Solar with 2 feeds from main 100A fuse

[CaptainHam]

Not DIY, I’m just trying to get my head around a planned install and want to ensure the installer does the right thing, but figured there would be a knowledgeable bunch in this subforum. Sorry in advance for wrong terms being used and general naivety…

From our main 100A feed, we have a split…the original supply (box on the right) feeds the main CU in the house, i.e., supplies basically everything in the house (which in turn supplies a tiny CU in garage for lights and sockets, but we can forget about that).
The box on the left is a retrofit switch which supplies an AC unit directly, and also supplies a second, larger CU in the garage for an EV charger and a hot tub.


The gubbins in the left cabinet shows where the split happens, I believe it’s called a Hendy block to split the tails, which was put in as part of the retrofit.



The solar kit (inverter and battery) will be installed in the garage, and ultimately using the cable connected to the “left switch” from first pic (as in, same cable that currently feeds EV charger and hot tub).

My question relates to how the solar/battery supply will feed the main CU (linked to “right switch”), either during the day (solar supply), night (battery supply), or during a power outage (if I activate the manual EPS switch that I’ve requested).

Will the magic simply happen and the power will find its way to where it is needed, and therefore I’m worrying about nothing…or is this a very complex setup and require lots of additional faffing to somehow link both halves / both the original main CU and the retrofit CU.
I definitely want to ensure that I can charge EV from solar during the day (via retrofit CU in garage) as well as power the house and the AC unit).

Hope that makes some sort of sense…

 

[CaptainHam]

I’m also worried that the AC will not be fed from solar or battery…it’s not linked to either original or retrofit CU, but instead fed from its own circuit directly from retrofit “left switch”…

 

[Hedges]

If your system is Grid Tie Net Metering, or Grid Tie Zero Export, power will just flow through the wires to where it is needed. In the case of zero export, a current transformer one wires from grid measures them, limits export to about zero watts.

Only if you have a system that provides backup when grid is down would there be a need for a disconnect relay, and wiring topology putting backed up loads downstream of that relay. In most cases, relay is inside inverter, so like a UPS, loads are downstream of it.

If you have different utility rates day vs. night, then timed switching of loads helps. Sometimes, batteries are added to suck up surplus PV during low rates, feed them into the wires during high rates. Again, either backfeed for net metering, or zero export.

Often installers will sell you on what they have available. They make money by doing a job. It is up to you to understand system capability vs. your needs, and any future additions (e.g. add battery backup later.) Price and available choices will be determined by what you buy the first time.

 

[CaptainHam]

It’ll be Grid Tie Net Metering so sounds like that is ok, thanks, hopefully including the AC unit which is stuck on its own not linked to either CU!

For EPS (off-grid backup), I think what you’re saying (and what I think I’ve read elsewhere) is I’d need a feed(physical connection via cable) from the new solar CU back to main CU in the house, to supply the house itself?

If so, I presume the AC unit will be unusable unless it too gets a physical connection from solar CU, but if so, this would rank as a first world problem that is not essential.

Agreed re: your last point. Installer is being helpful but I suspect I’m viewed as a difficult customer with all my questions so far. I just want to ensure I know exactly what I’m getting, and what new cabling is required anywhere, in order to meet what I’ve asked for and before I shell out £££ only to find out later that it doesn’t do all I was promised…

 

[Hedges]

All wires connected together including your neighbor and the next town will get the net metering power you produce. Also your A/C.
So long as all are behind one meter, the meter won't even be aware of the power going from PV panels to A/C.

Some hybrid inverters like SolArk (in US), Deye (elsewhere) may have 200A internal transfer switch, an be installed after meter and main circuit breaker, feed whole house even when grid is down. Of course, if you run an electric furnace in winter with no sun, battery will drain. Load management is key.

You should be able to see a data sheet for the system you're installing, understand what battery backup is available. Seller should be able to provide a design and price quote for a battery backup system, also a quote for a subset of that which doesn't include battery but supports it as addition. Get competing quotes for different brands.

Here is a residential 3-phase system that can provide PV and battery backup of select loads, all in one inverter box:

https://files.sma.de/downloads/STPxx-3SE-40-DS-en-20.pdf

Many products from SMA with varying capabilities, and from other vendors. SMA has quality products and I think competitive prices for what they offer, but you'll notice that the supported batteries are expensive. They do come with certifications, e.g. UL Listing for US, which some cheaper batteries (and inverters) do not.


Having and solving first-world problems is nice for comfort. I just got mine (avatar picture) up and running when the grid went down in California, 2020. It powers my whole-house air conditioner just fine. At night, I'm limited by small battery. Powering internet plus a window air conditioner it reasonably economical. PV panels are basically dirt cheap, will produce electricity for about 1.5 cents per kWh (amortized over 20 years.) Balance of system hardware including rack mounts, and batteries, drive hardware price, bringing that to 2.5 or 3 cents. Labor drives system price, bringing it to 3x or 4x hardware costs, maybe $0.10/kWh for grid tie, sky's the limit for battery backup. (ergo, DIY)

 

[CaptainHam]

Thanks Hedges, really appreciated...am feeling more reassured now about what I'm getting in relation to what.ive asked for. Electricity may as well be magic to me, hence why I won't be attempting any part of this install myself ?.

Just arranged a meeting with installer tomorrow so we can hopefully finalise the plans and get the ball rolling.