Solar PV battery options

unkel

Very good price even if the battery is small (I guess a 2.4kWh Pylontech?), what total wattage of panels do you have? And are they 100% south facing in a good solar area of Ireland?

bullit_dodger

https://www.boards.ie/discussion/comment/118192353#Comment_118192353

I'd echo that thought too - 10 years is quite doable. Not for everyone, but easily in the ball park for me. Ok, someone might be 11 and I'm sure we can find people with 15 or more (cause they bought stupidly), but as a line in the sand 10 years should achievable for most.

But to chuck a few figures on the back of the beer matt math at it, I paid €8500 for my installation. So going with 10 years, I need to "save" €850 a year for that to happen.

Just using the battery 365 days to get night rate during day time for me yields. €330/year (after losses), so to make up the rest of the €850, I will need to generate €520 worth of PV electricity. Lets assume a price of €0.16 (which is half way between my day/night rate) as not everyone of those units will be consumed at day rate (although virtually all will as I consume a lot - but let's be pessimistic with €0.16) that's 3250 units I need to generate. Since the estimated yield on my system (via PVSOL) is 3925 units, my "expected yield" is 21% higher than my "needed yield" to do 10 years.

That's assuming rates remain unchanged. Chances are if electricity prices increase I'll payback in less - my gut feeling is 8-9 years. I'm comfortable with that as a ballpark. Not trying to pin it down to x years, y months and z days here.....just a general ballpark.

*Course different consumption/costs/initial outlay will yield different payback times.

mrm

https://www.boards.ie/discussion/comment/118192529#Comment_118192529

That's really helpful bullit_dodger for those trying to decide on the jump without a system in place to track!

What is the system you have (for the €8,500)? Do you reckon it along your households daily lifestyle allows you to extract that 83% required from your generation figures? Is this dependent on the battery size essentially? Apologies for all the questions.

bullit_dodger

To be fair now - my consumption is very much an outlier in terms of what a normal household would use. I use 8000-10000 units a year, a fair chunk of that going into 1-2 high powered pc systems (500 watts each) which are on all day. Most households in Ireland are about 4000-5000 units a year, but I do expect that average to grow over the next few years as EV penetration sweeps across the country. Long may it last. I'll be getting on that myself.

Your consumption drives everything really. No point in purchasing a huge battery if you can't "cycle it". You'd be better off keeping you money and purchasing a smaller unit in terms of payback. Same with panels. Yeah, the general feeling, and one which I also subscribe to, is "as many panels as you can afford/fit" but there comes a point where your overkilling it.

Opinions will vary on this, and that's a good thing, but I think 4-5Kwp (ideally 5Kwp) in panels with a 5Kwhr battery is a solid good performing system for 80% of people. More panels, like 6-7Kwp in panels would be helpful if you have an EV. Beyond 7Kwp.....you'd have to have some compelling reason. Many out there would have a reason, but it would be ..... unusual.

Don't apologize for asking questions - never learn anything in life without asking! :-)

Bobeagleburger

https://www.boards.ie/discussion/comment/118192477#Comment_118192477

Yes, a 2.4kWh Pylontech.

5700W total. South West facing Galway.

mrm

https://www.boards.ie/discussion/comment/118192742#Comment_118192742

Would you increase the battery size from the outset if starting again? Or the array?

Bobeagleburger

https://www.boards.ie/discussion/comment/118192822#Comment_118192822

The battery probably. The plan was was to review the battery situation after a year or so of using the system. Will probably stick with that plan.

mrm

https://www.boards.ie/discussion/comment/118192682#Comment_118192682

Ah OK, but you see the issue here. You are looking for a payback saving here on a demand that is more than twice the average household consumption. My lowest quote is the same out of pocket figure as yours, but as I only require less than half the demand I am only seeing potential savings of about half your €850 (paper exercise saving about €475-495 - of course it could become more). Your 10 years look feasible; mine certainly do not. I'll post quotes in the other thread once I receive them all.

unkel

https://www.boards.ie/discussion/comment/118192742#Comment_118192742

So a nearly 6kwp system with 2.4kWh battery installed for less than €4.5k after subsidies? That is a really good price. And a low total cost of the system is the best way to keep that pay back period down, well done!

5.7kwp SW facing in Galway with zero shadowing at a typical roof angle will generate about 3.75MWh per year is my ballpark guess. So even if you used 70% of your production yourself (not a hope) and even if all of what you used is worth the higher rate (it is not if you put on your washing machine or dishwasher because they could run at night at the cheap night rate. Or charge your car, or heat your water) and if you had zero losses from electrons going in and out of your battery (you will lose at least 20% in reality) then a purely theoretical best case scenario is:

3750 * 17c * 70% = €450 per year, or a pay back time of 10 years. If we never get a FIT

See now, how your 10 year payback time is not realistic? Unless of course we don't get a FIT and electricity prices are going to rise by at least 20-30% per year, year on year.

bullit_dodger

https://www.boards.ie/discussion/comment/118193143#Comment_118193143

Ohh absolutely mrm. This is what I was mentioning earlier that you have to match the installation to the demand. The system I purchased would be a little overkill for you, so you wouldn't buy a 8.2Kwhr battery, nor an EDDI and you can knock €1500 or so off my spend. The EDDI tends to never pay for itself in my estimation. it's more of a "nice to have" thing. PM me and I'll give you an installer to try quote if your not getting any decent ones.

There is a certain "economies of scale" to be had in fairness with the larger systems, but ballpark 10'ish years should be doable. Ok, sure it might be 11 years (or if leccie prices rise it might be 9 years) and that's ok. We're not trying solve it down to the exact month.

Plenty of estimators about tooo if you want to get an another source.....

Calculator Result (electricireland.ie)

Solar Electricity Calculator (seai.ie)

Probably should be more appropriate in the "quotes" forum/discussion folder.

the_amazing_raisin

https://www.boards.ie/discussion/comment/118192682#Comment_118192682

I'd say your consumption isn't going to be an outlier for too much longer. I've 2 EVs in my house plus heat pump and electric cooking, so annual usage is around 10-12MWh per year. That's a fairly hefty €2k electric bill to try and get rid of, but it makes the payback easier 😁

We're both WFH at the moment which drives up heating usage, but that's balanced out by not needing to commute

I'm of the same mind that it's better to install the maximum number of panels you can in a residential setting.

the_amazing_raisin

https://www.boards.ie/discussion/comment/118192477#Comment_118192477

There are good solar areas in Ireland? I thought we ranged from mediocre to crap 😂

Jokes aside, it is nice that solar and batteries are getting to the price where they're affordable and viable in overcast Ireland. It's my next big spending item after busting the mortgage into shape

Of course that is partly down to the recent hikes in the prices of electricity. I saw Power NI announced a 20% increase blaming lack of wind (they should hang around Stormont more 😂)

Of course they left out the part where all the energy companies f*cked up and didn't bother to buy any long term gas contracts to lock in a price. Instead they relied on the spot price, which is fine as long as it stays low (spoiler alert, it didn't 😬)

mrm

https://www.boards.ie/discussion/comment/118193671#Comment_118193671

OK, I think I am getting closer to some of the issues I am causing myself from the offset. Could you give me an explanation of the following if not too much inconvenience:

• I would have thought the Eddi was essential to heat the water, which I will heat in winter with oil boiler but summer would be good to have it. Is the Eddi just a fancy automated system that I could just run myself by running the immersion from the solar generation? Any significant advantage to it or just live without it in the proposed system?
• What are the losses you refer to in previous posts on the water (Eddi) and the battery?
• What does the battery 'cycle it' reference mean?

the_amazing_raisin

https://www.boards.ie/discussion/comment/118193827#Comment_118193827

I'll chuck in what I know

The Eddi is just a controller that replaces your immersion heater controller. It'll heat the water when it senses power going to the grid. There are other products out there that do the same thing, Google PV diverter. If you're handy you could probably make one but it does involve working with power electronics, so stuff can go spectacularly wrong if you make a mistake

All systems have losses, you'll lose energy in the PV wiring, inverter, batteries and diverter. Batteries have internal resistance which means the energy in is more than energy out. Similarly heating water will result in some losses from the tank, unless you time it so you use the hot water immediately

Regarding battery cycling, the lifetime of lithium batteries is measured in charge and discharge cycles. In general more cycles degrades the battery and bring it closer to it's end of life.

How many cycles that is depends on many factors. Battery manufacturers will generally quote a cycle lifetime at a particular depth of discharge and charging/discharging rate. If you stick within this range then your battery will last a long time before it loses any significant capacity

Some folks do seem a little overprotective of their battery cycle count. It's understandable because it's an expensive piece of kit, but the battery is there to be used and should be sized according to your needs. It doesn't make huge sense to overspec the battery and undercycle it to try and make it last 100 years or something

randomname2005

https://www.boards.ie/discussion/comment/118192382#Comment_118192382

The seai calculator estimates 8 years for my system and I included the Eddi in the total. Now I couldn't put in my actual unit price as the scale doesn't go high enough for the new daytime results. And I don't know how the bonus credit will play a roll in payback times too, and how often it will be available. But as a rough estimate 8 years seems reasonable.

My reading of adding to pay back time is to make it longer. Did you mean it that way?

slave1

Seeing as this is solar battery thread…….the most cost effective method is to….

Max your panels

Min your quote

Sell grant aided Pylontech battery

Go DIY battery route

graememk

https://www.boards.ie/discussion/comment/118193827#Comment_118193827

The Eddi or other diverters can modulate or control the amount of power used by the immersion. If you have a 500w excess it will only put 500w to the immersion.

If you switch it on manually it's either 3000w or nothing. Drawback is that the cost of adding it would heat a lot of water using oil/gas, your chatting about an equivalent of 6-9c per kWh to heat water from oil/gas.

Battery losses. There are losses charging and discharging batteries, conversion losses, losses in the inverter etc. So there's about an overall 20% loss. If you put in 10kwh you can only get 8 out.

A full battery cycle is from 0-100. If you go from 50-100 twice that's also 1 cycle

the_amazing_raisin

https://www.boards.ie/discussion/comment/118195317#Comment_118195317

I don't even get the grant ☹️

47akak

If anyone has any advice on the BMS for my 42 2s2p Leaf module pack I'd appreciate it, other forums have been less than helpful. I think I know what I'm doing overall, definitely happy with the theory, and much of practical work but the BMS still slightly unnerves me and I've yet to buy one. I'll be putting 42 modules in to 7 packs of 6 (so get 6 modules connect them in parallel, then run the parallel packs in series) to give me a 14s12p (?) battery. Nominal 48v charging to 58.8v or less and discharging to I suppose 42v or close to.

At the premium end of BMS imo the Leafmon is way too much adding it all together, Rec BMS don't seem to do a 14s anymore, Techdirect have stopped their Leaf line for some reason and the Orion again is huge money. I don't mind investing in a premium BMS, no point in skimping if the Daly or whatever won't be able to balance such a large pack or will have other problems but for standalone portable Leaf packs (so 7 modules in series) many have used the 14S Daly BMS and soldered clips on. Seems to go ok.

Before I bite the bullet on a BMS is there any reason not to go with the Daly BMS such as the one linked for such a pack?

I don't think there's any reason to go canbus with Daly as checking the latest Sofar/Solis manuals there's no mention of it being supported and no mention on forums or on Daly's side, so one of the question is when the Daly disconnects the battery reaching the voltage limit does it disconnect the battery entirely or can you discharge the battery from that point automatically via Solis/Sofar? Or if that is the case in any event do you set the Sofar/Solis limit inside that of the BMS and so that siimply won't happen? Eg BMS cuts off at 4.2v but Sofar/Solis at 4.1 so the BMS never has to disconnect.

https://www.aliexpress.com/item/1005002205134036.html?spm=a2g0o.productlist.0.0.7ad04c33iYApM1&algo_pvid=7dff1a75-0a97-42d4-a8b3-ccef29030571&algo_exp_id=7dff1a75-0a97-42d4-a8b3-ccef29030571-1&pdp_ext_f=%7B%22sku_id%22%3A%2212000019273349584%22%7D

Any tips again much appreciated.

unkel

Be careful dude, you've linked to the wrong one! We're mostly having 16S setups for our LiFePo4 chemistries, but you need a 14S lithium ion one (14 * 4.2V = 58.8V fully charged). I'd just go with a Daly if I were you. And monitor the cells to make sure it does its job. I presume you got the Leaf modules an awful lot cheaper than our brand new LiFePo4 prismatic cells (per kWh remaining capacity?)

graememk

Also if going for a BMS that cant communicate, you will be running the inverter in Default mode, and with the sofar, it will "guess" the SOC from the voltage.

It will then count the energy in/out to adjust. If it is idle for 1 hour, it will "recalibrate" the SOC from the voltage again.

with Li Ion its not so bad, its discharge curve is fairly straight, in lifepo4 its very flat a 3.3v battery can be anything from 40% - 90%.

you could emulate a bms if your handy with a bit of code, a waveshare CAN device and an esp32, have something talk to the daly and then talk to the inverter.

DrPhilG

And that ^^^ = the reason I made sure I got a BMS that could communicate with the inverter...

Blue4u

Just an outside, but has anyone gone with acid battery instead of PV?

unkel

You mean lead acid battery instead of lithium? Yeah a few of us have. If you get one for really cheap / for free, it's a good start. But LiFePo4 is so cheap these days that even if you got the lead acid super cheap, it's probably still more costly per cycle than brand new lithium...

Major problem with lead acid is that it needs to be fully charged about once a week to keep it healthy. And you can only discharge to 50%, so you need double the capacity of lithium to make a fair comparison

47akak

https://www.boards.ie/discussion/comment/118214993#Comment_118214993

I could do it but it might take me until 2024. Once it's safe and doesn't require constant manual intervention I'm happy. Interesting though I'll look it up.

47akak

https://www.boards.ie/discussion/comment/118214059#Comment_118214059

Yes just browsing a bewildering array of BMS it will be that Daly equivalent for Li-ion 14s. Pulling the trigger on everything today will report back.

Battery will be a small fraction of LifePo4 cost per kWh.

poker--addict

https://www.boards.ie/discussion/comment/118195317#Comment_118195317

Is it even worth bothering with the battery via grant?

DrPhilG

https://www.boards.ie/discussion/comment/118218733#Comment_118218733

Absolutely. Get a battery using the grant, then sell it to fund the DIY one.

unkel

https://www.boards.ie/discussion/comment/118217500#Comment_118217500

A small fraction, wow! We pay roughly €1300 for 10kWh usable (including all taxes and shipping costs). A 24kWh early Leaf battery has maybe 14kWh usable at this stage, so if you pay a fifth per kWh, you got the whole pack for about €300-400?

poker--addict

https://www.boards.ie/discussion/comment/118218773#Comment_118218773

Maybe the installer would “buy it back”