What is a typical import amount when the battery + solar should have everything covered? My rate seems high.

[MrTWales]

I posted about this before, but now the summer is (almost) here I've been looking again.  I suspect that there is nothing that can be done about this and it's just one of those things, but why not check! Getting anything out of the installers is a nightmare but I will ask them without expecting a reply. 

 

This month, ie the two days, the battery hasn't been depleted or even close. I don't think there have been any times when the consumption is greater than the battery limit discharge amount plus the solar coming in. If there was then it wasn't for long, maybe the oven + kettle for two mins when the sun has hidden or something like that. But, the inverter app tells me that I imported 0.7Kwh today. Now I know that this isn't totally correct as the meter says the import has been 0.65Kwh since the end of the last month whereas the app tells me 0.7Kwh + yesterday's import (which I can't now see but I think was maybe showing as 0.3Kwh), so the actual import is lower than what the app says but still over 0.3Khw a day.

 

My question is whether 0.3Kwh per day is fairly typical? It seems to have been less on many other days tbf and there was more cooking today, but still it seems a lot if it's just a small cross over period. What really was irritating was importing 0.3Kwh on the best day I've had since getting panels (24.8Kwh, last week) - this just seems freaking annoying when I was pushing loads back to the grid! The setting seem faily simple and nothing stands out, not that I want to change anything unless I know what is happening. I tried wiggling the CT clamp position a bit but I don't think this helps. 

 

I also seem to be importing sometimes when in theory I shouldn't be, or at least the app says so. I will get getting a diverter fitted to feed the immersion heater, but I suspect that this won't help. This is less of a concern though as it seems to happen more when the solar rate is high so I'll be getting enough anyway mostly.

 

Anyway, any thoughts would be appreciated. 

[ProDave]

I would be chuffed if I got that low. So I would say well done.

[MikeGrahamT21]

Have a read of my blog, I covered this exact subject when I got my battery system installed, hopefully it’ll help you too.

 

My import on a day with no requirement to import is around 0.3kwh, I’ve explained the reasons why you will never get to zero in the piece.

[MrTWales]

2 minutes ago, MikeGrahamT21 said:

Have a read of my blog, I covered this exact subject when I got my battery system installed, hopefully it’ll help you too.

 

My import on a day with no requirement to import is around 0.3kwh, I’ve explained the reasons why you will never get to zero in the piece.

Thanks - can you link to the blog? It's just the way it is I guess but it seems odd that the installers don't mention this. Overall I've got more solar than I thought so I'm happy overall but they must get loads of queries about this.

[MrTWales]

47 minutes ago, ProDave said:

I would be chuffed if I got that low. So I would say well done.

Thanks. I hoped that there was something I could do, but at least I know so I'll stop fretting!

[MikeGrahamT21]

5 minutes ago, MrTWales said:

Thanks - can you link to the blog? It's just the way it is I guess but it seems odd that the installers don't mention this. Overall I've got more solar than I thought so I'm happy overall but they must get loads of queries about this.

theres 3 separate entries for the battery, updates on the progress i made

 

I too was disappointed at first but I did make good in the end with many tweaks from the manufacturer of the inverter, but it can never be zero, I went into it thinking that was how it would be, but totally understand now why it can’t be achieved, at least on a system like this with CT clamp

Edited April 2, 2023 by MikeGrahamT21

[MrTWales]

Thanks, I'll look through it.

[DamonHD]

I may be misunderstanding, but I do get to essentially 0 imports on some days, eg when we are away or have no large loads outside sunny times.  Look at the data under here for example: https://www.earth.org.uk/energy-series-dataset.html#V-imp

 

Partly I picked the Enphase ACB system to have very low import/export threshold before stepping in.

 

Rgds

 

Damon

Edited April 2, 2023 by DamonHD

[MrTWales]

18 minutes ago, DamonHD said:

I may be misunderstanding, but I do get to essentially 0 imports on some days, eg when we are away or have no large loads outside sunny times.  Look at the data under here for example: https://www.earth.org.uk/energy-series-dataset.html#V-imp

 

Partly I picked the Enphase ACB system to have very low import/export threshold before stepping in.

 

Rgds

 

Damon

 

Thanks, not sure I understand all that data but it is interesting. Looking at some meter readings I took, there have certainly been days when it's been 0.1Kwh per day (in fact 0.35Kwh over a 5 day period at one point). It's hard to know how much has, in theory, not been needed and is just down to how the systems work for any long periods but I'll have more idea going forward as solar + battery should cover the usage for long periods now and so far this month the battery has never been depleted, with lots more sun predicted over the next week. Maybe today was especially bad. Someone mentioned before than induction hobs can cause some import and I did use that rather then the gas hobs.

[markocosic]

The enphase unit Damon has is a precision tool designed to match import/export precisely. It's also small. Like using a teaspoon to stick Calpol into a child's face.

 

The hulking great batteries many have are not precision tools. Like trying pour a spoonful of Calpol from a bucket into a child's face?

[SteamyTea]

Is it to do with inverter minimum loading?

Seen it quoted at 200W, this would run my lighting load 50 times over.

In fact, I would be hard pushed to get a 200W load most of the time.

[DamonHD]

On 03/04/2023 at 11:48, SteamyTea said:

Is it to do with inverter minimum loading?

Seen it quoted at 200W, this would run my lighting load 50 times over.

In fact, I would be hard pushed to get a 200W load most of the time.

The Enphase seems to have a threshold of about 5W in either direction before stepping in (if it can, ie when not full/empty).  When I asked the tech director of the next best brand at the time he said that theirs was about 30W.  One UK manufacturer's director that I spoke to said their unit was 500W minimum to intervene, though he did at least listen to my observation that my night load peaked at ~100W including the fridge, and our day load would rarely hit 500W, so their unit would not actually be much use to us!

 

OTOH, the *peak* charge/discharge rate of my system is ~1kW, so it does not fully cover the peaky things such as the dishwasher or the oven, so I prefer to run the former when the sun is out or in the dead of night when grid demand is low.

 

Rgds

 

Damon

 

PS. Saga starts here: https://www.earth.org.uk/Enphase-AC-Battery-REVIEW.html

[SteamyTea]

10 minutes ago, DamonHD said:

The Enphase seems to have a threshold of about 5W in either direction before stepping in

Would have to change my 3W Poundland bulb to a 5W one.

I could live with 5W.

100W would not run the fridge. Would the kettle though, and that is important. 

May have to put the milk in first, then hope the fridge kicks in when the kettle is boiling.

Second thoughts, that would make horrible tea, so happy to pay the import duty on 0.3 kWh a day.

[DamonHD]

At our ~100W typical peak overnight load the Enphase covers ~95% of it (actually it overshoots a little to compensate and then rows back).

 

When the fridge isn't running and we only have ~20W of other 'vampire'/residual loads, the Enphase covers ~75%.

 

With the UK 500W-minimum unit, none of those loads would be covered at all.

 

Rgds

 

Damon

[PhilT]

On 02/04/2023 at 20:21, MrTWales said:

This month, ie the two days, the battery hasn't been depleted or even close.

from the luxpowertek screenshots you posted in your other thread it looks like you have a 9kWh battery? The first chart suggests a utilisation of only around 50% which would make your battery well oversized for your application for most of the year. Can you get onto any export tariffs? With a battery that size you could be force discharging the other 50% to export via the Octopus Flux tariff at 24p/kWh standard rate or 37p/kWh between 4-7pm

[MrTWales]

5 hours ago, PhilT said:

from the luxpowertek screenshots you posted in your other thread it looks like you have a 9kWh battery? The first chart suggests a utilisation of only around 50% which would make your battery well oversized for your application for most of the year. Can you get onto any export tariffs? With a battery that size you could be force discharging the other 50% to export via the Octopus Flux tariff at 24p/kWh standard rate or 37p/kWh between 4-7pm

Thanks, I need to think about this but when I've looked around I didn't think it was viable to change tarrifs now. I was with Green Planet but when they fell over I got switched to Shell and I certainly don't want to stay with them! All the switch websites say that it's not going to make sense to switch now. 

 

What I would like, if possible, is a dual rate where it's cheaper at night as I could charge the battery at night. Octopus used to have amazing rates but they did only offer them (or at least the rates I saw) if you have an electric car. I understood that getting any export payments was not worth jumping through hoops at the moment? I have what I guess is probably a medium sized system, on a flat roof, but it's doing pretty well compared to what I expected. The average generation this month is 17.6Kwh per day so for the summer I'm going to have weeks where I'm exporting a fair bit.

 

You are correct about the battery - it's 3 x 3.6Kwh, so about 9Kwh is useable energy as I have it drawing down to 6%. It's been useful as I don't think I've drawn from the grid this month, other than the small bits that you can't help (which still annoy me!). My average draw from the grid for March was 2.3Kwh and 2.6Kwh for February, which shows how well the battery copes with a good day followed by less sunny days. 

Edited April 16, 2023 by MrTWales

[Nick Thomas]

Octopus Flux gets you a cheap rate at night (2-5am) and an expensive rate during the day (4-7pm). The export payments mirror that, and are absolutely worth it, since they're enough to buy a unit in (over winter, say) for every unit you export (in summer, for example).

 

 

Edited April 16, 2023 by Nick Thomas

[MrTWales]

Wouldn't I need to do a few things in order to get paid for exporting? 

 

Saying that, even the import rates alone would probably make it work out better.

 

Edit - it seems that I just need an MCS cert and smart meter. The later is a bit of a faff given lack of space in the meter box, and the freaking installers haven't given me the certs yet, but it looks like a great option.

Edited April 16, 2023 by MrTWales

[S2D2]

9 hours ago, MrTWales said:

Wouldn't I need to do a few things in order to get paid for exporting? 

 

Saying that, even the import rates alone would probably make it work out better.

 

Edit - it seems that I just need an MCS cert and smart meter. The later is a bit of a faff given lack of space in the meter box, and the freaking installers haven't given me the certs yet, but it looks like a great option.

You also need the DNO response letter which your installer will also provide. If there is any outstanding balance, hold it back until they've provided these as they're very valuable documents now that export pays a sensible amount.

[SteamyTea]

12 hours ago, MrTWales said:

Kwh

The product of Kelvin, angular momentum and time.

And interesting derived SI unit.

[MrTWales]

59 minutes ago, S2D2 said:

You also need the DNO response letter which your installer will also provide. If there is any outstanding balance, hold it back until they've provided these as they're very valuable documents now that export pays a sensible amount.

Very true. All I have so far is a G99 cert - they told me that I'll get the warranties etc when the job is finished (which just needs the diverter to be installed) but I keep chasing them and getting nowhere. I held back £1k and have the diverter in a box, so they don't need to do much more really. 

 

What I'm wondering now is whether the diverter is even worth using for anyone on that Octopus tarrif if they have gas installed. I guess it may swing around with prices so it wouldn't hurt.

[MrTWales]

47 minutes ago, SteamyTea said:

The product of Kelvin, angular momentum and time.

And interesting derived SI unit.

Uh oh, have I used the wrong capitalisation? I can live with that given the dumb shit I do pretty much ever day.

[SteamyTea]

23 minutes ago, MrTWales said:

Uh oh, have I used the wrong capitalisation? I can live with that given the dumb shit I do pretty much ever day.

Yes, k (kilo, for thousand), W (watt, for joule, the unit for energy, divided by s, the unit of time) and h (hour, which is 3600 seconds).

So take your batteries at 10.8 kWh, that is 10,800 J.s^-1.3600 s^-1

The s^-1 cancel out, so 38,880,000 or 38.88 MJ.

Life would be so easy if we discussed energy in joules.

[Alan Ambrose]

He he. You have to remember that this is consumer grade equipment so pretty basic - you can’t expect industrial levels of precision. 0.5 kWh per day is probably a few % of your consumption - about as accurate as consumer grade gets. 0.5 a day is ~20 W bulb i.e. ~10mA i.e. very little current. Probably about as accurate as a consumer grade CT gets. Yeah, there could be an adjustment on the inverter to zero out the error, but 99% of owners will have no idea and care less.

 

p.s. Nobody evades the unit police

Edited April 17, 2023 by Alan Ambrose

[MrTWales]

Just checked and I've drawn 4.0kWh (THANKS TO STORMYTEA I'LL NEVER BE SO LAZY AGAIN WITH UNITS!) for the whole of April. I guess it's not too bad but it still annoys me a little more than it should.

Edited April 17, 2023 by MrTWales