That's a great opener, @fabz 🙂 

Let me respond to the last point first:

It would be pretty difficult to devise a way to export to the grid without first satisfying the demand from household appliances!
So I think the answer is going to be 'yes'!
If the sun shines, and the Domestic Hot Water (DHW) is already hot enough, then switch on other devices and use that excess electricity.

However, your description raises a number of other issues in my mind.
You might want to copy the following points and put them to your Social Housing Provider.

A: If all the tenants have their own (Smart) Meters, does that mean they receive the SEG payments as a reduction on their bills?
Or does it get paid to the landlord to offset the capital cost of installing the solar panels?

You will probably find that the SEG is so low that it's almost insignificant.

B: An Air-to-Water (Air-Source Heat Pump) should operate all day. It isn't like a gas-boiler which only switches on as required.
For the majority of that time the heat-pump will using peak-rate electricity from the grid (night-time in  summer, and most of the winter).

The only way you'll be able to operate such a system is if the heat-losses from the house are low.
Having adequate insulation is vital.
Have you got a heat-loss survey/report for each property on the estate?

C: Since the solar-inverter is to be grid-tied (ie it can export), your Distribution Network Operator (DNO) will state the maximum permitted output.
The installer or landlord completes a form which confirms the G98 credentials for the inverter.
That max export is usually 3.68kW (16amps), and will be guaranteed by the size/type of inverter.
For that reason your roof is likely to be fitted with just under 4kW of PV panels.

In full sun that's enough to operate the ASHP and direct a small amount to your DHW tank (using an immersion heater and a device called a Load Diverter).
But it's unlikely to supply enough current to start the heat-pump.

Starting a typical heat-pump compressor takes around 25-30A, which means it draws on the mains grid.
In turn, that means it's all the more important that the installer properly commissions the system so as to use as little energy as is reasonable in the circumstances.

If it turns off/on several times an hour, then the efficiency plummets.
Hence you'll be buying in electricity every time it restarts.

That phrase in green is stipulated in Part-L of the Building Regulations.
It's not sufficient for the installer merely to state that the system runs ok!

D: I'd be interested to understand why solar-panels are being installed, but no Storage Battery.

A PV Panel is relatively inexpensive to buy... around £100 per 350-400w panel.
The major costs are associated with the scaffolding and labour in fitting the roof-rails and wiring.

Compare that with an off-grid battery to directly operate a heat-pump... say £10,000 for 13kWh Tesla Powerwall 2.
Because you could then opt to refill the battery only during off-peak times, the cost of electricity is significantly reduced.
What would've been spent on scaffolding is instead invested in a permanent energy storage device.
That significantly reduces the payback period.

Blown away by your response, @Transparent; thanks.
At the moment, some of us are undecided about whether to opt for heat pumps or new storage heaters (27% more efficient than "dreadful"!).
For me it's a no-brainer but it's difficult to make a choice if you haven't got a technical background and you believe rumours of "noise", "ugly pipework", "false efficiency claims", plus the added disruption.
Your confirmation that household appliances are fed first by solar PV is the icing on the cake for this household.

Regarding your other points:
A: I'm assuming that 100% of SEG credits will be made to residents but I'll seek confirmation.
B: I should have mentioned that old double glazing will be replaced and cavity and loft insulation renewed and boosted to minimise heat loss. Once these are completed, a heat-loss assessment will be carried out.
C: We're located in London and fortunate in that all 30 or so properties are more or less South facing (in fact we petitioned for an all Solar PV system but that's another story...).
Thanks for the (new to me) info about the maximum output of the solar array and the start up power draw of the heat pump (30 Amps!).
D: I take your point about the trade-off between the cost of scaffolding and labour, versus the cost of batteries to power the heat pumps (combined with off-peak battery charging).
Each household is being offered a choice between new Storage Heaters or an ASHP. We've waited more than 25 years for this and feel over the moon that our HA has responded positively to our petitioning.
Work is due to start by next month so it's probably too late to propose any major changes. I'll report back on developments as they occur but a massive thank you for the information and advice you've so generously offered.

Hi, I've arrived here via My Home Farm, hoping to get some advice on ASHPs. We live in wet west Wales, and haven't yet made the switch to an ASHP from oil but we're thinking about it! Not sure where to post my questions ...?

@cookie197, welcome to the forums. Start a new thread in our ASHP section detailing your property and the questions you have.

Posted by: @cookie197

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We live in wet west Wales

If that's wet enough for hydro-generation, there would be a lot of interest here in an ASHP unit powered by water 🤔 

Posted by: @transparent

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Posted by: @cookie197

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We live in wet west Wales

If that's wet enough for hydro-generation, there would be a lot of interest here in an ASHP unit powered by water 🤔 

But when it is very cold, the water gets 'lumpy'. 🙄 

Given the extraordinary weather conditions across the world during 2023, I doubt that West Wales will be seeing any more lumpy water.

Have a look at the Satur-M 500-watt vortex generator, and you'll see what what's on my mind.
Prices start at 2500 Euros without an inverter.
That delivers up to 48v and max output of 12kWh /day

That goes a long way towards the electricity demands of a HP, and will produce most of its output in winter when it's needed.

Hi everyone. 

Just finished our self build with a 14kW Ecodan. Now moved and I'm learning how  to drive it!

Questions over how to maintain reasonable hot water temp most of the day, how to see what electricity it's using, what will be best for when CH settings will be best for our underfloor heating etc etc!

Cheers, John 

Hello. 

I have just discovered this forum while searching for help - today just with DHW. Once I've solved that I'll move on to the UFH.

I am enthused and motivated by the long discussion around tuning heat pumps and COP.

I'll start a fresh post with as much detail as I can manage about our system - and the current challenge.

thanks in advance for any help.

Derek

It's good to have you here @tadpole

Posted by: @tadpole

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I am enthused and motivated by the long discussion around tuning heat pumps and COP.

Well indeed!
Let's note here that commissioning the system is a legal requirement under Part-L of the Building Regulations.
Simply running it up isn't sufficient!

Part-L stipulates that it must be tuned so as to use no more (input) energy than is necessary.

Moreover the installation engineer must also train the householder to operate and maintain the system so that it continues to use minimal energy input.

We need a nationwide public-awareness exercise to ensure that everyone knows this.
It's a conversation which should be occurring in the pubs and coffee shops of the country.

Hello.

I live just outside York in a 50s semi-detached house with good loft insulation and cavity wall insulation. I spent last year installing triple glazed windows and new doors. About 3 weeks ago I installed 4.05 kW of Longi solar panels (5 facing east and 5 facing west), a 5.8kWh Solax battery, 3.68 kW Solax inverter and, last but hardly least, a 6 kW Ecodan ASHP. There were a few hiccups with the installation.  After the solar side was wired up my electricity consumption went up 10 fold!  Apparently a "CT clamp" was installed up side down, thus reporting solar input as coming from the grid. Quickly corrected. But it has made me feel rather nervous about the whole project.  I have several questions in my mind and was glad to come across this forum where I might have space to air my concerns.

Posted by: @minos

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Hello.

I live just outside York in a 50s semi-detached house with good loft insulation and cavity wall insulation. I spent last year installing triple glazed windows and new doors. About 3 weeks ago I installed 4.05 kW of Longi solar panels (5 facing east and 5 facing west), a 5.8kWh Solax battery, 3.68 kW Solax inverter and, last but hardly least, a 6 kW Ecodan ASHP. There were a few hiccups with the installation.  After the solar side was wired up my electricity consumption went up 10 fold!  Apparently a "CT clamp" was installed up side down, thus reporting solar input as coming from the grid. Quickly corrected. But it has made me feel rather nervous about the whole project.  I have several questions in my mind and was glad to come across this forum where I might have space to air my concerns.

Welcome to the forum.

Please feel free to ask whatever questions you wish and we will do our best to answer them.