Is my idea crazy or should I pursue it further? (EV as sole house battery)

[johnb80]

Just a note to add to @johnb80 post, the Victron capacities are in VA, not watts, so a 3000VA is around 2500watts with a correction factor of 1, like a toaster or other heater element type load, once you get into the other type loads, including anything with a capacitor, if not even going to attempt to come up with power efficiency factors.

I was keeping it simple (so I could understand it LOL)

The Victron units can be paralleled to increase capacity, but better still, is a load activated stepped turn on that feeds a second inverter into the AC supply side of the primary inverter, then turned off when no longer required ..... all programmable, not smoke and mirrors, but that Arthur C Clarke coined term sometimes comes to mind

Victron have really gone to town with the possible configurations. They all seem relatively easy and intuitive to configure and of course, there's a massive internet presence in forums etc with loads of experts ready to help.

Hopefully, if anyone wants to know, I can still remember how to do if asked .....

I'm sure you will along with the MMI that Victron supply it would soon come back to you.

The last item, if @johnb80 is referring to the Tesla Powerwall ..... I'd think twice about using one, they are built with cells containing cobalt, so susceptible to thermal runaway fire risk, LFP, LTO and Na+ suffer no such risk, last more cycles in a house battery load situation, and the salvage EV comes with all the battery monitoring, safety battery enclosure and the MG LFP variants output 220vac 50 hz at up to 7kw (7,000w divided by 220v = 31.8 amps) so make sure you use 5 AWG multi-fine strand conductor, 2 core and earth orange flex lead, to carry the load from the EV to the house power entry .... your call as to adding a plug and wall socket to make it a plug in appliance if it makes all concerned feel happier about it

The EV batteries do have some disadvantages, cooling & heating, the format of them is not ideal both physically and electrically, the BMS is designed for the car integration whereas the BMS units meant for domestic supplies work as designed and communicate with the inverter(s).

 

[Everest]

Thats my 10c I know not everyone agrees with me and I have even been christened 'some bloke in Lincolnshire' in some quarters, however, all what I have stated above I have installed in my home and it has been working for over 4 years without issue.

Totally agree with all that... you were one of the "others have done that" when I mentioned using V2L to charge home storage batteries.

Well, nearly everything you said...

Above 3.15kW you need to do a G99 application

... the pedant in me will clarify that the cut-off between G98 notification and G99 approval is 3.6kW (16A at nominal 230V). Not that any of us are likely to be deploying such small inverters anyway!

 

[johnb80]

Totally agree with all that... you were one of the "others have done that" when I mentioned using V2L to charge home storage batteries.

Aye, infamous for my battery projects LOL

Well, nearly everything you said...

Oh dear, you were doing alright hehe

the pedant in me will clarify that the cut-off between G98 notification and G99 approval is 3.6kW (16A at nominal 230V). Not that any of us are likely to be deploying such small inverters anyway!

Oh dear, I was wrong, how can I ever live it down, oddly though, so are you
The limit for G98 is 3.68kW or less and three-phase systems with an output of 11.04kW or less.

Gotcha!

 

[Everest]

It is indeed 3680W... in my defence, UK Power Networks round it to 3.6kW in their application forms. Not that we ever "see" the nominal 230V. It's either around 250V when we're exporting or 220V (if we're lucky) when charging.

 

[Bam Bam]

It is indeed 3680W... in my defence, UK Power Networks round it to 3.6kW in their application forms. Not that we ever "see" the nominal 230V. It's either around 250V when we're exporting or 220V (if we're lucky) when charging.

To be fair a lot of companies create 3.6kW inverters for this reason.

Went to check that and the second I checked (Fox) is indeed listed as 3.7kW so they obviously rounded up rather than down!

 

[johnb80]

To be fair a lot of companies create 3.6kw inverters for this reason.

Yes they do, it's also the reason why so many solar installers fit an inverter of this size to avoid the G99 application which leads to very poor installation performance. Switch the kettle and the toaster on for breakfast and you're importing from the grid.

Went to check that and the second I checked (Fox) is indeed listed as 3.7kw so they obviously rounded up rather than down!

Aye, I'm sure there will be a tolerance in there somewhere.

 

[mikgle]

Hi,

I've been learning more about solar/battery setups and it seems to me that a great DIY way to maximise savings would be to directly use a cheap old EV as battery storage and home power backup.

The car wouldn't even need an MOT, so long as it had V2L and a decent battery capacity left. This would seem to be far cheaper than buying a brand new home battery and also much less work than removing the battery from the EV and installing it on the outside of the house in a custom side building or shed.

The main drawback would seem to be the space that a whole car would permanently take up, but assuming that was available, it seems like a good solution.

What have I missed or not taken into account here?
Has anyone done exactly this (as opposed to taking a battery out of an old EV)?

Thanks in advance for your comments, I am still at the beginning of learning about all of this.

Do you mean go off grid, or stay grid connected? If the latter then the inverter will need to be DNO approved..

 

[mikgle]

Yep, makes sense. I am not currently thinking of a heat pump because of their huge electricity requirements.

They dont have a huge load requirement.. my 7kW vaillant usually kicks off using about 3kW for a few mins then ticks over at 1kW..

 

[NikLiverpool]

Yep, makes sense. I am not currently thinking of a heat pump because of their huge electricity requirements.

I can confirm this. I have a Daikin 11kW heat pump. When it kicks in it starts at 3kW for like 10 minutes and then it stabilizes at around 800 W.
Only time I see it hitting 4-5kW is if I hit the boost option for hot water.

 

[mikgle]

I can confirm this. I have a Daikin 11kw heat pump. When it kicks in it starts at 3kw for like 10 minutes and then it stabilizes at around 800w.
Only time I see it hitting 4-5kw is if I hit the boost option for hot water.

I think people see the power rating of a heat pump and assume its the input.. its not, its the maximum output. I just had my ASHP annual service and the SCOP, which is a measure of its efficiency, was 4.8. Thats 480% efficient!

 

[T1 Terry]

I think people see the power rating of a heat pump and assume its the input.. its not, its the maximum output. I just had my ASHP annual service and the SCOP, which is a measure of its efficiency, was 4.8. Thats 480% efficient!

As far as I know it is called the COP, coefficient of performance, the difference between the energy required to drive and the amount of work it can do.
In this case, the watts of electrical energy used to move the number of watts of heat energy. The systems with inverter technology do away with the start up load and instead, change the speed of the motor to produce the work required, much the same way as the inverter in an EV works ....
They can be set into "ECO" mode where they use even less power because they change the pump speed over a longer cycle and never let it attempt to achieve something that would require a crazy amount of energy.
As an example, some had the idea you had to turn the thermostat down to 16°C to make the system cool faster or better or some such thing, but that just wastes energy, by removing the water out of the air faster, even if the temp is still up around 30°C, it feels cooler .... the opposite when heating, remove the moisture from the air and the cold shivers go away ....

T1 Terry

 

[decrep]

As an example, some had the idea you had to turn the thermostat down to 16*C to make the system cool faster or better or some such thing, but that just wastes energy, by removing the water out of the air faster, even if the temp is still up around 30*C, it feels cooler .... the opposite when heating, remove the moisture from the air and the cold shivers go away ....

T1 Terry

how long have we Aussies had A.C. and most of us still don't understand this?
If I had my way aircons would be stuck at 24°C in summer and 22°C in Winter.

However I think this post is about water not air.

 

[mikgle]

The COP, coefficient of performance, will be higher in summer and lower in winter due to the difference in air temperature for an air source heat pump. The SCOP = Seasonal Coefficient of Performance and is the mean figure over a year.. in summer my cop will be over 5, in winter around 3.5 and the scop is about 4.8 overall.
Compare that to a modern condensing gas boiler which is reckoned to be a max of around 85% efficient in real life. So my ASHP is 5 x more efficient than a modern gas boiler, thus equalising the difference in cost of the fuel as well as being more sustainable. When you can get a cheap tariff like octopus Go, solar and a storage battery then you're on a winner
Gone off the subject a bit but it's great how the various electrcal technologies can combine to provide very cheap, sustainable energy and transport. I know it's not 100% sustainable especially over winter but its not far off, as overnight electric here is pretty much 100% renewable and then solar during the day. What's not to like?

 

[T1 Terry]

When we finally get our new house built, I plan to experiment with the idea about the temp deep in the ground remains fairly stable and a heat exchanging medium can be used to move this stored heat/cool into the house and be recirculated and this used to improve the efficiency of HVAC systems .....

T1 Terry

 

[decrep]

Here a metre down it's a stable 21°C, just having a concrete slab and no carpets can really help.

 

[mikgle]

When we finally get our new house built, I plan to experiment with the idea about the temp deep in the ground remains fairly stable and a heat exchanging medium can be used to move this stored heat/cool into the house and be recirculated and this used to improve the efficiency of HVAC systems .....

T1 Terry

Ground source are even more efficient than air source heat pumps..

 

[T1 Terry]

Ground source are even more efficient than air source heat pumps..

By combining fridge/freezer heat being pumped out with the circuit trying to draw heat in and dump the cold from inside the house, can add to the efficiency.
I remember seeing an evacuated tube solar heater that used some sort of oil as the heat movement medium, being sold by a mob that were one of the first to get into reselling stuff sourced from China. These things were designed for a lower temp climate than Australia, it would boil the water in the 250 ltr tank in less than a day.
Some builder ended up buying all the units they had and used then for in slab heating (concrete) and ran waterpipes parallel through one section of the slab and that was the water heater, just used a recirculating pump .....

T1 Terry

 

[Bam Bam]

Ground source and water source heat pumps will be preferable to air source.

Not many people have a lake, pond or river on their property so water-source is unlikely but I'll include it here.

The temperature differences of water and ground compared to desired house heating temperature won't vary as much seasonally as happens with air-source.

That said, I've been very impressed with our air source heat pump. It seems to get 4.75 average COP even in Winter.

It did drop to something like 3.6 on the coldest days, though, which is where the ground/water source would be better.

Don't have air conditioning with our air-water system, so there is nothing to be gained for having ground/water source in the summer. So the benefit of the ground/water source would just be for a few days a year. How much extra should you pay for better efficiency for a few days a year?

For as long as we remain mild in the UK and as long as the ASHP costs much less to install then I think they are the way to go.

For new builds I would say a ground source or district heating option would be preferable.

 

[Rolfe]

I was watching a TV programme the other evening that was a compilation of archive articles from the 1980s. (I was interested in the history of the 51st Highland division, and the regularising of the spelling of the Gaelic bible.) In the middle of it there was a segment about what was definitely a (sea) water source heat pump being installed in Iona abbey. It was amazing, and they said it was allowing them to dry out all the old stonework that had been exposed to the elements for centuries while the abbey was a ruin.

BBC ALBA - Prosbaig, Series 1, Episode 8

The 51st Highland Division is remembered at a special service held in Uist.

www.bbc.co.uk

 

[T1 Terry]

Ground source and water source heat pumps will be preferable to air source.

Not many people have a lake, pond or river on their property so water-source is unlikely but I'll include it here.

The temperature differences of water and ground compared to desired house heating temperature won't vary as much seasonally as happens with air-source.

That said, I've been very impressed with our air source heat pump. It seems to get 4.75 average COP even in Winter.

It did drop to something like 3.6 on the coldest days, though, which is where the ground/water source would be better.

Don't have air conditioning with our air-water system, so there is nothing to be gained for having ground/water source in the summer. So the benefit of the ground/water source would just be for a few days a year. How much extra should you pay for better efficiency for a few days a year?

For as long as we remain mild in the UK and as long as the ASHP costs much less to install then I think they are the way to go.

For new builds I would say a ground source or district heating option would be preferable.

We have a bit of a pond out the front, the Murray River, but that's a long way to run the pipes but we could always put a few coils in the rain water tank, it'd take a while to heat up 10,000 ltrs, but I'm not sure how much heating it would provide in winter ..... although it only drops to 0* for a few hrs in the morning maybe 3 days a yr ..... so it would probably store enough heat for that ......
Thanks for the idea, certainly worth a try ......

T1 Terry