Renamed - the immersion heater thread (was about about cost of SVR vs Go)

Following on from another thread where @Vipar wasn't sure whether it would be worthwhile switching to Go from the Standard Variable rate, I have created a simple spreadsheet to show the break even point between the 2 tariffs.

I have kept it very simple, taking no account of standing charge as we all have to pay that regardless. Also, no account of any conversion losses in the charging or of any switching of use from day to night for example washing machines.

If you know how much you use either daily or weekly or annually and the Octopus Go rates in your area this will work out the break even point between staying on a SV rate or switching to Octopus Go or vice versa.
The break even point is the number of kWh per week that you would need to use on the Go overnight rate in addition to the weekly home usage. So....
on Go cost is home use at day rate plus EV use at overnight rate
on SVR cost is home use plus EV use at day rate.

I have attached a spreadsheet so that anyone can use it to enter their own TARIFFS and DAILY consumption. (leave other fields alone to get results as I've not bothered with protecting anything )
Feel free to improve it if you wish though to suit your own needs.

I have also included a screenshot here of the tariff in my area, Yorkshire with costs based on daily usage of between 5 and 20kWh per day. This should give a flavour for most as costs don't vary too much.

Basically you need >35% of your weekly usage to happen during the GO night time period in order for the GO tariff to start being more cost-effective.

FWIW you technically also need to factor in the standing charge, as the rates tend to be different vs SVR. But as these are daily rates around 50p (so ~£3.50 per week) then it's essentially "noise" in the scheme of things.

Also a battery to shift the go rate to the day would also be beneficial - I'm looking at the off peak rate to charge the car every night (100 miles every day usage) and also charge a 10kWh battery and use that in the day. Unsure of whether to use solar as well, at the moment I think its pointless as the car will be charging in the night and we'll use the battery in the day. But, still researching...

siteguru said:

Basically you need >35% of your weekly usage to happen during the GO night time period in order for the GO tariff to start being more cost-effective.

FWIW you technically also need to factor in the standing charge, as the rates tend to be different vs SVR. But as these are daily rates around 50p (so ~£3.50 per week) then it's essentially "noise" in the scheme of things.

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Yes of course but I did specifically say I didn't include this noise.

jamie07051975 said:

Also a battery to shift the go rate to the day would also be beneficial - I'm looking at the off peak rate to charge the car every night (100 miles every day usage) and also charge a 10kWh battery and use that in the day. Unsure of whether to use solar as well, at the moment I think its pointless as the car will be charging in the night and we'll use the battery in the day. But, still researching...

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A battery would obviously be beneficial but unbelievably not everyone has one.

I am planning to use V2L during the day for things like the hedge trimmer, leaf blower, weed burner and tumble dryer which are all in, or easily accessible for use from the garage where the car will be. I have the adapter ready. Just need the car!! As I am already on Octopus Go, I run the washing machine and dishwasher at night, but I’d rather not trust the tumble dryer at night in the garage, and my neighbours would be mightily amused if I was hedgetrimming by torchlight in the early hours!
I have experimented with putting the immersion heater on for summer usage during the cheap night period, but it took way longer to heat the water than the gas boiler, so according to my calculations, the savings would be negligible, and not worth paying an electrician to install a proper timer switch.

Susanna said:

I have experimented with putting the immersion heater on for summer usage during the cheap night period, but it took way longer to heat the water than the gas boiler, so according to my calculations, the savings would be negligible, and not worth paying an electrician to install a proper timer switch.

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Although the emersion heater is pulling about 3.5 Kw's of electricity, it is set to call for power over the length of time ( 5 hours / night ) that your cheap off peak rate commences.
Ours is set to take full advantage of the full 5 hours at 4.5p/kwh from EDF.
Yes the modern gas boiler is much quicker to heat the water okay, but I still think the emersion heater is more cost effective option.
But I would value opinions on this matter folks.

I suppose much depends on how much hot water you need. I have found that 20 minutes with the boiler is ample for my morning shower. I don’t need hot water for any other purpose. The immersion heater needed to be on for over 40 minutes before the water was hot enough. I don’t think it would have been switching on and off in that short period. I also worked on an estimate of £80 for an electrician to install a timer, so I took that into consideration as to whether there would be any possible cost savings.

Gomev said:

A battery would obviously be beneficial but unbelievably not everyone has one.

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Can I ask what sort of set up you have? I was looking at the GivBat 9.2 (getting quotes at the moment) which I could use with solar down the line. I know if I include solar now the battery is zero VAT but don't think it will benefit us at the moment. If Octopus off peak tariffs go north a year or so from now then perhaps I would look at it again.

Susanna said:

I suppose much depends on how much hot water you need. I have found that 20 minutes with the boiler is ample for my morning shower. I don’t need hot water for any other purpose. The immersion heater needed to be on for over 40 minutes before the water was hot enough. I don’t think it would have been switching on and off in that short period. I also worked on an estimate of £80 for an electrician to install a timer, so I took that into consideration as to whether there would be any possible cost savings.

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Agreed @Susanna it depends on your usage case, as always.
The gas boiler has a much great heat output over the emersion heater and is therefore more capable of heating the water in the storage tank much much faster for sure !.
Each case will be totally different of course and there is no right or wrong way really, I agree.
I have just had a quick look at some boiler consumption rates on-line.
Snatched this quickly :-

"Using kW and kWh, you can work out how much gas your boiler is using and therefore how much it costs. A 24 kW boiler will use 24 kWh of energy per hour.
The cost is approximately 3.8 pence per kWh, which means it would cost around 91 pence to run a 24 kW boiler for one hour. This will change depending on the cost of gas and the size and age of your boiler".

Well, we can all dream about the times we had our gas at that low 3.8p/kwh.
More typically around 10 - 11p/kwh now !.
Yeah - A typical gas boiler rating of around 24 is an average size I guess, but some will be bigger or smaller, our's is a 28 unit so will be slightly more expensive to run.
We would need around 1 hours worth of boiler use to satisfy our hot water needs and sometimes more at the weekends.
So, 1 hour at 11p/kwh hour on gas is about £3.00 per day I think, less any standing charges etc.
If correct, that is roughly about £20 per week / £80 per month ?.
Emersion heater is rated at about 3 Kw's and will cost 13.5p at 4.5p/kwh per hour ( 3.0 x 4.5 = 13.5p ) when used for 5 hours per night is 67.5 pence per night, then over a week is £4.72p ( ish ).
Monthly around £19.00 ( ish ) ????.
So, in our case alone it was a worthwhile switch over from heating hot water from gas to electric.
The emersion heater timer was about £12 from Screwfix and I was able to install it myself.
Your hot water usage is about 50% less than ours, but it will depend on your own energy prices of course.
Load switching as much of our electricity usage into that cheap 5 hour window is absolutely vital in trying to reduce the size of our energy costs these days.
Car charging / washing machine / emersion heater etc all gets done in the early hours.
We have also purchased a air fryer and has reduced the use of our electric oven by around 50%.
My "Man Math's" are not the greatest, so I may need some direction / correction .

Nothing wrong with you’re maths Jeff as far as I can see
Les

Now Susanna I don’t know how your immersion heater supply is but if the immersion is on a 13amp plug as many are pull out the plug get yourself a plug in timer and plug the immersion heater into that set it to switch on when your electric is cheapest so if your on a cheap night rate it will heat the water tank over night ready for your shower in the morning
If the immersion is fed for a switched fuse spur then all you need to do is get a confident DIY person to remove the fused spur switch and fit a good quality 13amp single socket in it place a good Quality 13amp plug on the cable and then do what I have outline above with a plug in time switch cost around 15-20 pounds all in.

Just on thing to be aware off be sure the plug in timer you buy is rated for 3100 watts or higher.
Les

Just a quick edit I have been using a timer like I have described above for 3/4 years now called a GHoma rated 3200 watts great app for you phone as well and that’s how you set the timer got 4 of them in my home never had an issue with then cost was about £10 each if I remember correctly
Les

Well this thread has gone completely off topic.

Gomev said:

Well this thread has gone completely off topic.

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Situation normal .

Just been watching 'Modern Heroes' take on Octopus raising their cheap rate overnight charges. I'm on the flexible tariff & only charge my MG ZS EV about twice a month from around 50% to 80%, It wouldn't be worth my while going for the "Cheap" overnight rate as both my missus & I are retired & use the cheaper flexible rate of 34p/kWh during the day.

@Les burrows
Thank you for taking the trouble to reply in such detail. My immersion is on a fused spur, so it’s not something I can change myself. I will keep a lookout for a competent DIY person
My late husband would certainly have installed a timer switch in the blink of an eye, and I can do some stuff too. Not this though!

Susanna said:

@Les burrows
Thank you for taking the trouble to reply in such detail. My immersion is on a fused spur, so it’s not something I can change myself. I will keep a lookout for a competent DIY person
My late husband would certainly have installed a timer switch in the blink of an eye, and I can do some stuff too. Not this though!

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I’ve just ordered one of these instead, couldn’t be bothered to install a new switch (or pay someone to).

This will just push the existing switch off and on with no wiring needed with a set timer - let’s see how it goes!

https://amzn.eu/d/byRBryN

@johnnyc
I will be very interested in how you get on with this inventive little gadget. Seems like a fantastic way of controlling the hot water.

johnnyc said:

I’ve just ordered one of these instead, couldn’t be bothered to install a new switch (or pay someone to).

This will just push the existing switch off and on with no wiring needed with a set timer - let’s see how it goes!

https://amzn.eu/d/byRBryN

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Worth a try but I think these are more suitable for push button type switches like tv on/off buttons not to sure they can operate a rocker type switch like on a face plate of a fused spur but lets us know haw you go on please.
Les

Susanna said:

@Les burrows
Thank you for taking the trouble to reply in such detail. My immersion is on a fused spur, so it’s not something I can change myself. I will keep a lookout for a competent DIY person
My late husband would certainly have installed a timer switch in the blink of an eye, and I can do some stuff too. Not this though!

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Right you lot on here whose in the Northampton area with a screwdriver that could help this lady out. 30 minute job on a Saturday morning.
Les

Sorry about your loss Susanna.
Les