EV Discussion thread

EricMears

JKenH said:

I take your point, once an EV user has a dual rate tariff there will be opportunities to move some usage off peak, such as dishwashing, washing machine and tumble dryer (if they have timers) 

With 'GoFaster' (alas no longer available to new applicants) dishwasher, washing machine and tumble dryer can all be started just before bedtime - indeed you might even manage a second load.

FWIW,  our Average Unit cost for November has been : 17.4 ppu.  I don't think there will be many 'non-tod' tariffs that might offer me a better rate.

Petriix

Let's be absolutely clear. At 40p/12p you'd only have to shift ~ 20% of your home usage into the off-peak window before your saving money vs the cap price.

4 hours is 17% of your base load so that's already pretty close to breaking even. All it takes is pressing the timed start button on your big appliances or using a £10 smart plug.

Without much effort my home usage is ~ 40% off-peak so being on Go is objectively saving me money before you even consider the EV charging. What's more it's the cheapest fixed tariff you can get and protects you from any potential rises next year should the government decide to scale back support in April.

To somehow twist this money saving opportunity into a hidden expense is, at best, willful ignorance. 

Exiled_Tyke

Petriix said:

Let's be absolutely clear. At 40p/12p you'd only have to shift ~ 20% of your home usage into the off-peak window before your saving money vs the cap price.

4 hours is 17% of your base load so that's already pretty close to breaking even. All it takes is pressing the timed start button on your big appliances or using a £10 smart plug.

Without much effort my home usage is ~ 40% off-peak so being on Go is objectively saving me money before you even consider the EV charging. What's more it's the cheapest fixed tariff you can get and protects you from any potential rises next year should the government decide to scale back support in April.

To somehow twist this money saving opportunity into a hidden expense is, at best, willful ignorance. 

Agree with this all the way.  At this time of year the dishwasher and washing machine are set to go on at night and they are the bulk of my electricity use.  The only other big one is cooking and I'm not doing that between 12.30 and 4.30!  Currently my import is 70% off peak and 30% off peak. Come late spring it will be a few kWhs off peak and pretty much zero peak.

Grumpy_chap

Petriix said:

Without much effort my home usage is ~ 40% off-peak 

That's interesting and, at risk of going off the EV topic, I am interested how this is done.

I have always assumed I can only achieve this by shifting high energy loads and that really means heating.

Space heating and water heating is via gas and can't be easily shifted in any case. 
I have made a bit of a gain there by ensuring to manually switch the hot water heating off before showering so as not to leave a tank full of hot water to lose energy while out during the day or asleep at night.
IF I was looking to time-shift, I suppose the water heating could be done to turn off at 4 am or something.

The easy win would be the dishwasher.  We put this one when we go to bed every evening.  It has a timer, so could set that to run at 2 am if desired.

Some items could be tumble dried and not be too worried about creases.  Again, there is a timer built in to the device.  Opportunity to load-shift would be minor though as we always try to avoid using the tumble drier.  So far this winter, we have only used it three times.

Washing machine is a consideration, but we'd end up with clothes all creased so need more time ironing.  Plus, the morning routine in our house is so panicked and rushed that finding another few minutes to hang out a load of washing would be challenging.

I am quite certain that those potential time-shifts would not be anywhere near 40% of total energy demand for the house.  I always thought that ToU tariffs were little more than modern-day E7 which was not famed for actually saving money overall.

What are the methods that people use to shift large proportions of energy demand to the short night-time window benefitting from ToU cost savings?

Petriix

It very much depends on what high power loads you have but, in my house, 17% of my base load plus all washing, drying and dishwasher equates to 40% of total home imports. Our only other big appliance is the oven and we don't use it that often.

I do have solar panels which cover the daytime base load for 2/3 of the year but I've found it's mostly better to export what we can't divert into the car and use the cheap off peak window for the big loads. Otherwise you need at least 80% to be coming from solar or it's actually costing more. 

Grumpy_chap

Thanks, so the items I identified as candidates for time-shifting are the pretty much aligned with your actual time-shifting.  

I am intrigued as to what the 17% of base-load you have time-shifted is.

Time-shifting the oven is difficult, unless you want a slow-simmered stew for breakfast.

There is also a big clarification now in your claim. 
Originally "home usage" was 40% off-peak but now "home imports" which is a substantially different metric.
What percentage of time-shifted load is achievable when all (electrical) energy input is considered?

Petriix

That's a complicated question as I'll try to explain... 

My total usage since January (when I switched to Go) roughly breaks down as:

2041kWh total home usage 
743kWh peak import
490kWh off-peak import
808kWh solar self use

That solar was all used in peak times so my off-peak home usage is actually 24% if you include the solar as peak. 

However, much of that usage could/would have been switched to off-peak if I didn't have solar, but it's hard to estimate exactly how much. I'd guess about quarter so it's more like 33% off-peak.

The 17% base load is simply because 4 hours is ~ 17% of 24 hours. On Intelligent Octopus you get 6 hours (plus) off-peak so it automatically covers 25% of your base load; but you need a compatible car. 

JKenH

Petriix said:

Let's be absolutely clear. At 40p/12p you'd only have to shift ~ 20% of your home usage into the off-peak window before your saving money vs the cap price.

To somehow twist this money saving opportunity into a hidden expense is, at best, willful ignorance. 

OK, let’s have a look at that example of 20% off peak usage for an Octopus Go customer and compare it with a customer on SVT. For ease of calculation, let’s work the figures with peak usage of 4000kWh and off peak 1000kwh (although it doesn’t matter what the actual figures are provided the 80/20 ratio remains the same.)

Octopus Go

1000kWh @ 12p = £120
4000kWh @ 40p = £1600
total 5000kWh = £1720 or 34.4p

SVT

5000kWh @ 33p/kWh = £1650

so it is £70 cheaper to be on the SVT. 

The important point though is what is the effective rate you are paying for your off peak compared to SVT?

£1720 is equivalent of paying for 4000kWh @ 33p (SVT ) = £1320 plus 1000kWh @40p= £400

If you were on SVT you would pay a flat rate of 33p for all your usage but for the 80/20 user being on Octopus Go means you are paying the equivalent of 33p for peak usage and 40p/kWh for your off peak usage. 

I have no problem with Octopus Go. For some like @Michaels it works brilliantly but unless an EV user has significant off peak usage it can work out more expensive. Hopefully for most it won’t. 

That, though, was never my point in starting this debate: my point was that in most cases for the average EV user it is disingenuous to claim that you can charge your car for 5p or 7.5p or now 12p/kWh without the caveat that you pay more than the SVT for your peak time usage.

I would hope that people are not deliberately trying to mislead; they just haven’t thought it through. Having had this explained I to them I would hope in future calculations a more realistic rate calculated on their own experience will be adopted.

Grumpy_chap

Petriix said:

The 17% base load is simply because 4 hours is ~ 17% of 24 hours. 

AIUI, that time proportion does not necessarily equate to base-load energy proportion.  

My base-load electrical demand comprises:
 - things that are just "on", fridge, standby items, alarm, wi-fi router etc.
 - things that it is difficult to do much about other than energy-efficient fittings (which I take as a given in this forum), lighting, laptop, printer etc.  Things that are just "on" for large parts of the time

A purist might even argue that things like lighting are not in the "base load".

What do you consider to be "base load"?

The only thing is, that "base load" is really all quite a small power user so having 17% of that during cheap rate is not the same as 17% of energy automatically during cheap rate.

I am not quite sure what the hours of cheap rate are but assume something like midnight to 4 am.  In my house that would mean the second half of base load is all off, so I'd only be left with the fridge, standby items, alarm, wifi router and such like.

JKenH

Exiled_Tyke said:

Petriix said:

Let's be absolutely clear. At 40p/12p you'd only have to shift ~ 20% of your home usage into the off-peak window before your saving money vs the cap price.

4 hours is 17% of your base load so that's already pretty close to breaking even. All it takes is pressing the timed start button on your big appliances or using a £10 smart plug.

Without much effort my home usage is ~ 40% off-peak so being on Go is objectively saving me money before you even consider the EV charging. What's more it's the cheapest fixed tariff you can get and protects you from any potential rises next year should the government decide to scale back support in April.

To somehow twist this money saving opportunity into a hidden expense is, at best, willful ignorance. 

Agree with this all the way.  At this time of year the dishwasher and washing machine are set to go on at night and they are the bulk of my electricity use.  The only other big one is cooking and I'm not doing that between 12.30 and 4.30!  Currently my import is 70% off peak and 30% off peak. Come late spring it will be a few kWhs off peak and pretty much zero peak.

Yes, with your usage pattern (30/70), being on Octopus Go will save you money. (£1020 vs £1650 on SVT if your usage was, say, 5000kWh.)

Compared to SVT your effective off peak rate can be calculated as follows:

Octopus Go 
3500kWh@ 12p/kWh = £420
1500kWh @ 40p/kWh = £600
Total £1020

Which compared to if you were on SVT you pay
1500kWh  @ 33p/KWh = £495
plus 3500kwh @15p/kWh £525

Total £1020

Your effective off peak rate is 15p/kWh

Edit: £ sign deleted from £15p/kWh in last sentence.