Circular reasoning (Rolfe's solar energy system)

[Archev]

She's just emailed back saying she couldn't persuade her husband, who thinks "it's still too much of a leap in the dark". They were apparently shown an ex-demo Skoda Superb with only 800 miles on the clock at a great price, which ticked all the boxes as regards spec, and went for it. It does sound like a lovely car, as a car, but I think they're in for the worst of both worlds.

She says maybe she can persuade her husband next time. Oh well.

Nice try ?

 

[Rolfe]

I persuaded her, but domestic harmony and all that...

 

[Rolfe]

I'm glad I figured this lot out before I go away for a week, because I might be able to cash in.

The Eddi will be off, don't need any hot water in an empty house, and I can always turn it on from the app when I set off on the last leg of my homeward journey. The Zappi will be off, because the car will be with me. That's two complications out of the way.

• The battery will charge from 11.30 to 5.30. That's plenty of time to get to 100% even if it starts at rock bottom, so that's not a problem. The house will be running on the mains, off-peak.
• 5.30 to sunrise, the battery will power the house base load.
• After sunrise the house will be powered from the solar and the battery will recharge from what's left.
• Once the battery is at 100%, all the solar will be exported.
• At dusk, the battery will take over the house load until 11.30, when it will start to charge again, and the house will again be powered by the mains, off-peak.

So far so good, but this is where it gets complicated for me. There will be far more in the battery than is needed to power the empty house between dusk and 11.30, and that's what I want to export. But I don't want to export so much that the house has to draw on the mains before 11.30.

Calling anyone who has advice to chip in here, right?

The battery is 9.5 kwh, with a reserve of 4% that I can't touch. So roughly speaking there will be 9 kwh there to cover both the house load and any export. The amount the house will take when there's nobody at home is fairly predictable, except that it will start earlier if there's a lot of cloud and dusk comes early.

I've only got a few evenings when I didn't run a heater or something to go by, but left alone with nothing but the house base load, the battery doesn't seem to go below 90% by 11.30. (This will obviously alter as sunset gets earlier though.) 10% of the battery is 0.95 kwh. So say 1 kwh to allow for the house load (at this time of year). That suggests I have scope to export 8 kwh every evening while I'm away. That is £1.20. Every evening. This is looking a lot more attractive than Octopus's freebie hour.

This evening the battery seemed to drop by 42% in an hour of forced export. Which suggests that getting on for two hours of forced export might be about right to achieve the objective. (This is subject to change with sunset time, but I'm only looking at a week for now). The week away might be a really good time to try this out, without the complications of fan heaters and cups of coffee.

I expect it will be a bit more complicated if I'm home and using electricity in the evening, and I still haven't figured out whether it's wise to stop the export when the battery is a bit higher than the lowest it will go, but progress is being made.

Comments welcome.

 

[Caramaddy]

You have come a long way since the system went live. You have really got to grips with the system.
As you explained in an earlier post, you did not want to do loads of research before installing a PV/Battery system. You effectively stood on the shoulders of your neighbours experience and other quotes.

In hindsight, would you change anything? Supplier (Octopus) /. Battery / Eddie / inverter / type of solar panels? Installer?

 

[Rolfe]

Interesting question. I'm happy with Octopus and to be honest I really respond well to the cute wee octopus and the games and so on. I'm a sucker, so sue me. It's too early to tell if the battery is big enough for the winter days, but I suspect it will be. I could wish it discharged a bit quicker so that I didn't have to watch how many pots I have on the boil at once, but that's not a big issue, I don't do cordon bleu.

The Eddi is fine, but I wish it had a setting that allowed it to ignore the solar but do the scheduled charge, so I didn't have to keep turning it off and on. The same thing goes for the Zappi. You can't export anything while they're turned on without them getting in on the act, but then you have to remember to turn them back on again once the export has stopped. (Which now looks like being 11.30 rather than dusk.)

I would like an inverter that did 6 kw or even 7 kw, because the panels can generate up to 8 kw at noon on a sunny summer day. But that would undoubtedly have created more hassle with that bloody Callum and the infernal G99. The panels are great, but the way the fitters placed them has left a gap in full sun that would take another two rather nicely...

The installer has been great, no complaints there. And to be absolutely fair I did raise some of these points with him before the installation started. However I had just psyched myself up to shelling out £13,700 for the originally quoted system and his musings about the extra cost frightened me off. He compromised by offering to upgrade the inverter to 5 kw and apply for the G99 (which he thought would be nodded though, as I later discovered had happened with my neighbour) without increasing the quote.

So I think I did pretty well. I wasn't psychologically ready to spend any more money at the time, and I think I was lucky to be advised (by people in this thread) to ask about the more powerful inverter, and to get it at no extra cost.

Another thing. I've really enjoyed learning by fiddling with my system. It would have been a tedious slog learning all this in advance, and I wouldn't have learned nearly so much. Then getting multiple quotes and haggling about the specifications, spare me.

I think I've very much done the best I could have hoped for under the circumstances.

 

[Caramaddy]

Interesting question. I'm happy with Octopus and to be honest I really respond well to the cute wee octopus and the games and so on. I'm a sucker, so sue me. It's too early to tell if the battery is big enough for the winter days, but I suspect it will be. I could wish it discharged a bit quicker so that I didn't have to watch how many pots I have on the boil at once, but that's not a big issue, I don't do cordon bleu.

The Eddi is fine, but I wish it had a setting that allowed it to ignore the solar but do the scheduled charge, so I didn't have to keep turning it off and on. The same thing goes for the Zappi. You can't export anything while they're turned on without them getting in on the act, but then you have to remember to turn them back on again once the export has stopped. (Which now looks like being 11.30 rather than dusk.)

I would like an inverter that did 6 kw or even 7 kw, because the panels can generate up to 8 kw at noon on a sunny summer day. But that would undoubtedly have created more hassle with that bloody Callum and the infernal G99. The panels are great, but the way the fitters placed them has left a gap in full sun that would take another two rather nicely...

The installer has been great, no complaints there. And to be absolutely fair I did raise some of these points with him before the installation started. However I had just psyched myself up to shelling out £13,700 for the originally quoted system and his musings about the extra cost frightened me off. He compromised by offering to upgrade the inverter to 5 kw and apply for the G99 (which he thought would be nodded though, as I later discovered had happened with my neighbour) without increasing the quote.

So I think I did pretty well. I wasn't psychologically ready to spend any more money at the time, and I think I was lucky to be advised (by people in this thread) to ask about the more powerful inverter, and to get it at no extra cost.

Another thing. I've really enjoyed learning by fiddling with my system. It would have been a tedious slog learning all this in advance, and I wouldn't have learned nearly so much. Then getting multiple quotes and haggling about the specifications, spare me.

I think I've very much done the best I could have hoped for under the circumstances.

Please keep reporting your experience, it is a very interesting journey to follow.

 

[Rolfe]

I find that this exercise of telling the forum about it is extremely helpful in understanding what's going on and advancing my facility in using the system - and that's even before I count all the helpful advice I'm getting. So anybody that's bored, just scroll on past it.

I think it's very unlikely I would have figured out the advantages of exporting the contents of the battery in the late evening before going off on the road trip without the Free Energy thread. So even though that exercise itself turned out to be a waste of time, the learning was very much worth it.

 

[Rolfe]

Well, back to the actual system. That all went rather well. I let the battery export from nine till ten, and although I turned the heater on at some point, of course all that did was decrease the amount of actual export, it didn't change the speed of discharge. I left it for a bit as it was obviously too soon to continue, then discharged it again from about 9.35 till 11.30. I watched the app to see what happened and it all went smoothly.

The battery was at 8% by then, and at that point it stopped the export (though continued to run the heater), then at 11.31 which is when I had the charge set to start it did that. An hour and a half later it's at 53% and it won't have any trouble reaching 100% before 5.30. I'm not quite sure yet how much I managed to export, but that's not really the point as the heater swiped some of the potential export. I managed to get nearly as much as I could have hoped for back into the grid, so chalk this up as a success.

If it went to 8% in an hour and 55 minutes then 2 hours might be living a little dangerously, as I think it would have been at 4-5% five minutes later. So perhaps I should set the export for 9.35 to 11.30 tomorrow and see what happens.

The upside of this is that doing it as a regular thing (in summer) seems likely to increase the profitability of the system fairly significantly. (So that's one more black mark against the appalling Callum, as I could have been doing this all summer but for his foot-dragging.) I have literally no idea whether this exercise was assumed when calculating the payback time I was quoted for the system, or not.

If I'm really getting £1.20 a day for this, right through till the shortening days put a crimp in it, let's say for six months in the year but it might continue longer at a lower level, that's over £200 in a year. (It's late, my arithmetic might be up the creek. Surely it's likely there will always be something left in there most days?) At some point it becomes more economical to run the central heating in the evenings from say eight till 11.30 rather than use electricity which could be exported for 15p too. Have to think about that one.

The downside is that I don't see a way to automate this very easily, because of the changing day lengths. Do I have to keep changing the time the export starts to make sure it doesn't get to 4% before 11.30? This seems to work against my objective of finding a good modus operandi and then forgetting all about it. I'm already finding that I have to switch the Eddi off and on again every day, which is a pain to remember. Do I also have to keep changing the time of the export? Not sure. Getting tired here.

Another thing I have to do is to get some way back to my old "why do I care about how much electricity I use, I'll just pay the bill" attitude. I think this has been a reaction against my mother always nagging about switching off lights and so on. (Though no wonder she got twitchy about the electric fire she bought for me to use for my piano practice. I think the bloody thing was 2.5 kw with both convection and bar on, and she used to nag me not to put the bar on.) But all that was at a time when electricity wasn't all that expensive. I even used that electric fire in my first flat, in my bedroom, because it had no central heating, and wasn't appalled by the bills. I used incandescent light bulbs with no second thoughts.

Now there's a paradox. I can see what I'm using in much more granular detail than ever before, so I start to look for savings. I'm conscious of the £13,700 that somehow needs to be justified. But for goodness sake, I was doing crazy profligate things with incandescent light bulbs and these fan heaters when electricity was 31p/kwh. It's now 7p/kwh. A lot of the point of this was to let me go on being comfortable for less than a quarter of the price. It's objectively silly to get penny-pinching now! I'm fitting the low energy light bulbs I should have fitted years ago. I'm being sensible about the fan heaters. I'm maximising my grid export. Next goal is to stop obsessing about it and just switch on what I want when I want it. But that's going to be annoyingly difficult if I have to remember to switch the Eddi on and off again every day, and calculate whether I have the timed export right in the evening. Meh.

Tell you what. I am never going near Octopus Flux. Whatever Duward says.

PS. I did remember to switch the Eddi and the Zappi back on, and Octopus have given me the same slots as before, so it's all good.

 

[Archev]

Well, back to the actual system. That all went rather well. I let the battery export from nine till ten, and although I turned the heater on at some point, of course all that did was decrease the amount of actual export, it didn't change the speed of discharge. I left it for a bit as it was obviously too soon to continue, then discharged it again from about 9.35 till 11.30. I watched the app to see what happened and it all went smoothly.

The battery was at 8% by then, and at that point it stopped the export (though continued to run the heater), then at 11.31 which is when I had the charge set to start it did that. An hour and a half later it's at 53% and it won't have any trouble reaching 100% before 5.30. I'm not quite sure yet how much I managed to export, but that's not really the point as the heater swiped some of the potential export. I managed to get nearly as much as I could have hoped for back into the grid, so chalk this up as a success.

If it went to 8% in an hour and 55 minutes then 2 hours might be living a little dangerously, as I think it would have been at 4-5% five minutes later. So perhaps I should set the export for 9.35 to 11.30 tomorrow and see what happens.

The upside of this is that doing it as a regular thing (in summer) seems likely to increase the profitability of the system fairly significantly. (So that's one more black mark against the appalling Callum, as I could have been doing this all summer but for his foot-dragging.) I have literally no idea whether this exercise was assumed when calculating the payback time I was quoted for the system, or not.

If I'm really getting £1.20 a day for this, right through till the shortening days put a crimp in it, let's say for six months in the year but it might continue longer at a lower level, that's over £200 in a year. (It's late, my arithmetic might be up the creek. Surely it's likely there will always be something left in there most days?) At some point it becomes more economical to run the central heating in the evenings from say eight till 11.30 rather than use electricity which could be exported for 15p too. Have to think about that one.

The downside is that I don't see a way to automate this very easily, because of the changing day lengths. Do I have to keep changing the time the export starts to make sure it doesn't get to 4% before 11.30? This seems to work against my objective of finding a good modus operandi and then forgetting all about it. I'm already finding that I have to switch the Eddi off and on again every day, which is a pain to remember. Do I also have to keep changing the time of the export? Not sure. Getting tired here.

Another thing I have to do is to get some way back to my old "why do I care about how much electricity I use, I'll just pay the bill" attitude. I think this has been a reaction against my mother always nagging about switching off lights and so on. (Though no wonder she got twitchy about the electric fire she bought for me to use for my piano practice. I think the bloody thing was 2.5 kw with both convection and bar on, and she used to nag me not to put the bar on.) But all that was at a time when electricity wasn't all that expensive. I even used that electric fire in my first flat, in my bedroom, because it had no central heating, and wasn't appalled by the bills. I used incandescent light bulbs with no second thoughts.

Now there's a paradox. I can see what I'm using in much more granular detail than ever before, so I start to look for savings. I'm conscious of the £13,700 that somehow needs to be justified. But for goodness sake, I was doing crazy profligate things with incandescent light bulbs and these fan heaters when electricity was 31p/kwh. It's now 7p/kwh. A lot of the point of this was to let me go on being comfortable for less than a quarter of the price. It's objectively silly to get penny-pinching now! I'm fitting the low energy light bulbs I should have fitted years ago. I'm being sensible about the fan heaters. I'm maximising my grid export. Next goal is to stop obsessing about it and just switch on what I want when I want it. But that's going to be annoyingly difficult if I have to remember to switch the Eddi on and off again every day, and calculate whether I have the timed export right in the evening. Meh.

Tell you what. I am never going near Octopus Flux. Whatever Duward says.

PS. I did remember to switch the Eddi and the Zappi back on, and Octopus have given me the same slots as before, so it's all good.

All very fascinating stuff. I used to use a fan heater too. For oVer a year now I’ve replaced it with a couple of infrared wall panels. They’re cheaper to run and silent. I’ve found them very comfortable.

 

[decrep]

>>>>

The downside is that I don't see a way to automate this very easily, because of the changing day lengths.

Looks like you need an AI overseer, to control the whole thing for you.

 

[Rolfe]

I expect I'll work something out. It's not much of a gain in a single day, but doing it regularly every day obviously adds up, so it's worth putting a bit of effort into it.

Not sure what happened with the car charging overnight. The car is on 100% but the balance charge was cut short. I only needed 26% added so I thought asking for 30% would give enough time, but it didn't.

Charging started at 2.30 am as scheduled and continued normally until 4.30. I think that was the second of the two breaks between the continuous sessions Octopus scheduled. At 4.30 charging seems to have stopped. It started again almost immediately but this time the charging rate started more slowly and then fell off dramatically. The net result seems to have been that although the car did reach 100% before the scheduled slot finished, it was in the middle of balancing when the power was cut.

Normally I wouldn't worry, but big road trip tomorrow, lots of DC charging. I'm not sure if it would be paranoia to do the run to the bottle bank then give the car an hour on the granny charger to balance properly.

Interestingly, the Zappi is not displaying "EV full" but rather "waiting", as if it's expecting the car to ask for more. But it's on to plums anyway with today's weather forecast and in my experience if a balance charge is interrupted it doesn't start again.

 

[Bam Bam]

I think we are at the mid-point now on the journey to home electrification.

In the early stages it was just people who were confident to set up their own systems with home assistant etc. who were doing clever things.

It is now starting to be automated but not everything talks to everything else just yet. People without any special skills like me can use it.

Rolfe's issues are that the battery does not communicate with the Zappi/Eddi so they don't always interact as desired.

This was my reason for going with the Givenergy EVSE though it is new and not yet compatible with Octopus Intelligent - the same app controls the battery and the car.

In the future MyEnergi libbi might be competitive with Givenergy and you can get Myenergy for everything or Givenergy for everything (or Solax or Fox or Solar edge etc.)

In the future there should hopefully be much more seamless communication (probably Energy Company taking control of everything, for those who don't want to control it all themselves).

 

[Rolfe]

I suspect you're right, but I felt it was time to jump on the train. I also wonder, if we get too many people buying at 7p to sell at 15p, will they re-jig the tariffs dramatically?

I think my issue with the Zappi and the Eddi is that whoever designed them doesn't seem to have imagined that anyone might want to run them purely on the mains without taking solar excess. This seems perverse.

My other issue is that I haven't yet worked out how to export whatever is left in the battery before 11.30 and still avoid a situation where the house is drawing from the grid for a bit, without nannying the thing every time.

 

[Bam Bam]

I suspect you're right, but I felt it was time to jump on the train. I also wonder, if we get too many people buying at 7p to sell at 15p, will they re-jig the tariffs dramatically?

Eventually I think that will indeed happen.

There won't be that many people on Octopus Intelligent Go since it only works with a small proportion of cars/EVSEs so it isn't causing much of an issue for them.

Plus, at the moment Octopus are happy to pay 15p because there isn't enough solar to meet demand even on sunny days, so they can buy at 15 and sell at 20. However, once there is surplus solar and wind (as perhaps there was yesterday) the situation will change. Octopus are then buying at 15 and selling at 0p which isn't sustainable.

I predict that those who recently got solar + batteries are in a sweet spot. In a few years there will be lots of solar on the grid and energy companies will only be interested in peak-time export (4pm-7pm).

Solar export payments during the day will drop right down and self-use will again be the aim.

The Eddi will then come back into its own!

 

[Rolfe]

That prospect is why I was keen to master the art of managing to live on the solar before I got the export tariff. It's a skill I might need in the future.

 

[mikgle]

Ok my two pennoth and this is from experience..
The first thing I would say is you don't have to do everything, either at all or at the same time.
I have pretty well done everything over the last 10 years except wind and water turbines ie I have solar pv, storage battery (actually 2 ), evse, 2 x evs, ASHP. I have just had the gas disconnected. Ive had solar since 2015 and get a small FIT which should have paid for itself this year. I know there's no FIT now but on the other hand electricity is a lot more expensive than it was.

It all depends on your circumstances, as others have said, I would say you need to stay put for at least 10 years for solar and battery but an evse you could take with you if you move.

Depending on your roof situation, or size and aspect of your garden, I would say solar pv is almost a no brainer. Again depending on type of house, roof etc you should be able to get a pv system installed for around £6k, it doesnt have to be huge, a 3.5kW (G98) system would be fine.
To have an evse fitted would be say around £1k for a zappi, which qualifies for OIG and is great for solar integration.
So these rwo items is about half your estimated total cost and would negate no.3 daytime costs because the solar would mostly take care of daytime usage.
The addition of a small battery would perhaps cost another £2 - 3k (recommend Sunsynk) but could be done as and when can afford it. Dont forget your ev has a huge battery and this will soak up any excess solar, or you can export the excess and get paid for it.
Over time it then makes sense to utilise what you have and then an ASHP becomes attractive as you can use cheap rate and the battery and solar plus get virtually free hot water. Then in due course you could swap the gas cooker for electric and cut the gas off, saves over £120 pa and I'm sure the price of gas will be going up a lot as time goes on. By the way, my ASHP cost £8,400 after the £5k grant but the grant has been increased to £7.5k,.so now would have cost £6k Also I pay it off to BG interest free at £140/month for 5 years.

So you will have to do a few sums for what you can afford but I would also say its not necessarily the case that you have to get your money back on your investment. I look on it like a hobby and doing my bit for the environment. Somebody spending thousands on a family holiday doesn't sit down and work out when they would get their money back do they?
Good luck, we live in interesting times!

My quote doesn't include backup power facility, but it is for 18 panels.

If I make another 25 years I'll be pretty geriatric. I have no intention of moving, but realistically who knows. The point is really, do I spend the money on this, or hold on to it in case I want to spend it on something else. I have my annual chat with my financial advisor on Monday so we'll see what she says.

Thanks for the video links folks, I'll watch them later today.`

I should perhaps point out that this is my house. The roof faces just slightly east of south.

View attachment 25690

Looks good for solar pv! My first reaction is that you wouldnt need 18 panels.. 10 would produce over 4kWpeak. Mine produces 3kWp and is more than enough.. on the other hand, panels have never been so cheap

Home charger .v. Granny charger - the home charger is for convenience (to avoid the long time for Granny charging) - the electricity costs the same.

Not quite true.. once you've got a qualifying home charger you can get the octopus Intelligent Go tariff, this can save you a fortune on electricity costs.

 

[Bam Bam]

It all depends on your circumstances, as others have said, I would say you need to stay put for at least 10 years for solar and battery but an evse you could take with you if you move.

So you will have to do a few sums for what you can afford but I would also say its not necessarily the case that you have to get your money back on your investment. I look on it like a hobby and doing my bit for the environment. Somebody spending thousands on a family holiday doesn't sit down and work out when they would get their money back do they?

Well said!

It is often a case of planning ahead and getting new things as you can afford them. We came into some money and so got the solar and EV earlier than I thought. Others might have bought a sports car or a big holiday and have basically nothing to show for it.

We will have to get all houses ready for the new energy system at some point or other, so why not do it when the opportunity arises.

The one thing I would say is that buying things and then leaving them behind when selling the house might not be a bad idea.

Solar certainly adds to the value of the house and I think the same would be said for EVSE and heat pump - just include on the advert for the house how much you spent on it and that there are low bills and other people will be attracted to the house!

Evidence showed that solar at least adds several thousand on to the value of a house and I don't see why the other investments wouldn't do the same once people work out their value/importance/expense.

 

[mikgle]

Eventually I think that will indeed happen.

There won't be that many people on Octopus Intelligent Go since it only works with a small proportion of cars/EVSEs so it isn't causing much of an issue for them.

Plus, at the moment Octopus are happy to pay 15p because there isn't enough solar to meet demand even on sunny days, so they can buy at 15 and sell at 20. However, once there is surplus solar and wind (as perhaps there was yesterday) the situation will change. Octopus are then buying at 15 and selling at 0p which isn't sustainable.

I predict that those who recently got solar + batteries are in a sweet spot. In a few years there will be lots of solar on the grid and energy companies will only be interested in peak-time export (4pm-7pm).

Solar export payments during the day will drop right down and self-use will again be the aim.

The Eddi will then come back into its own!

I think there will always be a demand during the peak period 4pm - 7pm, therefore there will always be a premium paid for export during those hours. We are a long way off from having a regular surplus on the grid..

 

[Bam Bam]

I think there will always be a demand during the peak period 4pm - 7pm, therefore there will always be a premium paid for export during those hours. We are a long way off from having a regular surplus on the grid..

I agree.

But solar generation tends to drop off then (unless you've got a West-facing array for a few months a year).

That will mean that batteries will become more valuable over time. But if you've got battery you may as well fill it up from your own solar.

Hence this thread - once you've got one thing, the other things make sense!

 

[Rolfe]

Well, @mikgle, if you read on you'll see I got the 18 panels and slightly wish I'd filled in the remaining space under the right-hand velux window with two more. They can produce nearly 8 kw when they're not being strangled by the 5 kw inverter (i.e. when the battery isn't at 100%). They can produce stacks of export. On the other hand, on a day like today, they can just about support the house base load! Right now, at noon in August, they are generating 236 watts! Yes, I know.

I'm still getting to grips with how best to operate the system because I've only had my export tariff for about ten days. I see that yesterday evening's exercise with the battery sent 4.32 kwh to the grid, which sounds about right because I thought I had 8 kwh to spare, but then used about half of that to run the fan heater. So that's 65p for doing pretty much nothing, on an unfavourable day (heater use).

Honestly, the way the weather is, I think I'll have to turn on the central heating when I get back from this trip. The conservatory isn't getting enough solar gain to keep it warm even in the middle of the day, and when I left it last night (the room where the fan heater was going) the rest of the house was noticeably cold. In bloody August. Jet stream problems as usual I suppose.

I was looking at the weather for where I'm going in Sussex. 20C with sunny intervals. Perfect. Why did I ever move back home? I expect there will be plenty days in winter when I won't export any solar. Indeed, when there may be no actual generations. But I'll still have to see how well the 9.5 kwh battery copes with running the house from 5.30 am to 11.30 pm if there's no solar to help. Will there be anything left to export? Doesn't really matter, if there's enough that I don't have to import at peak rate prices.

I just hope we get a bit more sunshine next year. An Indian summer would be nice, too.