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Discussion Starter · #1 ·
Seems like EVs are pretty hungry in terms of % of overall house energy usage. Octopus go 5p/kwh for 4 hours per night is cheaper than pretty much everyone else (I think British gas have 4.7p but their day rate is quite a bit more than octopus’ 13p). So even if you want to precondition ‘from the wall’ it’ll still be cheaper than other tariffs.

Is this a no brainer if you have a smart meter?
 

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IMO : If cost is your only criteria it is one of the best. However, if you have a large EV battery or regularly drive high mileage or you value convenience then I would argue that there are better tariffs.

Many EVs can’t be fully charged in 5hrs on a regular home charger. Personally I value convenience over saving ~£100 a year so I’ve have gone for a tariff that has a much greater number of off peak hours so that I can fully charge my car ‘in one go’ just once a week. It also means that my family isn’t inconvenienced by being ‘limited’ to using washing machine, dryer, dishwasher etc in middle of night. This also avoids the risk of house fire while sleeping.

The size of the saving from taking Octopus Go tariff is less than the cost of one of the optional extras that people often specify when ordering their new car. Many of these extras are justified based on the convenience that they bring.
 

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Discussion Starter · #3 ·
I was wondering that - what am I losing. I assumed a painful daytime rate but its still cheaper than many other normal daytime rates from what I’ve seen? So the downsides are limited. We run the dishwasher overnight but yes things like cooker/kettle etc would be during the day. We have solar so that’ll offset some of it but its not a big set of panels and I don’t have battery storage to make the most of it.

what tariff are you on? Longer off peak woudl be interseting - was it SSE that have the off peak being basically all night and all weekend at around 9p? That could be an option
 

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Must admit I find Agile would blow my mind to figure out the savings...
Got into Octopus Go, and they had a test tariff where you could adjust the start time of the cheap - ours is 20:30 to 00:30. Gets most of the washing/dishwashing & most importantly, charging, done during those hours.
Effectively meant our 21k miles in our Kona have resulted in no change to our monthly payment, so ‘effectively’ free motoring (y)
Of course, they could change that for us....but I hope not: simple to understand & use.

Not aware of any good alternatives: I think Octopus are a great company with decent ethos (I swapped messages with their CEO prior to signing up, and have had a few positive interactions since with others there)
 

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IMO : If cost is your only criteria it is one of the best. However, if you have a large EV battery or regularly drive high mileage or you value convenience then I would argue that there are better tariffs.

Many EVs can’t be fully charged in 5hrs on a regular home charger. Personally I value convenience over saving ~£100 a year so I’ve have gone for a tariff that has a much greater number of off peak hours so that I can fully charge my car ‘in one go’ just once a week. It also means that my family isn’t inconvenienced by being ‘limited’ to using washing machine, dryer, dishwasher etc in middle of night. This also avoids the risk of house fire while sleeping.

The size of the saving from taking Octopus Go tariff is less than the cost of one of the optional extras that people often specify when ordering their new car. Many of these extras are justified based on the convenience that they bring.
You've just described Octopus GoFaster. Pick your start time and extend the period a bit if you wish.
 

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..... or the SSE or EDF tariffs (even more convenient but perhaps not as cheap as Octopus Go/Go-Faster)
 

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If you use off peak E7 for heating, Octopus do not have a competitive tariff. I use 18,000 kWh for heating pa and no more than 3000kWh for charging (in a post COVID year). Its an odd situation where gas heating is nearly a third of the cost of electric heating. Many E7 customers are not happy but OFGEM do not seem to be bothered. Caps on electricity charges do not seem to take the E7 tariffs into account.
 

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Gas may be 1/3 of the cost of leccy per kWh, but isn't electric heating close to 100% efficient while gas is more like 40-50%?
 

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If you use off peak E7 for heating, Octopus do not have a competitive tariff. I use 18,000 kWh for heating pa and no more than 3000kWh for charging (in a post COVID year). Its an odd situation where gas heating is nearly a third of the cost of electric heating. Many E7 customers are not happy but OFGEM do not seem to be bothered. Caps on electricity charges do not seem to take the E7 tariffs into account.
Does Octopus not have a reasonable tariff for E7 compared to other electricity companies, or compared to gas?

Ofgem doesn’t set prices of gas or electricity, other than the maximum tariff for variable rates. These tariffs are basically reflective of the costs, Ofgem doesn’t have a huge control over them and these rates go up and down with the underlying market costs. We have competition for setting prices (in the main) and it isn’t a fundamental role of the regulator. Even if it were, how are they supposed to subsidise electricity at the expense of gas? That would need Government action.

Electricity includes a price for CO2 but gas doesn’t : the great British public screams every time we try to tax fuel. So gas is cheaper than electricity (basically cross subsidised as the carbon costs are ignored.


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Gas may be 1/3 of the cost of leccy per kWh, but isn't electric heating close to 100% efficient while gas is more like 40-50%?
I think gas for heating is >90% efficient once it reaches your home (after ‘shrinkage’, compressor stations etc upstream). There is probably some further loss in the electricity to pump water around your radiators and in warming up pipes in walls which won’t be included in the gas calculations, but the conversion efficiency for gas to heat is pretty good.


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I think gas for heating is >90% efficient once it reaches your home (after ‘shrinkage’, compressor stations etc upstream). There is probably some further loss in the electricity to pump water around your radiators and in warming up pipes in walls which won’t be included in the gas calculations, but the conversion efficiency for gas to heat is pretty good.


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Thanks - had a look and condensing boilers can hit 90+% on condensing mode, and less otherwise.

I have a 16yr old non-condensing boiler about the size of a washing machine. It has been exceptionally reliable so will wait til it dies even though I suspect I'd save £300-400 a year in gas with a condensing system.

We use a lot of hot water so my plumber also suggests keep it til it dies despite him having a vested interest in doing a £££ boiler job!
 

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I think gas for heating is >90% efficient once it reaches your home
It can be if you've got a good condensing boiler running in condensing mode. Wonder how many people actually make sure they're running it in condensing mode though...
 

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I think gas for heating is >90% efficient once it reaches your home (after ‘shrinkage’, compressor stations etc upstream). There is probably some further loss in the electricity to pump water around your radiators and in warming up pipes in walls which won’t be included in the gas calculations, but the conversion efficiency for gas to heat is pretty good.


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Bit of a tricky one, this...modern condensing boilers are theoretically up to 90%+ efficient...however, they are rarely set up to actually act in condensing mode. That requires a low return flow temperature, below about 50 degrees C at most. Your average installer just turns the flow temperature up all the way and makes everything nice and hot. It works fine, but efficient it is not. A quick check is whether you can see a plume from the boiler outlet. If you can, then it's not condensing well as there's still lots of moisture in the exhaust stream. If the radiators are suitably sized, turning the flow temperature down helps but it's a complicated thing to get right.

EDIT: cross post with @cdlb's above. We agree...
 
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Is this a no brainer if you have a smart meter?
The only case where Go or Go Faster (if available) isn't a good tariff is for people with high overnight loads, who need an E7 or E10 type tariff.

Re comments about 4 hours (or 5 hour option on Go Faster) not filling an EV - I do wonder if people saying that actually have an EV! For most EV owners, 4 hours is enough to add back what they use - just plug in each night. Occasionally (not at present) we get back from a long journey and can't fully top up in 4 hours, but that isn't an issue as we never do two consecutive days of long journeys.

Having reliable scheduling is important, in our cases both the Tesla and Zoe are good in this regard.
 

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Re comments about 4 hours (or 5 hour option on Go Faster) not filling an EV - I do wonder if people saying that actually have an EV! For most EV owners, 4 hours is enough to add back what they use - just plug in each night. Occasionally (not at present) we get back from a long journey and can't fully top up in 4 hours, but that isn't an issue as we never do two consecutive days of long journeys.
They may be using a 3 pin rather than a proper charge point. 2.3kW constant for 5 hours gives you 11.5kW into your battery (assuming 100% efficiency). If you're running at say 3mi/kWh, that gives you 34 miles of range, so a 17 mile each way commute would use up the energy that you can put back into the car overnight on your cheap rate. If you drive more than that, your average battery level will whittle down over the week until you get a day off - how much of a problem that is will heavily depend on how long the actual commute is, what the actual mi/kWH is and the battery size. Of course, the obvious solution is get a 7kW charger and enjoy your 105 mile top up each night, but some people seem to be allergic to logic and reasoning...

Anyway, I could see how it is possible to be in a situation where 5 hours isn't enough, but it's probably easily fixable for a lot of people.

The assumption that I'm making is that everybody overnight charging would be able to fit a proper charger. I'm aware of this, but it feels reasonable to me - if you can have your own socket fed by your own energy tariff, I'd have thought that you could also have an EV charger...
 

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Discussion Starter · #18 ·
They may be using a 3 pin rather than a proper charge point. 2.3kW constant for 5 hours gives you 11.5kW into your battery (assuming 100% efficiency). If you're running at say 3mi/kWh, that gives you 34 miles of range, so a 17 mile each way commute would use up the energy that you can put back into the car overnight on your cheap rate. If you drive more than that, your average battery level will whittle down over the week until you get a day off - how much of a problem that is will heavily depend on how long the actual commute is, what the actual mi/kWH is and the battery size. Of course, the obvious solution is get a 7kW charger and enjoy your 105 mile top up each night, but some people seem to be allergic to logic and reasoning...

Anyway, I could see how it is possible to be in a situation where 5 hours isn't enough, but it's probably easily fixable for a lot of people.

The assumption that I'm making is that everybody overnight charging would be able to fit a proper charger. I'm aware of this, but it feels reasonable to me - if you can have your own socket fed by your own energy tariff, I'd have thought that you could also have an EV charger...
agree. I guess we could do the math but not sure I’m bothered - eg if you have a granny charger what woudl be the net result of a longer (but more expensive) off peak period to cover your slower charging? eg with something like octopus go and 5p for 4 hours, if you need more like 8 hours per day due to granny, then the other 4 hours would be 16p/kwh. A combined 11.5p/kwh overall. So if you can get 8hours less than that it would be worth considering.

EDF go electric 98 tariff gives you 9p/kwh 9pm-7am and all weekend and would likely be better for those with slower chargers. Its actually pretty tempting to me too - all weekend at 9p and evenings after 9pm probably helps offset the slightly higher 18p/kwh peak time during the week. I don’t have time of use data to do a real estimation though. Don’t suppose there are ways to simulate average usage curves and apply to different tariffs?
 

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Does Octopus not have a reasonable tariff for E7 compared to other electricity companies, or compared to gas?

Ofgem doesn’t set prices of gas or electricity, other than the maximum tariff for variable rates. These tariffs are basically reflective of the costs, Ofgem doesn’t have a huge control over them and these rates go up and down with the underlying market costs. We have competition for setting prices (in the main) and it isn’t a fundamental role of the regulator. Even if it were, how are they supposed to subsidise electricity at the expense of gas? That would need Government action.

Electricity includes a price for CO2 but gas doesn’t : the great British public screams every time we try to tax fuel. So gas is cheaper than electricity (basically cross subsidised as the carbon costs are ignored.


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No, it is by comparison with other electricity suppliers. When E7 was first introduced the price was 1/3 that of daytime price and was fairly close to cost of gas per available kWh.
I know that in the current set up, prices more or less reflect cost, but those who use E7 for heating will know that suppliers vary the night rate much more than day rates, with the fairly obvious ruse of catching out customers, many of whom are elderly and vulnerable. Even the switching sites are misleading as they use some sort of National average % night consumption to calculate the costs.
The main point though is that there is a move to switch heating away from fossil fuels, but there is no incentive to encourage anyone to move away from coal, wood, oil and gas.
There are incentives to install heat pumps, but they are probably not the best solution (although they may be part of it) as they still use electricity mainly in the daytime.
Storage systems to move consumption from night to day are more helpful so that wind power at night can be best utilised. Batteries are unlikely to be cost effective for storing enough power for heating so we are left with thermal storage. This can be made much more controllable than current storage heaters with very insulating materials and high temperature cores. They can be retrofitted to existing wet systems and although the capital cost is high, maintenance costs are minimal and they will last well over 30 years. How do I know? Well, I've had one since 1982.


Hence my interest.
 

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agree. I guess we could do the math but not sure I’m bothered - eg if you have a granny charger what woudl be the net result of a longer (but more expensive) off peak period to cover your slower charging? eg with something like octopus go and 5p for 4 hours, if you need more like 8 hours per day due to granny, then the other 4 hours would be 16p/kwh. A combined 11.5p/kwh overall. So if you can get 8hours less than that it would be worth considering. Eg EDF go electric 98 tariff gives you 9p/kwh 9pm-7am and all weekend and would likely be better for those with slower chargers
It depends a lot on how much your charger costs you. My charger cost £339, supplied, fitted, and massively subsidised by the government. Let's say that the charger lasts 5 years (i.e. the warranty period), then needs replaced.

£339 / 5 = £67.80 per year

Let's say I only charge overnight for my commute, 5 days out of 7, 46 weeks of the year:

5 x 46 = 230 charges per year

So the charger costs me 29p per charge, assuming the 5 year lifetime.

Taking your example, 5 hours on 5p/kWh and 3 hours at 16p/kWh, the entire charge of 18.4kW on a granny running full pelt would be 5 hours x 5p x 2.3kW = 57.5p + 3 hours x 16p x 2.3kW = 110.4p, so your total charge cost is £1.68.

The same charge at 7kW off peak would take take 2.6 hours and cost 92p. Add in my 29p for the charger, and the total cost is £1.21, so you're saving 47p per charge in this incredibly idealistic scenario, or £540 over 5 years.

If the replacement charger costs double of the original (assuming the wiring in the house is OK and I can just swap the box, it's probably about right), the saving becomes 18p per charge - less compelling, but it still becomes £207 over 5 years.

I wouldn't go booking a trip to Vegas to spurge the new found wealth, but it's still money I'd happily put into my back pocket.

Incidentally, the break even point is around an hour and a half on the higher rate, so if you can get everything you need on that tariff in 6.5 hours, the granny works out about the same.

So many assumptions in this maths that it's probably meaningless, but I'm at work by myself on a Sunday and need something to do to entertain myself during my lunch break...

Also, the benefit is nowhere near as compelling for my actual situation, as my PHEV has a tiny battery and can only charge at 3.7kW. I was jumping on the grants before they disappeared in the hope that it would be some cheap future proofing. So basically, I'm making a point about cost efficiency whilst also being fully aware that I've not followed my own analysis. I'm fine with it.
 
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