JamesPa

I agree carbon neutrality is important, but how are you saying a battery becomes carbon neutral. You seem to be linking it to solar and I confess I don't understand the linkage, unless for some reason you can't export any excess solar generation you may have to the grid and so, in the absence of a battery, it is wasted.

So it does. I probably was thinking that I couldn't easily apportion between the various rates given that they are somewhat interleaved, although the probability of Solar displacing consumption in the peak rate period is relatively low. In reality a better model might be 50% exported (at 15p) and the rest apportioned. If I plug that in Cosy without battery becomes about £90 less attractive.

I expect you will be offered a half hour slot with Henri, which is where I got my info from. They are taking customers now.

er Im now confused, isnt that what I have (in the first model, which is the only one that uses these numbers) or am I going mad?

True, I corrected the hours in the base model but not the cosy + battery models. It makes no difference and none of the calculations other than in the base model rely on this. I think I have,, I have three rates 25.81, 12.65 and 37.42 (which are the three cosy rates in Eastern England. One of the 'Battery' titles is wrong, it should say Go not Cosy. I thought about this a bit. You can move the dishwasher but are unlikely to change when you cook or make tea (not that making tea is a significant consumer). So I reckoned you inevitably use some of the high energy load during peak hours My car (e-niro) is suitable but as I don't have any charger (I just use a 13A socket) the combo is not. I had thought Octopus relied on the charger to do the on/off bit but checking back I see that I am wrong there are cars that will work without an accredited charger; I therefore presume that either the car or the charger must be accredited. I spoke with the Havenwise people yesterday. They integrate with Vaillant, Samsung, Mitsubishi and Daikin. Currently they charge £50pa for the service which targets cost optimisation with a ToU tarrif at the 'expense' of allowing the house to get up to 2C warmer than the target (which they regard as a minimum). I'm thinking that this is pretty cheap (I was expecting £10 per month which seems to be a standard 'service' charge) but this will be their first 'commercial' winter so I guess it has to be. I'm seriously tempted (but need to get the heat pump in first!). I do wonder whether their long term goal is to be bought out by Octopus and integrated into Kraken.

Yes me too (although it should be getting less with the EV and a bit of automation I have set up. The spreadsheet assumes 50% export in all scenarios, thats the allocation to sub-tarrif D. I dont think this particular assumption makes that much difference (for a 4kWp system) because most of the tariffs have a low rate around 15p or below. If the low rate is below you would ideally export excess solar anyway. If you have a much larger system then it could make quite a difference indeed.

Thanks, model corrected and attached in various formats. Precisely. As I say above I made somewhat lazy assumptions about how ToU tarrifs would, in practice, be used but others may be more aggressive. The interesting thing, for me, it to 'play around' with the assumptions to do a bit of sensitivity testing. Just doing this can give a very good indication what choice to make and whether the choice really matters given the uncertainties. For example its clear to me from this analysis and with my assumptions that I would be mad to stay on a fixed tarrif, but the choice between Agile, Cosy and Go is 'in the noise' of the precise assumptions, so unless I tie those down and follow through on them in practice its not worth sweating over which. This allows me to rule out Go because, although I do have an EV, I don't need a car charger, which is mandatory for Go. Likewise the battery case simply isn't made for me, so I can set that aside until battery prices fall by 30% or energy prices rise similarly. Models, and their assumptions, only have to be good enough to allow informed decisions to be made which often does not require anything particularly precise. Tarrif comparator.ods Tarrif comparator.pdf Tarrif comparator.xlsx

Attached a print out In response to your question, it really depends on the assumptions you make about when you operate the high-draw items (which is adjustable in the spreadsheet). In all my modelling I assumed that no account is taken of the tarrif when deciding to operate equipment, with the exception of car charging where I make more generous assumptions. I did this because it is the 'lazy' option which I fear many, including me, will default to, and also because it paints batteries in a 'good' light (my initial motivation for the exercise was to prove, or otherwise, that batteries don't make financial sense, so by painting them in a 'good' light any conclusion that they don't make financial sense is relatively robust). Cosy also might have an un-modelled advantage in the shoulder season when perhaps your heat pump struggles not to cycle. In this case operating the heat pump only during the cheap periods will likely reduce the electricity cost without materially compromising efficiency (because the heat pump was destined to cycle anyway). Interestingly Cosy Mk2 (with the three low price periods) is now entering its first winter. With any ToU tarrif, and a sufficiently capable heat pump controller, there is the opportunity to 'pre-load' the house, warming it up above the desired temperature before a high tarrif period kicks in. Thats exactly what homely and the like do. Cosy may be better suited to this than Go because the cheap periods are better distributed, but I didn't build this into my modelling. TBH I think Agile is even better suited to this behaviour than cosy because there is much more low price time even better distributed still. Although there is some uncertainty when the low price time will occur, in practice its pretty predictable. Of course Homely and the like have the advantage of looking ahead a day so they know what the future price and temperature is, and thus can be more intelligent about this optimisation than any timed controller can. The percentages of each load class assigned to the different prices within any one tarrif are adjustable, so if anyone wants to make radically different assumptions to see how it changes the picture they can. Even if you dont intend to buy a battery its quite interesting to look at the 19kW battery column where I essentially assume all, or nearly all, the electricity is at the lowest price. The trick would be to achieve this, or something close, without the upfront cost of a battery. With Agile, intelligent control and a house with a reasonably high heat capacity I reckon that may be close to do-able for the heat pump which is the dominant load. Homely, Havenwise, Adia, PassivUK (the four I know of, there may be more) are, I think, targeting more or less exactly that. In time I imagine energy suppliers will offer remote heat pump control with some sort of guarantee on minimum and maximum house temperature, so they can load balance. The technology that Havenwise is developing is particularly well suited to this case, as it doesn't require any hardware, just an internet connection. Tarrif comparator.pdf

Thanks, corrected. With that change it works out almost identical to Intelligent Go and a bit cheaper than my model of Agile (which is deliberately a bit pessimistic). Why do I suspect that all the variable price tariffs work out the very nearly the same for an average user unless you seriously 'game' them. OvO heat pump still the cheapest by a fair margin, with the health warnings above.

Here is a crude attempt at tarrif comparison for some assumptions set out in rows 5-11. The consumption figures are for me, but actually not atypical for UK houing I have modelled tariffs stand alone, with a 9.5kWh battery and a 19kWh battery, for which local prices (fitted) are currently 5K and 7K respectively The meat of it is to allocate the % consumption for each load type to the various timed tarrifs. This is a bit of an informed guess in some instances so you should substitute your own numbers. Where I am modelling with a 19kWh battery it is much less of a guess, as such a battery is large enough to cover a whole day (except car charging) for almost all of the year. My conclusion (which applies for me only) Dont bother with a battery, it doesn't pay, or doesnt pay by much (I might change my mind with the 'dont bother' bit if there is solid evidence of environmental benefit). If I were to trust Ovo, the Ovo heat pump tarrif is the winner Otherwise get Agile or Intelligent Go or Cosy and just be faintly sensible about use during the peak charging periods, without busting a gut. Agile with a bit of intelligent manipulation of the heat pump to use the house as an energy score (as in what Homely, Havenwise, Adi and Passiv purport to do) looks like its well worth exploring and probably the best bet in the short to medium term (There is also a plot of (UK) carbon intensity vs (Eastern England) Agile pricing, showing v poor correlation. I need to do this again with East of England carbon intensity which might show better correlation, so at the the current time its a case absence of evidence for correlation carbon intensity<->pricing, which is evidence of absence.) Criticism (preferably constructive) welcome. Tarrif comparator.ods Tarrif comparator.xlsx

Possibly, maybe probably, which is why I'm still holding out hope that hoping someone would come forward with some facts. I've also seen it claimed that price is not a particularly good proxy for dirtyness. I really don't know. I think somewhere you can download grid carbon intensity, so I suppose I could correlate the two!

Here is the response from Octopus, basically tarrif not available unless you have an EV and a compatible charger and they actually test that you do. "Thank you for your message and for your interest in our Intelligent Go tariff. I completely understand your perspective on the benefits of having a time-of-use tariff, similar to the old Economy 7. However, I must inform you that the Intelligent Go tariff is specifically designed for customers with an electric vehicle (EV). To switch to this tariff, you would need to complete a test charge with your EV, as this is an integral part of the onboarding process. Without an EV, unfortunately, it won't be possible to access this tariff. If you're looking for a time-of-use tariff without an EV, I recommend checking our other available options. Please let me know if you need assistance with anything else or if you have any further questions. I'm here to help!"

Thats a good question. |Another good question is - just suppose I have an EV but not an EV charger (so my charge rate is limited to the 10A you can get from a 'granny charger' and cant be controlled by Octopus - is the tariff still available). The latter question describes my current situation, and I have no need for an EV charger other than to meet the criteria of a tariff (which of course makes it less attractive). I will ask octopus!

I don't see your house (on which I congratulate you) as a special case for newbuilds (although it is in reality judging by whats going up in large numbers locally) but it is a special case for heat pumps. The vast bulk of our housing stock is existing stock and thus the vast bulk of the heat pumps we need to fit are in these, almost all with radiators. In that context, which from a climate change perspective is the larger one, your house is a special case. Likewise. Im working on a spreadsheet (which I will share once its done) but I am not currently finding (for my house - which is probably a fairly typical retrofit with a 7.5kW heat loss) the sweet spot for batteries at their current price. Givenergy, for example, is (around here) 5K for 9.5kWh and 7K for 19kWh. If they did the 19kWh model for 5K there might be a case. So far nobody has come forward with an environmental argument which would tip the balance, so its purely financial at the current time. The biggest challenge with working out the numbers is to estimate how long the battery will last (and thus how much of any more expensive period you can 'ride out'). Because the heat pump dominates the load, this is heavily time of year dependent, so somehow you need somehow to calculate the aggregate % of the total heat pump consumption which can be accommodated at a lower tarrif. This is not a trivial calculation! If anyone has magically done this I would appreciate them sharing their method. Definitely a concern. That said, the Ts & Cs don't currently appear to allow them to control the heat pump, which is one reason I think the tariff is unsustainable.

@IanB My advice, if a. the MCS recommendations are getting in the way and b. you have a coherent argument whey they are not appropriate for your house is - shop around. There are MCS installers out there that will depart, with justified reason, from the MCS guidance/recommendations. Of course they will still conform to the requirements of MCS, BUS and Building Regulations. Two years ago, when I embarked on this (still incomplete) journey, finding installers that would step outside the box was like looking for hens teeth. Now, as I look anew for quotes, it seems that a fair few more have recognised that the MCS recommendations are too restrictive, and are thus prepared to be more flexible whilst still meeting the requirements. This time around (knowing much more than I knew when I first sought quotes 2 years ago) I stated in my initial brief where I needed the installer to depart from the recommendations. I was pleasantly surprised that more than one came back saying 'yes, we know that they are too restrictive, we are happy to be flexible on this point). Slowly the industry is waking up to the real world.

Rubbish - ours runs at 35C and we don't run it during the day. So no impact on CoP or need for extra daytime/peak cost. I did say, if you have an insulated slab...... And it's not about designing around a tariff, it's about designing and building an energy efficient home. Working out which tariff is most cost effective is then pretty easy. Simon OK so we are talking very energy efficient newbuild. Even in this case there still is, at least in principle, a COP penalty (because you could, in principle, be running even lower than 35C) but, its relatively small - Instead of running at 35/30 you could, at least in principle, be running at something very roughly like 28/23, which would deliver very approximately the same energy on a 24/24 basis as 35/30 does on a 8/24 basis for an energy penalty of ~14%, which is certainly outweighed by the tarriff differential. This is , I agree, a relatively small COP penalty on a relatively small consumption and anyway might not be practical within the engineering limitations of the heat pump, so in this case I can see that Cosy might work (although you do still need to offset the elevated price paid the majority of time for the other loads which, unless you have an EV, may well dominate the heat pump load in this case) However Octopus don't solely sell to the tiny minority of people with highly energy efficient newbuilds, they also sell to the majority case of a house operating on radiators designed to operate at perhaps 45C with perhaps a 6-8kW load consuming ~6MWh/year for the heat pump. In this case the flow temperature would need to be turned up to about 70C to deliver the same amount of energy in one third of the time. In this, much more common, case, the efficiency would be clobbered (nearly doubled) unless you have a battery to extend the period at which you could operate on the low tarrif. So, unless someone can prove me wrong, I will stick by my current analysis (actually stolen from @JohnMo who originally made the observation) that the Cosy tariff is basically, for the average person/house, a battery tariff. Of course there are exceptions where it works in other circumstances, and you have quite possibly identified one. Please don't take this as an argument for batteries. I am doing the maths for me at present (I fit into the more typical retrofit category described above) and I have yet to find a scenario where batteries pay. So far as I can see the best bet at present is the OVO heat pump add on, although I struggle to believe this will be around for long. Failing that Intelligent Go seems (based on my current analysis) to be the next best as suggested by @Bramco, albeit in both cases without battery. The battery payback analysis is based on £5K/9.5kWh or £7K/19kWh, which seems to be about par for the course at present unless you self install).

Well yes (and no), if you haven't built the property yet! But who is going to design a property to suit an electricity tariff that may or may not survive for any duration. I say 'and no' because, if the pipes are closer together, then your 'baseline' case is to run at the lower FT corresponding to the closer pipe spacing..

If you only run the heat pump during the low rate periods then yes, but that will clobber the heat pump efficiency as you will need a higher flow temperature to deliver the same amount of energy. And you have to offset any saving against the extra daytime/peak cost. Ovo currently offers 15p/kWh for the entirety of your heat pump consumption irrespective of time of day, provided you have the right heat pump. I reckon that's unbeatable if you qualify, but also unsustainable for OVO

We already pay to have it taken away, called the daily standing charge. It is always hard to compare different systems, in different countries, so no point trying in the case of PV. Clearly excess isn't currently a problem in much of the UK since we get paid for export. Judging by how few solar panels there are down my road I don't think it's likely to be a problem even at the local grid level. So for now I think it's reasonable to assume that exporting it is sound environmentally. Presumably if we get to the point where too much solar is a problem we will be penalised for export which will improve the battery business case.

If cheap electricity prices aren't a reasonable proxy for carbon intensity, then the battery environmental argument is further weakened. I was hoping someone would respond telling me why home batteries are good environmentally, perhaps they still will.

I think so but would dearly love to be convinced otherwise To be clear I don't evaluate the case for ASHPs, electric cars or solar panels on a purely financial basis, the case is environmental (or, in the case of an electric car, its just a better driving experience all round as well as environmental) However I do for batteries, because I don't see the environmental benefits. If my PV produces excess it gets exported, which is then used by others so I can discount that potential environmental benefit. This leaves the question of whether it is better for the environment to do the job of grid balancing locally. I can see that on the extreme occasions when (until very recently) we fired up coal fired power stations it might have been, but that has gone. TBH the answer is I don't know whether local grid balancing using batteries are good for the environment, but haven't seen evidence that it is. It may be that ther optimum is just to charge my car, heat my water and do my dishwashing and clothes washing in the 'cheap' periods (which I presume are a reasonable proxy for carbon intensity) and leave it at that. These things are by and large easy to do and cost nothing (money or natural resources). If I were to see some reasonable evidence that batteries are good for the environment then I would change my assessment criteria for batteries. Im not a sceptic on this matter, just haven't seen much of a reasoned argument and am conscious that the MCS crowd basically sell them as an extension to solar panels to 'optimise self use' which doesnt confer an environmental benefit.

What are the U-values Pretty poor. Cardboard walls don't help.

The goods shed is an old folks home. The rather fine station building has unfortunately been demolished, which is a pity. I don't intend moving in, just making a model of it as it was in the 1930s. So far I have done the trackwork, land profiling and station building (which doesn't have an ashp so I guess we are off-topic).

Thats very interesting and useful thanks. I currently have sufficient things going on in my life that I don't need a code writing/control system project, much as I would probably enjoy it. I have yet to get the HP installed, although that is hopefully now not far off. At this stage a battery either has to pay for itself with very simple configuration, or Im not going to bother. Once my HP is installed and well controlled, and my 2mm:1ft scale model of Helston Station a lot further forward than it is now (two to three years hence I expect), I might yearn for writing some code. @JohnMo @S2D2 thanks for the figures. I will get some up to date quotes and reassess against the above priorities!

The installed prices I have found by a quick search suggest that 5k for 5kWh isnt far out. I don't have recent quotes, when I did try some while ago found it quite difficult to get battery quotes without solar or vice versa. Like all products in this sector it seems installed prices bear little resemblance to the product price. DiY is clearly an option to consider!