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Questions about V2G, V2H and V2Everything

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Mars
 Mars
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We don’t drive a lot, so an EV was never a priority for us to decarbonise, but it may be the next expensive thing we consider due to the flexibility of the car’s battery. So I have a number of questions.

I know that CHAdeMo vehicles (such as Nissan) have brought V2G compatible car models to the market and that Nissan Leaf cars can be discharged to the grid. As a homeowner, I’m not sure what the benefit of V2G is. Is it as simple as exporting electricity when it’s expensive and buying it cheap at 2am, essentially flipping energy. 

Far more intriguing is the prospect of V2H. If you’ve got a large battery in the car, using it to power your home seems a no brainer. Is vehicle to home available in the UK, and if so, which brands have vehicles? Can you recharge via PV? How much extra kit do you need to get this working with your home’s energy demands. Anyone done this or considering doing it?

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Majordennisbloodnok
(@majordennisbloodnok)
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We're certainly looking into this now.

We've made a lot of changes in the last year, and the only thing we are now looking back at and thinking we'd have done differently in hindsight is the sizing of the battery. Our ideal would have been quite a bit larger than the 6kWh one we have currently, and that's because it was sized before we found an installer to spec out and install the ASHP.

As a result, the idea of V2H makes a lot of sense to us, especially if it still allows us to export any excess to the grid as well. Nonetheless, we'll probably be waiting a little while before putting this into action given the imminent predicted change in the vehicles from using their current battery technology to using solid state batteries (lighter batteries, so roughly twice the energy density, so potentially much longer range) since a car with a 400 mile range could potentially allow us to get rid of our diesel workhorse altogether. It would also mean V2H could co-exist even better with a more frequently used car.

Still early days, so I'll be very interested in any experiences anyone has to share.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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 robl
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We have a 30kWh Nissan Leaf with V2G on a trial by OVO, which we've been on for almost 2 years.  The car is on our driveway connected by a Chademo connection most of the time to a wallbox made by Indra.  The charging and discharging is managed by Ovo, with the proviso that it is 80% full in the morning or at another time of our choosing.  Typically the car charges to 80% during the night, and discharges to 25% between 5pm-10pm, although sometimes the car alternates charging then discharging repeatedly during the day.  The 80% and 25% are chosen by us, to give good battery life and enough range for an unexpected short trip.   

We are paid 35p/kWh when the car discharges, and pay out 17p/kWh for our electricity (which includes charging the car for it later to export).  The rates are quite artificial due to it being a trial; shortly this trial will be over, and our elec bill might go up - at the moment our energy bill is approx zero (heatpump + PV, gas standing charge only).  We are likely to swap to the Octopus Go tariff after the trial, and I expect re-program our unit as a V2H only.

It's great to re-use a car battery for this, as it's quite large and generally available.  Of course battery prices are getting cheaper, and a home battery doesn't drive away when you need it! The cost of the V2G/V2H wallbox is quite high (new price £2.5k - £10k) due to low demand right now.  There is also relatively high parasitic consumption, of around 80W, equating to a significant 2kWh/day.  This is due largely to the chademo connection being constantly ready; the car plug has an electromagnet to prevent it being pulled out - this is always warm to touch, both the car and wallbox have large contactors constantly activated.  I understand Indra is working on improving these aspects.

We will keep it after the trial, and re-use it.  Consider that a 9kWh + hybrid inverter can be installed for around £5k, while it's capacity is a little smaller than our V2H used capacity, it is slightly more efficient.  Of course a newer car will likely have a larger capacity. 

 


   
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(@mattengineer)
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@robl 

Thank you for the review, I’ve signed up for the new trial that Indra is undertaking in to V2H and just waiting whether we’ve been accepted. 

Couple of quick questions, where you able to have the unit converted to V2H? 

I was wondering on how effective the inverter ramped up and down? One thing that really put me off the givenergy battery was that it would take in excess of 15 seconds to ramp up and down. 

I appreciate with this solution the standby losses are high because of the connection but I presume the car/battery take care of this? 

When you consider that Nissan produce a 62kwh leaf this type of technology could be a game changer for an ASHP. 

 

 


   
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 robl
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@mattengineer 

Yes, we had no trouble getting it changed to V2H.  I emailed Indra, they asked me for confirmation that I owned the unit - I did, as the trial with Ovo was complete.  Then they changed the programming remotely, from V2G controlled by Kaluza to autonomous V2H.  It has worked flawlessly since then as V2H.

We haven't yet managed to get Octopus to connect up to our smart meter sadly, so are on a standard tariff still.  I expect they will sort it eventually - I'm pretty sure it's a software issue, as our gas meter connects (it connects via the elec meter), but not the elec meter.  We still have a gas meter and boiler, just don't intend to use either any more, all being well will remove them next summer.

I believe that the Indra V2H is very fast at load matching, <1s.  I will perform some measurements to check (I'm an elec eng, and have some kit at work).  The Indra V2G/H has 1kVA reactive power I recall, which *sort of* doesn't matter - I guess it has massive filters on the mains side, but it means I need V*I not just I measurement.   


   
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 robl
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Here's a 'scope plot of it working.  Red is Voltage, Blue current on our mains tail, black is V*I. 

At the left hand side, there's very low real power, but a kVA or so reactive - if you look closely, the black line is on average at zero. 

Then at the left marker (vertical feint dashed line) a 3kW kettle is turned on, and left on.  It takes the V2H 600ms to completely compensate for it.

Enjoy 🙂

KettleTurnOn WithV2H

   
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(@mattengineer)
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@robl Thank you for posting, it’s really helpful to get real world views on equipment. 

My understanding of the V2H trial is that it will optimise self consumption with the optionality of schedule control. Simplistically, I’m hopeful that I can set it to charge only during off peak electricity and then discharge for the remaining 20 hours of the day. 

I presume your system does this through a CT clamp on the meter tail and the inverter ramps up and down (not sure if you have solar) to balance to nil. 

The inverter specs are stated as 6kw so in theory at low base load I.e. overnight the round trip efficiency will be quite low? 

Apologies for all of the questions, but it’s potentially a big departure / investment and I want to make sure that I have facts correct. 

Any other feedback / considerations that you think of would be welcome. 


   
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 robl
(@robl)
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@mattengineer 

We have 4kWp of solar, dno informed, about 9 years ago.  PV is brilliant, if you haven't got, get as much as you can fit and the dno will allow 🙂

We got the V2G unit just over 2 years ago.  First a G99 A1-1 form was sent to the dno to ask permission, and they allowed 16A export from it, potentially at the same time as 16A from the solar.  Ovo organised all this; I assume they asked for 6kW, but were bargained down to 4kW.

The above worked for the 2 year trial, with Ovo/Kaluza in charge of the unit charge/discharge, we got paid more when exporting than the import elec cost.  It wasn't a massive difference, but it was in our favour, and the unit came free 🙂

Now the trial is all over, and we've changed the unit(now ours) to V2H - it always had a CT clamp on the main tail, which feeds back to the Indra box, and now that is put to use as a feedback signal.  I'd have stayed on the scheme (mainly due to apathy if I'm honest!), but Ovo abandoned it - I think because not many people were on it, and they had bigger things to worry about (like absorbing people from failed elec companies).

I think the efficiency is good; pretty sure it's SiC parts in the box.  It doesn't get noticeably hot, nor does it run the fans on high (except on a mains cycle startup, that will scare you).  The major "efficiency" issue is the 2kWh/day loss due to keeping the Chademo permanently live.  If you do find efficiency figures, they will ignore this bit!  If you charge at night, discharge during the day, repeat, I think you would need an import of 13.5kWh at night to reliably get 10kWh back, leaving it plugged in 24hours a day.  Our unit is limited to 4kW (in and out), so we could get a max of 16kWh in that 4 hour window. 

TOU tariffs do make it all quite an effective financial tool, especially if your car is sat in the drive a lot.  The price difference from day to 4 hours of night is (oddly IMHO) high (Octopus or Eon).  I say oddly, as we seem to use gas all day and all night, there's a gas crisis, and I understand the most expensive kWh sets the elec price.

Pic of last month from gridwatch, orange is gas.

image

 

 


   
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(@mattengineer)
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@robl 

Again thank you for the insight, as I’m buying a leaf for the specific task I’m trying to work out which size. Old and cheap 24kw or 62kw which would be great if I upgraded to an ASHP. 

I’m incredibly keen on solar but struggling to find an installer I’m comfortable with. 

In terms of the losses from keeping the dc connection live presumably this comes from the battery rather than the grid. 

Interestingly watched a review of the solaredge battery and it seems to really struggle with inductive loads like fridges, with the owner still having just under a kw of grid draw per day with a full battery. 

It doesn’t sound like a lot but it’s c£124 a year at current prices. 


   
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