That's a good news story, @toodles 😍 

May I comment on the various eco devices you mentioned in your first post:

The Tesla Powerwall is indeed in short supply... as are the technicians who install them. However, they have the best ratio of storage-capacity for £s of the commercial storage batteries approved for connection in the UK.

Even so, the Powerwall spec says it has 5kW output, which is unlikely to be enough to start-up your forthcoming ASHP. Depending on the model you choose, that is likely to require around 25-30A of current when starting, which happens around 3 times/hour.

Do I assume that you have already obtained permission from your DNO for the three grid-tied devices you referred to?

• Storage battery
• Solar inverter
• Heat pump with associated SunAmp store

The first two require G99 approval because they both have the capability to export at 16A (per phase). The heat-pump installation is designated Low Carbon Technology (LCT). It has a demand which is about 50% higher than that anticipated when calculations were done for cabling to the majority of UK houses.

There is no overall formula to calculate what you may or not be allowed to connect. Each house is evaluated separately by an engineer when the DNO receives your application.

You really need to give them all the information at the outset. Don't apply for solar panels first, and then later reveal that you want a heat-pump and/or an EV charger! These technologies interact with each other and can cause over-heating of supply cables, losses at the sub-station or 'brown-outs" (voltage drops below 216v) which affect neighbouring properties.

Please discuss here on the forum if you require further clarity.

JoJu Solar carried out the solar PV installation and the G99 application went in last February and granted after about 10 weeks. Though consideration was being given to an ASHP installation then, nothing definite has been agreed to. I believe that the pump to serve our needs is likely to be approx. 7 kW load.

Regards, Toodles

Oops! I should add that that 7kW pump is likely to draw 1.7 - 2.2 kW approximately.

Regards, Toodles

That's an average electricity input you're quoting there @toodles

It helps you to calculate the running costs, but not the size of wiring or fuse.

Here's an example of a (more common) 11kW unit which I've just picked off the Daikin website:

Look at the coloured boxes I've added to the top and bottom parts of their very long specification page.

An 11kW unit takes an average 3.57kW of electricity to provide the designated output.

At the foot of the table I've added a blue box to show that a single-phase 240v unit is available. And this requires a 25A fuse in the consumer unit.

25A equates to 6kW (at 240v). And that gives us an idea of the power drawn when starting.

Once you know the actual model number of the Daikin ASHP which your installer suggests, then these are the salient figures which need to be checked on its specification page.

These points are exactly what this forum is geared up to discuss with you should you want help.

Yes Transparent, I realise that the fuse rating is indicative of the surge current that needs to be available but also find the minute symbols and text on some websites a little taxing; once I know the actual model proposed, I can re-visit the specification pages and enlarge them section by section to glean what I need. The chap who carried out the survey yesterday should be reporting back with size of unit required once he has ‘done his sums’ concerning heat loss and any changes required to the emitters. Thank you for the invitation to bring the details of the equipment chosen to this forum.

SSEN have been doing a huge amount of work on our street as they have had numerous failures in the last two or three years and are regular visitors to the road - last time, we had five vans, a digger and a mobile generator for about ten days whilst they scratched their heads over five separate holes in the pavement. I don’t think there can be much of the original cabling left now.

Regards, Toodles

@transparent

There are various further things to consider when a heat pump starts to operate.

It is not like starting a Direct On Line (DOL) induction motor, which would normally draw 3 times its normally operating current when it is first started. Modern heat pump compressors are variable speed, so are powered by a Variable Speed Drive (VSD), which basically takes the 50Hz, 240v supply, rectifies it to DC, and then generates an AC supply for the compressor motor, it being possible to vary the frequency of this supply, and hence the speed of the motor. The system may also employ a 'soft start', which reduces the inrush current to the motor. I have noticed with my own A2A ASHP that when is first starts up, the power draw is quite low, but then starts to build up as the compressor speeds up and starts to produce heat energy.

A further thing to consider is that the internal gas pressure within the system will be lower, hence the need to start the compressor to build the pressure back up. It will therefore not be starting under full load conditions.

The power rating in the specification will be at full load operation, and it should also be noted that the 25A fuse rating is also specified for 14kW and 16kW units, which draw a larger full load current.

Fortunately, I think I can rely on the MCS certified installer to ensure the right ratings for the complete installation are carried out correctly - I may have an interest in what they are doing but they should know what they are doing on my behalf!

I have just received the good news from JoJu Solar that Godot is bringing my Tesla Powerwall and it is to be fitted next week!

Regards, Toodles

Hi everyone! This year we have bought an electric car, installed Solar PV + battery and got an ASHP, and I couldn't be happier. I spent all of last year researching this stuff, trying to get my head around it, which frankly was a lot of fun and quite mind-blowing on occasion. Now that it's all up and running, I am addicted to monitoring, tweaking, and learning. This stuff has quickly become my main hobby, and like all my hobbies, it's a bit of a nerdy obsession... Anyway, I can't believe I only just found this website and forum - it looks like an amazing community for sharing experience and expertise. Looking forward to learning and discussing with you all!

Hi @scrchngwsl and welcome. That's an interesting array of eco-electric expenditure which you've made.

Apart from the technicalities and data which you're obviously enjoying, how do you now feel about your household's ability to:

1. better cope with the present energy crisis?
2. import electricity from the grid which is cheaper/greener?

Or do you find that regulations and the available tariffs prevent you from using your new acquisitions as you'd really like to?

... and I'm struggling to pronounce your forum ID. Are there some vowels missing? 😉 

@scrchngwsl, welcome to the forums. Please feel free to start a new topic dedicated to your setup and experiences. Look forward to hearing about it and how you’re faring.

Posted by: @transparent

Hi @scrchngwsl and welcome. That's an interesting array of eco-electric expenditure which you've made.

Apart from the technicalities and data which you're obviously enjoying, how do you now feel about your household's ability to:

1. better cope with the present energy crisis?
2. import electricity from the grid which is cheaper/greener?

Or do you find that regulations and the available tariffs prevent you from using your new acquisitions as you'd really like to?

... and I'm struggling to pronounce your forum ID. Are there some vowels missing? 😉 

Screeching Weasel 🙂

1. Yeah, much better. I've estimated that my bills might actually go down vs last year's, but we'll see!

2. I'm not sure about greener but cheaper for sure. I optimise for (a) minimising grid usage, and (b) using the grid at the cheap overnight rate (Octopus Go), which I'm guessing also makes it greener.

The available tariffs (on Octopus at least) are really interesting, but what limits me from taking full advantage of them is that nothing talks to each other. The battery/inverter, EV charger, and ASHP don't know about each other, so I have to do a lot of manual optimising throughout the day to make sure I'm not drawing more power than the PV / battery is able to deliver. Some of the kit has decent APIs that allow me to both monitor and control the devices, but the Mitsubishi Ecodan in particular doesn't have an API at all and all the workarounds are inadequate.

One thing I'd like to do in winter, when there is no PV generation, is run the ASHP at a higher flow temp overnight when electricity is cheap, essentially using the thermal mass of the (reasonably well insulated) house as a big heat battery. But I can't do this at present, as there is no API or schedule that allows me to set a ramp the flow temp up and down. I do this manually during the day when the solar panels generate excess, but I'd love to automate it all.

Having only had our PV panels working since 13th. August and not registered for export until 6th. September, I am still relatively new to the game too. With the powerwall being fitted next week, we should have a little more flexibility about import and export of energy. The system run by Octopus is probably as innovative as any company’s and staying green does give a warm feeling.

In the early days of PV output, much of our 8.1 kW array capable power was going straight to the grid and the day’s totals were in the 20-30 kW/h range; the rest we were using for the washing machine, tumble dryer (condensing heat pump model that runs at approx 0.8 kW/h), induction hob, 2 x combination microwave ovens and the immersion heater plus a 3 kw/h kettle. Using our solar panel produced power has been easy when the sun stays around for several hours at a time - and greatly satisfying too!

More recently, daily average harvest has dropped to 8 - 12 kW/h and we have not used much grid power during the daylight hours - but that will worsen now I know. At least when we have a battery in the system, we can store what might otherwise have been exported (though Octopus Agile Export is fairly generous really!) during the day when it exceeds our normal demand and use the energy during the low demand times. I shall be poring over the off-peak rates to determine when to charge the Powerwall - and then I hope not to need any ‘on-peak’ power.

This situation will change again when we have an ASHP (probably early in 2023) and this will I hope have as much of its’ needs catered for during the night and if the Sunamp Thermino needs any topping up, this will also be during the off-peak time - this should be straightforward and efficient as the unit will store energy with little loss for days. So Screeching Weasel, you are not the only ‘nerd’ who is enjoying such a venture! Being retired, I can afford to indulge my hobby and make the most of it too.

Regards, Toodles