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    • Martyn1981
    • By Martyn1981 5th Dec 16, 2:57 PM
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    Martyn1981
    On-grid domestic battery storage
    • #1
    • 5th Dec 16, 2:57 PM
    On-grid domestic battery storage 5th Dec 16 at 2:57 PM
    Hello!

    Right, as discussed elsewhere, battery storage for self generation (typically PV) is interesting (to some), and gathering momentum in the UK. So here's a thread to discuss it, and watch it develop.

    I've called it on-grid, as off-grid is so much more specialised. And domestic as commercial scale storage, or grid scale can be chatted about on the Green & Ethical energy issues thread.

    So, where are, well this article lists about 20 systems that are available or should be available soon:-

    Introducing CleanTechnica’s New Home Battery Overview Page

    Jumping straight in with personal opinions:-

    Economical - Not yet. Prices are falling fast, the range of products is expanding fast, and large numbers are being deployed in some countries, either because the price of leccy is high (Australia & Hawaii) or because subsidy schemes exist (Sweden & Germany).

    Where are we today. My needs are a 4kWh system. That's 4kWh of useable capacity, which would mean about 8kWh of lead acid (LA), or about 5kWh of lithium ion (Li-ion). My research has found batts in the high £2k and up range. I need the price to be nearer to £1.5k.

    The Tesla Powerwall II, installed is approx £6.5k, which works out at about £2.2k for 5kWh, but of course, it doesn't work quite like that, as smaller systems will cost proportionately more.

    Environmental - Tricky one this (to say the least). Until storage is needed, it's not environmental. Renewable energy (RE) generation currently displaces gas generation, which is a demand follower. Once gas generation is pushed down to zero (at times) we need storage, but we aren't there yet.

    However, to push gas generation down to zero, we need more RE, and to ensure it is viable/economic/profitable, we will need storage - chicken and egg situation.

    The advantage of storage to the environment, is to take peaks of RE and timeshift them to peaks in electricity demand. On a domestic level, this works quite well as PV generates during the day into the afternoon (or evening) depending on the month, so any stored leccy is available for the evening peak 5pm to 7pm.

    That's the background, and now here's a thread to discuss options, prices, economics, and watch things unfold. Enjoy.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
Page 51
    • mmmmikey
    • By mmmmikey 20th Jun 19, 12:27 AM
    • 229 Posts
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    mmmmikey
    I don't have this problem, but my then baseload is over 200w. If there's enough charge, I don't import anything overnight.

    Saying that, I'm slightly surprised, because this morning my batteries were supplying just 60w to make up the difference between generation & consumption.
    Originally posted by 1961Nick

    Hi - just to reiterate, I don't have this problem either with the PowerVault. My background / night load is of the order of 50W and it covers that, which I have to say was a pleasant surprise. I think hysteresis comes into play here - i.e. in the case of the PowerVault the battery needs to see a load of 100w to start discharging, but once it's started it keeps going until well below that. Having said that, as I pay < 5p per kWh overnight, it would take a long, long time for me to recoup my investment if I was relying on that at a saving of 3p or so per night Today's been a great example of the battery working well - only about 6kWh generated all day and the battery charging and discharging as the sun has come and gone and only about 0.3kWh of import. Still going strong as I type this.....
    • Solarchaser
    • By Solarchaser 21st Jun 19, 10:36 AM
    • 56 Posts
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    Solarchaser
    I would say it's down to the sofar me3000sp not anything to do with batteries.
    Its probably worth noting that I apparently have an older version of the sofar (2017) which is why it wont communicate every parameter with the solarman app, so perhaps one of the guys with a newer model can comment if its improved.

    On some overnight use the battery is fine with 50w output.
    The problem is that it's not consistent.
    If I was to take 10 overnights with base going from 50w to 180w (I assume its the fridge compressor cycling) then on maybe 3 of those overnight it will cover without going to standby, but the other 7, once it drops below maybe 150-200w then it will go into standby and let the grid take over.
    If the load at any point goes above 200w it will take over, but when it drops below 150w (ish) again, then it will go to standby.

    I purely use it as battery charging from solar, and discharging for load, no time of use, nor e7
    • mmmmikey
    • By mmmmikey 21st Jun 19, 7:41 PM
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    mmmmikey
    The problem is that it's not consistent.
    Originally posted by Solarchaser

    I think that some of the inconsistency may arise from occasional high mains voltages and the effect this has on the inverter operation. Powervault fitted an additional transformer to mine to reduce the mains voltage after monitoring it for a couple of weeks after initial installation and this made it more consistent. I think it was something to do with occasional high voltages overnight causing the battery to stop discharging briefly, then not starting again due to hysteresis effect I mentioned in an earlier post. Not sure if you monitor mains voltage and have noticed any correlation?
    • Solarchaser
    • By Solarchaser 22nd Jun 19, 1:06 AM
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    Solarchaser
    I dont monitor mains voltage, but the sofar does, it bounces about from 242 to 250 depending on time of day.
    The highest voltage is when the panels are generating , and the lowest is overnight for the last week...

    I'm not saying you are wrong, I've never really looked at it, but I cant see a 250v peak causing issues with the inverter, as its safety cut off is quite a bit higher.

    I think there is a hysteresis issue with starting back up, but there always will be due to the fact the ac systems can only ever work reactively.
    • mmmmikey
    • By mmmmikey 23rd Jun 19, 10:19 AM
    • 229 Posts
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    mmmmikey
    Interesting that the voltage is varying depending on generation rather than just natural grid variation, I wonder where it is being measured or if there is just a correlation between the 2 where you live? Scratching my head a bit but I recall something along the lines of grid tie inverters switching off temporarily at a threshold that is more suitable to mainland European use than UK, but I could be wrong here.


    As far as hysteresis is concerned, I can see that effect very clearly from last night's charts. I ate out yesterday and didn't have the normal cooking load in the evening, and without heating this time of year there's very little usage other than normal background. As generation gradually fell below usage in the evening, the shortfall was taken up by import, which gradually rose as genertaion fell. This never reached the level where the battery kicked in so my background load was met with import until about 21:00. However, when I boiled the kettle at that time it was enough to switch the battery on and start supplying, and at that point it continued to meet my background load all through the night. So the answer to getting your batteries to work overnight seems to be eating out and drinking lots of tea



    (Haven't worked out how to post the charts here, happy to do so if anyone is interested and call tell me how to)


    Thanks, Mike
    • Martyn1981
    • By Martyn1981 23rd Jun 19, 2:44 PM
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    Martyn1981
    Interesting that the voltage is varying depending on generation rather than just natural grid variation, I wonder where it is being measured or if there is just a correlation between the 2 where you live? Scratching my head a bit but I recall something along the lines of grid tie inverters switching off temporarily at a threshold that is more suitable to mainland European use than UK, but I could be wrong here.
    Originally posted by mmmmikey
    Hiya. PV inverters push up the grid voltage a little bit, think of it as having to be at a higher pressure to push the leccy out of the house, v's the mains pressure.

    UK has a 'pretend' voltage of 230V, but historical pressures mean it tends to be higher.

    The working range is -6% to +10% (216V to 253V), that's to say, the voltage the DNO's are required to maintain, and importantly the legislation states that it's their responsibility to stay within that range even with SSEG's (small scale electricity generators) on the network - wind, PV etc.

    As PV inverters will push up grid voltage, to avoid a spiraling problem, all but the very earliest models should shutdown when grid voltage hits 253V. Mine did it once, many years ago*. They will then check on the mains voltage and restart once it is below 253V again.

    *Classic example as it did it on a sunny Sunday afternoon when demand is low, so voltage can rise.

    Apologies for waffle, but there was a fun article many years ago with a DNO 'complaining' that reports of overvoltage (253V+) had increased ten fold due to PV.

    In reality, inverters shutting down due to overvoltage, meant homeowners where raising the issue with the DNO's. So the problem didn't really get worse, we just found out how badly some DNO's were at maintaining voltage in the 216-253V range, then they moaned that we'd caught em!
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Solarchaser
    • By Solarchaser 23rd Jun 19, 2:46 PM
    • 56 Posts
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    Solarchaser
    It's being measured from the sofar grid connection I assume, only place it can see grid voltage.

    My grid voltage has never reached cut off.
    But yeah I'd 100% expect to see the grid voltage rise in my home when I am generating, makes perfect sense.
    I'd reckon it's something like 1v per kw generated vs grid voltage.
    • Martyn1981
    • By Martyn1981 23rd Jun 19, 3:17 PM
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    Martyn1981
    I'd reckon it's something like 1v per kw generated vs grid voltage.
    Originally posted by Solarchaser
    Can I ask how you calculated/estimated that*, as it seems very similar to a figure I recall an installer giving me years ago on a different forum? I'm sure he said PV systems can push up the voltage by about 2-3V.

    *Simple, general terms only please. If it's very complicated, then just say so, and I'll take your word for it, I'm just a curious soul.

    Thanks.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • Solarchaser
    • By Solarchaser 23rd Jun 19, 8:17 PM
    • 56 Posts
    • 96 Thanks
    Solarchaser
    Haha I like that Martin, I'm afraid I have no complex calculations to dazzle you with, and tbh no actual proof of it either.

    It's taken from looking at the voltage in the morning vs mid afternoon vs night and noting morning voltage up around a volt, say 245v, then midday around 248v and then evening about 244, suggesting the early 1kw of pv pushed up a volt, the midday 4kw gave 3-4v and when no pv went back to grid voltage.

    I did it on a couple of different days, but its anecdotal at best tbh, and if quizzed on it I'd have to admit to suffering from confirmation bias.
    • JKenH
    • By JKenH 23rd Jun 19, 8:21 PM
    • 464 Posts
    • 2,259 Thanks
    JKenH
    Interesting that this issue of grid voltages is being discussed as coincidentally on Friday one of my inverters switched off when the DC input voltage spiked at 270v. It quickly restarted. The other inverter doesn’t show as switching off but as my data only refreshes every 5 minutes or so it could have switched off and back on without me noticing. (The inverters were about 2 minutes out of sync on the day.)

    The DC input voltage for one roof with 6 panels per string however is typically 30v lower at around 190v than the one which tripped out which has 7 panels per string and operates at about 220v so what exactly is the “DC input voltage” and is the issue completely unrelated to the AC grid voltage?
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps
    • Solarchaser
    • By Solarchaser 23rd Jun 19, 10:14 PM
    • 56 Posts
    • 96 Thanks
    Solarchaser
    DC input voltage is your voltage coming from your panels.
    The inverter uses this to make AC power.
    AC or Grid voltage is what's coming into your house from the main grid.

    It sounds like your panels are too powerful for your inverter if they are causing a shut down
    • joefizz
    • By joefizz 23rd Jun 19, 11:05 PM
    • 186 Posts
    • 172 Thanks
    joefizz
    So the answer to getting your batteries to work overnight seems to be eating out and drinking lots of tea
    Originally posted by mmmmikey

    In a way thats what Ive found ;-)
    To recap Ive the sofar solar and pylontech and find once it kicks in at night it sort of stays kicked in but there are variations on when the kick in occurs.

    When I first got the system you could hear it kicking in and out muliple times before settling into a steady state at night but either it has stabilised or Im more used to doing things differently (could be the addition of the 3rd freezer, but again thats a transient thing and not a constant load). My 'normal' background load is quite small relatively speaking and as I mentioned in previous posts Ive learned to increase my background load to get the most use out of the way I use my batteries.
    Counter intuitive to increase consumption to use less import but Ive only imported 14 units since 1st April.
    Will be interesting to see how it works this month with only background load at all times, I might end up importing more electricity for the month Im away from home than the previous 3 months using it all!
    • Martyn1981
    • By Martyn1981 24th Jun 19, 5:44 AM
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    • 13,672 Thanks
    Martyn1981
    The DC input voltage for one roof with 6 panels per string however is typically 30v lower at around 190v than the one which tripped out which has 7 panels per string and operates at about 220v so what exactly is the “DC input voltage” and is the issue completely unrelated to the AC grid voltage?
    Originally posted by JKenH
    As Solarchaser points out the issues are unrelated (DC v's AC voltage) as it's your inverters job to take the DC side and pump out on the AC side.

    If you Google your inverter make and model it will state the DC side limitations that it operates at, such as max DC watts, minimum and max DC volts etc.. Obviously they all vary, but 270V DC side sounds pretty normal, some inverters will go up to 400, 600, 800V etc depending on what they are designed to do, and how many strings they can cope with - two strings will halve the voltage and double the amperage for example, so the inverter should be chosen (and set up) to match the number of panels, panel specifics, etc..

    BTW, whilst PV panels vary, they generally operate at about 30V (or 50V for higher cell panels), so your strings varying by 30V with a one panel difference, sounds fine. Again, a quick Google of the specific panel will give its voltage figures if you want to do a quick check, look at the 'operating voltage' figure.
    Last edited by Martyn1981; 24-06-2019 at 5:50 AM. Reason: Added a BTW
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • mmmmikey
    • By mmmmikey 24th Jun 19, 6:23 PM
    • 229 Posts
    • 350 Thanks
    mmmmikey
    Counter intuitive to increase consumption to use less import but Ive only imported 14 units since 1st April.
    Will be interesting to see how it works this month with only background load at all times, I might end up importing more electricity for the month Im away from home than the previous 3 months using it all!
    Originally posted by joefizz

    Thanks - be interesting to hear how you get on. Having looked at the various charts a bit more carefully I'm now fairly confident that my background load is between the "kick in" and "kick out" thresholds. There are very few days where the panels don't cover the background load, so the only time this is noticeable is late afternoon / early evening as the generated power diminishes on a day when I'm not at home in the evening to cook dinner. On those days, the battery never starts and I use grid power all night (albeit very little!)



    My theory is that by putting something on a timeswitch that draws a few hundred watts at about 19:00 for a few minutes I should fool the battery into starting and keep running, I'll let you know how I get on. It's not going to make me rich though, maybe save 2p or 3p a night, but as everyone here knows these things are a matter of principle!
    • 1961Nick
    • By 1961Nick 24th Jun 19, 6:35 PM
    • 601 Posts
    • 2,736 Thanks
    1961Nick
    I've had a look at my grid voltage & it's between 232v & 241v. The lowest readings are at peak times as you would expect.
    4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North Lincs
    Installed June 2013 - PVGIS = 3400

    Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus Batteries - 12kWh
    • Martyn1981
    • By Martyn1981 26th Jun 19, 6:03 AM
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    • 13,672 Thanks
    Martyn1981
    First the good news. National Grid will pay homeowners with a Tesla Powerwall II upto $1,000 per year for the right to use the battery during peak periods for grid support.

    The bad news ........ well, the $ isn't a mistake!

    Power Companies Want to Tap the Tesla Batteries in Your Home
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • mickyduck
    • By mickyduck 26th Jun 19, 6:37 PM
    • 327 Posts
    • 346 Thanks
    mickyduck
    Forgive me if covered already but I’m on my phone so not easy to read etc...
    Just seen the edf power vault 8.2 kWh for 5k
    Is this now seen as a reasonable buy are we at the point when battery storage is sensible?
    Link to thread / posts opinions please
    3.995kWP SSW facing. Commissioned 7 July 2011. 24 degree pitch + Solar Immersion installed May 2013
    • legoman62
    • By legoman62 26th Jun 19, 7:12 PM
    • 2,810 Posts
    • 14,721 Thanks
    legoman62
    Forgive me if covered already but I’m on my phone so not easy to read etc...
    Just seen the edf power vault 8.2 kWh for 5k
    Is this now seen as a reasonable buy are we at the point when battery storage is sensible?
    Link to thread / posts opinions please
    Originally posted by mickyduck
    Is this it?
    https://batterystorage.edfenergy.com/powervault/powervault-with-grid-services/
    16 Sanyo Hit 250s.4kWp SMA 3.8kWp inverter. SW roof. 28° pitch.
    Minimal shade. Nov 2011 install. N.E Lincs Coast. Hybrid car
    • zeupater
    • By zeupater 26th Jun 19, 7:33 PM
    • 4,813 Posts
    • 6,479 Thanks
    zeupater
    Forgive me if covered already but I’m on my phone so not easy to read etc...
    Just seen the edf power vault 8.2 kWh for 5k
    Is this now seen as a reasonable buy are we at the point when battery storage is sensible?
    Link to thread / posts opinions please
    Originally posted by mickyduck
    Hi

    Good question ....

    The majority of the manufacturing cost of a domestic storage system will be the cells themselves, with other components being relatively minor ...

    At £5k you're looking at £600/kWh in total, so somewhere around £450-£500/kWh for the battery content .... that's against a background of bulk supply cell prices of around £135/kWh (~$175) in 2018 which is widely forecast to fall to below £80/kWh (~$100) sometime next year and around £40/kWh (~$50) for 2025 ....

    For ourselves (and most others!) it doesn't make any sense to get too interested until a fully installed system comes in at below £200/kWh with serious research and thoughts of sourcing starting at around £150/kWh .... of course, much will depend on government attitude to kick-starting the storage sector, but with recent announcements (VAT etc) it's not really worth holding your breath ...

    If you're looking at some kind of shared cost/shared service offering, be wary at the moment as most probably make more financial sense to the company offering a package than the customer who is paying what is effectively the full cost of the installation as well as shouldering the majority of the risk ....

    HTH
    Z
    "We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
    • mickyduck
    • By mickyduck 26th Jun 19, 7:43 PM
    • 327 Posts
    • 346 Thanks
    mickyduck
    Yes that’s it
    3.995kWP SSW facing. Commissioned 7 July 2011. 24 degree pitch + Solar Immersion installed May 2013
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