On-grid domestic battery storage

1961Nick

pinnks wrote: »

I get that but if the CT sensor is on the meter tails and the diverter only turns the load on if it sees export, why is it that the battery sees any load in the first place?

It takes the inverter a few seconds to ramp up or down when there's a large change in load...even longer when it has to flip between charge & discharge. During this short period the iBoost can see some export & so it starts to divert. The battery inverter sees this as 'load' & ramps up etc etc.

pinnks

I see. There is a switching threshold on the immerSUN which can be changed. it is "to ensure you don't inadvertently import". Default is 50W I think but could be anything. Might that "solve" the problem?

I don't have batteries yet but lose the benefits as and when. I did contact the makers of the EV charger Zappi to ask how it interacts with the immerSUN. They have a diverter called Eddi and it talks to the Zappi to decide who gets what. I think the Zappi can also talk to the immerSUN but can't remember. Whether this would solve the issue is a good question...

Martyn1981

pinnks wrote: »

The other thought was about DNO approval. If one already has approval, as I do, then presumably, as long as the batteries cannot discharge more than the DNO-approved PV system (5.25kWp for me), then nothing changes?

I'd hope that's the logic, after all if you are exporting some, or all of the PV generation, why would you export any of the battery capacity*.

Or, do they have to apply a theoretical risk, and add the battery discharge rate to the kWp.

I've got a 5.9kW approval, based on the sum of my original inverters, so I'd be happy with that as a battery discharge ruling.

*Only thing I can think of is being paid for export at peak prices due to a shortage in supply, but if your (or my) PV is generating strong, surely so is the rest of the UK.

pinnks

But who would tell you whether you need to seek further approval? Would a retrofit battery installer be that savvy?

1961Nick

Our power has just gone off & the house is now running on the EPS for the first time. I'm at 10 on the smug scale at the moment!:D

Hexane

pinnks wrote: »

I did contact the makers of the EV charger Zappi to ask how it interacts with the immerSUN. They have a diverter called Eddi and it talks to the Zappi to decide who gets what. I think the Zappi can also talk to the immerSUN but can't remember.

The Zappi will talk to the Eddi (I don't have the Zappi yet so haven't actually done this myself). I am pretty sure the Zappi won't talk to an immerSUN (I bought an Eddi based on the installer saying that it made sense to get the Eddi if I later planned to get a Zappi.)

I remember someone on some EV forum saying that they had got a Zappi and battery (and maybe Eddi) talking properly together, I think by means of the new hub released by the same company myenergi. I'll post if I find where I saw that, or googling some of the key terms might find it.

Hexane

Hexane wrote: »

The Zappi will talk to the Eddi (I don't have the Zappi yet so haven't actually done this myself). I am pretty sure the Zappi won't talk to an immerSUN (I bought an Eddi based on the installer saying that it made sense to get the Eddi if I later planned to get a Zappi.)

I remember someone on some EV forum saying that they had got a Zappi and battery (and maybe Eddi) talking properly together, I think by means of the new hub released by the same company myenergi. I'll post if I find where I saw that, or googling some of the key terms might find it.

The external forum thread was this one:
https://www.speakev.com/threads/myenergi-hub-peripherals-fw.131640/page-9

So it seems I had mis-remembered, there are a lot of complicated things in there including myenergi's own instructions for how to get a Zappi to co-operate with a "third party" (i.e. non-myenergi) immersion heater diverter by means of one or multiple CT clamps. Do check the previous page (page 8) for some guy saying his Zappi and battery were now co-operating properly. I think the idea is that once you have the myenergi hub, you can set priorities for battery, immersion heater diverter, and Zappi (maybe even more than one Zappi?) all to do exactly what they should, but best to ask myenergi exactly what functionality they are promising.

There are also a few people in that forum expressing impatience with myenergi's difficulties with newly released or promised products and updates - not my experience as my eddi has been 100% reliable once it had spent 2 or 3 days settling down, but, I haven't got into the world of firmware updates and multiple devices and batteries just yet.

Solarchaser

I can't see how you would need permission for the ac battery storage, as all its doing is interrupting the solar that's going to the grid, to charge the battery, and then later on using the battery to power your home.

Even when my battery systems are misbehaving, they never send more than 200w to the grid.

The problem you have with batteries plus immersion is the same problem as with two separate battery systems.

For dual battery systems, when load is high they may both be discharging, but when load drops one battery system responds faster than the other, so it drops output, but the other system is still pushing power out.... first system sees this as excess solar, so starts charging... double round trip losses.

For battery plus immersion then when Solar is good. Batteries start charging, still an excess going to grid, immersion starts running.
Solar drops, batteries monitoring solar vs grid reduces charging, immersion still running.
Solar drops completely, immersion is still running, and now batteries are discharging to run immersion.

If you are able to set the immersun to only work when there is a constant 200w (below 200w the sofar me3000sp has a little think about what it wants to do) excess of solar above what its using, then apart from wasting a couple of kWh of solar a day, you are golden, if not, then you will quite often end up with the batteries discharging to run the immersion.

Martyn1981

Solarchaser wrote: »

I can't see how you would need permission for the ac battery storage, as all its doing is interrupting the solar that's going to the grid, to charge the battery, and then later on using the battery to power your home.

I believe it's based on the possibility of discharge to the grid, not the practice.

So if you have a Tesla PWII that can maintain 5kW discharge, then theoretically, the household could discharge nearly 5kW to the grid if it wanted too from the batt, and even more if PV and batt pumping out at the same time.

If the theoretical exists, then the DNO has to consider it, in the same way that my PV permission had to be based on the whole kWp of my systems, even though E & W would never peak at the same time, in the absence of a single inverter that could cap at a lower max.

joefizz

Martyn1981 wrote: »

I believe it's based on the possibility of discharge to the grid, not the practice.

So if you have a Tesla PWII that can maintain 5kW discharge, then theoretically, the household could discharge nearly 5kW to the grid if it wanted too from the batt, and even more if PV and batt pumping out at the same time.

If the theoretical exists, then the DNO has to consider it, in the same way that my PV permission had to be based on the whole kWp of my systems, even though E & W would never peak at the same time, in the absence of a single inverter that could cap at a lower max.

With the AC based system it shouldnt really be a problem though. They will all be limited to a max 16A or 13A discharge due to their nature (need to work off a household spur). Of course the chances it could go rogue are a definite possibility but with thermal runaway the issue with the DNO would be the least of your worries ;-)
The fused/tripped spur should take care of that....


As for the immersion side of things, some of us have discussed this in the past and my view is that going forward all these diverters will become redundant. They are great as standalone bits of kit but they are just a switch. Nick has mentioned a wifi switch which looks interesting and allows you to turn the immersion on and off remotely. I havent really looked into that aspect a lot as its on the long finger but having the battery power available sort of negates the need to partially divert the load to the immersion.
So instead of just sending your excess to the immersion coil, you can send a full immersion load to the coil from the solar+battery. That sort of makes the diverters obsolete and puts you fully in control. Of course the actual mechanism for putting you firmly in control has to be decided ;-)
Wait until Nick gives us an update on how he is using the wifi switch and it might be a case of sticking the diverter on ebay and buying one or more of those ;-)


All of my current plans are mostly still theoretical, they need some sun to be tested out in practice ;-)