Intelligent Octopus Go works like a dream.

[Stuart Wright]

You do make a good point, however, in terms of fairness the guy round the corner with his Taycan needing 80kWh and his neighbour with a Outlander PHEV requiring 12 kWh to achieve 100% how can you differentiate between them. Individual customer demands can be massively different.

While I don't know for sure, I'm guessing that the intention of the tariff is to supply off peak electricity to conveniently and cheaply charge EVs at home to encourage EV adoption and also balance power use by planning when the electricity is used.
The point is not how many kWh are delivered, it's the intended use and when. The off peak tariff exists to encourage use off peak, and not during peak hours at a cheap rate. Whether you need 12 or 80 kWh to charge your car is not as important as it serving its purpose to encourage EV adoption. In my opinion.

I doubt there are many domestic 11 or 22kW EVSE in the UK. And it is a domestic tariff.

3 phase connections are very much used in domestic homes. It was suggested by the Renewable Energy Association in 2018.

REA calls for three phase connections for all new homes to unlock solar deployment

All new housing developments should be fitted with three-phase electricity supply instead of the current practice of ‘lowest cost’ single phase supply to allow greater deployment of residential solar, according to a new report out today.

www.solarpowerportal.co.uk

and there are plenty of other articles on it

The growing call for three-phase electricity in the UK | GivEnergy

UK homes use pre-WWII electrical standards. As we increasingly electrify our lives, the call for three-phase electricity is rising.

givenergy.co.uk

And I had my home upgraded to 3 phase last year.
It's true that there are not as many as there should be given the requirement for EV chargers for all new cars from 2030 (thank you, Labour) and air source heat pumps are to replace gas boilers in new installations from next year, but having a 22kW charger is and will increasingly be a perfectly acceptable use case.
My battery is 75kWh and since my car can take 16kW, it means I can charge it at a bit more than twice the speed of a 7kW charger. I would actually prefer to charge it as slowly as possible provided it has sufficient charge at the end of the session as that's better for the battery health.

 

[tsedge]

Ok that makes a bit of sense...but in reality if you plug in with 30% at, say 5pm and ask to add 100% by 6am presumably Ohme / Octopus start charging right away so it's likely your peak evening use would be at the lower rate. Once the car stops charging (say it reaches 100% by 3am) you would still be in the off peak window anyway?

It depends on the size of your battery. 50kWh at 6.4kW charge rate is only 8 hours, so could be mostly done at the core overnight hours.

 

[andyvee]

so it's likely your peak evening use would be at the lower rate

It would, but Ohme owners in my experience of the 6.5k in the FB group tend to set reasonably accurately how much they actually need. This whole thing exploded when Zappi was integrated as the users did no tbehave the same as the Ohme users who were used to an app where you specified how much you needed and let the app work it out based on tariff, rather than time based scheduling.

It depends on the size of your battery.

It also depends on the differential factor between what you require and what you schedule.

Easier to think in hours of charging.

If you only Require 2hrs of charging, but schedule 10hrs (MG4 LR 100% including estimated charge losses) and allow a 12hr charge window overnight, with Zappi/Wallbox you are going to game the system for an additional 4hrs of off peak.
With Ohme you will only game the system for the 2hrs of actual charging that takes place outside of the TOU period.

 

[Rolfe]

I'm a bit late to the party, and struggling to keep up here. I've had IOG for over two months, but I've only used scheduled charging once, which was an accident as I hadn't been able to discover how to turn it off in the app. (As everyone is no doubt tired of hearing, I still haven't had the documentation through to let me get paid for the solar I export, so I'm trying to use as much as I can straight off the roof, including charging the car.)

Most of this never even occurred to me when I got the tariff. It seems quite simple in the app to set the amount of charge I want to add, and when I want the car by, and let Octopus get on with it. I knew it was possible to get slots outwith the normal off-peak rate, but with a 51 kwh battery which I probably won't run down to empty very often, it didn't strike me that this would be something I would often encounter.

The question that arises for me is, why is it particularly beneficial to have off-peak prices outwith the normal off-peak times if you have a home battery? Once I get my export tariff (dear God how much longer is this going to take?) my plan is to charge my home battery overnight during the normal off-peak time, and also run the washing machine, dishwasher and (occasionally, I don't use it much) tumble drier overnight. I don't usually go to bed before 11.30 so I can just switch on whichever one I'm using before I go to bed.

So just using the normal 11.30 to 5.30 timings, I plan to charge the car, charge the home battery, and run these three relatively heavy-duty appliances as required. I'm assured this is all possible so long as I don't try to do it all at once, which I wouldn't normally do either. Apart from the nightly charging of the home battery, the other things only happen once or twice a week.

Then, I have the home battery to use during the daytime, full of nice cheap 7p/kwh electricity. I haven't tried this yet, I'm still doing the opposite (filling the battery from the solar and using it to run the house overnight), but what's the actual problem? I don't know yet whether the rest of my daily power use is going to fit into the 9.5 kwh capacity of the battery, but I would expect so. Sure, there will be more lighting, and the electricity needed to run the central heating boiler and so on, but I think it should work. I note that even the oven doesn't really hammer the battery once it's up to temperature. I'm a bit hazy about why there is such great desire to have more off-peak slots. Do you guys not have home batteries big enough for your requirements or something?

Last week I got home early afternoon with 7% remaining on my SE SR and requested an add 100% by 4am - I normally add approximately 10% to allow time to complete a balance charge (so I'm not gaming!).

I was allocated slots early afternoon and evening with the charge set to finish at 4am. At 11.30 I overrode the schedule by starting a bump charge as I wanted to see how long it took to complete the balance charge. It actually completed at 4.30 so it looks like 10% extra isn't sufficient to complete the balance charge. The balance charge took an hour to complete which is longer than I have seen before.

I guess in future if I add an extra 20% to the charge to add it isn't classed as gaming!

That's interesting because I was wondering how the Zappi managed balance charging with this system.

My car has always balanced for 30-35 minutes after getting to 100%. I've watched it on the granny lead and I've watched it on public type 2 chargers, and always about this length of time. So how long did you think yours balanced for? Did it seem to go for longer than that?

Incidentally I was a bit concerned that my car wasn't balancing (either at all or not for long) on the Zappi when it was on eco+ running directly from the solar. So much so that I deliberately charged it from 98% on the granny lead a couple of weeks ago to make sure it had happened. But then yesterday it balanced for 30 minutes on the solar, and right now this minute it has just reached 30 minutes from full and it's still balancing. So I don't know if it's learned, or what...?

 

[andyvee]

I'm a bit hazy about why there is such great desire to have more off-peak slots.

Some people don't have batteries so do it in order to cook their tea at off peak. Or run their ASHP. Or heat the hot tub. Or have a shower. Or run the tumble dryer.

Some with batteries are running low by late afternoon so do it to get a cheap top up. They may not have solar etc or it's winter and generation is lower.

Some people will always find a way of exploiting something to their advantage.

Some people don't realise they are unnecessarily forcing additional off peak as they don't understand that a fairly clearly labelled setting of how much charge to Add means exactly what it says on the tin. As others have said, Octopus could do a better job of communicating this.

I guess in future if I add an extra 20% to the charge to add it isn't classed as gaming!

What Ohme users find if charging to 100% and needing to allow time for balancing is that an additional 15% allows enough time. Should be the same for other EVSE TBH.

And that's not gaming. Not remotely similar to leaving set to Add 100% if you only need 30%.

 

[Rolfe]

Some people don't have batteries so do it in order to cook their tea at off peak. Or run their ASHP. Or heat the hot tub. Or have a shower. Or run the tumble dryer.

Some with batteries are running low by late afternoon so do it to get a cheap top up. They may not have solar etc or it's winter and generation is lower.

Some people will always find a way of exploiting something to their advantage.

Some people don't realise they are unnecessarily forcing additional off peak as they don't understand that a fairly clearly labelled setting of how much charge to Add means exactly what it says on the tin. As others have said, Octopus could do a better job of communicating this.

Yes, it had occurred to me that people without a home battery would be massively incentivised to do this, but that didn't seem to be the case for the people discussing it here. And I realise how some people might be doing it without realising it. I guess I'll see in winter whether I'm wishing I had a larger battery and getting tempted!

It seems to me that once you have a tariff like this, a decent-sized home battery is a no-brainer. But then, some people have nowhere to put it.

 

[Stuart Wright]

I have an installer coming to see me this week about solar/battery/home charger.

The shine has slightly worn off the reliance on the granny charger, partly because the winter weather dissuaded me from using the rapid charger five minutes walk away, and then they doubled the price of that charger so it's really not attractive any more. Having to think about what I'm doing the day after a long trip because the car won't be back at 100% till evening the following day. Now the weather is getting better I'd like to know I can have the car ready by morning.

Once you get a home charger you start thinking about a variable tariff. Then you think about the "variable" part, and what it might do to the price of your daytime usage, so obviously you start thinking about a home battery and storing cheap night-time power for use during the day.

Then you think about your roof, which in my case looks like this.

View attachment 25534

(That's Prospero in the drive, Caliban's predecessor. Sob!)

Then you think, well the amount all that would cost would buy a hell of a lot of electricity, and you're back at square one...

Do you feel like posting an 'after' photo from the same angle so we can see how it looks?

 

[Rolfe]

I posted this, taken about half an hour after the solar installation was completed, in the thread in the solar/batteries forum.

Looks great, don't you agree? (Pity the grass was so long, but it got cut a couple of days later.) I keep wondering about another couple of panels under the right-hand Velux window, but the normal installation is 18 panels in this system.

 

[Stuart Wright]

Having a battery makes a massive difference to how much you save/earn and completely changes how you use the system.
Assuming you're buying electricity at 7p and exporting at 15p.

With no battery, you use as much of the energy produced from your solar when you can. Maybe you charge the car at night. Or you charge the car during the day with a zappi, for example. Maybe use an eddi to heat your hot water. Unless you're at home/plugged in during the day, you're going to be exporting most of what you produce to the grid. And you're going to be paying peak rate for electricity when it's dark.

With a battery, you charge the battery and car (and hot water via immersion heater) at night during off-peak and then try to use as much of that battery power during peak times. If the battery is big enough, you can continue to use that battery power until 23:30 and use no grid power at peak times. And export as much solar as you can at 15p.

Looking at it purely from a financial perspective, any tariff which allows you to purchase cheaper at night than you get paid for exporting during the day makes the original USPs of the zappi and eddi redundant.
You're not going to charge your car using solar produced energy if you can charge your car at 7p at night and get paid 15p for exporting solar produced energy during the day.
And you're not going to put energy in to your eddi that you can get paid 15p for when it costs much less than that for the gas.

 

[Bam Bam]

Having a battery makes a massive difference to how much you save/earn and completely changes how you use the system.
Assuming you're buying electricity at 7p and exporting at 15p.

With no battery, you use as much of the energy produced from your solar when you can. Maybe you charge the car at night. Or you charge the car during the day with a zappi, for example. Maybe use an eddi to heat your hot water. Unless you're at home/plugged in during the day, you're going to be exporting most of what you produce to the grid. And you're going to be paying peak rate for electricity when it's dark.

With a battery, you charge the battery and car (and hot water via emersion heater) at night during off-peak and then try to use as much of that battery power during peak times. If the battery is big enough, you can continue to use that battery power until 23:30 and use no grid power at peak times. And export as much solar as you can at 15p.

Looking at it purely from a financial perspective, any tariff which allows you to purchase cheaper at night than you get paid for exporting during the day makes the original USPs of the zappi and eddi redundant.
You're not going to charge your car using solar produced energy if you can charge your car at 7p at night and get paid 15p for exporting solar produced energy during the day.
And you're not going to put energy in to your eddi that you can get paid 15p for when it costs much less than that for the gas.

Can't the Eddi and Zappi do clever things like ramp up and down and be set on timers?

In which case can their use be switched to overnight charging/heating and things like that while this cheap overnight + generous solar offer remains?

 

[Tight Git]

That's interesting because I was wondering how the Zappi managed balance charging with this system.

My car has always balanced for 30-35 minutes after getting to 100%. I've watched it on the granny lead and I've watched it on public type 2 chargers, and always about this length of time. So how long did you think yours balanced for? Did it seem to go for longer than that?

Incidentally I was a bit concerned that my car wasn't balancing (either at all or not for long) on the Zappi when it was on eco+ running directly from the solar. So much so that I deliberately charged it from 98% on the granny lead a couple of weeks ago to make sure it had happened. But then yesterday it balanced for 30 minutes on the solar, and right now this minute it has just reached 30 minutes from full and it's still balancing. So I don't know if it's learned, or what...?

Assuming you can see the attached graph from the Zappi it had started reducing the current at 03.10 and was still going at 04.30 (finished at 04.35) which is way longer than I have seen before. It had been balanced on a 7kW charger about 10 days before so it's not like it had been a long time since the last balance.

 

[tsedge]

It seems to me that once you have a tariff like this, a decent-sized home battery is a no-brainer. But then, some people have nowhere to put it.

It also isn't a no brainer if you might move house in the near future (yes, you could take it with you but with a uninstallation and reinstallation cost) or you rent or otherwise your circumstances might change or if you don't have much in savings or would have to borrow money to cover the cost (there is still a multi-year payback period).

It is a fact that people who are older, more settled and/or retired have both the predictability in their lives and the capital for these kinds of projects. But that's not everyone.

This is not a criticism at all, just an explanation.

That's interesting because I was wondering how the Zappi managed balance charging with this system.

My car has always balanced for 30-35 minutes after getting to 100%. I've watched it on the granny lead and I've watched it on public type 2 chargers, and always about this length of time. So how long did you think yours balanced for? Did it seem to go for longer than that?

Incidentally I was a bit concerned that my car wasn't balancing (either at all or not for long) on the Zappi when it was on eco+ running directly from the solar. So much so that I deliberately charged it from 98% on the granny lead a couple of weeks ago to make sure it had happened. But then yesterday it balanced for 30 minutes on the solar, and right now this minute it has just reached 30 minutes from full and it's still balancing. So I don't know if it's learned, or what...?

The Zappi knows nothing about balancing and cares nothing about it. It simply supplies the desired charge level until the car says "I'm finished" and this won't be issued by the car until balancing is complete.

So with connection to IOG via Zappi/Ohme/Wallbox balancing is automatic so long as the requested +N% amount is enough to cover the balancing.

With a direct connection between IOG and the car, balancing has been a problem because once the car hits the target percentage (eg 100%), the charge is ended.

For these cases, people have been using the Bump Charge capability to balance, since this uses minimal energy and will terminate when the car says it is finished. It doesn't matter if this is at the higher rate since very little energy is needed to balance.

 

[Rolfe]

Assuming you can see the attached graph from the Zappi it had started reducing the current at 03.10 and was still going at 04.30 (finished at 04.35) which is way longer than I have seen before. It had been balanced on a 7kW charger about 10 days before so it's not like it had been a long time since the last balance.

Not ever seen that. Again today my car balanced for 35 min on the Zappi from direct solar, so it seems to be possible and I can stop worrying that that won't happen. I think the problem may be if for some reason there's no excess the trickle charge will stop and not start again. I don't think I've ever left the car for as long as 10 days without balancing though.

Can't the Eddi and Zappi do clever things like ramp up and down and be set on timers?

In which case can their use be switched to overnight charging/heating and things like that while this cheap overnight + generous solar offer remains?

You can certainly set the Zappi to charge overnight, that's kind of its raison d'etre. But as far as I know the point of the Eddi is to use excess solar. You can also request it to heat the water (using battery power) any time you like though. I sometimes do that first thing in the morning to get the water hot, knowing that as the sun comes up the battery will soon recover the charge.

I have never understood why immersion heaters are not fitted with timers. When I bought my first flat, which had no central heating so I relied on the immersion heater for all my hot water, one of the first things I did was to cut the lead into the tank heater and wire in a simple timer. Worked an absolute treat. With central heating to heat the water it's less necessary of course.

I remember an aunt of mine who wasn't well off and had home economy down to a T, used to have a card she propped in front of the clock on her mantelpiece, saying "immerser on". Every time she looked at the clock she was reminded she had to turn it off. She could have done with my timer solution.

 

[Rolfe]

Having a battery makes a massive difference to how much you save/earn and completely changes how you use the system.
Assuming you're buying electricity at 7p and exporting at 15p.

With no battery, you use as much of the energy produced from your solar when you can. Maybe you charge the car at night. Or you charge the car during the day with a zappi, for example. Maybe use an eddi to heat your hot water. Unless you're at home/plugged in during the day, you're going to be exporting most of what you produce to the grid. And you're going to be paying peak rate for electricity when it's dark.

With a battery, you charge the battery and car (and hot water via immersion heater) at night during off-peak and then try to use as much of that battery power during peak times. If the battery is big enough, you can continue to use that battery power until 23:30 and use no grid power at peak times. And export as much solar as you can at 15p.

Looking at it purely from a financial perspective, any tariff which allows you to purchase cheaper at night than you get paid for exporting during the day makes the original USPs of the zappi and eddi redundant.
You're not going to charge your car using solar produced energy if you can charge your car at 7p at night and get paid 15p for exporting solar produced energy during the day.
And you're not going to put energy in to your eddi that you can get paid 15p for when it costs much less than that for the gas.

Oh, don't rub it in! I've been told by my installer that I've got approval for 5 kw export, but I still need to wait for some certificate to come through before I can apply to Octopus for the export tariff. Still trying to use every single sunbeam I possibly can.

Today, the car was charged by noon, when I started the washing machine. Then the Eddi brought the water back to temperature. There was a dip in the solar, but it recovered enough to dry the washing on the line in the afternoon, which was good. After lunch I took a power shower, which may seem odd at that time, but I had to do my hair colour and the best way to rinse that off is by having a shower. The Eddi promptly leaped in again, and the water was back up to temperature not long after I'd got out of the shower.

So there I am, sun shining, MyEnergi app showing EV full, water at target temperature, washing on the line, and all the showers I really want already taken. Export today, 8.2 kwh. Maybe not so much, but day after day this is already at a loss of almost £100 in just over two months, even though I try to use as much solar as possible. It's pure sadism.

Your last sentence was what I really wanted to know though. I don't have gas I have kerosene, and I genuinely don't know how to play this. It seems to me that during the summer it's better to use the Eddi than to fire up the oil boiler just to heat the water, which is what I've done in the past. But in winter, when the boiler is on anyway, is it definitely cheaper to use it for the hot water too, than to let the Eddi take some solar if it can get it? (I suppose in practical terms it might be better to use the oil boiler anyway, because there are going to be days when there's bugger-all excess to export and the water would just be cold in that case.)

Any thoughts appreciated.

 

[johnb80]

Your last sentence was what I really wanted to know though. I don't have gas I have kerosene, and I genuinely don't know how to play this. It seems to me that during the summer it's better to use the Eddi than to fire up the oil boiler just to heat the water, which is what I've done in the past.

Correct but during off peak OR a peak time charging session so youre paying 7p kWh

But in winter, when the boiler is on anyway, is it definitely cheaper to use it for the hot water too, than to let the Eddi take some solar if it can get it?

NO.

even if the boiler is on, the hot water tank will be a load on the boiler of 'x' amount of kWh needed. Oil is very expensive in terms of energy costs and in addition, burning oil is not very efficient

(I suppose in practical terms it might be better to use the oil boiler anyway, because there are going to be days when there's bugger-all excess to export and the water would just be cold in that case.)

My comments are assuming you can store sufficient hot water for the day to allow for heating off peak. Consider raising the temperature of your immersion heater which in effect gives you more water storage (caveat be careful from a potential scalding point of view).

Any thoughts appreciated.

Youre welcome - some bloke in Lincolnshire on the net that knows everything about nowt

 

[Rolfe]

Correct but during off peak OR a peak time charging session so youre paying 7p kWh

NO.

even if the boiler is on, the hot water tank will be a load on the boiler of 'x' amount of kWh needed. Oil is very expensive in terms of energy costs and in addition, burning oil is not very efficient

My comments are assuming you can store sufficient hot water for the day to allow for heating off peak. Consider raising the temperature of your immersion heater which in effect gives you more water storage (caveat be careful from a potential scalding point of view).

You're welcome - some bloke in Lincolnshire on the net that knows everything about nowt

Regarding that first, during the summer the Eddi automatically looks for surplus solar and uses it rather than exporting it, so I'm basically foregoing 15p export if I let it go on doing that once I've got that thrice-damned MPAN. Alternatives seem to be to use off-peak electricity to heat the water (somehow, need to figure out how to do that), or to run the kerosene boiler just to heat the water - as has been my practice up till now.

I thought from what Stuart said that the latter might be theoretically better, but he was talking about mains gas not oil, and you're right, oil is expensive. On the other hand, there have been times in previous summers when the boiler has only been used to heat the water and I seemed to use no oil at all for a couple of months, according to the outfit who come to fill up the tank.

I also remember the guy I spoke to on the MyEnergi stand saying to use the oil boiler because it can whack in more heat than the immersion heater (this surprises me) and it would be more economical. So I'm not really sure.

Usually I can store enough water for the day if it's brought to temperature the previous night. In fact it has been reasonably hot through most of a day when it was last heated by the Eddi the previous evening with the last of the solar, then the following day I let the Zappi have all the solar. It's bloody well scalding as it is when the Eddi has finished with it. (I have no idea how to change the target temperature. Long ago I did raise this with my then central heating engineer and he seemed to have no idea. All he did was change the position of the thermostat on the tank.) If I heated the water overnight I still have the option of using a bit out of the home battery to give it a boost during the day if necessary.

My feeling is that in summer when I don't need central heating then using the Eddi makes sense to save firing up the kerosene boiler at all. Having had a look at the app, I see where a schedule can be set, so I could presumably set it to heat from 4.00 or 4.30 to 5.30 am and then hopefully it would do for the day. In winter though, the boiler is on anyway, so I need to do some sums.

One litre of kerosene contains 10.35 kwh
One litre of kerosene cost 91.16p the last delivery I had (June)
Therefore kerosene costs 8.8p/kwh
Boiler efficiency rating is 90.5%
This brings price/kwh actually used to 10.4p

So the overnight electricity tariff is still cheaper (although I think we're assuming 100% efficiency of the Eddi there and I don't know if that's valid), but there isn't an enormous amount in it. Might simply come down to convenience.

But for sure you're right, the least economical thing to do is to let the Eddi go on harvesting solar excess, once I'm actually getting paid for it. (How long, O Lord, how long?)

 

[johnb80]

Regarding that first, during the summer the Eddi automatically looks for surplus solar and uses it rather than exporting it, so I'm basically foregoing 15p export if I let it go on doing that once I've got that thrice-damned MPAN. Alternatives seem to be to use off-peak electricity to heat the water (somehow, need to figure out how to do that), or to run the kerosene boiler just to heat the water - as has been my practice up till now.

Set a schedule in EDDI, just like Zappi

I thought from what Stuart said that the latter might be theoretically better, but he was talking about mains gas not oil, and you're right, oil is expensive. On the other hand, there have been times in previous summers when the boiler has only been used to heat the water and I seemed to use no oil at all for a couple of months, according to the outfit who come to fill up the tank.

Mains gas is circa 4.5p kWh so even after boiler efficiency is taken into account, it's still cheaper to use gas.

I also remember the guy I spoke to on the MyEnergi stand saying to use the oil boiler because it can whack in more heat than the immersion heater (this surprises me) and it would be more economical. So I'm not really sure.

Most boliers can transmit heat into the hotwater tank quickly, theyre usually well over 20kW compared to 3 kW for an immersions heater so yes, a boiler can heat it faster but not cheaper in terms of kerosene.

Usually I can store enough water for the day if it's brought to temperature the previous night. In fact it has been reasonably hot through most of a day when it was last heated by the Eddi the previous evening with the last of the solar, then the following day I let the Zappi have all the solar.

Thats fine, just use the schedule and enable 23:30 to 05:30 every day.

It's bloody well scalding as it is when the Eddi has finished with it. (I have no idea how to change the target temperature. Long ago I did raise this with my then central heating engineer and he seemed to have no idea. All he did was change the position of the thermostat on the tank.)

If it's scalding hot from your oil boiler the thermostat on the outside of the tank will adjust that. The immersion heater has a thermostat under the cap where the wire goes in, you could turn it down there if you wish but that effectively gives you less usable hot water.

If I heated the water overnight I still have the option of using a bit out of the home battery to give it a boost during the day if necessary.

Correct in the app you can boost for 'x' time

My feeling is that in summer when I don't need central heating then using the Eddi makes sense to save firing up the kerosene boiler at all. Having had a look at the app, I see where a schedule can be set, so I could presumably set it to heat from 4.00 or 4.30 to 5.30 am and then hopefully it would do for the day. In winter though, the boiler is on anyway, so I need to do some sums.

No point really in a short time, put it on for the 6 hour window, once the tank is up to temperature the thermostat will switch off the immersion and EDDI will see it as 'at temperature'.

One litre of kerosene contains 10.35 kwh
One litre of kerosene cost 91.16p the last delivery I had (June)
Therefore kerosene costs 8.8p/kwh
Boiler efficiency rating is 90.5%
This brings price/kwh actually used to 10.4p

Thats a very efficient oil boiler you have. There are additional losses such as water pump, oil pump, burner controls etc and losses in the pipework between the boiler and tank. which will raise that a little more

So the overnight electricity tariff is still cheaper (although I think we're assuming 100% efficiency of the Eddi there and I don't know if that's valid), but there isn't an enormous amount in it. Might simply come down to convenience.

Electric heating is usually considered to 100% efficient, there's very few losses powering EDDI and all what goes into the immersion heater ends up in your water.

But for sure you're right, the least economical thing to do is to let the Eddi go on harvesting solar excess, once I'm actually getting paid for it. (How long, O Lord, how long?)

Hopefully soon.~

J

 

[Rolfe]

Set a schedule in EDDI, just like Zappi

Mains gas is circa 4.5p kWh so even after boiler efficiency is taken into account, it's still cheaper to use gas.

Most boliers can transmit heat into the hotwater tank quickly, theyre usually well over 20kW compared to 3 kW for an immersions heater so yes, a boiler can heat it faster but not cheaper in terms of kerosene.

Thats fine, just use the schedule and enable 23:30 to 05:30 every day.

If it's scalding hot from your oil boiler the thermostat on the outside of the tank will adjust that. The immersion heater has a thermostat under the cap where the wire goes in, you could turn it down there if you wish but that effectively gives you less usable hot water.

Correct in the app you can boost for 'x' time

No point really in a short time, put it on for the 6 hour window, once the tank is up to temperature the thermostat will switch off the immersion and EDDI will see it as 'at temperature'.

Thats a very efficient oil boiler you have. There are additional losses such as water pump, oil pump, burner controls etc and losses in the pipework between the boiler and tank. which will raise that a little more

Electric heating is usually considered to 100% efficient, there's very few losses powering EDDI and all what goes into the immersion heater ends up in your water.

Hopefully soon.~

J

Thanks.

I can see where to set the schedule in the Eddi, so that's pretty easy. However, I don't really see the point in setting it for the entire cheap-rate period, as I'm not actually going to want it until the following morning. If it's "at temperature" at 5.30 it's fine, and there will be some losses from the tank during the night if it's hot from just after midnight. I would have thought an hour would be enough to get it there, it doesn't seem to take very long when it's running on the solar, although I can experiment.

I can see what you mean about the relative cost of gas and oil. In fact my boiler is quite new, I had it fitted in 2019, and my installer said it would be an improvement on the dying 20+ years old unit it replaced. I was surprised by how high the efficiency was said to be, but it's there in black and white in the manual. I certainly noticed a reduction in kerosene consumption once it was in, although with the prices going up the overall cost didn't change much.

However, I am now hugely confused about the operation of the kerosene water heater, and wonder if there's a problem with mine. It is set to heat from 6.30 to 8.30 then again from 4.30 to 10.30. This should be absolutely ample, I mean even over the top. It would be ample to over the top if it was the immersion heater set for these times! If the boiler is supposed to be delivering 20 kw then you could have fooled me, because the water has not been that hot, not for a long time.

I remember, as I said, way back when I first moved in here, complaining that the hot water was too hot, and all the engineer did was move the thermostat to a different place in the tank. I don't remember thinking it made much difference at the time. But lately, I don't remember if it's just since the new boiler went in, or if it was before then, the hot water has been pretty disappointing. I sometimes used the immersion heater for half an hour because it wasn't hot enough. If the kerosene boiler has been pumping 30 kw into it for eight hours a day then I don't know where that has been going.

But then, I did say that I went two months last summer when it was so warm the boiler did nothing but run the hot water, and when the regular delivery of oil came, the tanker went away again because the tank was still full. Hmm. I'm getting a bit suspicious about this. Boiler will be due its annual service in a couple of months so I'll raise the issue. I might not be going to use the water heating facility much from now on, but it might as well be working.

Another thing I remember was that a week or two ago I'd been hoovering up so much of the solar to fill the car (what with all these clouds) that the Eddi hadn't had much of a chance. It turned very chilly in the evening, so I turned on the central heating for about three hours. Rather than boost the Eddi I just turned on the water heating in the central heating at the same time. The result was nowhere near as hot as the Eddi has been achieving.

There's no doubt that the water is really really hot now, with the Eddi just harvesting surplus solar. I'm noticing that I'm turning the temperature dial of the shower way lower than I was when the oil was heating the water. Definitely something to raise with Ronnie in the autumn.

You know, I was actually going to start a thread about this because I didn't know what water heating method was the most efficient. But this has more or less cleared up my questions. If it's actually working properly (and I suspect that it may not be, and may not have been for five years) then the kerosene is massively cheaper than peak-rate electricity but about 50% more expensive than off-peak electricity.

 

[johnb80]

Thanks.

I can see where to set the schedule in the Eddi, so that's pretty easy. However, I don't really see the point in setting it for the entire cheap-rate period, as I'm not actually going to want it until the following morning. If it's "at temperature" at 5.30 it's fine, and there will be some losses from the tank during the night if it's hot from just after midnight. I would have thought an hour would be enough to get it there, it doesn't seem to take very long when it's running on the solar, although I can experiment.

It depends on the losses from your tank, our relatively new tanks, the insulation is so good the airing cupboard wasnt warm enough, I've fitted and electric heater in there to heat the cupboard. You can certainly set the schedule towards the end of the window to reduce the losses as you say, the only potential issue is if you dont give it enough time and therefore dont get your daily supply of hot water stored. Assuming a 220 litre tank, 15 deg C cold water and a target temperature of 80 deg C, a 3 kW immersion heater would need just over 5.5 hrs to heat the water. Obviously if any of the criteria changes tank capacity, temperatures, tank not empty etc it will change that time.

I can see what you mean about the relative cost of gas and oil. In fact my boiler is quite new, I had it fitted in 2019, and my installer said it would be an improvement on the dying 20+ years old unit it replaced. I was surprised by how high the efficiency was said to be, but it's there in black and white in the manual. I certainly noticed a reduction in kerosene consumption once it was in, although with the prices going up the overall cost didn't change much.

Oil boilers followed gas boilers being developed into condensing boilers which offer much greater efficiencies.

However, I am now hugely confused about the operation of the kerosene water heater, and wonder if there's a problem with mine. It is set to heat from 6.30 to 8.30 then again from 4.30 to 10.30. This should be absolutely ample, I mean even over the top. It would be ample to over the top if it was the immersion heater set for these times! If the boiler is supposed to be delivering 20 kw then you could have fooled me, because the water has not been that hot, not for a long time.

The capacity of your boiler will be well above 20 kW looking at the size of your house and its location. The boiler will have a flow temperature of the water coming from it and I would guess that would be set in the 50 to 70 deg C range, that will also set the maximum temperature of your hot water. If the immersion thermostat is set to 80 deg C that's why you're experiencing different hot water temperatures between immersion and oil boiler heated water.

I remember, as I said, way back when I first moved in here, complaining that the hot water was too hot, and all the engineer did was move the thermostat to a different place in the tank. I don't remember thinking it made much difference at the time. But lately, I don't remember if it's just since the new boiler went in, or if it was before then, the hot water has been pretty disappointing. I sometimes used the immersion heater for half an hour because it wasn't hot enough. If the kerosene boiler has been pumping 30 kw into it for eight hours a day then I don't know where that has been going.

Condensing boilers need to be able to condense the flue gasses by cooling them below 55 deg C. To achieve that the return water coming back to the boiler needs to be below 55 deg C. This is probably the reason why you're expressing disappointment in the hot water performance.

But then, I did say that I went two months last summer when it was so warm the boiler did nothing but run the hot water, and when the regular delivery of oil came, the tanker went away again because the tank was still full. Hmm. I'm getting a bit suspicious about this. Boiler will be due its annual service in a couple of months so I'll raise the issue. I might not be going to use the water heating facility much from now on, but it might as well be working.

I'm sure the water flow temperature can be easily adjusted BUT its highly likely to be detrimental to efficiency, no such thing as a free lunch!

Another thing I remember was that a week or two ago I'd been hoovering up so much of the solar to fill the car (what with all these clouds) that the Eddi hadn't had much of a chance. It turned very chilly in the evening, so I turned on the central heating for about three hours. Rather than boost the Eddi I just turned on the water heating in the central heating at the same time. The result was nowhere near as hot as the Eddi has been achieving.

Yes as per all the reasons stated above.

There's no doubt that the water is really really hot now, with the Eddi just harvesting surplus solar. I'm noticing that I'm turning the temperature dial of the shower way lower than I was when the oil was heating the water. Definitely something to raise with Ronnie in the autumn.

Worth asking but do bear in mind if the temperature is cranked up the efficiency will plummet, your radiators would be hotter too. I deliberately run our rads at 40 deg C or less from gas and/or heatpump so my grandson doesn't burn himself, he ended up crying with the temperature was higher at 55 deg C, he did learn from it and no harm was done other than the shock. The gas boiler efficiency rockets at the lower temperature.

You know, I was actually going to start a thread about this because I didn't know what water heating method was the most efficient. But this has more or less cleared up my questions. If it's actually working properly (and I suspect that it may not be, and may not have been for five years) then the kerosene is massively cheaper than peak-rate electricity but about 50% more expensive than off-peak electricity.

I suspect your boiler is working as designed and it sounds like it has been configured with low flow temperatures to achieve the high efficiencies you're reporting.

 

[Rolfe]

It's not a condensing boiler though, if I remember a conversation from five years ago correctly.

I hear what you're saying there, very interesting. I'll ask Ronnie what he thinks when he does the boiler service, because I may still need the central heating to heat the water if I need a boost during the day and don't want to raid the house battery for the power. The radiators can get quite hot, but I wouldn't cry if they were a bit hotter when the weather is very cold.

There is also a defect in the tank insulation that's been there since the thermostat was moved, so I should look at fixing that.