Victron

I've done a lot of lurking around here & dug deep into researching. I'm leaning towards a Quattro II system, not sure if I can afford it. This is the brief I'm going to approach solar companies with, any feedback on it would be appreciated.

Needs:
1. Maximised PV array size to get more power during Winter months (up to limit of inverter capacity).
2. Compliance with NC6 & qualifies for grant
3. Bird proofing
4. 10kW Battery (minimum)
5. Continue to provide power to the house during blackout
6. Divert excess energy to heat water
7. Load shifting (dynamic pricing management)
8. Configurable by user (manage load shifting etc.)
9. Access to chimney

Wants:
1. EV Charger (don't currently have an EV, may get one 4+ years into the future)
2. Support for adding a backup generator (outdoor connection)
3. Uninterrupted power to important circuits during blackout
4. Boost power in case of brownout (like Victron Quattro II or Multiplus II)
5. Victron Cerbo GX
6. Dynamic pricing management not dependent on cloud computing
7. Screen
8. European inverter company
9. 20kW Battery (ideally)

This ended up a big ramble, I had to put it into Gemini to tidy it up to make sense of my stream of consciousness so apologies if it reads too AI like and goes off on a tangent in places😋

A couple of things before we get into spec'ing out a system: what is your annual electricity bill at the moment? Do you have a heat pump, and do you cook with electricity? I ask because that dictates how much you could or should invest.

I’m in an all-electric house (including an EV) and consume about 16,000 kWh a year. Before I got my Quattro and battery, my bill was about €2,300 a year, but I’ve also had solar PV for about five years. The way I looked at it, if you spec your system big enough, you can realistically achieve a zero electricity bill and easily make a couple of hundred euros a year back from the grid.

If it pays for itself over 5 to 6 years, then €2,300 x 5 years is an €11,500 return—this is a very good payback, it could even cover a loan if you dont have the cash available.

At the moment in Ireland, we have a few very good smart meter tariffs with excellent feed-in rates. One is head and shoulders above everyone else (raise a glass to Mr. Pinergy!), and you can make decent money if you get a big enough battery to cover your daily needs during the winter months first. For the other 8 months of the year, you are basically making gravy. I have a 30 kWh battery, and during the winter, it covers an average of 90–95% of my consumption. Right now, my bills are actually €100+ in credit per month; this is my first summer on the gravy train.

Enjoy it while it lasts, though. As more people get solar PV, EirGrid isn't going to like us exporting back. We will eventually end up like parts of Europe where they charge you to export in the middle of the day or only give you 1 or 2 cents. Future systems will be all about storing and using your own PV later. I think we are a few years off from that, but the gravy train of the 25-cent feed-in tariff will definitely go.

I suppose what I am saying is that you might be better off going big. Looking at your questions, the blackout transfer function is high on your list. I can confirm that with the Quattro, you don't even notice when the power goes out—the lights and even the internet don't drop for a second. I do also a have an additional Anti-Islanding unit as back up and ESBN will want this to be grid compliant.

This is another reason to go big, perhaps into the 15 kVA range. If you just want backup on certain critical circuits, it can actually be more work trying to isolate them on your consumer board. Having a big-ass inverter-charger means you can back up the entire house its actually a bit simpler. I can be cooking with the heat pump running and everything else on without any issues.

As Unkel said, the EV charger is like a separate project and doesn't really have anything to do with what you are trying to achieve here. I actually moved my EV charger to the grid side of my system so that if the utility power goes down, the charger goes down too. I didn't want a scenario where the power cuts out in the middle of the night and the car starts sucking 7 kW straight out of my domestic battery. I can still charge the car from the battery if I really want to by forcing an export to the grid, but that is highly inefficient. That said, the faster you move to an EV, the quicker your overall payback will improve—saving maybe €300–400/pm compared to diesel?

As Victron's chief brand ambassador on boards.ie 😉, they are a Dutch company that has been making inverters for 50 years. They specialize in off-grid work, so they are built to be incredibly reliable. All of their control is handled locally on the Cerbo GX rather than relying on the cloud, and they update their VRM software regularly with new features.

They do have an official software called Dynamic ESS (DESS) for dynamic tariff control, which is designed to take advantage of day-ahead smart pricing. Some people complain about it, but it’s a fairly complicated setup because it has to predict both your solar generation and energy consumption per half-hour for the day ahead. I don't use it myself—I use Node-RED and developed my own management system instead. Having Node-RED running directly and locally on the Cerbo GX with active support from Victron is fantastic. If you can dream it, you can program it with AI these days.

When it comes to battery size, my mantra has always been: better off looking at it than looking for it. I have 30 kWh, and while I sometimes think I’d like more, I physically cannot put any more charge into it during the cheap three-hour night window I use. My system can go from 10% to 100% state-of-charge in three hours at a 10 kW charging rate, so there is no practical point in me getting more capacity. The 30 kWh setup is perfect for me. Ultimately, your battery size might depend on the inverter size you choose. But with 20kW that will cover more than enough if you dont have a heat pump.

One final note: since you don't have an existing PV inverter, you will need a Victron solar charge controller (MPPT) to get that power into your battery, so budget for that extra cost.

And don’t worry about birds nesting under the panels! That’s a UK thing for some reason—they seem to have a bird problem over there that we just don't experience here. I have yet to see a single post on Boards about birds nesting or unplugging MC4 connectors.

You might have more questions after all this, so fire away!

That MultiPluss ii 6K5 is painfully close!

Thank you @ECO_Mental & @unkel , you've been really helpful.