Domestic battery installation.

[Stumuz2]

We have just had a battery storage system installed in the last few days.
It's a 9.2kw givenergy system linked to our 4kw solar array.
https://www.givenergy.co.uk/pdfs/produc ... %209.5.pdf

So far it's working well.Effectively knocking off our electric bill.

Cost £5Kish installed.

[BritDownUnder]

The problem I have with grid connected batteries, in Australia at least, is that they cannot function properly in a black grid situation as they cannot charge when the grid is down from your PV directly, they seem to have to charge from AC. So when the grid goes off you just have what happens to be in your batteries and then it is a 'brick', a big brick.

Having said all that I will probably get a battery in a few months.

After that I will probably go 'off-grid' in a few years even if I stay living where I am in the middle of a small town.

[Stumuz2]

The problem I have with grid connected batteries, in Australia at least, is that they cannot function properly in a black grid situation as they cannot charge when the grid is down from your PV directly, they seem to have to charge from AC.

Good point. I will ask the installer who is coming round Monday to do the final commissioning paperwork.
Although, we will probably use the 5kw genny, via the changeover switch, in any sustained blackout.

Get back to you on Monday.

[Stumuz2]

Yes you are correct.
In a power cut, it will not charge from the PV, but we will be able to use the 9.2kw in the battery. If it's full.

In a prolonged power cut we would need to use the changeover switch to cut off the grid and plug the 5kw diesel genny in.

[BritDownUnder]

Yes. Same as Australia then. For the life of me I don't know why these household batteries usually don't have the ability to charge while 'off grid' or islanded. It would probably require a small extra circuit to convert PV DC voltage of about 300V DC to 48V DC to charge most batteries. It could be that most batteries are added on to existing solar PV systems so the DC goes into the existing grid tied inverter and the battery is charged from and feeds to AC mains voltage using the same circuit.

There is the worry amongst electricity supply companies that there will be a flight 'from' the grid amongst consumers in Australia in the next few years taking out the standing charges that the electricity retail companies like, leaving poorer consumers still with the grid.

[BritDownUnder]

Well I did get a battery installed - a Tesla Powerwall - and my only regret is that I did not get two of them as one is probably inadequate.

I watched the installers, the apprentice was born in Manchester and liked the Trafford Centre, and probably missed it a lot.
Half way through the installation after the three of us managed to lift the 120kg battery onto the wall they started installing another box they called the Tesla Gateway and I mentioned the lack of off grid charging from the solar PV and the lead installer said that was not the case. They changed the system of wiring so the Main circuit breaker in the distribution board had its output wired to this Gateway which had a large three phase contactor in it that made a satisfying clunk. The purpose of this was to isolate your system from the grid while the grid supply is down. After a while they finished wiring it and managed to take down my Zappi's (Car charger) CTs until they reconnected them.

The battery charged quite quickly being able to charge at 5kW and has a capacity of 13.5kWh. A small problem came when I then tried to charge the car as the Tesla battery tried to make a contribution which was just silly as the charging mode is set to make sure that no power is exported to the grid. I turned off the car charger and tried again and this time it did not charge the car but stayed off.

Getting the Tesla Powerwall to contribute or not contribute seems a bit hit and miss particularly on the the first day but there seems to be a bit of machine learning there as the second day it was better. I has also entered in my time of use tariff structure which also helped as it prioritised the most expensive electricity times and zeroed power imports at those times.

Then I simulated a power cut and to my great surprise it not only provided power to the whole house but also accepted all of the contribution from the PV system. The installer did say that mine was one of the few inverters that was compatible with this. I did notice that the contribution from the PV was about 6.5kW with the house using about 2kW and the partly charged Tesla recharging the remaining 4.5kW. This worked for about 50 minutes until I restored the power. What would have happened if the PV was too much for the battery charging plus house load or if the battery was fully charged I am not sure. I am not sure where the excess power from the PV would have gone unless the PV inverter was smart enough to reduce output. I am not sure I will try that without a bit of research.

As I said my only regret is not getting two Powerwalls. As they say in America - Go Big or Go Home. The Powerwall was Made in the USA BTW.

[Catweazle]

I'm pleased to see that many ev batteries are over 350vdc. You might be wondering why, I'll share. I run some CNC machines and I'm just acquiring some others at a good price. Typically these large machines require 3 phase supplies, often 415v, which makes them unattractive to the average hobbyist, however the inverters that drive the motors sometimes have a DC input option, often up to 520vdc. A DC input option might make it possible to operate these machines from surplus ev batteries, charged from wind or solar and without the ongoing costs of a heavy single or 3 phase mains supply. This could open up many income possibilities for rural communities.

[BritDownUnder]

I remember there was a company in New Zealand that made a converter that converted 240V single phase to three phase and looked like some Heath Robinson contraption and cost a bomb to buy.

The DC input to the CNC's variable frequency drive is certainly useful. I hope my battery lasts a bit more before it gets repurposed for that use. From an engineering point of view when you rectify three phases (415V AC line to line) with a six diode (or thyristor) arrangement you get about 525V DC as the output.
I have often thought of some uses for my excess power to make money but have never found the time to decide what that should be. I recall one guy at work had some kind of plasma cutter machine and made quite a bit of money.

[adam2]

Converters to derive 3 phase from a single phase supply are available, there are 3 different types.
Firstly a standard 3 phase alternator driven by a single phase motor These work well but both voltage frequency tend to fall with increasing load.

Secondly, a tapped transformer and a capacitor generate a fake three phase supply from single phase input. Cheap and the output frequency is locked to the input frequency. Voltage varies with load. Do not handle variable loads well.

Thirdly is a three phase inverter powered from a rectified single phase supply. These work very well and can change the frequency, for example to work 60 cycle machines from 50 cycle mains.

Or simply obtain a 3 phase supply. 3 phase is now available almost everywhere though there are exceptions, even in urban areas.

[Catweazle]

Connection to 3ph can be expensive in rural areas, the same areas that often have substantial empty buildings and no problems with neighbours complaining about noise. The capacity of supply can also be an issue, I have several machines with 11kw main spindle motors, peak consumption might be 30kw per machine, although the power meters rarely show more than 20% of that in real world use. A surplus ev battery can supply the peak power, allowing smaller connections.

I look forward to seeing some of the large surplus equipment - much of it mothballed due to electricity prices - being used in almost off-grid locations from renewable power rather than being exported to India or melted for scrap.

[clv101]

That's a really good point. Being able to use DC is big advantage.

[BritDownUnder]

That's a really good point. Being able to use DC is big advantage.

All three phase motor drives will have a part of the circuit where the mains frequency 3 phases are rectified to DC usually with a capacitor and maybe inductor to smooth things out and then after that point the DC is converted back to three phase AC again with semiconductors firing at specific times and for specific time lengths with a variable voltage and variable frequency.

A lot of rural supplies in Australia and NZ are single line earth return where there is a single conductor taking a single phase to your property - just to save money and copper/aluminium - and your neutral is just a spike hammered into the ground. The current goes back and forth to the transformer via the soil and rocks. A lot of HVDC also have this system and have huge earthing grids at their terminations.
Hence the three phase converters discussed earlier.

I did not appreciate quite how much power milling and CNC equipment requires.