Bidirectional charging with an EV.

[Vicario]

There's an article in today's Times (Money section) which might be of interest to the forum. (I can't do a link due to a paywall).
It's about people who buy electricity cheaply during the night to charge up their EV and then feed it back into the house during the day directly from the car battery. Surely there are massive safety implications. Apparently this facility will be common in a few years: at the moment it's just a trial.

 

[bernardgreen]

Surely there are massive safety implications

There are safety implications with just charging the car's battery. Adding more complexity to enable the battery to be discharged to supply the house will only add more safety implications. Especially if the cost of the system compromises the design of the system.

The safer the system the more it will cost, the more it costs the less likely customers will buy that system. They will prefer to buy a cheaper and probably less safe system

 

[Taylortwocities]

A similar article, that does not require a subscription, can be found here
https://theconversation.com/electri...your-house-heres-how-to-make-it-happen-171430

Benefits are obvious, but offset by the cost of implementation, change of your nice new EV charge point etc...

 

[RandomGrinch]

....and more charge/discharge cycles on the battery.
I wonder what manufacturers (and their warranties) will make of it?

 

[flameport]

It's not likely to become a big thing. Some people will no doubt use it, but not most.

The main problem is that it requires that your car is parked at your home all night and most of the day as well, which rather obviously means it's rarely being used as a car.
Such people would be far better having a fixed battery system installed and not having a car at all.

Most domestic use of electricity isn't during the day anyway, and the whole concept of cheap electricity overnight isn't likely to last much longer either.

Fixed battery system and solar panels is rather more practical for domestic use, where the batteries are charged during the day and the stored energy used in the evening and night.

 

[EFLImpudence]

As, eventually, the cost of charging a car will be far more than that for household use, there won't be much point.

 

[JohnW2]

.... and the whole concept of cheap electricity overnight isn't likely to last much longer either.

Whilst I strongly suspect that that is correct, I'm a bit more confused by the bit of the sentence which preceds it,namely ...

Most domestic use of electricity isn't during the day anyway, ...

Are you suggesting that night-time domestic usage is already greater than daytime usage? I would have doubted that - and, in terms of the total UK demand in general, that still remains at it lowest between midnight and 6am.

Am I misunderstanding what you wrote?

Kind Regards, John

 

[flameport]

While E7 starts at midnight, daytime doesn't end there.
Peak usage for most homes is between 4pm and 9pm.

For people to charge an EV overnight and then run their home with it would either mean the vehicle isn't used all day, or it has been used yet still has ample capacity remaining to run their home.
Neither of those are valid, as they either don't need a car or the one they have has a battery which is far too large.

It's also why solar panels on domestic properties make little sense on their own, as the periods of peak generation are those where electrical demand in the property is lowest.

 

[JohnW2]

While E7 starts at midnight, daytime doesn't end there. ... Peak usage for most homes is between 4pm and 9pm.

Fair enough, but since you went on to talk about the (E7 etc.) cheap night-time period, I assumed that your reference to 'daytime' was to the non-cheap E7 'daytime' period.

For people to charge an EV overnight and then run their home with it would either mean the vehicle isn't used all day, or it has been used yet still has ample capacity remaining to run their home. Neither of those are valid, as they either don't need a car or the one they have has a battery which is far too large.

All true, but I didn't comment on that - but I certainly do not see the practice as viable for most people. Also, if/when they find a way of applying the equivalent of fuel excise duty to EV use, if that is done in some way in terms of EV charging usage (rather than 'miles driven'), then it would be a crazy practice - since one would be paying a premium price (including 'excise duty') for electricity used within the household.

It's also why solar panels on domestic properties make little sense on their own, as the periods of peak generation are those where electrical demand in the property is lowest.

That's a bit of an exaggeration, certainly at present, since, in the absence of EV charging, "electrical demand in the property is lowest" at a times of day when the UK is largely in darkness during any season. During summer, a significant amount of generation is presumably during periods of fairly high domestic deman.

Having said that, I don't really think that domestic/local solar-generated power has much of a part to play in the UK, anyway.

Kind Regards, John

 

[bsr]

Hi, there are already pilot projects in place in the UK to provide some demand response to DNOs by V2G charging (vehicle to grid).

Flameport, as usual the problem for DNOs is evening peak. Most EV owners Charge to 100% overnight, set of for work in the morning, back at say 6pm. For a suitable financial incentive why not use 10% of remaining charge to help the DNO balance the grid, and charge back to 100% overnight when electricity is cheap.

 

[Harry Bloomfield]

Are you suggesting that night-time domestic usage is already greater than daytime usage? I would have doubted that - and, in terms of the total UK demand in general, that still remains at it lowest between midnight and 6am.

Most domestic use will be during the early evening, declining as the evening progresses. Only those on E7 and similar, will have a higher load during the early hours and those charging cars. In the future it is all set to gradually change as more will be charging their cars and many more using electric for heating to replace gas.

 

[JohnW2]

Most domestic use will be during the early evening, declining as the evening progresses.

Yes, I realise that is the 'normal' pattern, even if I am a big exception (see below). However, what confused me into asking flameport the question (to which you are now responding) was that he had written ....

.... Most domestic use of electricity isn't during the day anyway, and the whole concept of cheap electricity overnight isn't likely to last much longer either.

... and, particularly given the second part of his sentence, I had (wrongly) assumed that his "during the day" referred to 'day' vs. 'night' (e.g. in 'E7 terms'), not a perio stopping at or before 4pm!

Only those on E7 and similar, will have a higher load during the early hours and those charging cars. In the future it is all set to gradually change as more will be charging their cars and many more using electric for heating to replace gas.

Indeed, and I agreed with that in my original response to flameport.

Mind you, not so long ago flameport seemed to be challenging me for suggesting that very thing, instead suggesting that everyone would start charging their cars when they got home from work, right in the middle of the current 4pm-9pm peak demand time (rather than waiting until much later in the evening). However, as I responded at that time, if E7/whatever timings remained as they currently are, such that it was much more expensive to start charging ones car when one got home than it would be if they delayed the start of charging until around midnight, I reckon that a substantial proportion of EV users would delay the start of their charging

As intimated above, whilst one can talk about patterns of demand for 'average/typical' households, and certainly the total (or average) demand across all households, that does not necessarily mean much (if anything!) in relation to any particular individual household, since they are not all 'born equal', and mine must represent a fairly extreme deviation from the 'average/typical'. Below shows the average pattern of my installation's electricity usage over the past nearly 5 years (~1725 days) (which hardly shows 'maximum demand/usage' during the 4pm-9pm period ) ...

Kind Regards, John

 

[Harry Bloomfield]

Below shows the average pattern of my installation's electricity usage over the past nearly 5 years (~1725 days) (which hardly shows 'maximum demand/usage' during the 4pm-9pm period ) ...

I think we can agree that you are not a typical energy consummer..

 

[JohnW2]

I think we can agree that you are not a typical energy consummer..

I think we can

However, I'm not sure that I am necessarily all that atypical of energy consumers who have E7 (or similar tariffs). As I recently illustrated, what you saw in my latest graph represents ('only') fractionally under 50% usage at cheap/night rate. Given that E7 tariffs can require anything up to 40% night usage in order for them to be financially advantageous, I would doubt that (m)any of those who 'appropriately' have an E7 (etc.) tariff can be dramatically closer to 'typical' ("peak demand 4pm-9pm") than I am.

In my case, a very substantial proportion of my night-time usage (indeed, around 25-35% of my total usage) is attributable to water heating (I could use LPG, rather than electricity but, at least when I last did the sums, E7 electricity was a little cheaper) - and the graph below shows my average consumption over the past ~5 years excluding the water heating - so the night-time usage shown is mainly kitchen/utility appliances (primarily a dryer).

It took me a while to work out the reason for the little bump between 9pm and midnight. However, I eventually realised that I often go to my office briefly during that period and, in addition to minor factors such as lighting and IT equipment, since the room is often not heated during the evenings, I quite often put on a fan heater for a short period! I'm less sure why there is a (very small) progressive rise between about 10am and 10pm.

Kind Regards, John

 

[motorbiking]

Batteries in EVs are incredibly expensive, why would you waste your cars charging cycles by powering your home when you can fit a static battery for a lot less? Not to mention the loss of warranty (on Tesla's at least).