I have a PV array on one building connected to a grid tie inverter. I have added a Sunsynk 5 kW with battery in another building to provide power during grid outages. Its is not possible to have the Sunsynk in the same building where the PV array is, there is no space to mount it with the battery. So the question is how to get PV power to the Sunsynk? its either a long run of DC cable (25m) or some setup where the grid tie inverter feeds the generator input of the Sunsynk. 

Solar DC cable expensive. Is there an issue with using normal AC cable of the right gauge if it's in conduit? 

Any ideas welcome. 

Rob

Edited March 18, 20242 yr by RobM

Most GP wire is DC rated (although it is best to double check the specific brand with the supplier/manufacturer). So it is fine to use for long haul DC connections (just make sure of your voltage drop limitations - you will probably require thicker wire than the current limit would suggest).

Solar wire is primarily for environmental exposure, which you do not need in a protected conduit.

Otherwise, a micro-inverter on the panels with AC coupling to the Aux input should do it (but you won't get PV power when grid is off).

You mean like this? 

Sort of - On the Sunsynk you can configure the Aux input (NOT AC in) as a micro inverter input.

Micro-inverters are grid-following, not grid-forming, so they require an existing AC signal to 'boost'.  It is a limited setup suitable for feeding in extra panels over an AC link, but can only produce power when grid is present.

OOPS - I see the Sunsynk can do grid forming for micro-invertres - so they can work off-grid. BUT on-grid is an issue, as the Sunsynk can not control production on micro-inverters on-grid, and they will run at full power permanently, exporting all additional power to the grid.  Generally not acceptable unless you have a feed-in agreement...

So DC coupling will definitely be the best option.

1 hour ago, RobM said:

I have a PV array on one building connected to a grid tie inverter. I have added a Sunsynk 5 kW with battery in another building to provide power during grid outages. Its is not possible to have the Sunsynk in the same building where the PV array is, there is no space to mount it with the battery. So the question is how to get PV power to the Sunsynk? its either a long run of DC cable (25m) or some setup where the grid tie inverter feeds the generator input of the Sunsynk. 

Solar DC cable expensive. Is there an issue with using normal AC cable of the right gauge if it's in conduit? 

Any ideas welcome. 

Rob

My question would be what is the array voltage and current you want to get across 25meters. The higher the voltage the less losses(voltdrop) so that would determine your cable size. Not a problem using 4~6mm surfix in conduit over a distance of 25 meters.

2 hours ago, Skyelmad said:

You mean like this? 

Yes - that's the one option - to have the grid feed inverter feed PV energy to the second inverter. 

 

1 hour ago, JustinSchoeman said:

Sort of - On the Sunsynk you can configure the Aux input (NOT AC in) as a micro inverter input.

Micro-inverters are grid-following, not grid-forming, so they require an existing AC signal to 'boost'.  It is a limited setup suitable for feeding in extra panels over an AC link, but can only produce power when grid is present.

OOPS - I see the Sunsynk can do grid forming for micro-invertres - so they can work off-grid. BUT on-grid is an issue, as the Sunsynk can not control production on micro-inverters on-grid, and they will run at full power permanently, exporting all additional power to the grid.  Generally not acceptable unless you have a feed-in agreement...

So DC coupling will definitely be the best option.

Yip I think you're right - if I am running a cable and can use cheaper cable like suffix, less loss - array voltage around 350V

3 hours ago, JustinSchoeman said:

 

OOPS - I see the Sunsynk can do grid forming for micro-invertres - so they can work off-grid. BUT on-grid is an issue, as the Sunsynk can not control production on micro-inverters on-grid, and they will run at full power permanently, exporting all additional power to the grid.  Generally not acceptable unless you have a feed-in agreement...

So DC coupling will definitely be the best option.

Would the CT when set to No Export to grid not just send this extra power to the non essential and essential including battery charging? 

You can only control the micro inverter output power by frequency shifting the AC line it is feeding. But, if the grid relays are closed, there is no way you can shift the frequency of the entire grid to throttle the micro inverter.

1 hour ago, JustinSchoeman said:

You can only control the micro inverter output power by frequency shifting the AC line it is feeding. But, if the grid relays are closed, there is no way you can shift the frequency of the entire grid to throttle the micro inverter.

Thanks. I thought as the Sunsynk provides the grid reference when micro inverter input is active that this reference might be freq shifted to reduce the input from the AC coupled inverter. Not trying to shift the grid freq. 

43 minutes ago, Scorp007 said:

Thanks. I thought as the Sunsynk provides the grid reference when micro inverter input is active that this reference might be freq shifted to reduce the input from the AC coupled inverter. Not trying to shift the grid freq.

Technically, I suppose they could just keep the grid relay open. That way the inverter could still control the frequency. But then you could not provide power to the non-essentials.