Economy 7 - Electric Car & Immersion Heater.. A few questions

InfoH

Hi All,
Sorry if this comes across as a bit of a confusing string of questions.. I'm having a bit of a brain dump and would welcome any help and advice
So I'm currently with npower on a standard meter on a standard tarrif paying 17.35p per kWh
I'm moving next month and just found out that the house I'm moving to has an Economy 7 meter and instead of a combi boiler it has an immersion heater. I'm also getting a new car next month which is a fully electric car.. so obviously I'm taking a closer look at electric costs than I normally would..
The new E7 tarrif I'm looking at is 16.64p during day and 8.78p during the night
so to the questions that I had in mind:

• Is an immersion heater more expensive to run than a combi-boiler? I assume it is as electricity costs more than gas.. however I read that it works well with an E7 meter as I can set it to heat up during the night and use the water during the day.. does it stay hot long enough for that.. if I say want a bath in the evening?
• Are there some negatives to an E7 meter? from what I can see it's a lot more cost effective over a standard meter.. not sure why they aren't more common.. think maybe I'm missing some of the negatives?
• Is anyone aware of an E7 tariff better than the one mentioned above (E.ON)?

Thanks in advance!

MWT

There are many better E7 tariffs out there so do use one of the comparison sites to investigate your alternatives and do make sure they show you all options, not just the ones they can switch you to.

The best choice though may depend on which car you are getting and how often you need to recharge it.

You are going to need a smart meter to get the benefit of some of the more 'car' centric tariffs, and with some of those your usage during the peak period of 4-7pm is also a factor.

Do have a look at EDF with their GoElectric tariff for example as it offers their 'night rate' from 9pm - 7am and all weekend which could help with your evening water heating perhaps and makes car charging very flexible especially over the weekend....

There are cheaper prices with Octopus Go but more limited night rate hours ranging from 3 - 5 hours depending on when you want the hours to start. Also Octopus offers their Agile tariff which can work out a lot cheaper than many alternatives, but has a high peak rate between 4-7pm so does not suit those who need to use a lot of electricity in that time period... 

tim_p

What form of heating does the new place have?  It sounds like it’s all electric so it’s likely to be more expensive from the off without adding in an EV. 

InfoH

tim_p said:

What form of heating does the new place have?  It sounds like it’s all electric so it’s likely to be more expensive from the off without adding in an EV. 

It's gas central heating.. I made that mistake before!.. first thing I check now haha

tim_p

But water heating by immersion? Sounds odd but hey ho.  

Richie-from-the-Boro

Comment
No water pressure ? One cost effective work-around.is to:

Leave highly insulated PartL cylinder in situ/water controller/wiring/CU/ tariff in place.

Get E7 tariff to +/- 50% split and you have a winning offset of high day rate electricity with 365pa cylinders of angry bubbling hot.150 litres per day cheap rate.

Best of luck.

DragonQ

You need to be careful about this because from my research, economy 7 tariffs seem just bad generally. For example, this is my current tariff compared to the economy 7 tariff with the lowest unit rates from a few days ago (i.e. cheapest for me):

Standard: 21.945p/day + 10.752p/kWh
Economy 7: 18.35p/day + 7.95p/kWh off-peak + 16.26p/kWh peak

Basically the night rates are cheaper than the best normal tariffs but the day rates are relatively more expensive. If you're a high electricity user like me (thus these tariffs work out cheapest), you'd need to use well over 60% of your electricity in the off-peak hours for them to be cheaper.

Depending on how well the water tank is insulated, you might be able to run your immersion heater for say 40 minutes every morning and have enough hot water for the day. I have a gas boiler for heating but this works for me. Then you need to consider how many miles you're doing in the EV to work out how much it's going to cost you to charge at home.

For a case study, I already use ~3750 kWh/year even without an EV and with gas central heating and water. Let's be very generous and assume that 50% of my usage is for stuff running continuously. That means I use 3750/2 x 7/24 = 547 kWh/year during the 7 off-peak hours of every day. Now let's take my upper estimate for annual mileage (11,000) and a pessimistic average efficiency for a modern EV (235 miles from a 64 kWh battery), which means I'll use another 3000 kWh per year charging an EV. Let's now be generous again and assume all of my EV charging would be done at home during those 7 off-peak hours. Here's the final costs:

Standard: 21.945p x 365 + 10.752p x (3750+3000) = £806/year
Economy 7: 18.35p x 365 + 7.95p x (547+3000) + 16.26p x (3750-547) = £870/year

Economy 7 for me is a waste of time, even with generous assumptions. I suspect you'd have to use much less electricity during the day for it to make sense so please do your own calculations before deciding.

Biscuit_Tin

InfoH said:

Hi All,
Sorry if this comes across as a bit of a confusing string of questions.. I'm having a bit of a brain dump and would welcome any help and advice
So I'm currently with npower on a standard meter on a standard tarrif paying 17.35p per kWh
I'm moving next month and just found out that the house I'm moving to has an Economy 7 meter and instead of a combi boiler it has an immersion heater. I'm also getting a new car next month which is a fully electric car.. so obviously I'm taking a closer look at electric costs than I normally would..
The new E7 tarrif I'm looking at is 16.64p during day and 8.78p during the night
so to the questions that I had in mind:

• Is an immersion heater more expensive to run than a combi-boiler? I assume it is as electricity costs more than gas.. however I read that it works well with an E7 meter as I can set it to heat up during the night and use the water during the day.. does it stay hot long enough for that.. if I say want a bath in the evening?
• Are there some negatives to an E7 meter? from what I can see it's a lot more cost effective over a standard meter.. not sure why they aren't more common.. think maybe I'm missing some of the negatives?
• Is anyone aware of an E7 tariff better than the one mentioned above (E.ON)?

Thanks in advance!

InfoH said:

tim_p said:

What form of heating does the new place have?  It sounds like it’s all electric so it’s likely to be more expensive from the off without adding in an EV. 

It's gas central heating.. I made that mistake before!.. first thing I check now haha

Good one, haha!

There are increasing amounts of specialised tariffs now being introduced for those that have electric vehicles. Might be worth investigating. Ha ha!!!

matelodave

I was interested in DragonQ's comment that an electric car would do around 235 miles from a 64kwh battery which equates to  around 3.7miles/kwh - lets round it up to 4miles.
Assuming that you are going to charge from a 13a socket then you'll get around 12 miles for every hour of charging so 7 hours overnight (21kwh) will give you around 84 miles. You need a higher power charger to benefit from E7 if you intended to do more than 80 miles a day otherwise you will be consuming peak rate leccy. If you wanted to take advantage of some EV rates then you need a charger that's sized to recharge your car during the cheap period.
On the subject of heating your hot water - it takes around 8kwh to heat an average sized tank from stone cold to around 60 degrees - that's about 2.5hours with a 3kw immersion heater. As the tank seldom gets stone cold it will heat in about 1.5-2hours and a properly insulated tank will keep it hot all day depending on how much hot water you use. Learn to use it wisely and you'll have no problems.
However to make sure you get onto a decent tariff that would suit your lifestyle you should do some sums like DragonQ has suggested to work out what it's likely to cost you.
As an afterthought - if you've got gas central heating then I'd be surprised if the hot water tank wasn't heated by the boiler and that there's just a immersion heater in the tank as a standby/backup and would normally be switched off.

DragonQ

matelodave said:

I was interested in DragonQ's comment that an electric car would do around 235 miles from a 64kwh battery which equates to  around 3.7miles/kwh - lets round it up to 4miles.
Assuming that you are going to charge from a 13a socket then you'll get around 12 miles for every hour of charging so 7 hours overnight (21kwh) will give you around 84 miles. You need a higher power charger to benefit from E7 if you intended to do more than 80 miles a day otherwise you will be consuming peak rate leccy. If you wanted to take advantage of some EV rates then you need a charger that's sized to recharge your car during the cheap period.
On the subject of heating your hot water - it takes around 8kwh to heat an average sized tank from stone cold to around 60 degrees - that's about 2.5hours with a 3kw immersion heater. As the tank seldom gets stone cold it will heat in about 1.5-2hours and a properly insulated tank will keep it hot all day depending on how much hot water you use. Learn to use it wisely and you'll have no problems.
However to make sure you get onto a decent tariff that would suit your lifestyle you should do some sums like DragonQ has suggested to work out what it's likely to cost you.
As an afterthought - if you've got gas central heating then I'd be surprised if the hot water tank wasn't heated by the boiler and that there's just a immersion heater in the tank as a standby/backup and would normally be switched off.

Note that my estimate of 235 miles for a 64 kWh battery is pretty pessimistic, that's more if you're doing a lot of driving at 70 mph. You'd get closer to 300 miles with mostly city driving. Plus you're right, if you're doing a lot of miles per day and you don't invest in a 7.2 kW / 32 A dedicated charger then you may not even be able to fill up the car during 7 off-peak hours.

matelodave

Having a shufti around t'interweb it looks as though an EV will consume around 28-30kwh/100miles which is around the figure that you estimated (unless you are thrashing a Tesla down the motorway).

Of course your range will depend on the battery capacity so if you get a roller skate with a 24kwh battery then you'll probably manage to charge it overnight from a 13a socket, but any larger then I guess you want a 7.2kw/32A charger which would get around 50kwh (or about 180 miles) from an all night charge.