Variable Solar Storage with Batteries

[willbish]

21 hours ago, JSHarris said:

I'll lay money that the next generation Powerwall will have these 2170 cells, and there seems a good chance that it may well be cheaper than the current versions which use the older 18650 cells.

While other companies are reducing prices Tesla are quietly raising theirs

 

https://www.greentechmedia.com/articles/read/tesla-quietly-raised-the-price-of-the-powerwall#gs.4K90G1U

[Jeremy Harris]

54 minutes ago, willbish said:

While other companies are reducing prices Tesla are quietly raising theirs

 

https://www.greentechmedia.com/articles/read/tesla-quietly-raised-the-price-of-the-powerwall#gs.4K90G1U

 

 

Could be a sneaky tactic to be able to price the next generation Powerwall at a lower price  - they must be close to switching pretty much everything (except the Model S) from 18650 cells to 2170 cells, as that's now the primary product coming out of their cell Gigafactory. 

 

My guess is that in the short term the new 2170 cells are more costly to produce, even if they will be cheaper in the medium to long term, so now that Tesla has a significant share of the home battery market they may feel they can up the price without hitting that hard, whilst ensuring that the next generation is perhaps more competitively priced.

[MikeGrahamT21]

Came across these on ebay last night, still the same LiFePO but these support 100% DoD, same batteries used on the London Buses apparantly: https://www.ebay.co.uk/itm/BYD-B-Plus-2-56kWh-Solar-Battery-storage-100-DOD/322754585457?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

Still a bit top heavy on price, but not too bad considering the 100% DoD?

[Nickfromwales]

Ok. Picking up from the digression here;

 

and the interesting but not yet fully discussed installations / implementations here;

 

I feel it would now her a good time to chew the fat on exactly how 'plug n play' these battery systems actually are. Jeremy makes his point about suitability / economy based on convenience as much as fortification of consumption / offsetting import / smoothing peaks and troughs as it were, but I kinda feel that his core motive is for backup power for his ( quote ) frequent grid 'power cuts'. Sorry to pick on you again Jeremy but you make some important comments here afaic when considering buying a battery system. I just don't feel there was enough emphasis on the reasons for the promotion of it. 

 

My first glance understanding was it simply plugged into the main CU just like the solar PV does, but then I ask myself about current capacity limitations; when the house is at full wallop, eg induction hob going full blazes, the two ovens doing Sundays mixed game, the EV is plugged in filling its battery based belly, washer and TD are whizzing around etc etc and the grid dies aka a power cut. Simple for the PV, the inverter just switches off, likewise I think I read for the grid tied battery side. So no grid, then no PV then no battery? 

One assumes if all the loads that were running whilst the grid died are still present, then where does the juice come from to sustain or reinstate power ( albeit temporarily )?

If 10-15kW of electricity was being consumed as the grid died, would the system not have to be able to match and sustain that ( eg be sized accordingly ) for the system to be perceived as a "battery back-up"? I know its not sold or described as one, but it has been talked about and I feel there may be some disillusions for anyone reading that may leave them with the wrong understanding of what these systems are actually able to offer 'out of the box'.

So, my question(s) is about current capacity and load switching / shifting, for the want of a better phrase. Read on, I shall try and use my words more betterly.  

 

When the grid is up and the batteries are getting juice from wherever, it has the ability to lend itself to offset grid consumption to the property, giving what it can to the dwelling until depleted. That cycle goes on accordingly in a normal 24 period of charge ( assume PV ) and discharge ( offsetting grid consumption until 'flat' ). Happy days. This is what I'm going to refer to as generic, off-the-shelf, use. 

 

Now, lets look at the other ( possible ) side of battery use, as in an understanding of the above utilisation but with the requisite that the system will frequently have to deal with grid power outages and has been purchased with a desire to mitigate against this eventuality. ( Lets remember folks, anyone in very adverse powers failure zones could simply buy one of these and just charge it directly off the grid, eg NO PV,  as an alternative to a generator ). Its here I think the creases could do with a bit of ironing.  

 

So, you get a power cut as the grid just died for whatever reason. 

Now, the games half cooked, washer hasn't finished cycle, cars still wanting another couple of kW to fill its belly, and the kids run around screaming that the wifi's gone off aka the 4 horsemen have arrived. 

 

Nowt. Your sat in the dark, batteries charged but going nowhere as their inverter, like the PV one, has been told to go nite nite as the grid tie has been lost. So, accepting the game will spoil, and the sprouts will have to be a lot crunchier than usual, you go looking for the torch. Why you cry, as you have some expensive batteries that you should be benefiting from, shouldn't you?

Simple;

a) if looking at this retrospectively, you'll have a generic electrical wiring system in your house and the battery system cannot support everything thats connected to your CU. If it did get connected to the CU the battery system MCB ( trip switch ) would go past its rated capacity and just trip out as;

b) you bought a battery storage system NOT an UPS ( uninterruptible power supply ). 

 

So, back to Jeremys point about the two sets of outputs. One is grid tied and is hard wired into the house CU, ( CU1 ), and then you have the second outlet which essentially could just be made off to standard 13A double socket labelled "failure power". Now you have choices as to how to best utilise the second outlet, which is live during a power cut but is typically not connected to anything. So unless you have bought a bank of these things, sized to exceed the maximum current usage of the dwelling, you cannot just 'changeover' fully from grid to battery with the flick of a switch ( or by automation ) as the aforementioned systems just don't have the capacity to do so. Rough maths : the 9.6kW setup would run a standard electric shower for an hour or so for eg. 

 

If I get what Jeremy is proposing to do in his house, if he goes for such a system, it would indeed be a type of changeover arrangement. A second CU, ( CU2 ), which has the 'essentials' supplied from it and is separated from the mains supply CU1 tails by a changeover switch ( manual or automated ) that selects either "grid" or "battery". Most importantly though is it would ensure that the battery system cannot ever connect to CU1 during power failure. What you would then need to do is to be mindful that CU2 does not have the ability to exceed the MCB rating of the battery system second outlet, or it will trip out on over-current. So, afaic, the above essentials would typically be lights, fridge and freezer, internet / wifi and maybe a single 13a socket that you can plug an extension lead into in desperation ( PC / laptop charger for eg so you can continue working from home ). Heating and hot water I would class as non essential, and trying to suggest you use the power reserves stopping your freezer from defrosting to keep the house warm is bonkers. Buy a "grid has gone down" jumper  

So this is really to stop any thoughts about cheekily being able to just pop the battery power on and carry on as normal until the battery goes flat or the grid electricity comes back on.  Not going to happen unless you've spent about £12k on 3x 9.6kW systems or the equivalent ( again rough maths ). 

 

The other thing I wanted to highlight is that the cost of the system is one thing, if its for a generic plug n play install. The cost of using it for a bit of failsafe against grid failure is another. 

The scale goes from just a socket on outlet 2 of the battery system and you just go plug an extension lead in for the fridge / freezer, all the way up to Jeremys far better option where there is just the flick of a switch and its all taken care of. Anyone who's considering a battery system should NOW put some serious thought into gleaning these 'essential' circuits back to said CU2 and just linking the tails together for now. Not much cost or complexity now, during the planning phase, but a lot messier and less practical after the event as, for eg, if you, retrospectively, migrate the fridge freezer onto CU2 then that likely means you've had to just move the entire kitchen ring across so everything not needed under power fail would need switching off manually to preserve stored power. Vampire loads would be a serious problem for a smaller battery system so a bit of thought now could see you getting good results, sustain of essentials, without having to provision for a bigger system.

Now for the killer;

Folk also need to remember that if they have PV that is already near matching or even failing to match their current level of consumption, then there will no be little or no PV left over to charge the battery system, eg if your space heating and DHW is already all electric ( SA  / willis heaters / ASHP ) then battery tech may need a proper look at to see how exactly you'll charge it. Your hot tank will grab a bit of grid electricity if PV hasn't cut the mustard, but will your battery system also have to keep doing so to stay at its peak charge / discharge capacity / duty. For sure you'll be able to discharge the suggested systems, at those capacity ratings, but be sure you can fully charge it again or you'll hugely reduce the lifespan of the system by abusing it.

For those looking to buy and just plug it in, the price seems tempting to say the least, but for anything else its time to look again at the peripherals and triple check the maths, more so with the bigger system which will need longer to properly recharge. The smaller system seems to be the safe position, or look to bump that up alongside upping your PV array if battery storage really means that much to you. 

 

Ok, boffins, have at me!  

 

 

 

 

 

[ProDave]

You are quite tight that your battery system cannot support big loads like your massive induction hob, and in the event of a power cut, it can only supply loads isolated from the grid, otherwise it would try and power the whole town.

 

For a new build, (probably a bit late for mine as most of the wiring is done) you might want to consider making an additional ring final covering the whole house for "essential circuits" such as the fridge, boiler, some lighting, a few easy access general purpose sockets etc, and make it so just that 1 circuit can be changed over to the stand alone output from the batteries in the event of a power cut.

 

We perhaps better not mention the "widow maker"  cable.

 

I have been giving a great deal of thought to battery storage, and one thing that has always struck me, Is I like to know how things work, so I would like to know the logic built into it to decide when it charges and when it discharges. As that information is unlikely to be detailed, I still favour the approach of make my own, then I get to program how it works.

[Jeremy Harris]

For info, the Sofar systems I've been looking at, that use the Pylontech battery packs, have a maximum output to the house (or the emergency backup outlet) of 3 kW, so they should easily integrate into any normal house CU, much like a PV system.

 

In many ways you can look at an AC coupled battery system like this as just an extension of your PV system, that happens to be able to "generate" up to 3 kW at night, as well as during the day.  The battery system can also add power during the day when the PV is generating, if the household load exceeds the PV output and the battery has enough charge.  This means that if, say, your PV was generating 1 kW and you wanted to run the washing machine, that draws 2 kW at peaks, then whenever the washing machine needed more than the 1 kW from the PV system the battery would kick in to deliver the additional power, rather than let you use power from the grid.

[SteamyTea]

On 22/07/2018 at 11:54, Nickfromwales said:

Ok, boffins, have at me!  

Basically sums it up.

On 22/07/2018 at 12:16, JSHarris said:

rather than let you use power from the grid.

And you end up with flat batteries.

 

I know that with some sophisticated control and wiring that a system can cope with sudden grid disconnect.  I designed such a system 15 years ago, but realistically it is not viable.

 

What is viable for unexpected, but frequent power loss is a cheap generator and an extension lead or two.

If your gas central heating needs power to work, put a plug on the end of the lead and plug it into the generator.

[Jeremy Harris]

7 minutes ago, SteamyTea said:

 

And you end up with flat batteries.

 

 

Shouldn't matter.  If the idea is to use your battery storage to reduce grid import, then I can't see why it matters if the battery provides a boost during the day, when it might otherwise be charging.  Depends on battery capacity and charging capacity, but taking the 9.6 kWh Sofar system as an example, that can only discharge at a maximum of 3 kW, so the odd kW or so for short periods during the day when the PV isn't quite generating enough to run all the house demand shouldn't really have much impact, and the battery may well charge up again within the next half hour, anyway.

 

The standby power situation changes this a bit, and ideally the system needs to be clever enough to only allow daytime power top up (to avoid import) to a set battery state of charge, leaving a reserve for backup power purposes.  

 

I had looked at getting a generator for the power cut problem, but ideally I'd like something like the old Lister autostart, that fired up when the grid goes down.  Generators like that tend to be a bit pricey, especially if you need to be able to deal with relatively high peak loads.  Factoring the cost/convenience of a battery/inverter system versus a generator backup system isn't that straightforward, either, as any generator would need to be run periodically, serviced, have fuel changes etc, all of which make it less attractive from an operating viewpoint.

 

 

[Nickfromwales]

29 minutes ago, SteamyTea said:

And you end up with flat batteries.

Not quite. The SoC controller won't let them get that far. They'll shut off when it nears the critical point. 

[SteamyTea]

Ideally, in my mind, what is needed is something that charges up on the lowest CO_2e emitting power source and only discharges to offset the highest CO_2e emitting times.

This would require some central control and demand modulation, but should not be that hard to do.

[MrMagic]

Just thought I'd share some info here - recently had a quote for a Pylontech based system to be installed - it's actually coming in quite competitive compared to the DIY route.

 

Pylontech batteries are £834 inc 5% vat each, 3 off + inverter, cabling, certs etc for an installed price of approx £3800 - so £3800/6kWh useable = £633 per useable kWh installed. Not quite Tesla PW 2 territory £500/kWh installed, but certainly heading in the right direction.

 

[MikeGrahamT21]

On 21/08/2018 at 21:11, MrMagic said:

Just thought I'd share some info here - recently had a quote for a Pylontech based system to be installed - it's actually coming in quite competitive compared to the DIY route.

 

Pylontech batteries are £834 inc 5% vat each, 3 off + inverter, cabling, certs etc for an installed price of approx £3800 - so £3800/6kWh useable = £633 per useable kWh installed. Not quite Tesla PW 2 territory £500/kWh installed, but certainly heading in the right direction.

 

Yeah thats not too bad, wheres that from?

 

Trouble i'm having is the G59 form which needs to be filled out for the grid supplier. I'm going to email a DIY shop and see if they would be able to help at all. I've taken a look at the form but wouldn't know the answer to most of the questions on there.