Additional Charging capacity

[cojmh]

I am after some advice (again).

Now that I have my batteries working with my inverter - I have found that my inverter is limited to 2.5KW of charge/discharge despite my PV and batteries being capable of nearly 5KWh.

I am not so worried about the discharge rate as there is nothing much I use that will go too much over the 2.5KWh apart from the cookers which I don't think we can cover anyway. Or the electric showers which are soon to be replaced with using the hot water tank.

So really I am just after extra charge capacity.

I received the following message from Nowty - but I moved it here as I thought starting a new thread would probably be best?


Any room anywhere for some extra PV and connect to a charge controller and tee it into the DC side of the battery stack (like Joeboy).

Or like me if you can get hold of a cheap second hand Sofar ME3000SP you can connect it up without any CT clamps and use the test mode to force charge your batteries, again tee'ing it into the DC side. That would give another 60A to take you roughly to the max rate of the battery stack and the 25mm DC cables. Legality is a bit dubious because the DNO would say its another bi-directional inverter even though I am only using it as a battery charger.


In answer to this - Unfortunately no more space for Solar panels unless I put some on the garage when I get the roof replaced (from flat to pitched) - but this is a few years away (5-10 years away I expect)

The second option sounds interesting but I don't fully understand how it works without the CT clamp?

I am assuming that the AC connection to the charger will be to a new 16A breaker in my consumer unit

On the DC side of the charger would be the standard positive and negative cables which would go to spare Positive and negative terminals on the Pylontech battery stack? I think it would probably be good to put a breaker in this connection too?

So my questions are:

1. Is my understanding above correct or have I got the wrong end of the stick?
2. How does the Sofar unit know when to charge the excess generated power to the batteries?
3. There does not need to be any communication between the Sofar unit and the batteries?
4. How much is a reasonable price for a sofar ME3000SP unit?

Many Thanks,

Jon

[nowty]

My ME3000SP comment was based upon using it to charge from grid overnight during off peak periods rather than diverting excess solar to the batteries.

About a year ago or so quite a few came up on ebay cheap (circa £250 to £300), because some installers persuaded customers to replace them with Lux units to take advantage of Octopus Agile tariffs. Not seen many come up since then.

[cojmh]

Thanks for the response.

So the unit you were talking about would perhaps not be able to do the charging that I needed to do? Is it even possible to charge one battery bank with two chargers?

I realise that both chargers a full power would have to be less than the charge capacity of the battery bank, but I am concerned about damaging one or both of the chargers if I tried to.

I know that I can potentially replace the hybrid inverter - but if it is working and there is another solution I am keen to explore the other options first.

[nowty]

Thanks for the response.

So the unit you were talking about would perhaps not be able to do the charging that I needed to do? Is it even possible to charge one battery bank with two chargers?

I realise that both chargers a full power would have to be less than the charge capacity of the battery bank, but I am concerned about damaging one or both of the chargers if I tried to.

I know that I can potentially replace the hybrid inverter - but if it is working and there is another solution I am keen to explore the other options first.

You can but you have DNO issues and getting two inverter chargers working in parallel is very experimental. I.e. it does not always work and can become unstable.

Another way I have used is to use some cheap Chinese DC PSUs and feed them into an MPPT charge controller as if they were solar panels. You can turn the PSUs on with WiFi sockets and even have several in series to up the voltage. That gets around the DNO issue as the power can only flow one way. But you just have to turn them on manually when you have excess solar. Many years ago I used this trick to transfer excess power from an off grid system to on grid system in order to get around the DNO rules.

[Tinbum]

I use some ELTEK chargers and have them connected to the battery pack with a CAN lead and CAN Bridge.

https://camelot-forum.co.uk/phpBB3/view ... ilit=eltek

ME3000Sp have gone up a lot in price and seem to go for about the £350 + mark. Prices of Pylontech batteries are now vastly inflated as well. I paid just under £1000 and now I've seen them as much as £1600.

[cojmh]

I think I don't full understand the complexities involved.

The problem I have is that a maximum capacity the PV cells can produce just shy of 5KW .... If we are using very little of this power at the time of generation it will charge the batteries ... But due to the 2.5KW charge limit on the inverter we could potentially lose 2KW+ to the grid .....

So I recently bought the Eddi to divert solar power to the HWT etc. Which means that I would now not loose this additional power to the grid .... But the only issue is that whilst still useful the energy is not in the form I want most (electricity).

So the aim is to try and be capable of charging the batteries at 5KW so that I can ensure I maintain my ideal priority:

1. (Highest) direct use at the time
2. Battery storage
3. (Lowest) HWT and other surplus diversion

My questions are I suppose:

Am I being too obsessive about this priority?

From the reading I have done on this forum it would be too unstable to add in addition controllers to try and feed the batteries first .... And as such the only really viable solution would be to upgrade the hybrid inverter at some point?

I realise that there are a couple of work arounds above .... But in my mind for it to work if I am not here it needs to be automatic really ... (So not a criticism of the solutions above per se ... Just they don't quite fit my needs)

Thanks for the help so far

[nowty]

I understand what you want and we all want that priority, mine does it because I have a 6kW battery charger in my SMA Sunny Island. Then the Immersun (like the Eddi) boosts hot water and storage heaters.

My 1st observation from another of your threads is your on FITs and you have a 5kW hybrid inverter so your batteries are DC coupled with a 2.5kW charger. You also have 14kWh battery (or will have when the last one arrives). That puts you straight away in an awkward position because you cannot charge the batteries from any other power source other than your existing solar PV via your hybrid inverter.

So the obvious option would be to change your hybrid inverter to one with a higher battery charge rate but then most don't go above a 3kW charging rate so your not gaining much unless you can find one which has a higher limit but still is consistent with your DNO inverter approval.

If you want to charge the batteries in winter from the grid, your going to have to fit another AC coupled battery inverter and move the batteries to that or else it will be fraud if you have FITs. There is technically a way of changing your generation meter to a bi-directional one but I've never heard of anyone who has actually managed to do it.

Personally as you have a good sized hybrid inverter, batteries and an Eddi, I think your over thinking it and I would run your system as is with your batteries and see how you get on. If its a sunny day your batteries are likely to still fill up with the 2.5kW charger.

[nowty]

Just had another thought.

You could disconnect, say 3 of your existing panels from your hybrid inverter and connect them via a charge controller and tee them into the DC side of your batteries.

The downside would be when the batteries are full the charge controller would throttle back and you would have a net loss on the total generation, therefore reducing your FIT income.

Again, probably not worth doing.

[cojmh]

I understand what you want and we all want that priority, mine does it because I have a 6kW battery charger in my SMA Sunny Island. Then the Immersun (like the Eddi) boosts hot water and storage heaters.

My 1st observation from another of your threads is your on FITs and you have a 5kW hybrid inverter so your batteries are DC coupled with a 2.5kW charger. You also have 14kWh battery (or will have when the last one arrives). That puts you straight away in an awkward position because you cannot charge the batteries from any other power source other than your existing solar PV via your hybrid inverter.

So the obvious option would be to change your hybrid inverter to one with a higher battery charge rate but then most don't go above a 3kW charging rate so your not gaining much unless you can find one which has a higher limit but still is consistent with your DNO inverter approval.

If you want to charge the batteries in winter from the grid, your going to have to fit another AC coupled battery inverter and move the batteries to that or else it will be fraud if you have FITs. There is technically a way of changing your generation meter to a bi-directional one but I've never heard of anyone who has actually managed to do it.

Personally as you have a good sized hybrid inverter, batteries and an Eddi, I think your over thinking it and I would run your system as is with your batteries and see how you get on. If its a sunny day your batteries are likely to still fill up with the 2.5kW charger.

Thank you for the detailed explanation - some of it is right on the limit of my understanding so forgive me if I am being thick.

The issue with changing out the inverter, as I understand from you explanation, is that I would have to go for something like an 8KW hybrid inverter in order to get a 5KW charger .... Unfortunately this would exceed my current permission with the DNO so I cannot do it without their permission ....

So I am assuming if I try to go this route and get permission then aside from the fact they may say no it would possibly stop the FIT payments ..... Is that right?

Does anyone know if this has ever been done?

Secondly - I don't full understand the FIT fraud bit - possibly because I am not sure I understand the DC coupled and AC coupled bit.

What I think you are saying is that currently the batteries are DC coupled and hence the energy that is put into them does not show up to the meter until it is used ...... I.e. it is stored before the generation meter ever sees it. Which in turn means that if I charge them from another grid source and the energy is then used it will show up as generated power as opposed to energy originally from the grid .... Hence the fraud bit. Is that about right?

If that is the case then I am a bit lost as to how people expand their current systems with an additional 'off grid' PV system and batteries .... (If that is what they are doing?)

Might be that the FIT stuff is the limiting factor here for expansion?

Again sorry if this is all elementry stuff .... This is a big learning curve

[nowty]

Batteries can either be DC or AC coupled.

The cheapest way of doing it is the way you have in that you have a single inverter which connects to both your batteries and solar panels. Because you have FITs you have a generation meter which is downstream of the hybrid inverter so your understanding is correct that you cannot charge them from the grid or from additional solar panels as it would have the effect of clocking up the generation meter and therefore would be fraudulent. If you did not have FITs then it would not matter in most cases. I assume you have a full 5kW DNO export approval for the 5kW hybrid inverter ?

Assuming you have DNO approval for a 5Kw inverter there is nothing wrong with simply changing your inverter to another 5kW model which has a higher battery charging rate. I would not even bother contacting either your FIT provider or the DNO if you did this.

OFGEM Guidance on adding battery storage to FIT systems.
https://www.ofgem.gov.uk/sites/default/ ... idance.pdf

An AC coupled system is a second completely separate inverter for batteries only. In that case you can charge them with excess solar from the FIT system, additional Solar panels or from the grid as the power does not go through your FIT generation meter. This is what I have, its much more flexible but costs more as you need two separate inverters. It does also need a separate DNO approval, there is a fast track process for 3.6kW systems, but as you already have a larger hybrid inverter than 3.6kW that process wont apply to you.

So people expanding their systems with batteries normally go down the route of a second AC coupled battery inverter, especially if they already have a FIT system. Generally having an initial FIT system causes all sorts of problems if you want to expand your system.

But people having an initial system installed generally go for the hybrid approach as there is no FIT issue anymore and its a cheaper install.

I still maintain my recommendation to just leave as is and see how it goes over the summer.