Would it be cheaper to use elecric immersion vs gas now?

wmgy85

Hi all,

Looking for some help with my maths...

I'm currently on Octopus Go for my electric car, meaning I only pay 5p/kwh between 00:30-04:30

My gas rate is now 7.2p/kwh 

I currently have a solar diverter for my immersion, so when my solar batteries are full it heats the tank of water - fine for the summer.

During the winter (no solar) I charge my batteries on the cheap night rate. I'm now wondering if I should also heat my hot water at this time using an immersion timer?

My boiler is 94% efficient, so here is my maths with an assumption is takes 4kwh to heat the tank to 60c:
Gas 4kwh = 4.3kwh used = 4.3x 7.2p = 31p
Electric 4kwh = 4kwh used = 4x 5p = 20p

Am I right?

MattMattMattUK

wmgy85 said:

Hi all,

Looking for some help with my maths...

I'm currently on Octopus Go for my electric car, meaning I only pay 5p/kwh between 00:30-04:30

My gas rate is now 7.2p/kwh 

I currently have a solar diverter for my immersion, so when my solar batteries are full it heats the tank of water - fine for the summer.

During the winter (no solar) I charge my batteries on the cheap night rate. I'm now wondering if I should also heat my hot water at this time using an immersion timer?

My boiler is 94% efficient, so here is my maths with an assumption is takes 4kwh to heat the tank to 60c:
Gas 4kwh = 4.3kwh used = 4.3x 7.2p = 31p
Electric 4kwh = 4kwh used = 4x 5p = 20p

Am I right?

Where are you getting the £0.05 per kWh electricity cost from? 

Also to add the 94% efficiency of the boiler is the theoretical maximum of the boiler itself, likely it will not operate at that level and there are additional losses in the hot water system as a whole, 75% overall is probably more realistic. 

pochase

Main problem I would see is that you only heat your tank once per day and the water will be cooling off during the day.

Would work if you take your shower/bath in the morning and live with warm water getting cooler during the day.

Is your immersion heater on a timer?

QrizB

MattMattMattUK said:

Where are you getting the £0.05 per kWh electricity cost from?

OP wrote (and you quoted):

wmgy85 said:

I'm currently on Octopus Go for my electric car, meaning I only pay 5p/kwh between 00:30-04:30

OP, yes you're right, you're one of the rare cases where it makes sense. I'm another.

Do keep in mind that, depending exactly where in your tank your immersion is, you might not be able to heat the whole of it electrically. Mine only heats the top 60% of the tank (and takes 6kWh to do so) and I'm expecting to still need a gas top-up on bath night.

MattMattMattUK

QrizB said:

MattMattMattUK said:

Where are you getting the £0.05 per kWh electricity cost from?

OP wrote (and you quoted):

wmgy85 said:

I'm currently on Octopus Go for my electric car, meaning I only pay 5p/kwh between 00:30-04:30

OP, yes you're right, you're one of the rare cases where it makes sense. I'm another.

Do keep in mind that, depending exactly where in your tank your immersion is, you might not be able to heat the whole of it electrically. Mine only heats the top 60% of the tank (and takes 6kWh to do so) and I'm expecting to still need a gas top-up on bath night.

Totally missed that part!

On that basis I should buy an electric car!

QrizB

MattMattMattUK said:

On that basis I should buy an electric car!

Octopus Go has gone up in price since September, but it's still pretty good.

In my region it's 7.5p/kWh from 0030-0430  then 30.61p/kWh at other times, The SC is only 24.11p/day too.

MattMattMattUK

QrizB said:

MattMattMattUK said:

On that basis I should buy an electric car!

Octopus Go has gone up in price since September, but it's still pretty good.

In my region it's 7.5p/kWh from 0030-0430  then 30.61p/kWh at other times, The SC is only 24.11p/day too.

Yep, had a look, 7.5p for me as well. 

I do plan on getting an electric car, but not just yet as Covid hit my business hard and cost me around £150k minimum, I want to make sure I am back where I need to be before any major outlays, but I hope that those deals will still exist in some form in a year or two. 

wmgy85

pochase said:

Main problem I would see is that you only heat your tank once per day and the water will be cooling off during the day.

Would work if you take your shower/bath in the morning and live with warm water getting cooler during the day.

Is your immersion heater on a timer?

It's a brand new tank with very good insulation - the hot water can last for several days if only having showers 

The immersion is not on a timer yet, but only £20 to add one on 

wmgy85

QrizB said:

MattMattMattUK said:

Where are you getting the £0.05 per kWh electricity cost from?

OP wrote (and you quoted):

wmgy85 said:

I'm currently on Octopus Go for my electric car, meaning I only pay 5p/kwh between 00:30-04:30

OP, yes you're right, you're one of the rare cases where it makes sense. I'm another.

Do keep in mind that, depending exactly where in your tank your immersion is, you might not be able to heat the whole of it electrically. Mine only heats the top 60% of the tank (and takes 6kWh to do so) and I'm expecting to still need a gas top-up on bath night.

My immersion is near the bottom of the tank, assuming heat rises I would say it covers 75%??