Immersion boost & Tesla Powerwall

[Nigel52]

My original requirements were circa 14 panels, immersion boost, battery and UPS if a grid failure.

Firstly first company answered everything liked the quote asked for site inspection and never turned up and stopped communicating.

Second company was a local friends recommendation, lovely guy again looked good but the stress of the market has left him unwell and he sadly backed out.

Third company again local recommendation which I have gone with is installing panels and inverter 9th October but has recommended the Tesla Powerwall but is saying delivery June 23 - Mar 24. However, I can’t have immersion booster/EDDI as won’t work with Tesla battery. However, Tesla will give me some protection from grid failures.

I’m wondering if I would be better off changing to another battery supplier (they do Solaredge) and EDDI immersion boost. Sadly it does seem as though I will lose ups option for grid failure.

What a total minefield.

Any thoughts please?

[Fintray]

I have an immersion diverter and it works fine with a Powerwall.

[Nigel52]

Interesting. My supplier is adamant it wii screw up the Tesla battery monitoring.

[Fintray]

When the Powerwall was first installed I noticed that the diverter (which I installed on my first PV system) was draining the Powerwall. This was because there will be a slight export if the load changes when the Powerwall is supplying the power (before it settles at zero export), this caused the diverter to start diverting and there was a to and fro between them. I cured this by upping the export minimum to about 100W so any slight export would not be picked up by the diverter.
I can't say that there has been any effect on the monitoring that I have noticed.

[Andy]

if the battery takes priority for charging you can set the Eddie to not use electricity until a set target is exported. For example 150W. This means the two won't fight each other. The Eddie will always leave 150W exporting so if the battery has capacity it will use it.

[Andy]

I’m wondering if I would be better off changing to another battery supplier (they do Solaredge) and EDDI immersion boost. Sadly it does seem as though I will lose ups option for grid failure.

What a total minefield.

Any thoughts please?

You could go Victron or SMA for UPS support but good luck finding anyone willing to install them at the moment. Most installers want the quick and simple and move on to the next job. Not much help I'm afraid. My experience was much the same as yours. Are you in the north of Scotland?

[Nigel52]

I’m in Poole Dorset which is not exactly out of the way.

[Andy]

I don't think the guy I'm using would go that far :<

[Oldgreybeard]

It's pot luck, TBH. Sometimes the diverter may play ball sometimes, sometimes it won't. The key issue is that a race condition can occur, and this is unpredictable. Unless the diverter and the battery system can set which takes priority, which usually means either getting them to communicate with each other or setting one to a different threshold before activating (which is wasteful).

I've been struggling with this for some time. I would like the hot water diverter (an Eddi now in my case) to take priority. The bodge I have that almost works is to fudge the battery CT setting, so it misreads and thinks that there is no export when in reality there is. This gives the Eddi a chance to jump in first and grab whatever export there is, and once it has done this the battery system doesn't get a look in. The downside is that the battery system reports duff data.

The fix is to add another CT to the Eddi, so it knows when the battery is charging or discharging. I've just got another CT to set this up, but at the moment it's not easy to fit this CT, as the battery system is outside the house in an outbuilding, fed from an outdoor distrubution box that goes directly to the meter. I'm in the process of getting this rearranged, so the battery system supply comes from the house. As soon as that is done I'll be able to use the battery system CT to tell the Eddi what's going on. Then it's just a matter of setting up the Eddi to read the battery system charge/discharge and ensure that the hot water always has priority over battery charging.

TBH I'd like more flexibility, as there are times when it makes sense to charge the batteries first rather than heat the water. There is a way to do thins, but it involves a fair bot of tinkering. I'd need to switch the battery inverter to passive mode and then control it via Home Assistant and MQTT, through the RS485 Modbus connection. I'm fighting shy of this for the time being, as it's an added layer of complexity that anyone else who comes to work on the system may struggle to understand.

[Nigel52]

I guess the question is do I push it with the supplier and insist on adding an EDDI booster?