How to rig up an off grid AC system

[Moxi]

Sorry for the title, not sure of the correct terminology, normally I would undertake copious reviews and studies to determine the solution but I am trying to stop procrastinating so much and going for a faster solution.

A while back I was fortunate enough to get a sunnyboy 1100 for free, its currently stored in the turbine bunker and I was hoping that I could set up an AC ring main for the bunker and the gardens which are all across the road from the cottage.

Is it as simple as buying a pure sine waive inverter, connecting it to a battery to produce an "artificial grid" for the sunny boy to synchronise to, then plug in the DC panels to the sunny boy to supply power and then fit a battery charger to the battery to charge it from the "artificial grid"

Over-simplified to an extent but just trying to confirm the basis is sound or otherwise ?

Moxi

[Saladin]

Hi Moxi,

It's that simple if you get the right kit. The kit is not simple, far from it. It's hella sophisticated. Synchronising to AC is not easy. I have a pile of e-waste to demonstrate the difficulty.

The SB sounds old like it might not support FacDelta derating. You can still make it work it'll be a lot clunkier though.

First you need the right off-grid inverter. That's AC coupling capable. Also an interface like the RCC02

Then the newer sunny boys would be better for this.

To be honest for 1100W I'd keep it simple and DC couple. AC coupling is a bittova pain in the hoop to dial in.

Here's Studer's white paper on frequency control integrating old clunker SBs etc. You can also use line voltage creep etc.

I believe you can achieve the same with Victron Multiplus and SMA sunny Island. I've good experience with Studer they're the most rugged out there.

[Moxi]

Cheers Saladin,

I was starting to gather that its more involved due in part to the lack of early replies, sure enough in the mean time I resorted to type and started to look at the details available on the where I started coming across the sort of thing you have noted.

Moxi

[Tinbum]

It's not too hard to do but you do need the proper kit.

I run off grid using SMA Sunny Islands. My first iteration was with a Trace inverter which was back a long time ago. https://www.windandsun.co.uk/pages/trace-inverters

The inverter has to be able to use any excess energy in the grid to charge the battery to enable it to control the grid. For example you can't use a Sofar ME3000SP EPS to run a grid as that inverter isn't able to 'back' charge the battery internally on the EPS outlet.

[Saladin]

I AC coupled an SB1700 with 1kW of panels onnit to a Studer AJ 1200 rudimentary inverter just to see what would happen. It worked grand until the battery was charged then tripped AJ overvoltage which aunty-islanded the SB1700. Bittova bull in a chinashop method. You could make it work with a Tristar PWM in diversion mode.

I've also AC coupled Studer XPCs, SIs and a C2600.
I think most transformer designs are reversible. That doesn't mean they support any kind of battery charge control.

The XTMs are designed to handle GTIs. They can proportionally increase frequency, or voltage or dump power upstream depending on your preferred regulation method.
I husta have an XTM dumping upstream triggering an iBoost...also messy the overspill is a big issue with CTs. Nothing beats a Tristar on response time and accuracy.

The best application for an SB1100 in my opinion is plugged into a radial on a 13A socket at your mum's house or some other installation with a ridicolously high constant daytime import (farm/workshop etc..) with 3 panels on it and rely on the abundant permaload to prevent backfeeding.

Even when you do get frequency control to work; running modern SBs in parallel is a right pain too. The hysteresis plays havoc. Doable if you cascade them with a wide frequency band. DC controllers are much better at playing nicely together. Hence I run 2:1 DC to AC coupling.
Thuther thing is AC coupled systems can't self-recover.

[Tinbum]

Even when you do get frequency control to work; running modern SBs in parallel is a right pain too. The hysteresis plays havoc. Doable if you cascade them with a wide frequency band.

I don't find it a problem. I use an Arduino to frequency control loads and then if it runs out of loads the 4 SB's/Tripowers throttle back depending on how I have set their frequency curves. The only slight problem I have is that the oven clock gains time.

[AGT]

Personally I would keep the pure sine wave inverter away from the grid tied inverter magic smoke will be released.

[Moxi]

I need to rethink this to ensure I get the right kit and that I don’t impinge on any regs.

Primarily over a period of time I want to put up quite a lot of extra pv in the gardens, up to 3kW of any of this would ostensibly go straight in to the EV6 battery ideally anything more would then go under the road back to the house and be used there or go into the house battery via the ac coupled solis but it’s this second element that I cannot see how it can be done - it’s been a busy day so I’m hoping I am just tired and missing an obvious solution.

It also need to be done in discrete chunks as the kids are getting older and needing more time and money so I have to plan campaigns in between their needs.

Moxi

[Saladin]

I don't find it a problem. I use an Arduino to frequency control loads and then if it runs out of loads the 4 SB's/Tripowers throttle back depending on how I have set their frequency curves. The only slight problem I have is that the oven clock gains time.

My two SunnyBoy HF's like to leap frog. It's a function of how fast the micro-grid increments the frequency according to which GTI is responding to the frequency. I may have built my own paradox.

Clocks..haha..time's not real..if we all stop believing in it does it still exist? I live in the eternal now and I'm running a nominal 52.8hz (Schumann resonance extended) because it phase locks to the planet's 8th harmonic and I find the binaural beats therapeutic...that and I'm building a resonant field to go beyond the matrix...either way the clocks are gonna be wrong...not despiting the fact all they are doing is referencing the rate of rotation of the planet and that's inconsistent because the more of the ice sheets we melt and ground water we pump the more mass we send to the equator and slows the spin of the planet..

Primarily over a period of time I want to put up quite a lot of extra pv in the gardens, up to 3kW of any of this would ostensibly go straight in to the EV6 battery ideally anything more would then go under the road back to the house and be used there or go into the house battery via the ac coupled solis but it’s this second element that I cannot see how it can be done - it’s been a busy day so I’m hoping I am just tired and missing an obvious solution.

Fwiw I can do that. DC or AC couple solar in the bunker to a Studer Xtender and that will "export" anything beyond absorption power upstream in your case to the feeder cable from the house, I would put a second Xtender at the house (grid former acting as network primary) that can charge the house battery from the bunker and the Solis.
You could take it further and make a micro network where one Studer becomes the voltage source and the downstream become the current source.
I've implemented exactly this based on stand-alone casemount inverter-sets.

The secondsol link I posted earlier is good. The used 4kVA inverters are going for ~€700 there last time I checked, I've bought two from them and they're still going. At that age I replace the line filter caps and they're generally good for another decade. I have quite a few myself seemed safer than a savings account the way the money printers inflation is going. Jury's out on that one...I''ve water damaged one, lightning damaged another and one's in quarantine because I have too many spares to care why it's taking out RCDs.

This topology is pretty easy to implement* (relatively for an electro-technical type). You effectively only need to enable 3 settings on the RCC-02

In terms of impinging on regs. You can program the system to only run forwards...ie. only battery charger load supply and stand-alone when capable. You can split the rig to have your network compliant gear on the network and the off-grid off-grid if you have an abundance of over-supply.

[Saladin]

If the house has a battery and the bunker has a cable why does the bunker need a battery etc?
Can't you put PV on the bunker and export to the house with a second AC coupling inverter in the house on the same battery albeit a larger one if needs must to absorb the extra capacity and run the extra load?
In terms of efficiency one battery is always better than two unless there's cell disparity issues.