Circular reasoning (Rolfe's solar energy system)

[GaryMG4]

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.

Hmm but being on Go with the granny, I get 5 hours at 8.5p as opposed to 6 hours at 7p but there's an awful lot of 1.5ps in £1k before I benefit.

 

[Rolfe]

That's where I started from. Look at how much electricity I could buy for the cost of this system. It's arguable that it's not cost-effective. But I like it and I like playing with it and it gave me a good feeling when my car was running on sunshine, so that counts for a bit!

 

[mikgle]

Well, @mikgle, if you read on you'll see I got the 18 panels and slightly wish I'd filled in the remainng 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.

Ah I hadn't realised the time lapse from when you started the thread, my apologies!
Yes I see you are near Kirk Yetholm, used to go there for holiday years ago and I expect the amount of sunshine is very different from here in sunny Devon, not that we've had a lot but much more than you I guess!
It is very addictive I find, this area of renewable energy, like looking for the holy Grail of sustainability but it keeps us off the streets! Summer isnt quite over so lets hope for the best!

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.

Not in summer, with a battery you can export everything during the day, apart from running the house necessities until 11.30pm, then fill up at night for 7p/kWh...
winter is different, so a change of strategy then and thats the beauty of Intelligent Go, you can run the heating and charge up everything at a lovely low rate for 6 hrs, then hopefully solar will kick in around 9.30am..

Concerning whats been said earlier about heat pumps.. I've had my Vaillant air to water 7kW system for 18 months now and am pretty sure it is saving me money. ok gas is cheaper than peak rate leccy but when you factor in I'm basically running the heat pump either on solar, battery or mains at 7p/kWh, about the same as gas,and that the ASHP is about 350% efficient in winter (my experience) then it will work out much cheaper, this includes hot water too. Its also a better kind of heat, more whole house, without cold spots.

 

[Rolfe]

I've heard so many conflicting things about heat pumps, with some people loving them and others complaining that they're never warm. I like the idea of whole house heat, indeed. But then I hear about radiators and pipework having to be replaced and insulation upgraded (that last is a good idea on its own anyway) and the house practically torn apart, and it's off-putting.

Anyway, I had a new oil-fired boiler in 2019 and a new oil tank last spring, so I won't be replacing that in a hurry.

Total solar export today, 3.7 kwh. Be still my heart. I think there are going to be a lot of days like this coming up. There's still a bit of excess, but that'll be lucky to recharge the battery after I boiled the kettle! (Ooh, spoke too soon, the battery has got back to fully charged, but export is now down to about 50 watts. I expect the battery will have to take over the house soon, a fair bit earlier than it usually does.)

 

[johnb80]

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

Zappi just needs wiring correctly but Rolfe doesnt take on board my comments and explanations because I'm just some bloke on the internet. The inverter is doing exactly what it should, it sees a load and feeds it.

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.

Comms between the EVSE and the inverter are needed to stop batteries discharging with any wallbox OR arrange the wiring so that the invert cant see the load from the wallbox.

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.)

Libbi is horrendously expensive and not made by MyEnergi anyway, it's a rebadged unit from Kstar. It will integrate nicely with the other MyEnergi products but will cost you more than £1000 per kWh.

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).

If the world had got its act together and released a standard for comms everything could work with everything else. We need a www standard for solar, batteries and inverters, just imagine how good that could be, sadly that boat has sailed.

Hmm but being on Go with the granny, I get 5 hours at 8.5p as opposed to 6 hours at 7p but there's an awful lot of 1.5ps in £1k before I benefit.

Have a look at tomato energy, 5p for 6 hours every night, no restrictions on equipment and 40 p standing charge.

 

[Rolfe]

My only issue with the Zappi is that there is no setting where you can tell it to ignore the solar excess but still have it turned on so that it will charge overnight - either from it's own schedule or from an Octopus scheduled charge, so far as I can see.

Same thing with the Eddi. They seem to have been designed by someone who didn't imagine anyone would prefer to export solar rather than charge a car or heat a water tank.

 

[Bam Bam]

My only issue with the Zappi is that there is no setting where you can tell it to ignore the solar excess but still have it turned on so that it will charge overnight - either from it's own schedule or from an Octopus scheduled charge, so far as I can see.

Same thing with the Eddi. They seem to have been designed by someone who didn't imagine anyone would prefer to export solar rather than charge a car or heat a water tank.

That is just a toggle switch on the Givenergy EV app. In fact it is the top option on the settings page.

Hopefully MyEnergy have a "suggestions/requests" email line to request new features.

 

[johnb80]

My only issue with the Zappi is that there is no setting where you can tell it to ignore the solar excess but still have it turned on so that it will charge overnight - either from it's own schedule or from an Octopus scheduled charge, so far as I can see.

Same thing with the Eddi. They seem to have been designed by someone who didn't imagine anyone would prefer to export solar rather than charge a car or heat a water tank.

Supply Grid Export Threshold, set it to a high number, that should do it

 

[Rolfe]

I'll look at both of these when I get back, thanks. Right now I don't need to as I have enough hot water and a fully charged car and I'm off first thing. Brighton, here I come!

 

[mikgle]

That is just a toggle switch on the Givenergy EV app. In fact it is the top option on the settings page.

Hopefully MyEnergy have a "suggestions/requests" email line to request new features.

I suggest you call myenergi and explain what you want to do, or an email to support.. they are very helpful.

 

[Rolfe]

Solar export was 3.7 kwh today, total is now 10.1 kwh after dumping the battery into the grid. So 6.4 kwh from the battery.

In other news, I realise I was doing the sums wrong, the profit is 8p/kwh because obviously the battery has to be recharged. So that was 51.2p worth. I think that's realistic. I didn't have the heater on so there wasn't much more than the house base load to power. I reckon this could net about £100 a year, doing the sums properly.

In even better news, I have figured out my mistake with the timings and how to avoid pulling peak rate power by accident. Of course, the export tariff still applies even when the import tariff is off peak. Just shoot me now.


ETA: sorted. The battery discharged from 90% in two hours almost exactly. I had set it to do this starting at 9.30. The danger was that if it had dropped below 90% before the discharge started, then it would completely discharge before 11.30, leading to the house drawing peak rate power for a bit. Although admittedly not much unless the mismatch was large. I've now set the discharge to start at 9.40, so at this time of year it won't hit rock bottom till after the off peak tariff has begun. I've given it till 11.45 in case it starts a bit higher and needs a bit longer to empty. Then I've started it charging again at 11.50.

This will probably need tweaking but it will do for now. I can go away for a week and forget about it, then reassess. It will need periodic adjustment as sunset time changes but I can figure out how to minimise the need for that. There might even be a setting that will be OK for months if not all year. But at least I now know I don't have to nanny it.

More thought required, but later.

 

[Rolfe]

Sorry about the stream of consciousness. Should be asleep, got a 450 mile drive tomorrow.

I think I've worked it out. I need to start from the other end. The battery takes just over three hours to charge from rock bottom. I don't need it to be fully charged until 5.30 am. So it should start to charge at 2.15, say. To export takes two hours, allowing for the fact that it won't be starting at 100%. Thus the battery doesn't need to start discharging until after midnight.

However, there's no benefit to starting the discharge later than 11.30. Everything after that can be taken from the mains. Logically, therefore, I can start the discharge at 11.30. The longest that will take realistically is 2 hours. So the battery can start to charge at 1.30.

Split the difference. Set the battery to start discharging at 11.30. Set it to charge from 2.00 till 5.30. Plenty of time for everything. The grid gets whatever is left when the off-peak tariff kicks in. Then the battery recharges ready for morning.

This should work all year round, no need to nanny, no need to change the settings, ever. I think it will also hold up during car charging, although the excess might go into the car rather being exported.

Now I feel silly not having realised this at the start. Learning curve! Now to change these settings. I ought to be asleep, but I'll sleep better having solved the problem. (Good grief, I have an actual PhD and it took me this long? Glasgow University will probably disown me.)


ETA: doing that in the middle of the night has caused some interesting things to happen. The battery stopped charging and started exporting again. It should all come out in the wash though. I suppose there is a bit of leeway in the timings to do a bit more 7p/15p cycling, but I think that's getting over-complicated and the benefits would probably be small.

 

[GaryMG4]

Have a look at tomato energy, 5p for 6 hours every night, no restrictions on equipment and 40 p standing charge.

Hadn't seen anything about them until now, looks an attractive offering with another 2 x 2 hour slots at 13p on top of the 6 hours at 5p. I wonder how long they will survive at those prices?

 

[johnb80]

Hadn't seen anything about them until now, looks an attractive offering with another 2 x 2 hour slots at 13p on top of the 6 hours at 5p. I wonder how long they will survive at those prices?

People said similar about Octopus when they started up, look at them now. With shrewd buying, efficient operation, lots can be achieved. I just don't see a downside to giving them a go, I have selected them for my business premises and I think it's highly likely I will be transferring to them for my domestic supplies too. As I said earlier, theres zero risk in giving them a try, I'm not paying them up front for energy, only in arrears. I'm just clarifying with them about my usage i.e. 99% off peak.

 

[Rolfe]

So far so good on the night-time export. I'm 450 miles away but following it on my phone. Wednesday (yesterday) was the first full day of my new setup and it was working by itself with only the baseline house load, which is a good test.

I exported 8.63 kWh from the panels and 7.16 kWh from the battery. Total export 15.79 kWh. So my rough calculation is that that's £2.36 export income, but from that has to be subtracted 50p, which is the cost to recharge the battery at off-peak prices. Actual profit £1.86. Or, leaving the solar out of it and calculating 8p per unit net profit from battery export, that's slightly over 51p profit on the battery exercise in a day, which I think is what I calculated in the first place. Considering that the standing charge is just over 61p/day, I'm covering the bulk of the standing charge this way.

Of course this will reduce when there is more house load and I cook in the evenings, also as the days shorten, but it's a useful little chunk of change as it adds up.

It's a bit ironic today. I'm sitting in Portslade within spitting distance of the English Channel watching the rain pour down, while my panels in Scotland are generating 5.34 kWh, the max they can with the 5 kW inverter. Exporting 4.81 kW. The sun is obviously splitting the sky at home.

 

[johnb80]

So far so good on the night-time export. I'm 450 miles away but following it on my phone. Wednesday (yesterday) was the first full day of my new setup and it was working by itself with only the baseline house load, which is a good test.

I exported 8.63 kwh from the panels and 7.16 kwh from the battery. Total export 15.79 kwh. So my rough calculation is that that's £2.36 export income, but from that has to be subtracted 50p, which is the cost to recharge the battery at off-peak prices. Actual profit £1.86. Or, leaving the solar out of it and calculating 8p per unit net profit from battery export, that's slightly over 51p profit on the battery exercise in a day, which I think is what I calculated in the first place. Considering that the standing charge is just over 61p/day, I'm covering the bulk of the standing charge this way.

Of course this will reduce when there is more house load and I cook in the evenings, also as the days shorten, but it's a useful little chunk of change as it adds up.

Every little helps, it's surprising how it builds over the year.

It's a bit ironic today. I'm sitting in Portslade within spitting distance of the English Channel watching the rain pour down, while my panels in Scotland are generating 5.34 kwh, the max they can with the 5 kw inverter. Exporting 4.81 kw. The sun is obviously splitting the sky at home.

Maybe theres truth in Sun Shines On The Righteous?

 

[SimonS]

It won't do that without telling me, though. If I do get a time outwith the window where the battery is set to charge then I can always do something then. Either reject the smart charge and do as you say, or set the battery to charge at the same time as the smart charge window.

I see it can be done either way, really. I note that when I asked for 70% earlier in the week, which does need six hours, I was actually given 11.30 till 5.30. I checked precisely for that reason. I don't mind doing it Octopus's way most of the time, I'm getting a good deal from them. And obviously if I come back needing more than 70% I'll either have to do it over two nights by your method, or ask Octopus for a scheduled charge then deal with the battery issue separately.

It's obviously pretty flexible, and I'm interested to see as the time goes on what slots are actually allocated. I can always reject them if I don't like what I'm offered.

Back on the 16th April when you were starting to plan this install I posted some advice as follows:

On Forums/Facebook you will see with monotonous regularity people ask why their charger 'stole' all the electricity out of their battery. Having the charger on its own consumer unit means the Grid CT clamp can be placed between the two consumer units so that a house battery system (if fitted) will not see any current drawn by the charger and you will avoid the house battery being drained.

It seems that the message was not passed on to the installer or they ignored it.

A second point relates to you exporting from the battery. The Export tariff T&C's have an important clause at 4.5.1 Namely:
4.5.1 We are not obligated to make Export Tariff payments to you:
(i) for any ‘Brown Export’ – i.e. exported electricity not generated by an eligible generation asset, (including standby generators, batteries and technologies not supported by the Smart Export Guarantee).
As long as you can show that what you are exporting has been generated by your panels then you will be fine. What is not permitted is exporting energy that you have imported. i.e you can't buy it for 7p and export it for 15p. (Exporting what you have imported is allowed during the winter saving sessions).

 

[Rolfe]

Interesting. I ought to read all this. But I see plenty of people talking about dumping what they have in their battery back into the grid, so it must work somehow. (I note it does say "are not obligated to" as opposed to "will not", so that seems to allow a bit of wiggle room.)

I can see there ought to be a better way to work this if I knew how to set the system up to do it, so I need to investigate that further.

What I'm talking about is that the system always uses solar generation in preference to the battery, if there is any generation happening at all. So, at sunrise, first the solar takes over the base house load and keeps supplying that all day. Then it will recharge the battery, then it will heat the water (unless I have turned the Eddi off) and only then will it start to export. Any time I use any electricity during the day it preferentially uses the solar, then the battery. But once the kettle has finished boiling or whatever, the battery then recharges from the solar. All the while supplying the house base load.

This was perfect before I had the export tariff. The battery supported the house load through the night, then recharged off the solar. The solar was used as much as possible during the day, and the battery was at 100% when dusk came to get back to supporting the house.

However it's different now. I have the battery set to charge overnight, obviously. So it's at 100% when the off-peak period ends, and only has to support the house load until the sun comes up, when it then recharges back to 100% and stays there all day from the solar generation. It takes over supplying the house load just till 11.30, when it charges up again (unless I dump what's in it first.) Without that discharge, it doesn't get below 97% before sunrise or below 93% before 11.30. It's just sitting there almost fully charged 24/7.

As far as I can see it would be more beneficial to use what's in the battery during the day and export the output from the panels. In fact, what I have been exporting from the battery is precisely the result of the way the system is set up - the battery is full of solar generation because I can't see any way to stop that happening, hence the desire to dump it in the evening.

It would be better if I could set the system up so that all the solar is exported and the house runs entirely on the battery during the day right through till the next off-peak price period when the battery recharges. But I can't see how to do that.

I have noticed however that in another thread someone else is talking about doing exactly that, so I should go over to that thread and see if I can figure out how they're managing to do it.

 

[johnb80]

A second point relates to you exporting from the battery. The Export tariff T&C's have an important clause at 4.5.1 Namely:
4.5.1 We are not obligated to make Export Tariff payments to you:
(i) for any ‘Brown Export’ – i.e. exported electricity not generated by an eligible generation asset, (including standby generators, batteries and technologies not supported by the Smart Export Guarantee).
As long as you can show that what you are exporting has been generated by your panels then you will be fine. What is not permitted is exporting energy that you have imported. i.e you can't buy it for 7p and export it for 15p. (Exporting what you have imported is allowed during the winter saving sessions).

The last part of this is your interpretation of 4.5.1?

If you look at Smart Export Guarantee, it states:

"If you have an energy storage system in your renewables installation, you can still apply for SEG. For example, your battery could store electricity from the grid before exporting it later.

Energy suppliers don’t have to pay you for non-renewable electricity exported to the grid, but some may choose to do so.

Some suppliers may only pay the SEG for the electricity your low-carbon system generates itself. If this is the case, the supplier may ask you to show how you separate generated electricity from the electricity you got from the grid. Speak to your installer about how to do this."

I do get paid every day for excess energy I have remaining in my batteries that I dont need to use. 4.5.1 seems a very grey area and open to interpretation in different ways. I dont see how anyone can prove where the electricity in batteries has come from when you have solar and grid supply. As Octopus state, theyre not obligated to make payments but in my case they do, all of the electricity in my batteries comes from Solar PV and/or Octopus which is renewable electricity.

What a confusing situation.

 

[Rolfe]

Indeed, John, quite confusing. I would still like to use my battery during the day and export the solar though, so figuring out how to do that is the next step.

In other news I got back from my road trip last night on 5% battery, so I'm all set to plug in tonight for the half-price charge. I doubt if I'll gain £2 on it, but why not! (I would have charged last night, but today I only had to collect the cat from the cattery a mile away so it was no chore to leave it till tonight. So long as it's done for me to do another 100 miles on Wednesday.)