3 output be limited/capped? If so, then an export limit of 4kW or so, would be doable, hopefully with no clipping, as the battery is DC side.

For example, even on a good day when the system is generating say 6.5kW, then as long as the battery has been emptied ready, that's over 5hrs of battery charging at 2.5kW (with 4kW use/export) before it will be full.**

Also requires pretty fancy battery management as many systems prioritise battery charge over export, so left to their own devices the battery gets filled up pretty quickly. I have 8.5kWp panels with 6kW inverter and in the Summer the battery can be filled by 09:00.

Yep, I tell mine (in the better gen months) to discharge in the morning, to create space. Good time to charge the BEV(s) unless you are on a good export tariff.

NedS

Martyn1981 said:

I was pondering this part:

Obviously the additional solar array would depend on what the DNO grants us and not worth doing if they do not grant 7kW?

Can the PW3 output be limited/capped? If so, then an export limit of 4kW or so, would be doable, hopefully with no clipping, as the battery is DC side.

For example, even on a good day when the system is generating say 6.5kW, then as long as the battery has been emptied ready, that's over 5hrs of battery charging at 2.5kW (with 4kW use/export) before it will be full.**

If the PW3 can do this, then any DNO export limit of 4kW+ should be OK for you. Although there may be times in the winter when you want more than 4kW output*, but just saying, in case that helps.

*Way out of my depth now, and no idea if the PW3 can do this, but it may even be possible to set a max discharge rate higher than the max export rate (these aren't exactly the same thing). For instance 4kW export, but 6kW discharge, so if you needed 6kW for the ASHP, there would actually be zero export, so in compliance with the DNO.

Apologies if I'm misleading you.

**Edit - Just to say, I have 6.72kWp of PV, running through a 3.68kW capped inverter with no clipping, so long as there is space in the battery, as it can handle (upto) 5kW DC + (upto) 3.68kW AC.

AFAIK the PW3 can charge (from AC through the inverter) at 5kW and can discharge at variable settings between 3.68kW, 4kW, 5kW... up to 11kW peak, as set in software to match the DNO rating.

What I'm not sure is how fast it can charge from a 7kW solar array at peak output if there is no or minimal load - can the PW3 charge at rates higher than 5kW from a DC source as this isn't going through the inverter? (e.g, if we have 7kW generation on the roof and the house is only drawing 500W, for example).

Screwdriva

NedS said:

I've just been looking at Intelligent Octopus Flux, and although Tesla batteries are not compatible yet, this does look like the tariff of choice in summer for any large net exporters.

Does anyone have any information when Octopus expect to add Tesla compatibility to Intelligent Octopus Flux?

I have spoken with a senior leader at Octopus. Tesla is in the pole position in the IOF queue. There are legacy issues on yielding control of Tesla's software that are being negotiated. No commitments were made and no exact timelines were shared but I heard Q1 2025 alot. Till that day comes, it's standard Flux only. 

Martyn1981

NedS said:

Martyn1981 said:

I was pondering this part:

Obviously the additional solar array would depend on what the DNO grants us and not worth doing if they do not grant 7kW?

Can the PW3 output be limited/capped? If so, then an export limit of 4kW or so, would be doable, hopefully with no clipping, as the battery is DC side.

For example, even on a good day when the system is generating say 6.5kW, then as long as the battery has been emptied ready, that's over 5hrs of battery charging at 2.5kW (with 4kW use/export) before it will be full.**

If the PW3 can do this, then any DNO export limit of 4kW+ should be OK for you. Although there may be times in the winter when you want more than 4kW output*, but just saying, in case that helps.

*Way out of my depth now, and no idea if the PW3 can do this, but it may even be possible to set a max discharge rate higher than the max export rate (these aren't exactly the same thing). For instance 4kW export, but 6kW discharge, so if you needed 6kW for the ASHP, there would actually be zero export, so in compliance with the DNO.

Apologies if I'm misleading you.

**Edit - Just to say, I have 6.72kWp of PV, running through a 3.68kW capped inverter with no clipping, so long as there is space in the battery, as it can handle (upto) 5kW DC + (upto) 3.68kW AC.

AFAIK the PW3 can charge (from AC through the inverter) at 5kW and can discharge at variable settings between 3.68kW, 4kW, 5kW... up to 11kW peak, as set in software to match the DNO rating.

What I'm not sure is how fast it can charge from a 7kW solar array at peak output if there is no or minimal load - can the PW3 charge at rates higher than 5kW from a DC source as this isn't going through the inverter? (e.g, if we have 7kW generation on the roof and the house is only drawing 500W, for example).

Don't know mate, but am interested (just for knowledge). But so long as you have a decent export rate, or need the leccy for something, then at least this would allow you to avoid any clipping (like me). So if the system maxes (sustained) at 6kW to 6.5kW then even a 4kW export limit, would allow you to avoid any clipping for about 5.5hrs if the battery starts of empty, or close to empty. [Based on 2.5kW DC being stored and 4kW being consumed/exported.]

Doesn't solve the problem if you can't use the leccy or export at a good price, but assuming you can then I'm hoping that this might put your mind at ease about the economics, if the DNO doesn't allow a higher export limit.

Couldn't resist, so looked up the specs, and on page 2 it seems that 5kW DC is the max, 8kW with additional PW3's.


Edit - I assume (but not sure) that in your example, if you were generating 7kW, and hadn't told it to export, then it'll charge the battery at 5kW until full, whilst sending the 2kW excess to the house, with 1.5kW being exported.

In reality, I'd expect a 7.2kWp system to sustain 80% in long hot conditions (June(ish)), so ~5.76kWp. Perhaps 90% for shorter periods when it's cold, maybe a clear sky in April or October, so that's 6.48kW but less often, and for less time. And for more normal conditions, perhaps in the middle at 85% so 6.1kW. Obviously, it can get spikes when clouds pass, or after a sun shower etc, may even exceed 100%, but only for perhaps 30-60s, so not really relevant to your concerns.

thriftytracey

Our battery is in the loft and the cable runs from the loft into the meter cupboard in the kitchen, a straight run more or less.

Is the Tesla kit owned by the appalling muskrat?

NedS

Thanks everyone for the input.

We've ordered a Tesla PW3 with and additional 8x445W bifacial panels which will give us a total of 7.2kWp of solar (with 11.04kW continuous discharge capability from PW3), so we will see what the DNO offer comes back with.

Martyn1981

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.

Qyburn

When I applied the DNO specified two separate limits, export, and for total system size. My interpretation of what they said is that because G.100 limitation isn't perfect, they have to consider the impact if the full power was exported.  The figures they gave me were 1.3% voltage rise at the allowed export power. 2.3% if exporting at total system size, ie if export limit failed.

Reed_Richards

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?