Hybrid without batteries or grid tied with Auto transfer switch? Will it work?

[barnabyrees-jones]

I am in the process of designing a system for deployment in Southern Africa and looking for some help/input from fellow solar installers and enthusiasts. Their grid is somewhat hopeless and is often turned off due to lack of supply - load shedding. I am looking at the possibilities I have ahead of me, I understand a hybrid inverter and PV system tied to batteries would provide backup power when the grid will be out but I was wondering if there is another option with the use of an automatic transfer switch in association with a grid tied PV system. Solar + Storage is still very expensive (even more so in Africa) and the majority of households will be unable to afford the extra cost of batteries.

If an automatic transfer switch was fitted to a grid tied PV system with no batteries, is there a way of disabling the anti-islanding or enabling backup power on standard grid tie inverters. Or are there any inverters that have this option. The majority of installed PV systems will not be large enough to allow off-grid, but most of the load-shedding takes place in the afternoons or when sun is usually out and shining, hence my question of getting the grid tied solar to keep producing to tie the households over for the couple of hours of load shedding.

I'm aware that most of the earthing arrangements are TNCS systems, so a local TT system will have to be installed for safety.

Does anyone know if a hybrid inverter will perform to the use I need without batteries attached? Also, what it the switchover time of a hybrid battery system/automatic transfer switch - is it quick enough not to disrupt electrical equipment (similar to UPS)

When selecting automatic transfer switches, what sort of specs are needed for domestic with regards to poles and amp ratings. Does it need to be sized to the incoming grid supply or the loads in the household? Most incoming main feeds will be 100A 240V, but I imagine in most households they will be using a lot less than that.

Many thanks in advance, Barns

[jflorey2]

If an automatic transfer switch was fitted to a grid tied PV system with no batteries, is there a way of disabling the anti-islanding or enabling backup power on standard grid tie inverters. Or are there any inverters that have this option. . . .Does anyone know if a hybrid inverter will perform to the use I need without batteries attached?

Only such inverter right now that I know of is the SMA inverter with the US option - that gives you about 1500 watts of power, assuming that the sun is out and the array is capable of more than that.

[Mike90250]

Except for the 1 SMA inverter with the emergency outlet, no.
GT inverters rely on the GRID to absorb their output, if they are not fully loaded, they overvoltage and shut down.
Off-Grid & Hybrid inverters require large battery banks

[kingofbanff]

Except for the 1 SMA inverter with the emergency outlet, no.
GT inverters rely on the GRID to absorb their output, if they are not fully loaded, they overvoltage and shut down.
Off-Grid & Hybrid inverters require large battery banks

If he did have batteries and they were already fully charged what stops it from overvolting and shutting down? Is there another piece of equipment in the system?

Thanks

[barnabyrees-jones]

So there is no way of getting into the programming of the inverters and shutting down anti-islanding if fitted with auto transfer switch to isolate from grid. If the system was combined with immersion heater - iboost, immersion etc. Wouldn't that suffice as a dump resistive load and prevent over voltage/shutdown? I'm sure that could be rigged to heat pool water or water tank. Thanks for replies so far!

[jflorey2]

If he did have batteries and they were already fully charged what stops it from overvolting and shutting down? Is there another piece of equipment in the system?

In a hybrid system, the charge controller prevents overvoltage. It takes less and less power from the panels as the batteries reach full. If the grid is connected, then the inverter pulls power out of the batteries so they never reach full, and the charge controller transfers as much power as it can into the batteries.

[jflorey2]

So there is no way of getting into the programming of the inverters and shutting down anti-islanding if fitted with auto transfer switch to isolate from grid.

No.

If the system was combined with immersion heater - iboost, immersion etc. Wouldn't that suffice as a dump resistive load and prevent over voltage/shutdown?

No. There would always be too much or too little load to match the solar generation. You would have to match it exactly and then actively regulate the load to ensure that the two always balanced perfectly, and that would be a design problem that you don't want to take on.