Newbie Advice Sought

[kla456]

Answering nowty's questions:
So lets begin with your system, you appear to have 7.4kW of PV, but what size and model of inverter(s) do you have ?
SolarEdge SE300 (2) in 2 strings.
Do you currently have any sort of export limitation now ?
Yes, see next answer
Do you currently have approval for 7.4kW export ?
DNO's reply to my application for 10kW expansion to existing 7.4kW array:

Our network study also highlights that the existing export capacity is at the maximum that can be connected at this point of supply, therefore reducing the PV request would not resolve this issue in this instance.

Do you currently get FITs and therefore a generation meter ?
Yes, Yes

On appeal against the 7.4kW restriction, I got a revised offer for a 4kW extension :

With the export capacity restricted to 7.4kW, the maximum power station capacity that can be installed at this supply point is 11.4kW. The power station capacity is the aggregate of all of proposed and existing inverters (i.e. 7.4kW existing + 4kW max additional power station capacity = 11.4kW).

If you would like to reduce the request to an additional 4kW PV inverter but with the total export capacity restricted to 7.4kW, then we would require an updated G99 form and schematic drawing detailing how the system will restrict the export.

I expect to accept the revised offer for a total of 11.4 kW of grid-connected even though I was looking for an additional 9,000 kWh of generation to reach my target of net zero (the 2050 objective) - what do you think?
I expect this can be achieved without disturbing my FIT.

I need to reflect on the rest of your message and will reply later.

[kla456]

Dear Stinsy,
That's a great answer to my questions and a great explanation.
Yes, I am battery hesitant - I have a resistance!
Also, you might have noted my minimal export with the current set-up. Immersuns, 24/7 heat pump, watching the GEO monitor, a home-charged EV, and a sunshine-conscious wife to the Pavlov standard, all make for an efficient set-up with negligible export - no present need for batteries. But, need another 9.000 kWh/annum to get to nett zero and that could bring a new challenge - but not if Rippled?

[nowty]

OK so you actually have 7.4kW of PV and only 6kW of inverter power (2 x 3kW inverters), therefore maximum export of 6kW. However you might have had an export limit from the DNO of 7.4kW from the outset which would have been a G59 application back then.

The DNO has said you can have a maximum of an additional 4kW of inverter power (and that would might a battery inverter) as long as the max export is no more than now or 7.4kW.

FITs complicates matters with your existing system because you need to agree on a system to keep both the DNO and your FIT provider happy. Theoretically you could add 350W of PV panels to each string to keep within the Spec of that inverter, but would need to be agreed with the FIT provider who would dilute your FIT rate slightly. But that sounds like its too little to be worth it.

A second separate system does not require FIT provider approval and the DNO says you can have another 4kW inverter power and however many panels the inverter spec can take say 5kW or 6kW of panels depending upon the inverter. You could use a 4kW hybrid inverter to which both PV and batteries can be connected (but in this case the batteries are DC coupled). But its the export limiter which is awkward in getting something to work with the existing system.

Something like a Sofar HYD4000-ES
https://www.sofarsolar.com/product-deta ... %206000-ES
That would give you a 4kW inverter and allow 5.32 kW of panels to be added and batteries too. It can be configured for zero export, although that might be an optional add on. There are others on the market including solar edge.

The alternative is as has already been outlined to add an AC coupled battery inverter up to 4kW, add batteries and charge the batteries from a solar array via a charge controller. That still officially requires a G99 application but they generally have the G100 zero export built in.

So for me, the 4kW Hybrid inverter option is probably the best solution and you don't need to use batteries with them from the outset, they can be added later if required.

[kla456]

Ok, but is it not 11.4 kW export limit (subject to a new G99 application) less the 2 x 3kW existing inverters leaving a potential of 5.4 kW for new inverters?

[nowty]

Ok, but is it not 11.4 kW export limit (subject to a new G99 application) less the 2 x 3kW existing inverters leaving a potential of 5.4 kW for new inverters?

Whether the DNO is allowing you an extra 4kW or 5.4kW inverter is debatable and so is whether you have another 1.4kW of additional export allowance or not. Their response to you does not match your current system but it may match what you told them if you said you have a 7.4kW system. They may have assumed you already have 7.4kW of inverter power which you don't.

Fitting a separate system with anything other than a zero export setting is unlikely to work (either practically or with the DNO). It might work slightly enhanced with an export setting of 1.4kW. Otherwise you need to re-design your whole system like I did, then you have a more expensive change and have issues with your FIT provider.

[Stinsy]

Here is what I'd do:

1) Leave your existing system alone so as not to disturb your FiT arrangement.

2) Fit an additional solar array, inverter/charger, battery system to take up the rest of your DNO allowance.

For example the 5kw LuxPower inverter is designed for an 8kWp solar array. It is a cheap-and-cheerful made-in-china inverter, I'm not an expert on every inverter available I just know this one because it is the brand I have, I'm sure other brands do an identical job. But it is a decent example.

See here for the specs: https://www.luxpowertek.com/uploads/BR2020-20-22.pdf

The inverter will target zero export so on a dull day when all your solar together is only pushing a few kW it will put all the excess that would otherwise go to the grid into the batteries no-matter which of your solar arrays is actually producing the power. When the batteries are full, or if the inverter hits its 4kW max charge rate it will allow power to be exported at which point the solar diverters on your hot water tank would kick in and take up the rest of the power.

This would mean that your heat pump and other overnight electricity usage would all be powered by your own solar generated the previous day.

If you wanted even more solar after that you could build an additional solar array to feed the power directly into your batteries (via a charge controller).

[nowty]

Those Lux Hybrid's also have a zero export function, and a max export limit which would be handy if your allowed another 1.4kW of export.

Page 55
Section 6.4.3
https://www.luxpowertek.com/uploads/07_ ... 1.0-26.pdf

https://www.luxpowertek.com/hybrid-lv.html

Depending upon what your DNO agree with,

LXP4k Can have 7kW PV
LXP4.6k/5k Can have 8kW PV

[Paul_F]

• 16 MWh/year seems like a lot for a Passivhaus - do you have a breakdown of what it's being used for?
• It's likely to be easier to reduce consumption than increase generation. Replacing Immersuns with a heat pump is likely to be a good bet since that's likely to reduce your hot water consumption by a factor of 3 or so.
• Washers and driers - how many and what type? Hot fill washing machine might be helpful if a lot of washing is being done and you're using a heat pump for your hot water. Similarly, a heat pump drier is likely to be a lot more efficient than a standard one.
• Are you on single phase or 3-phase at the moment, and is 3-phase available? As a rule of thumb you would be able to get 3x the export on a 3-phase connection, and if 3-phase is easily available it might be a lot cheaper than batteries. It also supports fast car charging overnight, which will be of interest when you get a second car.

[kla456]

I agree with Paul_F's post that I have excessive consumption for a Passivhaus - and only 3 persons in the house. I don't have a breakdown but there are some explanations:

• EV is charged at the house

A granny flat within the 260 Sq.m building envelope, which is rented
[/list]Family sleeps with open windows in spite of heat recovery/fresh air system
[/list]Overzealous washing and cleaning of everything

We already have a heat pump.

I fought many battles over a couple of years about open windows and overzealous cleaning to the point of domestic disharmony.
I've given up on fighting - it's not worth it - now, we consume what we consume. But, I am not allowed sufficient PV expansion for net-zero so energy management should be part of the solution and Octopus Agile/GO app on the phone has brought a new interest in energy management.

Have you noticed that energy reduction quickly slips into increased comfort?

I am on single phase. I believe 3 phase is available - DNO hinted that as a possible option, but I think I can get where I want to be without that scale of change.

Regarding the Passivhaus specification, the house is a bungalow from 1950 extended to 2-storey and brought to Passiv in one refurbishment (2014). I over-egged the spec with 240mm of wall insulation (200mm platinum EPS outside and 40mm warm board inside), plastering outside brickwork for airtightness, quad-glazing, 3 x heat recovery/fresh air external wall cassettes (Vaventis fresh-r), etc. Airtightness posed some challenges on the roofline and eaves. We got to 1.1 ac/h after two pressure checks and left it at that (1 ac/h is Passiv standard for refurbs).

A funny story: I removed the raised timber ground floor and replaced it with concrete and an underfloor heating system. There was a very large space under the timber ground floor which I filled with blocks of 200mm thick floor insulation (high density). I removed the radiators but I kept the gas boiler - waiting to see how the building performed before changing to a heat pump and disconnecting the gas (both done now). Imagine my shock when I noticed the concrete floor gradually sinking leaving visible margins under the skirtings! Took a while to realise that insulation was softening and compressing under the weight of 9" on concrete (6"+screed and tiles). Anyway!

[nowty]

I fought many battles over a couple of years about open windows and overzealous cleaning to the point of domestic disharmony.
I've given up on fighting - it's not worth it - now, we consume what we consume.

I told you we were from a parallel universe, done all that and got the T shirt.

SWMBO insists on open windows, then complains its too cold and can we have the heating turned up a bit. Its already set at 23.5 degrees. Then pollutes the internal air with masses of volatile perfumes and cleaning chemicals.

She runs the washing machine at 50 degrees with additional stain remover and excess fabric conditioner. And the clothes she puts in the washing machine are practically clean to start with. She asked me the other week what tray 1 was for in the detergent dispenser. I dare not tell her its for a pre-wash in case she starts using that too.

I really would like to install a heat recovery ventilation system but fear all my effort would go to waste.