Has anyone figured out what the real-world AC to AC efficiency of their battery and inverter is? I’m on Agile export and trying to work out what the price difference with my import needs to be to break even. Looking at the difference between “AC charge today” and “battery charge energy today” it looks about 97% (similar to data sheet claims of 96.5%)? Which would suggest 94% in total taking into account both charge and discharge losses.
Mine is the same. You might be the last person on Agile though! That 35p/kwh unit cost is too much for me to justify Agile
I think agile will eventually be competitive again. Most of us are shielded by the price cap from the true cost of grid electricity. Come April 2022, prices will likely jump again. It is also possible that as we get out of winter Agile's wholesale price link will drop.
Agile is a good idea in a free market. I'm just glad I'm not paying the free market prices at the moment.
Do you think that off-peak electricity prices will rise to meet peak prices as everyone charges their car overnight ?
@kwnc, my gut feeling is that there will still be a desire to keep people on overnight consumption and make that attractive by keeping prices low.
It all comes down to how grid power is generated, if the flatter the overall demand the better for the network and even with larger scale EV charging overnight it just balances all that day/peal time demand - the vast majority of the population still work daytime hours and we all tend to eat within an hour or two at the usual meal times etc.
New EV chargers installed after April 22 (IIRC) won't let you charge at peak times as standard, you will be able to override this but the 'get home plug and charge' mentality will be limited to flatten that curve.
Another oddity of the process is the way electricity is bought, if Octopus (as the clear leader in smart tariffs) buy a load of overnight energy months in advance the cost is tiny and will likely remain so as its back to the limitations of the grid generation system - they need to use it even with the surge aspects of generation being taken offline.
As long as it remains proportional, ie Go is around a quarter of the cost of a standard unit and the on peak Go rate also remains within a couple of pence of Tue standard rate too it's still all worthwhile.
As for Agile I've only got a 1p split on my SEG rate at 4p Vs the Go rate of 5p - Agile turns it all into a massive gamble even with a 6kwp south facing array.
I don't see export rates ever getting to the point where they are consistently close to import rates so battery makes sense. In the USA a number of states have mandated 'net metering' where you get a large proportion of what you export back as a credit on what you import making the grid effectively a battery storage system. In the early days of solar I had a friend whose meter ran BACKWARDS when he was exporting and the grid was effectively his battery (in addition he got the best FIT). Of course his PV system was small and expensive.
A friend of mine is still operating like that - he has tried to get the meter changed, but when they came the once, they couldn't do it and haven't been back since.
bear in mind the criteria for acceptance on "Go" have changed. They now say you must have an EV to be accepted onto the tariff. Thats for new contracts and renewals. I am far from happy with that as it I dont have one so when my term finishes the costs will change dramatically. E7 is nowhere near as efective.
I dont understand why Octopus changed that rule. The use of the energy makles no difference to them, and my weekly import is abou tthe same as a small EV. The push for grid levelling etc seems to has been lost, and earlier adpters of domestic storage are victims of that change.
Seye Yep, I spoke to Octopus in the week and they said pretty much that I can't get Go.
They offered agile outgoing - which might be an option - but is going to need a heck of a lot of control logic locally to make it work properly. (Or at least cost effectively)
I did say exactly what you said about the battery - but what I suspect is that with battery storage we are using less energy - if you have a EV you will use more.........
Though you could have an EV or hybrid and battery and never charge the car. Wonder what a cheap hybrid or Ev would cost. Probably not economical.
I nearly wrote a long post yesterday, but thought better so I didnt bore people....
The jist was that due to stupid counter intuitive and counter productive policies I may actually end up with an EV quicker than expected. I have 2 perfectly good cars so dont need to change and the global impact of changing them when not required is far greater than the small amount of fossil I burn, especially now I am working at home
So now the mad economics....
If you use a lease deal with tax breaks eg. salary sacrafice or business lease, you can get an EV for £350/m for a smaller one. I was thinking that anyway but it was still going to cost me more than I have now but it was close after taking into account maintainance, insurances, roadside recovery and then fuel savings. EV lets you keep "Go".
If I then add on the domestic savings of "Go" vs "E7" and that gap keeps getting wider, then the equation actually turns negative
Add to that the current enahnced resale value of a seciond habd car, I can afford a lease for a few years whilst EVs become more mainstrsam and hot the second hand market ( 3 or 4 years )
Totally against the spirit of being green due to large negative impact of a new car, and disposal of a perfectly good older one.
So don't assume its not economical. Factor in all aspects including your domestic use. I suggest a exercise in a spreadsheet ;-)
I think I will be getting a shiney new car for exactly this reason. I am very annoyed and frustrated that the sales pitch for "Agile" of grid leveling and seld sufficiency etc seems to have been lost in the race for EVs.
Seye As usual we are on exactly the same page 😆 Excel here I come!
Trouble I have is that I do about 25k a year as I travel around the country for work.
And We (in the past) have driven across Europe on holiday.
So whilst I could probably work with a 250/300 mile real world range in the U.K. it wouldn’t work realistically for travel across Europe. (Last trip was Italy. Got just south of Munich- 700miles - in a day. That wouldn’t be possibly with an ev without a massive amount of planning and luck.
The only alternative is changing the wife’s car. And that would mean going from almost no cost to a significant one.
But I will run the numbers for fun 🤩
Of course, if Agile became a bit more reasonable that might change the situation - it looks pretty good today (for the first time in months!)
anglefire I think i have reached the point of when, not if. My decision is now really whether to change the my car, larger family SUV, or my wifes small(er) car. Until recently mine did 20k miles a year so needed to be fit for motorways and nice and comfy. The other did 5k of local driving. Covid and other work related changes, have changed all that. Mine now does max 5k and the other car 15k. That looks like the new pattern for the next few years at least.
Logic would say my wife should get the new car. Her run-about isnt ideal for a motorway. The fuel savings for that do sway the equation. So logic would say I swap that one with a smaller EV. Only 100miles a day so small battery is ok. That wouldnt do the long family visits but I would still have the existing family car for that.
But, lets be honest, I want a new car. I have just been trying to justifiy it for a long while ;-) So do I actually change the bigger one? That would have the battery capacity as well as functionaity I need, but at a lots higher price point. I will then just have accept she becomes the main driver my new toy? It would be foolish to have that sat on the drive most of the time when she is commuting regularly.
Excel can get me a long way towards making the decision to change. What to change is a little more subjective & definatley emotional. I havn't worked that bit out yet. My "Go" finishes in March so I need to decide sometime soon
@anglefire really mad economics now, which I seriously looked at when I had a caravan. For the few weeks a year I need to tow it was potentially more cost effective to just borrow / rent a car for those times. for 48 weeks a year I didnt need a car that could tow 1500Kg. If I took that constraint out of the main equation my choice of car for the other 48 weeks was a lot wider. We simply agreed as an extended family that we could share a tow car if necessary, just paying for insurance etc as and when required
Seye I ran a Land Rover discovery 3 for 7 years. It was great - We bought a caravan (Twin Axle) - and I used to offroad too - several trips in the UK and the Pyrenees as well as once to Poland. And holiday'd abroad with 6 of us (Family and the inlaws)
But at 234k miles and an average of 24mpg it was becoming too expensive to run - so bought a BMW 530d - but whilst it was a lovely car and very quick (Too quick - potential license killer!) it wasn't big enough - by that I mean the cabin space as well a boot space was tiny.
So I changed it for a Skoda Superb - same physical footprint but feels 2x as big inside. I've had it for about 2 1/2 years now and done just under 50k - slowed down due to working at home but its going back up again, but isn't quite so bad.
So I prefer to have a larger car with enough space to do everything. Not sure whats about that makes any economic sense. Especially factoring in that I get a fuel card which does all my mileage and I just pay tax on it. Not sure how the company would pay for the electric.
But trying to persuade the wife to change her car may be a bridge too far. She has only had it 12 years come February. And about 27k. Its just not worn out or even close to it.
On the EV front got an E208, it's mostly used by my wife as a community nurse - she had a Mazda CX5 before hand.
Cost wise on Go the E208 is between 1.5-2.5p a mile depending on time of year compared to the Mazda which was coming back as 12-13p a mile when diesel was an average of £1.20 a litre.
Based on 12k a year and factoring in only savings from fuel costs and the current lack of tax the payback period is under 3 years for the car. My wife gets paid per mile for work and I used the price split between the same model petrol compared to the EV.
That's before you get into the cheaper and less frequent servicing costs (16k miles or 2 years) at £200 for what is really just a new cabin pollen filter, brake fluid change and any software updates etc.
EVs are also cheaper on finance deals new as they are expected to have far stronger residual values at the end of a lease period.
My wife's use is also terrible, average journey is between 1 and 10 miles with upwards of 30 mins per journey and multiple short journeys per day - basically the car gets cold so it chews battery at this time of year heating it back up.
Range wise I wouldn't want to push anymore than 150 mile round trip in winter but it'll happily do 200 in summer.
If you only occasionally make journeys above that 150 miles figure and can live with the size of the car I can't recommend switching enough - it's fun thing to drive too unlike the Zoe which I hated.
As for EV use Vs battery use, 50% of my expected annual consumption is all for the EV so over 3600 kWh - having a home storage battery just shifts the other half into the Go hours it doesn't add any extra demand which is what I think Octopus want.
That all said a combined household fuel bill of under £1200 for car, house electricity and heating for a year is something I can more than live with. I'm also expecting that figure to come down by a fair amount for 6 months over summer.
For whatever reason our electric consumption it about 6000kWh pa - 3/4 adults live here. Youngest is at uni for most of the year.
Eldest works for the NHS and has shifts and a uniform to wash.
Did just have a look at the Octopus salary sacrifice scheme - works out at about £600p/m for an Ioniq V - all included - current Skoda costs about £3000 a year all in as I own it outright. Plus I get tax back for business miles so its less than that.
Numbers just don't work - unless I'm missing something.
The numbers are quite different depending on term, mileage and deposit. Salary sacrifice depends on standard or high rate payer
https://www.nhsfleetsolutions.co.uk/
25000 miles, 36 montrhs, std rate tax
HYUNDAI IONIQ 5 ELECTRIC HATCHBACK 125kW Ultimate 58 kWh 5dr Auto [Tech]
std paint & wheels etc
Salary Sacrifice
Monthly Gross Salary Sacrifice:
£ 757.00
Savings on NI:
£ -90.84
Savings on Tax:
£ -137.32
Savings on Pension:
£ -70.40
Total savings per month: £ -298.56
Monthly Take Home Pay reduced by: £ 458.44
Monthly Car Tax Liability: £ 7.25
Total cost per month: £ 465.68
Same car. 20000 miles and high rate tax payer
Salary Sacrifice
Monthly Gross Salary Sacrifice:
£ 693.38
Savings on NI:
£ -13.87
Savings on Tax:
£ -242.68
Savings on Pension:
£ -86.67
Total savings per month: £ -343.22
Monthly Take Home Pay reduced by: £ 350.16
Monthly Car Tax Liability: £ 14.49
Total cost per month: £ 364.65
So depending on your own fuigures substantially less than £600
Compare the market and check what schemes are oprnto you
same place. VW ID4. only 6000miles a year and high rate tax payer = £209/m
offset say £40 domestic fuel bill saving by having access to "Go" = £169/m
The parameters of the equation make all the difference, so may work for you or may not. Thats really low miles, but for the runabout to keep access to "Go" looks reasonable. Silly thing is ID4 is only £10 more than ID3
MikeMessy I thought you had to be on Agile Import to get Agile Outgoing? Though after seeing the last 72 hours of prices it might be time to switch back!
That’s a good question. I have asked it!
Octopus aren’t very quick at getting back to emails. Though it is Christmas/new year.
THALL that's my understanding, I think they refer to having your cake and eating it with being on any of the Go products whilst on Agile outgoing.
Agile remains fairly decent again with some negative pricing over the last 3 days for some periods - still hot worth swapping away from Go as you just can't rely on Solar at this time of year.
yandards True, I do need to plan how to use Agile to charge my ev. I will try the automated features on here and the Zappi to get the best from Agile. On the zappi I know I can set a max price per kwh to charge so could set charge if under 5p. I would love that feature for my GE battery too.
You can be on Economy 7 and Agile Outgoing, but that's the only other one along with Import of course.
THALL No, you can’t have Agile and Go. But you can have Agile outgoing and their flexible (eco 7) tariff. Between 16:30-19:30 most days outgoing rates are 30p whilst incoming rates are only 20p.
I now have all my paperwork in place to sort my export tariff. But still can’t get confirmation that I can go on fixed export and remain on my fixed import tariff. I think I can but want confirmation.
Regarding the OP on charge/discharge efficiency, is it really as high as 94% round trip efficiency with say the 8.2kW battery and 3kW AC coupled inverter? The EV Puzzle on youtube did an efficiency test and got the discharge of the battery to be about 85% efficient on his 5.2kW battery and charge to be similar so a round trip efficiency of about 70% Also his 3kW inverter would only do about 2.4kW continuous charge/discharge. I am just about to invest in 3 x 8.2kW with 3 x 3kW AC coupled inverter so keen to understand the true efficiency especially the discharge power I can realistically expect with say 24.6kW of storage. Any thoughts or experiences appreciated.
Kryten I don't have any hard figures to back this up other than 10 months of use and looking at the dashboards a lot, but I would estimate the truth is somewhere around 20% round trip losses and is the figure I've used when doing the man maths on electricity tariff import/export brokerage calcs.
Efficiency will also be temperature dependent.
There are more efficient systems out there, e.g. Powerwall which I think claims 5-6% round trip, but in consideration of these you have to weigh up the additional capital outlay. The RoI is very long.
@Kryten
Over December I had days where PV didn't charge the battery at all. I was charging the battery to 100% and it discharged to 4% every day. That has allowed me to use the portal to get some figures for efficency as many of the variables have been removed from the calculation.
I picked a week were this was the case
Charge Discharge Percent
7.9, 7.39, 93.54%
8.1, 7.31, 90.25%
8.1, 7.4, 91.36%
8.1, 7.17, 88.52%
7.8, 7.38, 94.62%
10.4, 9.9, 95.19%
7.9 7.47 94.56%
average pervcent = 92.58%
Kryten thats a lot of storage and power. I am intrigued. Whats your use case?
I only have a single 8.2 battery with 4kW PV. I nearly bought a second battery but backed off when I did the maths for ROI and looked clsely at my energy usilisation graphs
Kryten That is a lot of kit! Can I ask why all the GE over a higher capacity powerwall? 24.6kw is just under my heaviest day in the year and I run an Air Source Heat Pump and all appliances are electric, hob oven etc.
THALL cost I'm guessing, hardware wise that little bundle is around 10k plus install costs for 7.5kw peak output and 24 kWh of storage.
A single Powerwall install is about 9k installed for 5kw peak output and 13kwh of storage.
Pretty compelling reason to not go for a Powerwall option!
yandards I retract my question lol
Kryten I'm very curious why you would need 3 x 3kw inverters ?
Three 8.2kwh batteries could be connectedd to 1 inverter and give you the same storage capacity and only when you went above 3kw would you importing. OK that might happen if you run a lot of appliances at once. So lets assume you got to 2 inverters, that will supply up to 6kw. You would only need the three inverters if you are regularly exceeding 6kw. Are you going to be running an ASHP ?
Thanks for the feedback all. I run a business from home which is rather tech heavy so I consume on average 27kW a day with 23kW being outside the Octopus Go hours. My plan is to charge the 24.6kW of storage during the 4 hour off-peak rate and then run off battery power for the rest of the day. In order to charge an 8.2kW battery in 4 hours each will need their own 3kW inverter as 2 batteries on one inverter will not be able to charge fully. I can get a full system installed for just under 12k and would save 2k a year (or thereabouts) so payback would be 6 years based on the new 7.5p/30p Go rates (note I have an EV). The gamble is if these off peak rates go away, but with other suppliers offering similar off-peak products combined with a need to balance the grid in the short term its a gamble I am willing to take. The Money would not be making me anything in the bank anyway and there is an element to the geek factor in all this. I could go with solar also but I have a yorkshire stone slate roof and the installers I spoke to don't fit to them due to no one offering a warranty on such a mounting system. Also payback on PV is more like 10yrs when comparing to saving 7.5p charge rate of a battery. Should these off-peak rates disappear I would then add solar and forgo the warranty if I have to as a backup plan. As people say the Tesla PW2 option would be £18k for slightly more storage so not cost effective. Also in UK do you not have to have it installed with Solar? I know this seems to be the case in America. Anyway hence my query on efficiency as this helps with my man maths. Thanks
Seye Are your charge/discharge percent figures based on stats provided from the inverter? Or calculated elsewhere? Thanks
Kryten
1) energy graph in the beta portal
2) Select "Generation" and then scroll through weeks to find a week where no generation to battery ( I have many recently )
3) Select "battery in" for that week, Just show "grid to battery". They are the charging figures
4) Select "battery out" for the same week, No filter for destination. They are the discharging numbers
Kryten Sadly my home runs at 22 - 27kW load per day. I have 1 8.2kw battery, 1 hybrid invertor and 4kW PV.
I recently orderd a second battery but have now cancelled that order having really looked hard at the numbers
My tariff is Octopus GO Faster 5. I can not charge 2 8.2kWh batteries in the window so I would need addition inverters to fill. I could only charge to 13kWh offpeak ( the constraint you raise ). The additional inverter would only be required for 6 months when PV isnt topping up the batteries. I really would only get the benefit from those for a few minutes a day in supplying load e.g. kettle etc and if the battery runs out by the end of the day thats irrelevent as the grid mid day would be the same energy as at the end of the day if the batteries supplied it and then ran out
I looked at my Octopus bill. Thats quite handy as it shows a clear breakdown of peak vs offpeak. due to load shifting etc that averaging about 1.5 : 5 over the year. PV is already allowing my single battery to last until 10pm, only 1.5 hours short of recharge, and its only Jauary
The key is the Octopus rates and the difference between peak and off peak. As they have changed the rules saying you need an EV I changed my investment strategy. My spare cash is buying an EV rather than more storage, so I keep the cheep rate over night. I was going to get one anyway. This has just accelerated that thinking. You alreqdy have one so you are a step ahead
Shame PV is not an option for you. I uinderstand your use case and you are a little restricted with your options
Your maths may be different to mine, but clearly you understand the thinking.
After working my use case through my 'head' outcome was different to my 'heart' one
Seye I do have one option for pv but it's not ideal. My garage roof is normal slate and is east/west facing with the east being clear view and the west having possible shading from the house. The east side would take 4 maybe 6 panels at a push and according to the energy saving trust solar calculator could generate 1,800kWh/year so on average 8 months of the year maybe 7-7.5kWh a day (does that seam realistic?) The west face could take 5 maybe 8 panels at a push and generate 1,500kWh/year so maybe 6kWh a day. I need to crunch the numbers again to see if a 2 battery option with this amount PV topping the battery up to get me through the evening till I can top up again on off-peak rate. But this option only works for 8 months of the year. PV is more guess work on working out the return on investment.
Kryten true, but is a "known unknown" but you can make resonable predictions for that so its not too unknown, but I accept its a gamble. Yes some years are worse than others, but you can work out a weighted average prediction reasonably well.
We all have no idea whats going to happen to electricity prices. Reasonable bet there will continue to be a gap between peak and offpeak, also reasoinable to expect that will widen. But thats another "known unknown', but harder to plan for. The risk is the gap decreases in say 5 years when other energy sources are in the mix too. ( I dont think it will )
The third "known unkown" is what will happen to the econmics of batteries and inverters. As they become more mainstream the market dynamics will change due to suplly/demand/compitition. Could they be like EVs and get cheeper? No idea.
The gamble there is costs incurred by deferring investments vs costs saved as kit is better and cheeper in a few years
The nice thing with this system is that it is modular. You can always add to it later
As always.... you pay your money and make a choice.
Its a bet regardless
Back on the topic of inverter efficiency, does anyone have any view/stats on how quickly the Givenergy 3kW AC coupled inverter picks up the load, so if you switch on an appliance how quick does the inverter start supplying the load. This bit I have not researched much yet but does the grid CT clamp detect the load being drawn from the grid and start providing the increased output? A read this can be up to 30 seconds in some instances, also after the load drops off how long do you leak battery storage to the grid until the inverter reduces the power. I guess the inverter is always fighting to keep grid usage at zero. So even with enough battery and inverter power to see me through the peak period will i expect to still see some grid usage and loose some battery power to the grid. Any idea on %? Thanks for the info so far!
Kryten Not sure on the reaction speed and loss. I know the GE system is slower to respond than other systems on the market... But according to the data here on the portal I am exporting between 0.1 and 0.2 kwh everyday. That is not from excess solar but from switching. However, you are best to check your homes smart meter and compare to the GE data. I used do this and initially the readings between the smart meter and the GE system were as much as 10% out every single day. I no longer look.
Kryten I don't have accurate hard numbers per se, but some data based on my own current clamps attached to inverter load/export and grid import/export - with a 5 second sampling rate.
Generally I seem to be exporting between 0.3kWh to 1kWh a day - and that's with the battery and/or the iBoost trying to mop it up. That's with solar (4kw array) generating excess over demand and over-runs from high loads switching off.
How much I'm importing due to a short delay before the inverter responds is a much harder one to quantify. Here's an example of a load coming off at 15:02:40 to 15:03:00 (from 3512W down to 237W). You can see the battery export (the yellow) coming off a few seconds later at 15:03:00 to 15:03:15. In that period there's an over shoot/export (the green) for about 20-30 secs, (the battery drops to near zero as solar takes up what load remains)
To be honest it's only of passing interest for me - I don't think over-all it makes a huge £ difference against the savings made from not importing at peak rate?
I have a hybrid system. Its now dark so effectivly working like an AC system now.
I can see my house load changing from from 1.1kW to 3kH ( cooker hob tripping on and off ). Battery output is <5s behind that moving from 1.1kW to 2.5kW ( as thats the max my inverter does ).
The over power is a similar lag.
I only capture data every 5s so can't say if its actually quicker than that but I think it is. Expect 2s or 3s to respond
Firmware does keep getting improved to speed this up, but I have never seen 30s and I have had the system running a year with this level of monitoring.
I can see that most when the ironing is being done. Lots if on/off cycles happening quite quickly. If the resonse was slow the curves would be flat. They are not
THALL if they are that far out you should contact GE. The EM115 meter is accredited for energy monitoring. That means it can be used for billing. It iisnt in this case but it shows you should have confidence in it. If that is different to your meter something isnt right somewhere.
I know GE have identified issues with meters in the past.
If you have the billed amounts I would send those to GE tech support if they are quite different to the measured ones. That may be symtomatic of a wider issue
Octopus billed kWh / GE measured kWh = %difference
17.62 / 17.83 = 1.012
17.23 / 16.92 = 0.982
12.78 / 13.02 = 1.018
16.14 / 16.47 = 1.020
16.27 / 16.28 = 1.000
Thanks all, great information. I will ignore battery load reaction times it seems then as pointed out it’s a very small amount in the grand scheme of things.
I don't have any figures to prove it but I'm pretty sure that on the AC inverter changing between different levels of either charge or discharge happens very quickly (within 1 or 2 seconds) but I think changing from charge to discharge and vice versa is a bit slower (maybe 5 seconds). In the grand scheme of things it's really not much either way.
Seye I've not investigated but it stands to reason the EM115 meters Power readings will always be slightly out. Given it's usually fitted in the fuseboard it's reference voltage is likely lower than that taken directly at the smart meter tails coming into the house.
hoggy Depends how far away the meter is from the source - by EM is about 18" from the incoming smart meter so the voltage difference won't be measurable between the two. In my case anyway.
anglefire of course YMMV, mine is a submain board away with 2 EV chargers between it and the incomer.
hoggy one of my roles at work is metering - but industrial stuff - not particularly installing but setting up energy monitoring systems. Biggest one I’m involved in currently has about 2500 meters. Biggest issue is volt drop on the ct’s - there is a spec for distance verses conductor size and a corresponding % error. Not particularly relevant but thought I’d mention it 🤣
Seye GE have been out and adjusted the em115 while fixing another fault. It is better than that 10% difference it was when first installed but still not as impressive as yours. CT's seem to have a general acceptance of 0.5 - 5% difference. I think mine is down to 5%, just under. Not checked it since September.
@Kryten I wouldn't place too much sway in the numbers provided by the Energy Saving Trust site, its more than a touch out of date and really doesn't get into the gains to be had from battery storage etc.
The only way to get some decent numbers from a split array with potential shading is to get an installer to provide a generation quote for the array size, that'll at least give you some more refined numbers to work with.
As an example I have a 6kw south facing array (so roughly the same size as your proposed east/west) and even on dull days over December it was producing a kwh, December was 86kwh in total which is pants frankly. Role back to September when I had it installed and my highest generation day to date was 32.8kwh on the 20th.
Yes I'm further south than you (Oxfordshire) but it wouldn't be unreasonable to assume you could expect solar to run your demands on a good generation day for 6 months of the year. My panels were not mega expensive, about £150 a unit for 375W half cut panels (Longi) and I've hit the limit of the hybrid inverters peak input at 6kw of production anyway.
@Seye inspired by your calcs I did the same comparison between the import readings on the GE portal and Octopus for my system - GE is reading an average of about 2.5% low for me (over the last 10 days)
Kryten from playing with the system and a kettle I have come to the conclusion it is about 3 seconds. There is also a logic bounce for about half a second where it does not know if it should charge or export if you have used more energy that solar provides, and you switch off. There is a short period where it exports what it was discharging to handle the load. then a short time where the solar exports, then it reverts back to using the solar to charge again.
If you switch high loads every 5 seconds, then this would be a disaster? But who does that? In reality even the kettle boils for 4 minutes - so the .5 of a second of panic at the inverter plus the 3 seconds of import or export is not really noteworthy.
anglefire the length of meter wire is accounted for in the calculations. Dont cut it short or coil it into a loop....
anabanet yes with solar installs I’m sure you are right and they come pre-wired - ct’s we use commercially don’t come with tails and you have to calculate the cable size to suit the distance.
anglefire there is an option to extend CT clamps using CAT 5 ethernet cable for the myenergi kit - maximum of 100m though. I have my CT grid clamp on the GE side extended with CAT 5 and it's pretty close to the Octopus figures.
I'm usually within 100w of consumed values which is great. A caveat though, the numbers tend to be off on days I've lost internet recently (Virgin completing scheduled maintenance).
The CAT 5 run is around 15m in total and runs parallel to the supply cable from the inverter - I think it was shielded (CAT 5e) which should help keep the signal clean.
Biggest issue Is volt drop. The signal is ac anyway (well I would assume it was as the em115 is a pretty standard meter. ) so won’t be interference. It may be a 1a secondary ct rather than 5a which will help with volt drop. Especially using Ethernet cable.
anglefire hence the max 100m requirement to get it operating within the tolerance.
I don't know if the E115 meter has an option to send data packets based on the CT Clamp input, arguably easier to leave it as an AC waveform from E115 to the inverter as it also gives frequency data then.
The EM115 connects to the inverter over modbus so has access to all it's data.
Getting a new 3.0 and 8.2 commissioned tomorrow. I will buy an export/import meter and put that inline with the inverter. That way I can measure power in and power out. I will start with a 100% charged battery, cycle for a week, and fully charge the battery to 100% and compare.. . .
I had my GivEnergy system (One AC coupled Giv-AC3.0 inverter and two Giv-Bat 9.5kWh batteries) installed just over two weeks ago. Although I did not ask for it (or expect it) my installer included a MID approved Emlite-ECA2 Import/Export meter directly before my inverter as well as the two required 115-Mod energy meters for Grid and PV.
Although my inverter has an Emergency Power Supply (EPS) output this has never been used.
According to the GivEnergy portal I have a Total of:
Solar To Battery 82.20 kWh
Grid To Battery 103.83 kWh
So Total To battery of 186.03 kWh
Battery To Home 154.70 kWh
Battery To Grid 28.78 kWh
So Total From Battery of 183.48 kWh
Giving round trip efficiency of 98.6%
However my MID approved Emlite-ECA2 Import/Export meter gives:
Total To battery 218.90 kWh
Total From Battery 161.10 kWh
Giving round trip efficiency of 73.6%
I am confused, can anybody tell me what is going on?
ZenSlo The Emlite figures are before conversion losses but the GE figures are after conversion losses.
I don’t know exactly what you mean by “conversion losses”.
If you mean the losses made by the inverter in converting AC to DC and then DC to AC that means that when people are calculating the benefit of importing power at one tariff and exporting it at another they should reduce the expected “gain” by 73%?
Is that everyone else’s understanding?
ZenSlo Effectively, yes. the 73% you have will be for all in/outs you have and a chunk of that may be at low power which has a lower efficiency (more losses relatively) than at high power. So flat out import at cheap and export at expensive will have a better % but you still do have to consider the losses in any payback potential.
Even if the inverter ran at 95% efficient, pulling in 10kWh AC to the battery and then sending it out again would leave you exporting around 9kWh
Thanks for that.
PS And a special thanks to Rubikcube, I just looked at your "incorrect-em115-wiring" post and then the photos of my installation!
Whilst it is not causing me any communication problems as far as I know, but guess how my twisted pair wiring is connected?
If you feed 10 kWh to an AC3 you will only get 95% in ie 9.5 kWh. Your inverter and battery will consume DC from the battery at a rate of c. 50 W/hr then when you convert DC to AC you will lose another c. 5%. Net result depends on storage time, 10 hours leaves 8.5 kWh. The 50 W/hr goes whatever you do, it's the cost of existing and is only "free" if it's from your PV.
[ EDITED : Just noticed this was tagged as AC coupled ! sorry]
Asked the same question in a different thread, but still worrying me. If I compare Battery In to Battery out on my newish gen2 5.0 + 9.5kWh battery, it seems consistently to be 70-75% efficient. What I couldn't work out was this:
1) true reflection of appalling performance.
2) Something wrong with the install/Hardware
3) peculiar to my use. PV only charge, battery mostly full in this weather, and half empty at sunrise.
4) The way the kWh stats are being collected and / or estimated
Also I am not clear where the efficiencies etc are estimated. I understand the concepts, but I haven't seen a definition of what is measured.
For example, If the app/registers show 10kWh generated PV, is that after AC conversion, or raw DC power. If I look at the various flows, some going to the battery, some to home some to export, which is the true figure ? As the battery charge from PV is DC -> DC. Which figures are before/after conversion, where are the estimates of losses happening.
In general I seem to be seeing almost lossless ( or even gain ! ) between PV kWh and consumption kWh + export kWh. The only horrible losses seem to be between battery remaining capacity and battery out kWh., Or battery In / Battery out.
If I have now understood things correctly the best way for me to calculate the actual savings from using my AC Coupled Inverter and Batteries, with no export tariff and ignoring my existing FIT payments is:
Within each time period use the GivEnergy portal to estimate the proportion of my battery charge from PV and from the night time tariff.
Divide the Emlite-ECA2 meter’s export value during this period in two in these proportions.
For the PV proportion I have saved that many kWh at my day rate.
For the night rate proportion I have saved the difference between the day rate and the night rate increased by about 35% to allow for the round trip [in-]efficiency of 73% as measured during the period.
I have ignored any battery power that is inadvertently exported.
Is this a reasonable way to do this?