On-grid domestic battery storage

Solarchaser

zeupater wrote: »

Hi

As mentioned numerous times, there's a sweet spot on batteries where the charge rate can absorb the PV output, the capacity is high enough to compensate for 'normal' periods of poor generation whilst not being too large to justify the additional benefit (returns eventually flatline!) and the discharge rate covers the majority of well managed high loads (ie sequential appliance usage where possible), without expecting to cover the highest demand conditions such as cooking Sunday lunch (hob+oven+ ... etc) ... which you seem to have recognised.

The issue that most miss is that the sweet spot changes in line with overall electricity consumption & usage patterns ... this is why it's not unreasonable to suggest or recommend that efficiency improvement measures are considered before configurations are settled & purchase decisions are made ... it doesn't make sense to have to justify decisions after the fact by unnecessarily 'burning' energy as an accounting exercise! ...

I find the information on lags in demand following interesting as it confirms something that was discussed on here some time back regarding 100% of energy being supplied by a battery and achieving zero exports .... also the on the <200W 'decision making', that's a useful observation that seems to confirm something that I pondered some time back related to the management system working on a clamp based sensor as they tend to display this effect at low currents which is probably why most setups I've come across (/seen) use something similar to the SMA energy meter which should be more reliable (/accurate) & react faster ...

Regarding the clamp based export/import monitoring, do you know whether the system measures & compensates for daily grid voltage variance, PF etc, or does it simply take the voltage from a variable within the management system? .... there's lots of potential for import/export performance issues just on this simple point alone!


HTH
Z

Hi Z, let me first off say, apologies, I've read my own post there, and it's fair to say I went over the score in the first few sentences. It's a weird thing, I've been reading this thread for so long, I almost feel like I know you and Martin, when in fact that's not the case at all, and you certainly dont know me, so apologies for the overly familiar chastising.:A

I'd love to run things sequentially in order to normalise demand, but as I'm sure is a common story here, this project is mine, the wife... not so thrilled with it, nor the amount of time I spend rewiring and then monitoring.
The only change she has made is putting the machines on timers to run in the morning, she doesn't give a hoot if the washing machine, dishwasher, tumble dryer are all on, she will still go for a shower.
This is one if those things I'd love to change, but am powerless to do so, so all I can do is try to make the system respond to as much of it as possible.

I agree about buying, then adding to justify, however... I'm producing alot more energy in the bright winter/spring days than I thought I would,( and alot less in the overcast days than I thought), i didnt realise this as I previously had no way of monitoring before the sofar, which means even on the days where the solar covers the washer/dryer being on several times, the car charging etc, I'm still pushing 5-10kwh to the grid.
I really didnt expect this, and it's made me think of things to absorb this, like a hot water tank, though I'm not clear on how this would work with the gas combi, as the wife wouldn't accept me putting in another another tap on the sinks etc.

It makes me wonder about switching the showers over to mixers as a way of shaving the peak outputs too, bearing in mind this is April, I'd imagine June and July will be even more productive than the 30-40kwh good days I'm having now.

So yeah I have been thinking about some sort of pool heater to be used in the summer when the kids inflatable is out.

I guess this is where I disagree with mmmmikey, for me the money saving part isn't about building up savings to sit on them, so to speak, it's about freeing up money spent on boring stuff like energy, and putting it towards a holiday, or stuff for the kids, or toys for me to enjoy, and so heating a hot tub you couldn't afford to previously, for *free* is a good use in my opinion.
The green part is if I'm not buying fossil fuel electricity, because I'm producing my own green stuff.
I'm not running a ice car, so fossil fuel saving.
I understand and appreciate the arguement about sending it to the grid to reduce fossil fuel energy, but being Scottish, I'm just too tight to view it that way, if I send back 7kwh, I've wasted a quid is my view:D

In regards to the sofar clamps, and how they account for voltage etc, honestly no idea.
I assume all voltage is taken from its mains connection, the clamps only measure current coming or going.
What I do know is that the voltage doesn't vary much, from 243 to 248 is most I've seen, and I put that down to my generation increasing the voltage, as I'd expect.

From my own completely unqualified observation, based on the energy graphs from supplier vs the sofar, the clamps are about 5% out.

But whether that's 2% at 7kw and 30% at 200w, I've no idea.
I like the idea of a more accurate form of monitoring, but it would be cost and hassle dependant

1961Nick

zeupater wrote: »

Hi

The monitoring I referenced wasn't your household monitoring, but the clamp based current import/export monitoring that the storage solution uses to manage charge & supply from the batteries ... for this to have full effect the voltage & PF at the time of a sampling must be considered, else there's an increased likelihood of unplanned imports or exports creating a charge loss to the grid or unnecessary imports. The frequency of the sampling is also quite important ... I did have a scan through the specification but either missed the relevant detail, or it simply wasn't there ... that's why I'm interested as it could explain the reaction lag that both yourself & Solarchaser have observed, for example a 5-10 second sampling frequency on a regularly switched high load such as a resistance hob may (or may not on averaging logic!) have a significant effect ... all depending on the interaction between the two frequencies!

I can understand the logic behind solution cost reduction through employing relatively cheap current based sensors as opposed to accurate measurement within a control environment, but the logical extension of inaccuracy would be for the designers to protect against unnecessary imports or exports by building a power switching threshold into the management system, which could account for the approx 200W mentioned .... on a 3000W maximum charge/discharge, 200W would represent around a 6-7% minimum threshold, which would adequately cover a 10V grid variance (4%) and have a little in reserve to cover PF issues, which would be one way of approaching a potential cost related issue ....

Just for context & comparison, monitoring import/export using the SMA metering solution samples every second and operates within a 1% accuracy tolerance ( link ) which could equate to a considerable performance difference in marginal generation/demand conditions! ....


HTH
Z

I've been at home today & these are the current figures from the inverter:

Import: 1.98 kWh
Usage: 6.80 kWh
Export: 0.13 kWh
Energy Charged: 7.86 kWh
Energy Discharged: 1.99 kWh
Generation: 11.84 kWh

Actual import is 1.91 kWh so that clamp is about 3.5% out.

Actual generation is 11.83 kWh so that's remarkably accurate for a clamp.

(The SOC graph suggests a carry over of about 1.5 kWh from yesterday)

Nobody was at home yesterday & the export was 0.04 kWh for the whole day.

Solarchaser

Purely in terms of sampling, the sofar looks oiled it's about twice a second, going on my many trips to the sofar unit, watching the power change as small clouds come over, lights are switched on and off etc.
For me, the lag is purely about kicking the electronics to ramp, and I think that's the key, it doesn't go 0kw to 3kw, it starts ramping pretty instantly around 250w and continues to ramp till it's at full output.
My assumption... and it is only an assumption is that this to to protect the longevity of both inverter and batteries as shock loading is much more damaging than gradual.

I'm interested in v2g but much more interested in v2h if I'm honest.

I can't see electric companies paying enough to make it worthwhile emptying your car, and then potentially refilling it at a cost, plus losing part of your fit in the process.
Though attached only to my non fit system would make it more attractive, I still dont think the numbers are anywhere near matching... especially as you have to pay to play.

I noticed edf were advertising you could get a system from them at a reduced price, but the battery kWh price was quite a bit over what I was getting them for as a normal punter, and they are obviously getting a good bulk discount.

For me at the moment the pylontech batteries offer the best bang for buck, plus they are modular.
£750 for 2.4kwh, most systems use 80% so 2kwh useable, makes it £375/kWh
The edf offering for powervault 3 was 8kwh for £5k with their 2k discount making £610/kWh though it does include the inverter and says it does 100% dod which probably means it's a 10kwh battery using 80%dod... call me cynical
It does also say 5kw charge , but only 3kw discharge, which for me puts it against the sofar with 4 pylontech batteries which is currently £4700 on Ebay.

You get into the realms of individuals though.
While I'm happy to rewire etc, I appreciate many are not, so the powervault may represent an ok investment to some.

Kev

mmmmikey

Solarchaser wrote: »

I disagree with mmmmikey

Great - you've fallen into my trap - now I can wade in and cross-examine you in detail, before assinating your character (Just kidding of course!)


Very interesting post, thanks, which has had me on the 'phone to PowerVault asking about thresholds. As a low user (very low in the summer), if the batteries only start delivering power when grid import exceeds 200W that would seriously dent the economics for me, to the point where it might not be worth it. I've asked for clarification on this - I have to say although it's a bit frustrating waiting for them to catch up with their installation backolg, I've found PowerVault very helpful. The guy I spoke to believes there is a zero threshold but is going to check and get back to me.



Will post back here when I get a response.

Solarchaser

mmmmikey wrote: »

Great - you've fallen into my trap - now I can wade in and cross-examine you in detail, before assinating your character (Just kidding of .

:D:D
Very good sir, very good :T:T

1961Nick

mmmmikey wrote: »

Great - you've fallen into my trap - now I can wade in and cross-examine you in detail, before assinating your character (Just kidding of course!)


Very interesting post, thanks, which has had me on the 'phone to PowerVault asking about thresholds. As a low user (very low in the summer), if the batteries only start delivering power when grid import exceeds 200W that would seriously dent the economics for me, to the point where it might not be worth it. I've asked for clarification on this - I have to say although it's a bit frustrating waiting for them to catch up with their installation backolg, I've found PowerVault very helpful. The guy I spoke to believes there is a zero threshold but is going to check and get back to me.



Will post back here when I get a response.

You got me thinking so I've just done some tests on the ME3000SP with the aid of Hive. It's gone cloudy here so generation is around 500w at the moment.

I gradually increased the load to create import. The inverter switched from standby to discharge at 120w. I was able to reduce the load right down to 20w discharge before it went back into standby.

Lot's of Hive lamps are ideal for this sort of testing!

zeupater

Solarchaser wrote: »

... For me at the moment the pylontech batteries offer the best bang for buck, plus they are modular.
£750 for 2.4kwh, most systems use 80% so 2kwh useable, makes it £375/kWh ...

Hi

Excluding the sofar system, installation etc of course !!

Don't forget, your own system was expanded from a pre-owned 2.4kWh base to 7.2kWh represents just over £310/kWh, so applying the 80% as above would be a tad under £400/kWh plus to which most would need to add installation & sign-off costs ...

Just checked for indicative prices for that 7.2kWh setup & around £3900 seems to pop up quite often, so add a small 19" rack with space for possible future expansion (double to 12U?) then that's likely £4100 ... so around £570/kWh before installation ...

What's a Powerwall these days? ... not looked for a couple of months, but £450-£550/kWh (depending on package!) fully installed including ancillaries & VAT ??

Yes, accepted that there's a huge difference in battery capacity and how this dilutes the base cost of the control systems etc, but alternatively the PW2 has a slightly larger (20%) nominal charge/discharge rating and allows short-term peaking (does anyone know for how long? - I assume a few minutes max!) to around 5kW, which would likely suit baseload + standard kettle or soaking-up PV generation cloud edge effect etc, so it may simply mean that parallel or multiple systems wouldn't be required for many (/most) ...

What I'm trying to convey is that in order for the industry to not be tarred with the same brush as the 'double glazing' salesman used for decades, expectation management is quite important on what we all hope will soon be a consumer product. It's not a price-point that's possible to achieve if you cut corners or buy pre-owned, it's what the consumer would do, and they (/we?) don't all hold the relevant skill-set & qualifications to install & appropriately sign off a DIY installation ... I doubt that anything would change on that front unless/until guidance is changed, all homes are equipped with commando sockets and all systems are effectively PnP (That's 'Plug & Play', not 'Post & Packing' before acronyms are unnecessarily raised again! ... ) ....


HTH
Z

mmmmikey

1961Nick wrote: »

I gradually increased the load to create import. The inverter switched from standby to discharge at 120w. I was able to reduce the load right down to 20w discharge before it went back into standby.

PoweVault got back to me by email a few minutes after my last post - they are really good at answering technical questions quickly! The thresholds for their system are 250w export for charging and 100w import for discharging. Allowing for the hysteresis you have identified I can live with that, so panic over Looking forward to getting the thing installed so I can start playing with it.


One of the things I'll have to work out is the interaction between the Solic 2000 immersion controller and the battery charging system. The Solic has a virtually zero thershold so will grab export before the battery does, which is OK in the summer when there's plenty of export for both, but for the rest of the year the ideal would be to prioritise the battery and then let the Solic have what's left, topping up the hot water with overnight E7 if needed. But there's no out the box way to control this. Not a deal breaker because I've based my sums on only using solar for battery charging for 3 months and using E7 off peak for the rest of the year, but some scope for limited optimisation.

zeupater

mmmmikey wrote: »

PoweVault got back to me by email a few minutes after my last post - they are really good at answering technical questions quickly! The thresholds for their system are 250w export for charging and 100w import for discharging. Allowing for the hysteresis you have identified I can live with that, so panic over Looking forward to getting the thing installed so I can start playing with it.


One of the things I'll have to work out is the interaction between the Solic 2000 immersion controller and the battery charging system. The Solic has a virtually zero thershold so will grab export before the battery does, which is OK in the summer when there's plenty of export for both, but for the rest of the year the ideal would be to prioritise the battery and then let the Solic have what's left, topping up the hot water with overnight E7 if needed. But there's no out the box way to control this. Not a deal breaker because I've based my sums on only using solar for battery charging for 3 months and using E7 off peak for the rest of the year, but some scope for limited optimisation.

Hi


... with the TV (50") and normal LED room lighting included we normally consume ~120W before the refrigeration cycling - even with the heat-pump ticking over we usually sit at a total load somewhere around 260W, so it could be a major issue when high efficiency results in low power imports/export levels in both poor PV generating conditions & overnight ...

... anyway, it's just another thing for everyone to consider (/re-consider), particularly those with average or lower than average demand!

HTH
Z

1961Nick

zeupater wrote: »

Hi

Excluding the sofar system, installation etc of course !!

Don't forget, your own system was expanded from a pre-owned 2.4kWh base to 7.2kWh represents just over £310/kWh, so applying the 80% as above would be a tad under £400/kWh plus to which most would need to add installation & sign-off costs ...

Just checked for indicative prices for that 7.2kWh setup & around £3900 seems to pop up quite often, so add a small 19" rack with space for possible future expansion (double to 12U?) then that's likely £4100 ... so around £570/kWh before installation ...

What's a Powerwall these days? ... not looked for a couple of months, but £450-£550/kWh (depending on package!) fully installed including ancillaries & VAT ??

Yes, accepted that there's a huge difference in battery capacity and how this dilutes the base cost of the control systems etc, but alternatively the PW2 has a slightly larger (20%) nominal charge/discharge rating and allows short-term peaking (does anyone know for how long? - I assume a few minutes max!) to around 5kW, which would likely suit baseload + standard kettle or soaking-up PV generation cloud edge effect etc, so it may simply mean that parallel or multiple systems wouldn't be required for many (/most) ...

What I'm trying to convey is that in order for the industry to not be tarred with the same brush as the 'double glazing' salesman used for decades, expectation management is quite important on what we all hope will soon be a consumer product. It's not a price-point that's possible to achieve if you cut corners or buy pre-owned, it's what the consumer would do, and they (/we?) don't all hold the relevant skill-set & qualifications to install & appropriately sign off a DIY installation ... I doubt that anything would change on that front unless/until guidance is changed, all homes are equipped with commando sockets and all systems are effectively PnP (That's 'Plug & Play', not 'Post & Packing' before acronyms are unnecessarily raised again! ... ) ....


HTH
Z

It is possible to source a ME3000SP, 3 x Pylontechs, 2 mounting clips, A/C & DC isolators, & DC cables for £3085. That's about £430/kWh The cost of installation will depend on how much you can do yourself. The cheapest way, & to conform, is to install everything yourself & then get a sparky to connect it to the consumer unit for you.

The cost of my 12kWh system installed was £380/kWh. If you went all the way to 19.2kWh it'd be down to £346/kWh.

Pylontech also make a US3000 plus 3.5kWh battery. Discounts are poor at the moment but it might not be long before they catch up with the US2000 plus discounts.