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I hope I'm understanding this correctly - the quotes I've had so far for PV system plus battery seem to differ mainly in the inverter / battery charging system.
They either have a hybrid inverter, or they have a standard string inverter with a separate AC charger for the battery.

Are there any inherent advantages of either system? My gut instinct is that a hybrid system is likely to be more suitable - seems to be the more modern way to do it, but I don't know enough about it to judge.

Thanks in advance

How would the separate units charge the battery from PV without drawing on the grid? With a hybrid unit I believe you can have it use whatever PV is generated/surplus. Can the separate units do that? Can the charge rate on the separate unit be set or is it fixed?

Might help to tell which models are being proposed for the different approaches.

Countrypaul wrote: ↑Tue Apr 26, 2022 3:44 pm How would the separate units charge the battery from PV without drawing on the grid?

Use of the CT that comes with it.

richbee wrote: ↑Tue Apr 26, 2022 3:28 pm I hope I'm understanding this correctly - the quotes I've had so far for PV system plus battery seem to differ mainly in the inverter / battery charging system.
They either have a hybrid inverter, or they have a standard string inverter with a separate AC charger for the battery.

Are there any inherent advantages of either system? My gut instinct is that a hybrid system is likely to be more suitable - seems to be the more modern way to do it, but I don't know enough about it to judge.

Thanks in advance

Don't think their is much between them really. Easier to have a single unit and probably cheaper. Different if you already have the PV and are on fit payments though.

Generally a single unit will be cheaper and take up less space. Some hybrid inverters have slow charge-discharge rates in comparison to AC-coupled. There is not much in it TBH. Often it comes down to what is available on the shelf and what has a 3-month lead time such is the world we now inhabit!

The standard 3.68kW hybrid inverter is only going to push out 3.68kW into the house irrespective of how much solar and batteries are connected.

A 3.68kW string inverter could be pushing put 3.68kW and the battery inverter could be pushing out a similar amount of power simultaneously too if the house load was high enough and under G99 light touch application.

A larger hybrid inverter could be used but requires a full G99 application.

If you have FITs then the hybrid option is almost a non starter if there is a grid charging option.

I prefer the two inverter approach as it generally more power, speed of response and flexibility. I also have FITs.

My understanding is not 100% but if you have a AC charger for the batt does that not mean it goes PV inverter DCto AC, AC charger inverter AC to DC, and then batt inverter DC to AC as against hybrid inverter going straight PV DC to batt which is more efficient.

With FITS are you forced to go the hybrid route so that you are unable to export more than is allowed.

You can see i am confused. Someone please clarify.

Ken

Yes you are correct that you can end up with a lot of voltage conversions but a hybrid inverter still has to convert the High Voltage DC from the panels - typically 200 to 500 volts - down to the 50 (ish) volts required by most standard battery stacks, so there is still some conversion to do. Modern inverters are reasonably efficient.

The issue with FiTs systems is they don't want you having batteries on the generation side of the FiTs generation meter as they could be charged from the grid and then discharged through the meter so you get a FiT payment. You can do it if you have a certified "bi-derectional" generation meter fitted. This "deducts" any import used to charge the batteries from and export "generation" recorded.

Ken wrote: ↑Wed Apr 27, 2022 8:15 am My understanding is not 100% but if you have a AC charger for the batt does that not mean it goes PV inverter DCto AC, AC charger inverter AC to DC, and then batt inverter DC to AC as against hybrid inverter going straight PV DC to batt which is more efficient.

With FITS are you forced to go the hybrid route so that you are unable to export more than is allowed.

You can see i am confused. Someone please clarify.

Ken

Your first point is correct but its not a huge difference. And in summer you generally have so much excess power from Solar it makes even less difference apart from maybe less export but if your on a low export limit like me then makes no difference. And in winter if your charging the batts from the grid, it makes no difference at all.

With FITs, if your system cannot charge with grid and your not charging the batts with extra panels via charge controllers there is no issue with FITs. Marshmans comment about bi-directional meters is correct but I have never heard anyone actually going through with the process, really depends if your FIT provider wants to play ball or not.

Again with FITs is if your on deemed export like most folk, then adding an extra system with DNO authority should be ok, the export limit is irrelevant to FITs in that case but if your on measured export with FITs then it might invalidate your export payments. I remember a long time ago at the old place someone was told by a FIT provider who was on measured exports that if they added another non MCS system they would have their whole FIT contract torn up. Whether that was legally correct or not is debatable, but folk like me on full FAT FITs are quite reluctant to contact the FIT provider about anything apart from giving them my generation meter readings.

Definitely agree re only contacting FITS provider when necessary. Even now, the understanding of the rules & regs re retro-fit storage is very variable across energy retailers - even within the same retailer! A bit like dealing with DNO's, once you find an informed an helpful person, stick with them.

(I made the mistake some years ago of asking some questions of SSE before I installed storage / additional PV and they told me FITS payments would stop for everything.)

Having gone through a few of these installs the advice is spot on - hybrid units can be an easier install (especially the "All In One" models also including the battery stack) and can make the DNO approval process slightly less complex.

If you want flexibility to monitor/control/do more complex things now or in the future, (FITS situation not withstanding), then separate boxes.

Not unlike the integrated/separate units debate for hifi!