Posted by: @transparent

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Good morning @amiddlemass 

I realise that @jamespa and I  are discussing different subjects with you simultaneously.
Let us know if this is getting too confusing.

I'm going to leave the storage battery issue to one side temporarily, and address only the electricity supply to the bungalow.

Please give your architect, electrician and heat-pump installer the URLs of this topic.

 

It's unlikely that you have the Consents which you think you've received from SP Energy Networks.

There are two entirely separate assessments which the DNO has done:

• G99 application for solar panels, inverter and storage batteries
• LCT application for heat pumps

 

An LCT (low carbon technology) application is also required for any proposed EV charger, although we don't know if you ever intend installing one.

 

Both assessments are made with reference to the local substation transformer, the supply cables to you, and those to your neighbours.

The calculations are dictated by the laws of physics, based on the information which you (or your architect/electrician) have provided.
They cannot be 'adjusted' to make allowances for something which wasn't known at the time.

Physics doesn't work like that.

 

Three things aren't clear to me at this stage:

1: Was an LCT application made for the ASHP system, or was this omitted on the grounds that you intended running them from storage batteries?

We need to recognise that the heating system will be operating directly from the grid (bypass mode) when the batteries are being recharged.
Both demands can operate simultaneously.

 

2: Did any such LCT application make clear that there were to be two 10kW heat pumps?

The DNO process the application by first checking a database held by the Electrical Networks Association (ENA) which has data for all appliances for which grid-connection is approved.

The next stage uses a software modelling tool, into which is fed the supply characteristics for your area.
It's possible that the software only recognised the requirement for one 10kW heat pump.

 

3: G99 applies where there is more than one appliance which can export to the grid.

If there is an inverter which handles connections for both your solar panels and batteries, then that's only one appliance.
A single inverter would already have G98-certification for grid-tied operation.

So why was a G99 application made?

 

Hi Transparent

Thank you for your comprehensive reply.

I will check with the plumber about the LCT application, he has been dealing with the ASHP grant paperwork and did all the specification with an outsourced supplier as part of that.  I expect and hope he has done such a thing, as you say they do run at the same time as the batteries are being charged and I never said that the plan was not to do so - it simply would not make sense to not max out the use of cheap electricty on whatever tariff I end up with.... 

The architect was involved only in the principle of an ASHP being part of the planning application, I dont think they would have got involved on this side. Or are you saying they should have always been involved?   I will check with the plumber / ASHP installer first anyway.

The G99 was done by the solar and battery supplier. My apologies for confusing the two, I had misunderstood your original question I think, but I understand they are different. 

I think he said it needed to be a G99 not G98, because of the size of my installation, 10kw solar and 10kw inverter.  DNO was done before the solar was installed and granted permission for the 10kw inverter is what he told me. 

Solar installer said the MCS paperwork is still being processed and should be with me in the next week or so. I have chased so I can register with Octopus to export spare during summer.   Solar was only installed late Dec so substantially after and totally seperate to the ASHP installation.

Posted by: @adam

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The architect was involved only in the principle of an ASHP being part of the planning application, I dont think they would have got involved on this side. Or are you saying they should have always been involved?

That's going to depend on the nature of your contract with the architect.

For a new-build, it's usually the case that it is given an Architect's Certificate on completion.
You need that for a number of reasons:

• it will be requested by the purchaser's solicitor in the event of the house ever being sold
• it forms the basis on which you can obtain house insurance
• it demonstrates to a Building Control inspector that the calculations have been undertaken by an adequately qualified professional

If you're not going to obtain an architects certificate, and hence be covered under his firm's professional indemnity insurance,
then on what basis will you address the above three issues?

I didn't employ an architect for my contemporary extension to a 1930's West Country farmhouse (photo below).
I created my own drawings, and took it through the Planning Application myself.
And I elected to use the local authority's in-house Building Control dept under a Building Notice arrangement.
So I know that there are other routes available.

For example I've previously used a site-insurance company that specialises in self-builds,
and they passed on the site to be covered by their sister company for the first year after completion.
That formed a base level of documentation which is then 'trusted' by third parties.

Posted by: @adam

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I think he said it needed to be a G99 not G98, because of the size of my installation, 10kw solar and 10kw inverter.

That's not the case.

G99 is concerned with the effect on the grid, rather the the capacity of what's used within the property.

The only reason I can see, which required that application to be made, is because you wished to export more than 16A (3.68kW).

Posted by: @transparent

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That's going to depend on the nature of your contract with the architect.

For a new-build, it's usually the case that it is given an Architect's Certificate on completion.
You need that for a number of reasons:

• it will be requested by the purchaser's solicitor in the event of the house ever being sold
• it forms the basis on which you can obtain house insurance
• it demonstrates to a Building Control inspector that the calculations have been undertaken by an adequately qualified professional

 If you're not going to obtain an architects certificate, and hence be covered under his firm's professional liability insurance,

then on what basis can you address the above three issues?

Architect brief was design (including the SAP calcs which took feedback from the ASHP and Solar suppliers), planning submission, and Building Control submissions and coordination, but not Project Management.  This is a renovation, not a new build if that makes any difference?

So should I expect a certificate at the end given it is a renovation?   

We have had little reason to contact him lately as most of the building control items for this phase of work were inspected and signed off a few months ago, since then its all been internal work like plastering etc.... I will get back in touch at some point but the project is going to take 12-18mths more to complete so a long way to go before final sign off from Building Control and any architect certificate, let alone ever planning to sell or such like.

I appreciate the advice on why its needed though, a solid reminder not to forget!

Posted by: @transparent

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Posted by: @adam

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I think he said it needed to be a G99 not G98, because of the size of my installation, 10kw solar and 10kw inverter.

That's not the case.

G99 is concerned with the effect on the grid, rather the the capacity of what's used within the property.

The only reason I can see which required that application to be made is because you wished to export more than 16A (3.68kW).

Yes you are correct, I do now recall that is what he actually said, he successfully obtained us the ability to export 6.4Kw on a single phase during the DNO application.  I think that was why he said G99 now I think back...

In theory we might exceed 6.4kw generation on an exceptionally sunny day during summer, but that's where the batteries come in to store up any surplus we cannot export in real time. 

The most Ive seen this month was around 3.3kw for a few mins during bright sunshine.  Im told 85% of maximum is a realistic top end, so 8.5kw is possible but not sustained I suspect.  Time will tell...

Posted by: @adam

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Posted by: @jamespa

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Ok that's clearer.

It's a pity about the manifold pumps, they effectively stop the ashp having the control it needs to make sure everything works properly.  I wonder if they are actually needed (did your plumber do the calculations?)

I definitely wouldn't enable dhw and space heating simultaneously, you are likely to lose too much heat to the ufh. 

Ok I will give that a go then.  I think this is such a fundamental change however that I need to do this in isolation of any of the above reinstatement of the volumisers.  If I impact the amount and hotness of the Hot water then my wife complains very quickly that she has had a cold shower.  Making the change to run the two loops together could deffo slow down the hot water production I feel albeit would have the benefit of turbo charging the HEAT loop during the cheap electricity period meaning it would likely turn off after the DHW timer turns off for an hour or so running of the residual 55C heat in the loop for the hot water.

Ive got mixed feelings about how that will pan out, but its deffo worth a try, as you say loosing the HEAT loop for two periods of 2.5hrs a day whilst the DHW kicks in seems to put the UFH on a back footing always.

Ooops - I have just re-read your reply and you said "wouldn't" advise... I mis-read that as "would"!!!!

Ok I will leave it as it is then and focus on the other setting changes, likely on the WC curve first, then after a couple of days try out the volumiser settings learnt from the Chofu manual as per my prior post!

Posted by: @adam

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he successfully obtained us the ability to export 6.4Kw on a single phase during the DNO application.

[...]

In theory we might exceed 6.4kw generation on an exceptionally sunny day during summer, but that's where the batteries come in to store up any surplus we cannot export in real time.

Erm... you mustn't do that!

The configuration of the inverter must limit export to the 27A which the DNO Consent states.

May I explain why...

To make electricity flow from an inverter back to the grid, it must raise its output voltage:

By doing that, your inverter is increasing the grid voltage for all the houses which share the same phase from your local substation.

The parameters within which the grid operates are defined by Section 27 of the The Electricity Safety, Quality and Continuity Regulations (2002).

The domestic supply voltage must be held within 230v minus 6% to plus 10%,
which equates to 216v - 254v.

The G98 Standard against which all grid export devices have been certified, stipulates that the device must switch off within 2mS of the voltage straying outside those limits.
It may only reconnect to the grid after a randomised delay beyond the moment when the grid voltage is re-established within the specifications.
That delay is typically around 1-minute.

So if your inverter takes the line voltage above 253v then it will disconnect itself,
as will all the other inverters of houses on the same phase as your bungalow.

Here's a graph of an inverter which has (correctly) got its export-limitation set at 3.0kW (12A):

It stores the solar-input into the battery (blue) until that is full.
Thereafter it exports solar generation to the grid (red) shortly before 3pm.

But generation above 3kW is discarded, giving a flat top to the graph.

That's a particularly primitive example from 2021.
But it neatly demonstrates the export-limitation operating.

Inverter firmware has progressed a lot over the past 4 years, and I would expect your 10kW inverter to be a lot smarter! 🙂 

You should also not rely on being able to export electricity as a source of revenue.

That facility is still being extended, although commercial solar generation is increasingly being curtailed due to over-supply.

Here's a plot from a prospective connection to the Distribution Grid in the West Country by a solar farm which was then seeking planning permission.

The darker the colour, the less export would be permitted from that site.

You can tell that the 'problem' is due to excess solar generation in the area, rather than wind-turbines, because curtailment will only be applied during daylight hours.

The ANM plot for an area with excess wind-generation looks quite different.

Britain has far more 'Offers to Connect' to the grid than it will ever require.

The Dept for Energy Security and Net Zero needs to instruct Ofgem (the Regulator) to reduce or remove the payments for export from domestic sites.

Every additional site increases the risk that inverters will exceed the 253v limit, resulting in a Cascade Effect as hundreds of other inverters sense the voltage and also disconnect.

It was a Cascade Effect which caused the blackouts across Eastern England on Friday 9th August 2019. A lightning strike on the National Grid north of London caused the immediate, short-term loss of 150MW of ‘embedded generation’. Power was lost to 1-million consumers at 5pm.

You cannot rely on being permitted to export 6.4kW indefinitely.

That assessment is based on the current state of the Distribution Grid in your location,
and your Energy Supplier being permitted to buy electricity from its customers.

Posted by: @transparent

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Posted by: @adam

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he successfully obtained us the ability to export 6.4Kw on a single phase during the DNO application.

[...]

In theory we might exceed 6.4kw generation on an exceptionally sunny day during summer, but that's where the batteries come in to store up any surplus we cannot export in real time.

Erm... you mustn't do that!

The configuration of the inverter must limit export to the 27A which the DNO Consent states.

Apologies I may have worded that badly... I meant we might in theory generate more than 6.4kw with the 10kwp array, however the we would always cap our export at the DNO stated limit.  Anything generated over the cap would be put into the batteries to be exported later in the day once we drop back below the limit.   If the batteries get full before we can sell it, then yes, it would be "lost".

The Sigenstor inverter has AI mode which pro-actively manages expected generation, use, weather forecasts and many other including dynamically reading the daily rates on a variable export tariff such as Octopus Agile Outgoing, to maximise ROI but it is always hard limited by the parameters setup by the MCS installer which are in accordance with export limits in the DNO. 

As a safeguard these are set by the MCS installer and cannot be overridden by customers tinkering no matter what.

I haven't (yet) done any research on the Sigenstor inverter,
but I'm posting a block diagram which is an approximation of your electrics as I've understood from your text-based descriptions.

Please feel free to amend this.

1: I'm interested to know what you believe will remain 'live' in the event of a power outage.

• Most grid-tied inverters with G98 certification will simply switch-off, leaving nothing operational.
• Some will continue to run appliances connected to their "off grid" output, whilst no longer exporting to the grid.

2: What do you think can be run from energy stored in the batteries (when the grid is operational)?

• Many will only used stored electricity (and solar) to power devices on the off-grid output.
• Others will allow all in-home devices to take power from the batteries, but not permit stored charge to be re-exported back to the grid.

The device which makes this distinction possible is the Current Transformer (CT clamp) around the incoming cable from your meter.

Posted by: @adam

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Ooops - I have just re-read your reply and you said "wouldn't" advise... I mis-read that as "would"!!!!

Ok I will leave it as it is then and focus on the other setting changes, likely on the WC curve first, then after a couple of days try out the volumiser settings learnt from the Chofu manual as per my prior post!

Please post back on how you get on.

You need to give some thought to those ufh loops, they can't be allowed to suck energy out during dhw cycle.  Removing the ufh pumps would be ideal but I don't know if the chofu water pump has sufficient power to do without them.  Presumably your plumber did the calculations and decided they were necessary?

@transparent 

Hi Transparent

diagram looks broadly correct I think.

1) in the event of a power failure nothing will work, I know that.  Sigenergy sell a seperate “gateway” device that gives uninterrupted power supply in the event of power cuts. We did not buy one of those.

2) anything can run off the batteries including solar export providing the total capacity on the inverter isn’t exceeded.  

Any excess beyond the inverter capacity or remaining battery life, just comes from the grid.  

In reality when on battery there’s always a delay from the CT clamp to inverter responding to changing loads and some is drawn from the mains as it ramps up to the new demand level.

In theory an owner could top up the batteries with off peak electricty then export it back later in a peak period but with the losses through the inverter each direction and factoring in the duty cycle life on the batteries it would be very unlikely to make sense.

Posted by: @jamespa

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Please post back on how you get on.

You need to give some thought to those ufh loops, they can't be allowed to suck energy out during dhw cycle.  Removing the ufh pumps would be ideal but I don't know if the chofu water pump has sufficient power to do without them.  Presumably your plumber did the calculations and decided they were necessary?

will do, I’ve not made any changes today, I am gathering my thoughts on everything learn from here and the Chofu manual first but I will decide what to change in a day or so.

i think I mentioned before that the builder did the floor, screed UFH pipes and manifolds and spoke with the plumber who amended his ASHP design.  The issue discussed at the time was the impact a thermostat in each room would have, no mention of the manifolds having their own pumps being an issue.

i can realistically resolve the issue by dropping the room temp on each thermostat during DHW cycles so it is resolvable albeit somewhat of a kludge solution.  

With the HEAT loop valve closed there isn’t really too much scope for extracting heat out of the floor, it’s just going to loop it around so more of a case that it pauses putting additional heat in for two periods of 2.5hrs a day. Running the manifold pumps would be a waste of power though for sure.

i still have no real idea why the plumber decided adding volumiser tanks was necessary. I’m going to quiz him tomorrow as powering them seems to cause several issues!

Posted by: @adam

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i still have no real idea why the plumber decided adding volumiser tanks was necessary. I’m going to quiz him tomorrow as powering them seems to cause several issues!

I still am not sure you get the point of volumiser tanks.  They add water volume to the system.  They don't need power.

Grant and others take the opportunity of the existence of a tank to add a backup heater which performs a separate function.  Many volumiser tanks don't have one.

Heat pumps specify a minimum volume of water on the system and a volumiser tank is added if the system volume is less.  Because you have zone valves your system the available volume could be negligible if both valves close simultaneously.  That may be why you need the volumisers. 

It's quite likely your system would be better without the zone valves, heatmisers and volumisers, but without the hydraulic design I can't be definitive about that.  The second biggest mistake heat pump installers seem to make is adding unnecessary complexity (the biggest mistake is oversizing).

Posted by: @jamespa

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I still am not sure you get the point of volumiser tanks.  They add water volume to the system.  They don't need power.

Grant and others take the opportunity of the existence of a tank to add a backup heater which performs a separate function.  Many volumiser tanks don't have one.

Heat pumps specify a minimum volume of water on the system and a volumiser tank is added if the system volume is less.  Because you have zone valves your system the available volume could be negligible if both valves close simultaneously.  That may be why you need the volumisers. 

It's quite likely your system would be better without the zone valves, heatmisers and volumisers, but without the hydraulic design I can't be definitive about that.  The second biggest mistake heat pump installers seem to make is adding unnecessary complexity (the biggest mistake is oversizing).

ok fair point but what’s confusing me, which I have not said, is that as soon as he had installed the tanks he came and apologised and said they needed their own power supply, which I had to pay the electrician to add in, much to my annoyance.  So I guess in my head I wanted to get them working given I paid to have them connected up and thus I’ve been thinking they needed to act out their full capabilities.

Perhaps though he never intended them to be immersion heaters simply add volume as you say.

I don’t think it’s an issue when both manifold completely shut down as the HEAT supply would be turned off then on the ASHP so no volume at all needed but potentially I guess only one small room could remain on with all others off, in which case the point is valid.  I guess the introduction of room stats made the system volume variable / unpredictable.

maybe the answer is simply then to leave their immersion heater aspect disabled permanently and just accept they are inactive volumisers. Could possibly even throw the power supply off to each of them to make sure of it!

I think I proved to myself over the last week the immersion feature seems to be a bad idea anyway even in very cold weather.