Solar PV battery options

poker--addict

https://www.boards.ie/discussion/comment/118417517#Comment_118417517

Also looking at using a 2.5 to unlock grant and then selling and upgrading DIY. Is it easy to shift a 2.5 battery? dont see any on donedeal right now?

DrPhilG

https://www.boards.ie/discussion/comment/118418939#Comment_118418939

No problem shifting them. I sold 2 of them via here a few months back.

unkel

https://www.boards.ie/discussion/comment/118418127#Comment_118418127

No! You're only supposed to do that with systems up to 36V.

bullit_dodger

https://www.boards.ie/discussion/comment/118419111#Comment_118419111

Lads it's fine (totally FINE!)..... as long as you only lick ONE terminal at a time. Don't ever lick two together, like you did back in the day when you were a kid with a 9V battery!

LOL!

E30M3

To anyone who has replaced Pylontech batteries that were already installed I was just wondering is it a good idea to re use the long Pylontech Power Cables and replace the Pylontech Battery Terminals with Ring Terminals and use those cables from your LfeP04 Battery bank or is there a reason for not taking this approach?

Geeyfds53573

The Pylontech battery, the connection on the cable would be of no use to the LiFePO4 setup which would use a lug. Normally there is a fused switch before the inverter you would be connecting the diy setup to. Also the next user of the Pylontech would need the cable I’d assume.

SD_DRACULA

https://www.boards.ie/discussion/comment/118428572#Comment_118428572

I was wondering about this myself, can we just buy a set of pylontech cables and cut the end that connects to the battery and add a ring terminal there?

E30M3

https://www.boards.ie/discussion/comment/118428791#Comment_118428791

That was my question Dracula but you phrased better that I did. I have the cables having sold the batteries and it seems like a logical approach to take but I may be missing something

reklamos

I really see why no reason why you cannot reuse the cables. Just cut plugs off and put the proper lugs on them.

poker--addict

i am sure it is buried in the 52 pages of the thread somewhere, but how are people finding battery life after 5 years, particularly those of you who are perhaps maximising cycles by charging from grid at night to discharge when day electricity rate kicks in?

reklamos

https://www.boards.ie/discussion/comment/118430192#Comment_118430192

We do not have that data yet. If you look at spreadsheet the oldest setup are 2-3 years old. So it will take a while to get that data but again everyone's mileage will be different as settings, setup and the way it is used will be different. LiFePo battery when used properly and kept at good temps will last for long time. SoH will drop overtime but again 5 years is nothing for it when used properly. I think the big problem is that due to their cost, baterries are undersized for most setups. Which means they are charged/discharged at full throttle and also could go through multiple cycles in a single day.

poker--addict

the multi cycles thought is what triggered by query actually! I figured if using them right you always cycle them - in summer you fill them during the day and drain later, in winter even if there is no solar it would make sense to charge on the night rate to avail of night rate during the day. Then I was thinking would the small gain of artificially securing night rate during the day be largely wiped out by the cost of cycling the battery.

bullit_dodger

https://www.boards.ie/discussion/comment/118430436#Comment_118430436

Bear in mind that you also have other batteries like the Givenergy one that I have which "behind the curtain" is a 10Kwhr battery, but it's sold as an 8.2Kwhr battery. Meaning that when the capacity of the battery drops in a few years, you -still- see 8.2Kwhr as the capacity.

reklamos

https://www.boards.ie/discussion/comment/118430687#Comment_118430687

if it is sized properly you would only cycle ones a day. Pylontech are rated for 4500 cycles, if you do not push to the max it can got to 6000 cycles. It should last over 10 years.

garo

https://www.boards.ie/discussion/comment/118430687#Comment_118430687

I did the sums on this over two years ago and found that the amortized cost for a cycle was around 5-6c at that time. Battery costs have come down by about 20% since then. And electricity costs have gone up making night rate charging an attractive proposition even for Pylontech owners.

Battery degradation is a complex topic and there are multiple factors:

1) Temp extremes: Operation at high temps reduces battery life. Charging at low temps DRAMATICALLY reduces battery life.

2) Depth of discharge: Long periods below 10% SOC can be bad. LifePO4 handles being at 100% better than other Li ion chemistries.

3) Age

I doubt any of us is going to hang on to a battery for more than 10-12 years. And one full cycle a day gives us 3650 cycles in 10 years, well within the Pylontech rating. So charging at night won't meaningfully impact battery life for most of us. Once I came to this realization last November I decided to start night rate charging. It's also better for the environment. I kept DoD to 80% which reduces stress on the battery and keeps it reasonably healthy.

yankinlk

https://www.boards.ie/discussion/comment/118431671#Comment_118431671

Ive been thinking we could use a pinned FAQ - this is great info and could be part of it!

One more thing to help battery life - dont charge at night on max rate over a short period. Maximize the night rate period of 11pm to 8am and charge it low and slow. Theory here is a slower rate of charge will generate less heat and help extend the life of the battery.

poker--addict

Presume all installations come with a BMS that allows you to set charge rate and DoD?

paulbok

Getting my install today.

Was supposed to be a 5kw puredrive battery, but these are out of stock at the moment, so the installer (a Boards favourite) is proposing a 4.8kw Dyness battery.

Anyone have one of those?

yankinlk

https://www.boards.ie/discussion/comment/118431858#Comment_118431858

I do. Probably the same instaler. No complaints so far.

graememk

https://www.boards.ie/discussion/comment/118431815#Comment_118431815

The bms are built into the batteries. Although it's usually the inverter that you normally set the DOD.

DrPhilG

I don't think there's a huge difference on most of these. Pylontech, Dyness, Puredrive etc.

bullit_dodger

https://www.boards.ie/discussion/comment/118432080#Comment_118432080

Agree with you there Phil. Ultimately they store electricity, and give you back electricity. The quality of the electricity you get back isn't any better/worse from one to the other.

Course depth of discharge, dis/charging rates, battery "fade" overtime all these things matter, but as garo mentions above, if you don't abuse them by charging them in sub-zero temps, or at full charge rate -all- the time, I reckon most of us will have batteries operating at 70-80%+ in 8-10 years. Even multiple cycles a day is fine I think, again as long as it's not full charge/discharge rates.

The way I look at batteries is that you bought them to perform a job. Not using it to do said job is like having a car and not driving it cause you will wear the thread on the tires. Like a 10 year old car, it ain't going to be shiny, but it'll still get me to the shops :-)

Bif

Hi. I was considering adding another 5kw battery to my current 5kw Puredrive. Is there much involved from an installation perspective?

THE ALM

https://www.boards.ie/discussion/comment/118432667#Comment_118432667

Not a lot. Fitting bracket to wall and then connecting the relevant cables.

Looking to see how we get on with the battery we have and if I could pick another one up at a reasonable price I will be doing the same.

Purestorage II DC Battery Video - YouTube

Bif

https://www.boards.ie/discussion/comment/118432730#Comment_118432730

Looks straightforward. Thanks. Must check the pricing.

Jonathan

https://www.boards.ie/discussion/comment/118432928#Comment_118432928

Let me know if you find any Irish resellers.

THE ALM

might be worth looking at a group buy if enough people are interested, will send off an email to puredrive and see what they say.

Bif

https://www.boards.ie/discussion/comment/118433021#Comment_118433021

Great idea. Thanks.

SD_DRACULA

https://www.boards.ie/discussion/comment/118433021#Comment_118433021

I hear the worst part about adding another battery you need their proprietary cables which are somewhere between 150-200 quid and the battery should not come in at more than 2k.

Not a bad idea to ask for a group price, might be interested too if the price is right

poker--addict

How are you all maximising return on your batteries? Any tips or strategies?

Avoid it charging off night rate in summer if you know you will have excess solar relatively quickly during the day, but night rate charging it fully in winter knowing the solar wont restock it for the day?

bullit_dodger

The exact strategy you'll deploy really -very- much depends on your usage, the size of the battery, the forecasted weather.

But generally, in winter if you have high usage, and a big battery....this time of the year it's a no-brainer. Battery starts to charge for me at 00:15 and then charges at 1.5kw for about 5-6 hrs to finish about 6-7am. Then it's fully charged and set to discharge at 8:15am onwards until it's depleted (day rates starts at 8am in winter). The battery is usually depleted about 4-5pm in the afternoon, depending on what generation we get during the solar day. Works out about €1/day in savings.

Summer is the opposite, you want your battery empty at 9am (when day rate starts in the summer) so that it can soak up as much free leccie as it can from the panels to use later on in the day when the sun goes down, you have the washing machine on and the sun goes behind a cloud.

Tricky times are the 1-2 months in Feb-March and Oct-Nov where you need to kinda look at the forecast and decide what to do. Most people don't bother as depending on the setup, it may involve a trip up to the attic to change it on the inveter, but if you have remote access, you might set it to charge to say 40% to give you some night rate, and then leave the rest for solar.

To be honest, even a super-automated optimal system would only save you €10's at most a year.

poker--addict

Must be an app that can check the weather and make a judgment call based on parameters like expected cloud/sun/rain?

The strategy you describe is what I was thinking alright.

bullit_dodger

https://www.boards.ie/discussion/comment/118437293#Comment_118437293

It's actually a little tricky for an app to do it, but it certainly can be done. I've got it about 60% written myself but then again I am a software engineer - so that helps. The problem is that to do it "properly", you have to get it to learn your system. See what the forecast was going to be and then cycle back and see what the "actuals" were for those forecasts, then work out ranges and decision trees based on the various values that have happened historically. Some of it is statistical analysis and then figuring out how the supplier codes their interfaces.

Is it worthwhile? No.... it's completely overkill, but it's a fun project to keep the mind active. For 90% of people, they would be perfectly fine setting it to charge at night rate 1st of November, and then swapping that 1st of March to 50% charge at night, and then 1st of April 0% charge at night. Again, it's probably of the order of €20/year or something that you'll end up improving, if that.

poker--addict

In terms of economics then, roughly, am I missing anything major here.

Assuming 10kw battery, which will actually only have 7.5 or 8kw usable as you cant deplete them?

Assuming day rate around 23 cents, and night rate around 12 cents. Difference is 11cent.

1. Three winter months: battery gains little from the sun, so gain comes from charging at night and depleting between 8am and 11pm. 8kw/day saving 11 cents/hour . 30.4 average days in a month. 8kw x .11c x 30.4= 26.8 euro/month for 3 months = 80.4euro
2. Five summer months: 8kw deplete in evening and overnight, avoiding night rate of 12 cents. Maybe a small bit saved during the day as clouds pass. Call it 1 hour on the day rate?22cents. So 8kw x 12cents= 96cent+22=1.18ex30.4 daysx5months=179.36e
3. Four shoulder months: 35.87/summer month, 26.8/winter month. split the difference = 31.3e/month for 4 months=125.2e

125.2+179.36+80.4=384.96e/year saving on a 10kw battery.

Does that make sense? Is there other angles those of you more familiar have? That payback period is not fantastic. As bad as the feed in tariff is, it wont help the equation if considered too.

bullit_dodger

You're pretty close to what i got before. I wrote an exe to do the math for me with various tariffs. Here's what I had (with my settings)

Basically your talking about €400 a year or there abouts for battery payback. But, and this is a big "but", you have to be able to cycle the battery everyday 365 days a year to get that. You go away on holidays on the Dart to Bray and there's no on in the house to use the leccie, then you don't get the savings completely.

There are also losses to take into consideration that you may not have factored. You put 10Kwhr into a battery, you won't get 10Kwhr out. I went 7%, but the battery I have is on the efficient side. 12-15% is more typical.

poker--addict

There is so many ways to think about all the options. I have at various times been ready to pull trigger on no battery, small battery, large battery, and I might be back to no again!! Definitely easier if one can DIY but its still not miraculous.

We also have to wonder what the price and technology will be like in 2 years, especially when you see the size of the ev car batteries and their relatively cheap price. Going to sleep on it! Might just get the panels on the roof, and make sure its left ready for batteries!

bullit_dodger

I think the general strategy of getting a small battery (to avail of the €600 grant), selling that battery on donedeal.ie or some other site, and then taking that money to co-fund a DIY install is a good way to go. I didn't personally do that - but it's a solid strategy.

One thing in favor of an off the shelf battery though, is that it will pretty much pay for itself .....and without a battery at all, your going to be wasting production of your panels. So the panel payback timeframe increases a lot without one. FIT notwithstanding, but that will be rubbish. Rubbish.

Most people would be probably be suited with 5Kwhr. 2.4Kwh is too small to get through the night, and 10Kwhr for the average household is too big, so 5-6Kwhr is the goldilocks. :-)

yankinlk

https://www.boards.ie/discussion/comment/118437495#Comment_118437495

Thanks this has helped me...As much as I want to upgrade from 5 to 10 - cause i would definitley get use out of that in Winter - with my East/West setup - im skeptical I will be able to FILL a 10KW battery in Summer. SO by this logic if im not cycling everyday of the year im not gonna get paid back.

bullit_dodger

Ahh you'll fill it no problem in the summer, the question is would you be able to use 10Kwhr from when the sun goes down in the evening (7pm) to when the sun comes up in the morning 6am.....especially if you are like me and have a East/West split. Don't forget that 12am your then only recouping night rate for the electricity you have in the battery.

Filling it in summer is easy enough. 3 hrs of sunshine at 3kw (when you might have 5kwp) and your battery is full!

yankinlk

I reserve the right to change my mind. (and hopeful) but i think for now maybe i should go the full year (oct) before i make that call.

https://www.boards.ie/discussion/comment/118437549#Comment_118437549

That's a sensible idea. I'm doing the same.

championc

If you need to get approval from the financial controller, just give her access to an app (like MyEnergi), and she'll go mad when ever pulling power from the grid :)

yankinlk

https://www.boards.ie/discussion/comment/118438522#Comment_118438522

i might try that at the next board meeting. To be fair the CFO is making great strides in using big ticket items after 11pm already and the electric shower is growing cobwebs.

paulbok

https://www.boards.ie/discussion/comment/118437495#Comment_118437495

This is my first full day of production and already the battery was in use. Around midday, I was producing more than the house was using so got approx 25% of the battery(4.8kw) charged. As the sun pretty much died around 2pm, I'll have reused that bit from the battery by now.

Definitely worth having a battery similiar to your panel setup, e.g. 3kw panels and 2.4kw battery. Up to a point I suppose.

THE ALM

https://www.boards.ie/discussion/comment/118433388#Comment_118433388

Have an email sent to Puredrive so will wait for a response.

Looking at the video clip linked earlier it implies that all cables are included, will find out in due course I suppose. Hard to get a price for the battery, seems to be ranging from £1500-£2500.

SD_DRACULA

https://www.boards.ie/discussion/comment/118439628#Comment_118439628

Don't think they sell directly to people I think only to trade. Here's hoping.

bullit_dodger

https://www.boards.ie/discussion/comment/118439583#Comment_118439583

I also wondered previously if there was an (ideal) ratio of battery size to panel Kwp. Assuming you size your panels correctly to match (needed) production that is, the figure I came to was about 50% greater. e.g. if you have 4Kwp in panels then you'd have 6Kwhr in storage.

Where did I get those figures? Guess work to be honest mostly. The reality is that there are so many variables that it's impossible to have a general figure. Some people are 100% south, others east/west with the same Kwp.....so consequentially they will generate and consume differently. So they will need different sized batteries to get to night time rates (if that's in fact one of the objectives). So it's hard/impossible to have a ratio for it.

One thing I've noticed is that 2.4Kwhr battery is waaay better than nothing, but really it's just too small for the average household in Ireland. Average household needs ~5Kwhr these days.

championc

Battery sizing is down to your consumption. Not everyone can install the amount of panels that they would ideally like.

I bet the average house will consume 0.5kWh from 18:00 - 00:00 - so 3kW, although on a poor day, you won't even get to 18:00.

IMO, a 2.4kW is totally pointless. Yes, nice to see excess during the day get used, but really not likely to get you very far.

bullit_dodger

https://www.boards.ie/discussion/comment/118440699#Comment_118440699

Not sure I agree with you there championc that it would be pointless. A 2.4Kwh has it's uses. If you were to graph "usefulness" verses "capacity" those first couple of Kwhr are the ones which are easily filled and used. So in some respect they have the highest utilitarian value. it also has the ability to help give you ability to turn on the kettle (2kw) and not draw from the grid when you might only be getting a solid 1.2Kw from the sun. Sort of trickle charging over time to fill up and then giving you "some" ability to turn on larger loads without importing when the sun is shining. Along with helping reduce your export of course.

But yeah, I think 5Kwhr for an average household is needed these days. 2.4Kwhr as you say doesn't tally with the loads we place on them.

poker--addict

I think it is fairly complex - I know I have changed my mind from no battery to 2.4 to 5 to 10 and back to none! As small as the feed in tariff is it doesn't help what is not a no brainer economic decision.

A larger system needs one and the economics make sense, although it will take time to recover the spend, but it will depend on things like an EV and how easily you can shift power between night and say. To maximise value out of any of size beyond the smallest, it seems to me you need household buy in to think about what time they are putting a demand on their house grid, so those looking to setup and forget probably should not be spending a fortune on a battery bigger than their system.

There is an argument for no battery too, on a small to medium system - batteries are only going to get better. The price..up or down..who knows, but judging by EV batteries and their capacity, i'd bet on bigger batteries with lower prices/kw.