Can a solar system on my shed supply AC to my house?

[martinindevon]

I have a situation where the only place solar panels will work well is on a 9M x 2m flat roofed shed in the garden.
The shed has ducting between it and the little guest house we have, the guest house has a 63A supply from the main house (Buried SWA) and its own consumer unit of course. The 63A supply for the guest house comes from the 100A incoming mains supply - it's in parallel with its own MCBs with the feed to the consumer unit in the main house.

What I'd like to do is install a solar battery system optimised for self consumption -so solar and battery stored power used first then seamlessly fallback to the grid, to reduce monthly electricity bills.

I can see how I could do this for the AC loads in the guest house since I can insert something like a victron MultiPlus or MultiGrid + charge controller and cable the 63A incoming via those controllers then return the AC output from them to the Guest house consumer unit.

What I'm not sure about is if there are any controllers that can have a single AC connection for both input and output so that I could potentially power AC loads in the main house also from the Guest house / Shed based solar system via the existing buried SWA cable run (with a current limiter of course).

 

[Al D]

Look up grid tied and hybrid inverters. You should also check the laws and regulations governing your area about installing them.

 

[martinindevon]

Yeah I'm looking at grid tied and hybrid invertors. So far though they all seem to have AC in from Grid and AC out from the inverter to power separate AC loads.


What I'm wondering is if there are any with a single AC input/output. So logically I can do this:

 

[TomC4306]

Actually, in your 2nd diagram, swap the inverter and loads boxes.

I am doing exactly what you want to do.
AC comes into the house at the main breaker box, goes out to the All in One inverter through a circuit breaker.
Also inputted to the AIO is the battery subsystem with solar panels.
Settings on the AIO allow me to harvest and use all of our solar production.
Inside the AIO also exists an automatic transfer switch which is also governed bt the settings.
Operationally, it works like a reverse UPS. The circuits I have assigned to the system run on solar and battery until a set low voltage point and then the ATS switches to grid as a backup.
Then the sun comes up in the morning and begins charging the batteries until another previously set voltage level at which time grid is disabled again.
Hope this helps.

 

[Al D]

I might not be understanding what you're thinking, but hybrid inverters are supposed to power your house when the grid goes offline. I'm a bit confused by what "other AC loads" mean to you.



And as a related side note, hybrid inverters allow your solar panels to supply electricity to the grid, thus reducing your bill. You won't be using your batteries to save your wallet, you'll be supplying the solar to the electric company. You can search for "net metering" if that's of interest.

 

[martinindevon]

Thanks - I'm glad to have this beginners corner to try and get this straight in my mind ;-)

Actually, in your 2nd diagram, swap the inverter and loads boxes.

I realise that is how it ought to work but it can't, that's the issue. The only place I can put the solar panels and the invertor (the shed) is distant from where the power gird connects to my property (in the main house).
This is the current wiring diagram (the blue shed bit doesn't exist yet).


Now the Guest House and shed are close enough (and have ducts between them) that I could reroute the incoming AC connection from the house to go via the Solar Shed first and make it look like this:

That would mean that the guest house could be powered from solar & battery until they are depleted and then failover to the Grid.
Victron call this 'AC Ignore' in their world, where effectively the solar solution acts as an off grid power setup but can supplement or failover from the solar battery to the grid connection if and when it needs to.

There is a guide here: https://community.victronenergy.com/storage/attachments/3299-virtual-switch-ignore-ac-lesson.pdf

But the victron equipment expects the AC input (from the GRID) to be isolated from the AC output (to the loads). However I only have a single cable between the house and the guest house so I want to see if I can find an inverter that only needs a single AC connection for both Grid and Load.

Or does that simply not exist and if I want to power the loads in the main house but still fail over to grid AC then I'll need to use the existing cable from the house to the guest house as the AC in on the inverter and run a new cable for the AC loads back to the main house from the output side of the inverter?

 

[Hedges]

Grid-tie inverter like Sunny Boy on the shed.
Battery inverter like Sunny Island anywhere upstream of the loads you want to get backup power.
This is called "AC coupled" PV. When grid fails, battery inverter opens a relay to disconnect grid and provide an "island grid" to loads and to the GT PV inverters.

 

[martinindevon]

This is called "AC coupled" PV.

Thanks Hedges. I agree, it looks like an AC coupled solar inverter is exactly the right thing for the shed. Like the look of the Sunny brand products in general will go learn / investigate. Thanks for the steer!

 

[SeaGal]

Not sure

The only place I can put the solar panels and the invertor (the shed) is distant from where the power gird connects to my property (in the main house).
This is the current wiring diagram (the blue shed bit doesn't exist yet).

View attachment 103921

Not sure if you've progressed this yet. The issue I see is the 50m distance between the inverter and the grid. Depending on cable size, it could result in a significant voltage rise, which could (if your grid is on the high side of normal) result in too high voltage in your shed and guest house.

Imagine, for example, if your grid is around 250V - 252V, and there's a voltage rise of around 4 - 6V due to the underground cable, then the shed and guest house could be receiving 254V to 258V, which is above limits, but within the G98 cut-off voltage of the inverter. So either make sure the underground cable is big enough or, better still, run a separate underground cable from shed to house, just for the inverter, to connect to the grid and then the existing buried cable supplies the guest house and shed with power.

 

[chilly2]

I have a situation where the only place solar panels will work well is on a 9M x 2m flat roofed shed in the garden.
The shed has ducting between it and the little guest house we have, the guest house has a 63A supply from the main house (Buried SWA) and its own consumer unit of course. The 63A supply for the guest house comes from the 100A incoming mains supply - it's in parallel with its own MCBs with the feed to the consumer unit in the main house.

What I'd like to do is install a solar battery system optimised for self consumption -so solar and battery stored power used first then seamlessly fallback to the grid, to reduce monthly electricity bills.

I can see how I could do this for the AC loads in the guest house since I can insert something like a victron MultiPlus or MultiGrid + charge controller and cable the 63A incoming via those controllers then return the AC output from them to the Guest house consumer unit.

What I'm not sure about is if there are any controllers that can have a single AC connection for both input and output so that I could potentially power AC loads in the main house also from the Guest house / Shed based solar system via the existing buried SWA cable run (with a current limiter of course).

Hello Martin,

Keith at Sunsynk just made a short YT video on a similar AC couple option. Maybe he might be able to advise.