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Orientation, glazed area, occupants, background load, how much you cook, how much washing is done, how many teenagers you have that leave windows and doors open continually. It’s very difficult to isolate the space heating requirement from everything else IMHO FWIW. Arotherm plus 12kW heating 1970s house, 200m2 or so, consumes 5MWh pa for space heating.

How strong is your floor

Battery storage is a key requirement. I'm looking at this as well, the idea is to set the ASHP to draw less than the inverter is capable of producing for DHW generation, then tweak via automation the cylinder set point (upwards) when batteries are approaching full and still charging, maybe 5°C up each time, to help use the energy on-site. Since the ASHP will multiply the PV energy generated, when eventually the batteries are full and the tank at 70°C the there will be more left over for feed-in than if an immersion diverter were to be used (and it will cost nothing to implement other than my time). At least that's the theory.

For the benefit of the search, I reached out to the manufacturer who provided the following detail: The priority for the inverter is set time charging > home use > excess solar power for battery charging. Therefore, the inverter charges the battery in the day time when there is more than enough solar power.

@ToughButterCup I can across this definition of the RS485 MODBUS interface, if you like tinkering: https://www.scss.tcd.ie/coghlan/Elios4you/RS485_MODBUS-Hybrid-BACoghlan-201811228-1854.pdf

@ToughButterCup - can you help me understand the battery charging capabilities of the product? I’d like to charge at night (on e7) which I see in the manual there is a timed program for, but also have it charge from the PV in the day as normal. The manual isn’t clear whether setting a timed charge program will stop it charging from PV?

Just leave it on standard variable and benefit from the cap, for now, at a bargain 31p per kWh.

I am looking for the total depth required for these batteries once the cabling is all done on the front. If you have these and are able to measure the installation depth required that would be very much appreciated.

You obviously haven't met my teenagers! 430kW a month...

By heat exchanger, I meant a plate heat exchanger that provides hydraulic separation between the property heating circuits and the ASHP circuit, so that glycol is only needed in the short ASHP circuit between it, the DHW cylinder, and the heat exchanger. There is always a temperature drop across them and hence this increases flow temperatures and reduces COP.

@mediaNen - I let the DHW cylinder go cold yesterday and ran a legionaries cycle over night. 250 litres heated (according to the pocket sensor) from 18°C to 67°C - 14.2kWh. DHW consumption 6kWh and environmental yield 8.5kWh, total 14.5kWh. 4.17 is very good; I presume you have under-floor heating and probably no heat exchanger? For February, with average temperature of 6.8°C my system achieved 3.4.

The main thing @designerC with retrofit is that the way the system is used likely needs to change - if replacing a oil or gas boiler say 20kW with a 10kW ASHP, it will need to run twice as many hours to produce the same amount of energy. When designing the system, focus relentlessly on reducing the design flow temperature and sizing pipes enough to provide 5K drop across radiators.

For those with smart meters, register them with loop - it will show the 'phantom load' and simulate the impact of solar and battery.

It's been at or around 70p for ages before hand. Also prices quoted are usually exc.VAT (at 5%)

I have an Arotherm plus 12kW with radiators set to a 0.65 curve. Over the year the average COP for heating is ~3.45. For interest: At 28p per kWh on the cap from April, 8.1p per kWh effective. Gas will be 7p on the cap, 90% efficient, so 7.7p per kWh effective. Oil currently about 88p per litre and 90% efficient so 8.9p per kWh effective

Thanks. I'm really interested in the backup power capability of the unit. Do you have batteries attached to it?

Any concerns or experiences with this inverter please: Datasheet-Solis-RHI-3-6K-48ES-5G-EN.pdf (zerohomebills.com)

One way to check would be to let the DHW go completely cold, then heat it to some temperature. Since you then know the quantity of water heated and by how much, as well as the consumption and yield to do so, it can be checked with some degree of certainty. By observation, we know that the working number is greater than yield/consumption and from the manual, "The working figure is the ratio of thermal energy generated to the operating current used." My understanding is that yield is the energy collected across the coil. So thermal energy generated would then be consumption + yield - losses. Though I've not seen it written anywhere directly.

Thank you @PeterW - much appreciated. I don't mind having separate batteries. The ASHP is 5.4kW max draw (20A) and 12kW output. Those boxes look very interesting.

I'm looking for a PV system that can also run off-grid and with a small generator attached. The Sun 8k hybrid seems to do everything I need. But the solar companies are telling me that micro-inverters are the way to go. In the end, are the advantages of the micro inverters worth the extra cost? The idea of a single inverter which can take PV/Grid/Generator inputs and charge attached batteries is pretty attractive, not least because with 8kW output it will also run my heat pump.

The COP is (Yield+Consumption)/Consumption roughly - more like 3.7

Thanks. Is it also the case that the battery (which has an emergency outlet) will not charge in a grid failure situation?

Thanks. I was concerned that feeding back to the grid, or generator in this case, with excess PV might cause some issue.

I’m looking to have an 18 panel array with Enphase IQ7+ micro inverters installed, with an 8kWh GivEnergy battery, GivEnergy 3kW charge controller, and Eddi for immersion control. However I would also like a manual changeover switch with a comando outside for a small inverter driven generator. Question is: can the changeover can be used with the solar and storage? if so, what would need to be specified to do this. Keen to retain the solar and battery functionality when on generator as it will greatly reduce the generator size needed. Many thanks!

The 5K dT is because this provides an average surface temperature only 2.5K less than the flow temp so minimising flow temperature required. The reason for balancing flow rates is to minimise the temperature gradient across the buffer. But the heat pump water pump is running a short loop in 28mm pipe and will likely be achieving 2050lph (the flow rate is shown on the heat pump interface btw). The radiator circuit is likely a smaller pump through much more resistance so will probably always be lower.