Costs per unit

QrizB

gospete said:

I've been toying with the idea of replacing them with something more efficient. I've seen the Fischer adverts ...

I see Gerry has got here already but, really, DON'T DO IT.

Not only will the heaters cost you as much as (or more than) replacement storage heaters to buy, the electricity to run them will cost almost twice as much, for as long as you have them.

BeerSavesMoney

If you have a smart meter if might be worth looking at the Go Faster tariffs. I’m in the NW and currently paying:

01:30 - 20:30 :	15.78p/kWh
20:30 - 01:30 :	5.50p/kWh

There’s various start times and lengths for the off peak period.

All Octopus tariffs have no exit fee and you can check them all out here: https://octopus.energy/tariffs/

Ignore the get a quote button and just enter your postcode towards the bottom.

Swipe

BeerSavesMoney said:

If you have a smart meter if might be worth looking at the Go Faster tariffs. I’m in the NW and currently paying:

01:30 - 20:30 :	15.78p/kWh
20:30 - 01:30 :	5.50p/kWh

There’s various start times and lengths for the off peak period.

All Octopus tariffs have no exit fee and you can check them all out here: https://octopus.energy/tariffs/

Ignore the get a quote button and just enter your postcode towards the bottom.

Just 5 hours at those times would not suit storage heaters. They'd be cold by 5pm.

BeerSavesMoney

Swipe said:

Just 5 hours at those times would not suit storage heaters. They'd be cold by 5pm.

It’s a good thing I don’t have storage heaters then!

The latest start time for my region is 01:30 for 5 hours, not sure if that’s any use as I’ve never had storage heaters but wanted to mention it as a potential option. 

How long roughly do they need out of interest?

QrizB

BeerSavesMoney said:

Swipe said:

Just 5 hours at those times would not suit storage heaters. They'd be cold by 5pm.

It’s a good thing I don’t have storage heaters then!

The latest start time for my region is 01:30 for 5 hours, not sure if that’s any use as I’ve never had storage heaters but wanted to mention it as a potential option. 

How long roughly do they need out of interest?

UK storage heaters are sized for E7, assuming you get 7 hours of heating input. If you intend to charge them in 5 hours they need to be 7/5 the size (ie. 2/5 larger).

Example: the Creda TSRE100 is designed to give a steady 1kW output for 16 hours. It charges at 2.22kW which means that in 7 hours it can store 15.54kWh of heat (~16 x 1kWh). If it only charged for 5 hours you would only charge 11.1kWh so it would run out after 11 hours, 5 hours too soon (or you'd only get 0.7kW out of it for 16 hrs, not 1kW). To store the same amount of energy you'd need to buy and fit the larger TSRE150 which charges at 3.3kW.

(Note that both these heaters have a supplemental "boost" heater which runs on full-price electricity. If you already had the heaters and didn;t want to replace them, you could instead use the boost heater on colder days.)

There was a thread on this recently and I ran the numbers for E7 vs Go Faster for one consumption pattern; see here. Tariffs may have changed in the past week and that particular consumption pattern is very heavy on off-peak use.

bristolleedsfan

gospete said:

I have just switched electricity supplier - from Scottish Power standard variable rate to Octopus 2 year fixed.
At the time, I didn't do a cost per unit comparison, just the projected £/month figure.
For some reason I subsequently decided to a unit comparison for interest - the figures surprised me...

My current unit cost with Scottish Power variable rate is much less than my new Octopus fixed rate.

It is probably apparent that I am new to this switching process but I've got a couple of basic questions.
1. Is it realistic to compare a variable rate with a longer term fixed rate?
2. Because the unit costs on my new fixed rate seem high, is it because Octopus have already factored in the upcoming prices increases? which makes switching less attractive than I thought.

gospete said:

Thanks. Yes I am electric only and have storage heaters which are quite old. At times I've been toying with the idea of replacing them with something more efficient. I've seen the Fischer adverts that say they can replace storage heaters but from what I can make out they have very little storage so I wouldn't get the benefit with having Economy 7.

Random comparison, Obviously better to do full market comparison, both no exit fees, South West Region

Day 22.88 p/kWh  Night unit rate: 14.37 p/kWh  Standing charge: 25.75 p/day  Octopus Direct 2 Year Fix

Day 24.99p per kWh  Night rate 11.22p per kWh  Daily standing charge 25.75p day  EDF Direct Fixed March 24

coffeehound

QrizB said:

UK storage heaters are sized for E7, assuming you get 7 hours of heating input. If you intend to charge them in 5 hours they need to be 7/5 the size (ie. 2/5 larger).

Example: the Creda TSRE100 is designed to give a steady 1kW output for 16 hours. It charges at 2.22kW which means that in 7 hours it can store 15.54kWh of heat (~16 x 1kWh). If it only charged for 5 hours you would only charge 11.1kWh so it would run out after 11 hours, 5 hours too soon (or you'd only get 0.7kW out of it for 16 hrs, not 1kW). To store the same amount of energy you'd need to buy and fit the larger TSRE150 which charges at 3.3kW.

(Note that both these heaters have a supplemental "boost" heater which runs on full-price electricity. If you already had the heaters and didn;t want to replace them, you could instead use the boost heater on colder days.)

There was a thread on this recently and I ran the numbers for E7 vs Go Faster for one consumption pattern; see here. Tariffs may have changed in the past week and that particular consumption pattern is very heavy on off-peak use.

@QrizB your example is pessimistic in that it assumes the NSH is required to be charged to full, whereas the reality might be that it is used at lower input settings most of the time.   There are of course many factors to consider with this such as what criteria were followed in specifying the NSH capacity, how bad the winter outdoor temperatures get and for how many nights per year etc.  If the NSHs were properly specified for E7, it would only be on the coldest winter nights that they would need to be set to maximum charge rate, and pro-rata for less cold nights.   If the NSH input controls were generally set lower throughout the year, then there is the scope to increase the charge rate over a shorter time to achieve the same energy storage.

If assuming the simplest input control as an example, the old 'simmer-stat' style that permits a percentage of the available input power to be taken as a simple duty cycle -- i.e. setting the input control halfway takes in 50% of the available power during the off-peak period -- then you could generalise a rule-of-thumb that says if the user seldom needs to set the input control over (5/7 x 100%)  about 70% of maximum, then they should be able to obtain adequate heat storage within five hours most of the time.  They should therefore also be better off using the 5-hour Octopus tariff and setting the input control higher so that it is charging for a greater percentage of the time -- subject to running the numbers.

A fly in this ointment is that (from above posts) the charge period ends much earlier, and so it could end up being out-of-sync with the household's hours, so something else to consider there.  But it's an interesting proposition, especially for EV owners.

QrizB

coffeehound said:

@QrizB your example is pessimistic in that it assumes the NSH is required to be charged to full, whereas the reality might be that it is used at lower input settings most of the time.

You're absolutely right, but knowing nothing about the poster's NSHs I wasn't happy usong a more optimistic scenario. I'd rather someone was pleasantly surprised by lower-than-expected bills than furious about higher ones!

coffeehound

The Go Faster tariff certainly could be a good move if the stored capacity is high enough and it could last the 19! hours between top ups.  With the hours BeerSavesMoney mentions, the householder could at least go nuts with direct heaters after 8.30 in the evening