ASHP Water Tank and Solar Excess..

[MMcGill]

Hi all - I've read lots of the threads on this but haven't really found a decent solution - I may have missed something!

 

I've recently completed my self-build. I have the following;

 

1 - Three Phase power supply

2 - EcoDan ASHP and Water Tank

3 - Solar 13.5kwh on the various roofs 

4 - 10kwh of battery storage (looking to increase to 15kwh)

 

My challenge is that I generate significant excess of solar since April, probably about 20-30kwh a day... I don't have an electric car yet and if I did would only make use of that excess when the car's at home! Ideally I'd like to optimise the hot water...

 

The ASHP hot water heats 24x7 at the moment and tank temp is set to 50 degrees - ideally I'd set the 24x7 to something less, lets say 40 degrees and then set a preset to come on during peak sun, lets say 11:00-15:00 at a much higher temp - lets say 60 degrees... I'd then hope that the use of showers etc wouldn't drop it much past 40 degrees meaning most of the hot water is always being generated by the solar....

 

Bit of a faff and relies on me figuring out presets (has anyone taken this type of approach)...

 

The only alternative would be something like a MyEnergi Eddi - but... using the immersion wouldn't be as efficient and more important - I'm waiting for the three phase one to become available!

 

What approach have you done and what can I learn!

 

Many thanks! 

[Conor]

Off peak tarrif and time ASHP to heat water then. Sell excess solar during the day - if you have an export agreement with your electric supplier. For me, the off-peak rate and microgen export rate are the same, so I still prefer to load off peak, and let excess solar go to the grid. 

[MMcGill]

If only - I forgot to mention - Octopus have been absolute rubbish - I'm still waiting for a working Smart Meter (and have been since October last year)... 3 phase is a challenge for them all (lack of qualified engineers), on top had a faulty comms unit, then the comms unit couldn't get a signal... now waiting for an SKU2 comms unit to hopefully sort that - based near York...

Edited June 12 by MMcGill

[JohnMo]

12 minutes ago, MMcGill said:

ASHP hot water heats 24x7

I don't let mine do that, it's available to heat from midday to midnight. Found that work fine. I also have a diverter to immersion. If it's sunny ASHP doesn't come on.

 

But keep it simple, you won't be popular if you mess up. I would keep ASHP set as is, possibly change the times. You have a battery use a cheap immersion timer to switch on immersion at asset time. Or set up some logic - if PV generation is x_kWh and battery is above x% switch on immersion for 30mins, repeat (no idea how you do that but it's been mentioned before).

[MMcGill]

If only the ASHP could be 'smart' enough to know when the PV generation is in excess and boost the tank temperature - that would be perfect, perhaps Home Assistant - but beyond me....

 

I agree - an immersion option would be best, will likely go down the Eddi Three Phase route when it's available.... looking to future proof as much as possible...

[Mr Blobby]

13 minutes ago, MMcGill said:

Ill likely go down the Eddi Three Phase route when it's available.... looking to future proof as much as possible...

 

Why do you need a 3 phase Eddi?

 

Surely it's a single phase immersion and the Eddi nets the total of 3 CT clamps on the meter tails?

[JohnMo]

Is this 3 phase?

 

https://www.tradesparky.com/solarsparky/accessories/miscellaneous/growatt-groboost-hot-water-diverter?affiliate=product_feed&utm_source=product_feed&utm_medium=product_feed&utm_campaign=product_feed&gad_source=1&gclid=CjwKCAjwjqWzBhAqEiwAQmtgT4NybsNmb99vZxGAhTc2mgxifbz38oME_ZzdKHxk_z65l8binR9gvhoCGFYQAvD_BwE

[PhilT]

You have an enormous battery, isn't it easier to let the battery power the heat pump, then it doesn't matter if the sun and water heating are out of sync, the battery always buffers between the two, making best use of excess solar

Edited June 12 by PhilT

[MMcGill]

1 hour ago, Mr Blobby said:

 

Why do you need a 3 phase Eddi?

 

Surely it's a single phase immersion and the Eddi nets the total of 3 CT clamps on the meter tails?

Good question - I assume that as I'm three phase I need a three phase Eddi, certainly their website asks what your power is and points you to that version (coming this summer). Does the single phase have three clamps as an option - I thought it only had one?

[MMcGill]

1 hour ago, PhilT said:

You have an enormous battery, isn't it easier to let the battery power the heat pump, then it doesn't matter if the sun and water heating are out of sync, the battery always buffers between the two, making best use of excess solar

I don't seem to be able to live within the battery - showers all happen 6-7am which creates quite a load to reheat - the battery has pretty much been depleted through the prior evening (cooking dinner etc) and night by that stage

 

[PhilT]

57 minutes ago, MMcGill said:

I don't seem to be able to live within the battery - showers all happen 6-7am which creates quite a load to reheat - the battery has pretty much been depleted through the prior evening (cooking dinner etc) and night by that stage

 

Try what you suggested, but only during the day 11am-3pm. You must have a few shower hungry people in your house. A tank full at 60degC would last me 3 days, but there are only two of us.

[SteamyTea]

2 hours ago, MMcGill said:

showers all happen 6-7am which creates quite a load to reheat

Shorten the shower times.

My shower uses the same amount of water as a bath half decent bath full.

Edited June 12 by SteamyTea

[Mr Blobby]

6 hours ago, MMcGill said:

Good question - I assume that as I'm three phase I need a three phase Eddi, certainly their website asks what your power is and points you to that version (coming this summer). Does the single phase have three clamps as an option - I thought it only had one?

My understanding is that myenergy devices talk to each other over Ethernet so 3 phase zappi is connected to meter tails and then to Eddi over cat 6.

You must be installing an EV charger, right?

 

[MMcGill]

Yes - Already have the 3 phase Zappi installed, was required to get house signed off (no electric car quite yet though!)

 

[joth]

What battery do you have? (And what inverter is it connected to?)
Rather than worry about the PV at all, really the main thing you want to know is "Is the battery full". Whenever it is, then put the ASHP into "DHW boost" mode. The ecodan this is fairly easy: you need a relay to close input IN11 (the so-called Smart Grid Ready feature) which tells it a switch-on recommendation. Then in the settings, you configure a DHW target temp boost of +10C or whatever in the smart grid settings -- see page 22 of the FTC6 installer manual

 

 

The tricky bit is knowing the battery is full - very battery dependent. 

 

 

 

Note I'm assuming that you can charge the battery at the rate of excess energy generated, i.e. 13kW minus your base load. If you are limited on the battery charge rate you may indeed want to trigger the DHW boost sooner, based on grid export exceeding a threshold or PV generation above a certain level.  this should be possible from a correctly shelly energy monitor, and a 240V coupling relay to connect into the FTC6 - see https://www.instructables.com/Shelly-EM-Auto-Toggle-Based-on-Solar-Panels-Produc/

 

 

Edited June 13 by joth

[Wil]

My version for the OP is:

 

I use HomeAssistant in the middle of batteries and solar and ASHP. I have 3phase heat pumps, single phase immersion in a 300ltr UVC. 5kWp solar and 26kWh batteries.

 

ASHP is set to 24/7 keep the tank above 48degrees.

Batteries charge overnight on cheap electric car tariff, bit of morning usage knocks them down to approx 90%.

2x grown ups shower in the morning pre-solar, 2x kids in the evening, post-solar.

If sun comes out during the day, solar boosts batteries back up. If batteries change above 95% and solar >500W (just a check to make sure the immersion doesn’t come on when charging batteries at night with cheap rate- if the batteries go up during the day it can only come from solar) then-

I turn the immersion on (limit stat set to max). It heats the tank for 1hour or until the batteries drop under 85%. If the immersion is on and batteries hit 98% (solar still > immersion)  I turn the car charger on. Then boost the ASHP buffer tank. Until it all drops back to 85% battery and I let the batteries take the solar until it hits 95% and kick off again.

If the sun doesn’t shine enough, the batteries hold my house load and if the tank drops below 48, the ASHP kicks in to top it off.

 

TL;DR Basically use the batteries as a diverter for solar to immersion. Forget complicated 3 phase or trying to use the ASHP. Let the solar pump the immersion and take the tank to max (about 85dC in my case- make sure you have anti-scald fitted!).

[JohnMo]

On 13/06/2024 at 16:54, Wil said:

My version for the OP is:

 

I use HomeAssistant in the middle of batteries and solar and ASHP. I have 3phase heat pumps, single phase immersion in a 300ltr UVC. 5kWp solar and 26kWh batteries.

 

ASHP is set to 24/7 keep the tank above 48degrees.

Batteries charge overnight on cheap electric car tariff, bit of morning usage knocks them down to approx 90%.

2x grown ups shower in the morning pre-solar, 2x kids in the evening, post-solar.

If sun comes out during the day, solar boosts batteries back up. If batteries change above 95% and solar >500W (just a check to make sure the immersion doesn’t come on when charging batteries at night with cheap rate- if the batteries go up during the day it can only come from solar) then-

I turn the immersion on (limit stat set to max). It heats the tank for 1hour or until the batteries drop under 85%. If the immersion is on and batteries hit 98% (solar still > immersion)  I turn the car charger on. Then boost the ASHP buffer tank. Until it all drops back to 85% battery and I let the batteries take the solar until it hits 95% and kick off again.

If the sun doesn’t shine enough, the batteries hold my house load and if the tank drops below 48, the ASHP kicks in to top it off.

 

TL;DR Basically use the batteries as a diverter for solar to immersion. Forget complicated 3 phase or trying to use the ASHP. Let the solar pump the immersion and take the tank to max (about 85dC in my case- make sure you have anti-scald fitted!).

Have reread the above with interest. Have had a PV diverter, which failed. I think with batteries a normal PV diverter may not do the best job. As you say use the battery as buffer for the PV, run a 3kW immersion at 3kW rather than micro switching at low wattage. Just limit the run time but leave as something meaningful. I have added my ASHP as the first port of call to divert excess electricity. ASHP has a double set point, so use a Shelly relay to switch to a higher flow temp than normal WC to buffer heat into the floor. Will set the second threshold at a slightly higher battery SoC, to then divert to immersion.

 

Basic kit for the immersion divert is a Sonoff POWR3, a manual switch to allow the Sonoff to be bypassed manually, total spend £45. If the smart relay fails it's £30 to replace. Diverter is silly money and not really needed with a battery. If you get paid for export, just export 

 

[Wil]

@JohnMo My goal was to limit/ avoid peak electricity use hence the batteries as the buffer to allow for the sun going behind a cloud etc. If I let my ASHP (18kW 3phase) take the solar, I can’t guarantee it won’t pull way more than the solar can give. Once it starts the HW cycle I don’t want to be faffing in and out- hence just let the immersion go (it can also go much higher).

 

I went for the 3kW immersion at 3kW as it avoids complication and the batteries are more than capable of buffering that.

 

My issue is the ASHP is huge so can eat the batteries pretty quickly at full chat. This hopefully wouldn’t be an issue on a more modest system