Solar PV battery options

graememk · 18-08-2021 05:26PM

You'll need to build in some automation now too!

Another thing to take into account.. there's about a 20% overall loss due to conversions too to take into account.

Im measuring the power going to my storage inverter and out of it and it's 20%. Roughly about 15% on charge and 5% on discharge.

I can now log the power going to and from the the battery on the DC side, I must see how that adds up.

For the cost of the batteries are you including the extra cost the hybrid inverter is over a straight solar inverter?

I'll stick a screenshot of my stats since the start of the year too might give you some more real world data to work from

unkel · 18-08-2021 06:06PM

https://www.boards.ie/discussion/comment/117772987#Comment_117772987

Do you not load the battery up in winter at least?

My night rate is 4.8c and my day rate is 16.8c (both incl VAT), so the savings are substantial

graememk · 18-08-2021 06:25PM

https://www.boards.ie/discussion/comment/117773129#Comment_117773129

Its now 20.27 and 5.83, but its fixed for one year, and going on how the likes of flogas are hiking prices...having a fixed plan is nice.

Screenshot of my spreadsheet

Theres a chunk in the middle that does all the calcs, efficiency. I lost a few days of stats at the end of july due to a power blink corrupting some data.

8.6 kwp, (orignally 7.2 kwp, added 4 panels in April), 10kwh of storage. - Savings are still slighty high, eg dishwasher is on during the day now, but its only 2 of us so its not on that often etc.

slave1 · 18-08-2021 06:29PM

https://www.boards.ie/discussion/comment/117773129#Comment_117773129

Can't seem to multiquote on this version of boards, I was just saying don't factor in any savings from PV fed battery over Winter, absolutely charge off the grid but factor in that cost of charge.

I did have a battery but sold it

SD_DRACULA · 18-08-2021 07:00PM

https://www.boards.ie/discussion/comment/117773129#Comment_117773129

Who is that with, seems quite low.

bullit_dodger · 18-08-2021 07:10PM

https://www.boards.ie/discussion/comment/117772987#Comment_117772987

Yeah, I accounted for a loss of 15% by adjusting the "night rate" to 12 cents over the actual night rate of 10.5 cents, done in both Model 1 & 2, as follows.

Day cent/unit €0.211

Night rate cent/unit €0.104

Night rate (with losses) €0.12 (Upped the rate to €0.12 due to losses putting into/taking out of the battery, I assumed 15% losses hence €0.12 cents)

The logic being that I have to "pay more" in cash to fill the battery i.e. I'll buy 10 units to actually fill 8.5Kw.....if you follow?

Also I did exactly do as you suggest i.e. that I derrive zero PV gain for 215 days (not just winter). In reality, you'd probably get "some" charge on many of those days, so the ROI would be a little quicker than what the math says.

Main thing I wanted to see was what range we're talking about for break even. is it 2-3 years, 10 years, 20 years......or basically never. Looks like for me, the payback is in in the 8-9 year range. Ok, maybe it's 7-8 if we start counting all the partial charges, and maybe it's 10 years if the battery degrades quicker than spec'd, etc but there should be a break even point there within a decade sometime. Again, I wanted the battery anyway but that's kinda nice to know. Perhaps others who are on the fence about a battery may find it useful - but do the math. It may not be a "given" for your situation.

Looks about €350-€400 / year saving with my load and size battery.

Interesting little project. Hey that's why we're all here, right? :-)

slave1 · 18-08-2021 07:25PM

I'm tracking my Payback, currently looking like almost bang on 9 years but that will shorten with all these electricity hikes we are seeing

bullit_dodger · 18-08-2021 07:58PM

That 9 years slave1, is that for the battery alone, or your complete installation? If its the battery, it's nice to see that my back of the beer matt math is in the same ballpark.

The real winners though are you folks out there who've built your own 10Kwhr systems (or greater?) for 2000 euros or less. Your probably breaking even in 4-5 years. Not having it installed yet I'm guessing a little, but I suspect 8.4Kwhr is probably fine for me, but..... I'm very tempted to kick off my own DIY build next year. Watching the work that DrPhilG did was making me jealous :-) Even a small 1-2Kwhr battery as a project would be fun. Assuming I didn't kill myself in the process. (Only takes 30ma or so to kill you!)

slave1 · 18-08-2021 08:10PM

Complete installation, I sold my battery setup and went straight inverter as payback not there. If I go battery it will be Sofar and large (10kWh+) DIY system like Phil.

just no time at minute, lots of household mini projects going and no spare time

graememk · 18-08-2021 08:34PM

https://www.boards.ie/discussion/comment/117773199#Comment_117773199

Ive worked out the multi quote - you just keep clicking the quote button of the post you want to quote when making a post

https://www.boards.ie/discussion/comment/117771411#Comment_117771411

Yep, The running voltage of it is 51.2 v which is bang on for a 16s pack. 80% of 200ah cells is 8192Wh.

unkel · 18-08-2021 10:28PM

https://www.boards.ie/discussion/comment/117773619#Comment_117773619

Smart move. Making the most of the ridiculously generous subsidy that came with installing a battery. If you went for a battery install and sold the battery, it was cheaper than going with a non battery install. And you get to keep the hybrid inverter, so cheap and easy to add a battery later. Not many people on here believed me when I said (numerous times) that the battery install was free. But that's real life proof of it. Obviously this only works if your installer did not take the piss with the install costs.

unkel · 18-08-2021 10:29PM

https://www.boards.ie/discussion/comment/117773314#Comment_117773314

I switched to Energia EV plan, as soon as it was launched. They let me break my contract (for free) and those prices are fixed for the year. I do realise that soon after they increased those prices.

garo · 19-08-2021 08:42AM

https://www.boards.ie/discussion/comment/117774174#Comment_117774174

You got pretty lucky with the fixed for a year bit. Most other plans are seeing price increases mid-contract.

irishchris · 19-08-2021 09:13AM

https://www.boards.ie/discussion/comment/117774849#Comment_117774849

And several of them at that. Mine has gone up three times in less than 5 months to a combined 39% increase. Definitely worth trying to get fixed contracts if possible

okmqaz42 · 19-08-2021 10:00AM

https://www.boards.ie/discussion/comment/117773356#Comment_117773356

Where you getting .21c per unit. My base rate is .18 and once I add standing charges,pso and vat I’m up to .32c/unit based on about 2000 units in the last full year. Apologies if I’ve missed something in the calculations. But I think if you factor in all the charges the ROI on the battery for the sunny months gets a bit better?

garo · 19-08-2021 11:10AM

https://www.boards.ie/discussion/comment/117775179#Comment_117775179

There are several providers with different plans. My current VAT incl rate is 0.1808 after the latest increase and some others are offering lower rates. You don't want to add PSO and standing charges because you will have to pay those regardless and the battery won't save on any of that.

unkel · 19-08-2021 11:16AM

https://www.boards.ie/discussion/comment/117774849#Comment_117774849

That was nothing. 4 years ago I had a fixed total cost contract (€720 per year) from Just Energy. For unlimited electricity use 😎

They had terrible financial systems. Somehow they didn't take my first direct debit and mid contract I changed banks, immediately updated them with my new details, but they failed to take payment. And then they couldn't take payment over the phone either. A few years later they left the Irish market and I had paid only about half of the above 🤣

KCross · 19-08-2021 11:23AM

https://www.boards.ie/discussion/comment/117774849#Comment_117774849

You can still get a fixed price contract from Energia. The night rate is good but the day rate is poor on that plan now. Might suit some people though who have EV's and Solar PV with batteries.

If you go for a variable plan then you are open to the changing market prices. Nothing new in that.

garo · 19-08-2021 11:28AM

Never realised that fixed rate electricity plans existed until yesterday. Yes I see the Energia EV plan is still fixed rate. Put the numbers in my spreadsheet and I save 60 Eur with the EV plan but then I lose out on the fantastic gas rate I have from BGE in their best dual fuel offer I am currently on.

BGE plans are actually pretty competitive for new customers: https://www.bordgaisenergy.ie/home/our-plans

SD_DRACULA · 19-08-2021 12:43PM

https://www.boards.ie/discussion/comment/117775594#Comment_117775594

Yeah I just switched to their standalone electricity and gas and it's the cheapest that I could find, 15.60c and 4.55c vat included.

bullit_dodger · 19-08-2021 02:05PM

https://www.boards.ie/discussion/comment/117775179#Comment_117775179

Yeah - as garo mentioned when doing return on investment calculations, you need to keep standing charges and additional levies out of the calculations. You pay those if you use 1 unit or 1000 units - but of course different day/night rates across the different providers would change your payback timeframe positively/negatively. Strangely enough, counterintuitively if you are on cheaper rates your payback time increases, as the "value" that you can store in your say 8.4Kwhr battery is diminished.

Airtricity, who I'm with on the whole looks like it one of the more expensive ones, but truth be told I've been lazy. I signed up with them back when I bought the house in 2013 and I've not looked at the market since. Same with my phone. Sometimes I'm an idiot :-)

I don't have an electric car. Does anyone know if that EV plan from Energia requires a car? I would think that it does, but curious. That rate of 4.55c is outstandingly low - and it alone would make me think about switching

SD_DRACULA · 19-08-2021 02:37PM

It's not 4.55 where did yous get that?

That's the EV one, day rate is garbage but topping up battery in winter is worth it I'd say.

I guess if you have smart meter the day/night is out of the picture 😥

bullit_dodger · 19-08-2021 03:30PM

Hmm, I thought someone posted that figure of 4.55 (it did seem exceptionally low), but reading through the thread.....it would seem that it's just me being a plonker! Apologizes for the misinformation folks.

Still, sub 6 cents is a great rate. The pricey "day rate" for people with solar and a largish battery would be offset quite a bit. If you could move your loads to night time and were pretty diligent in doing that, you'd save a few quid I'm sure.

I wish boards wouldn't butcher snippets (above), but for the laugh I plugged in those figures for me. 7.77 year breakeven for battery with those rates.

graememk · 19-08-2021 06:06PM

https://www.boards.ie/discussion/comment/117776575#Comment_117776575

It's gone up since then, that was in April I think it was at 4.something cents.

unkel · 19-08-2021 06:35PM

4.79c incl VAT 😁

garo · 20-08-2021 10:02AM

https://www.boards.ie/discussion/comment/117775912#Comment_117775912

I use more gas so their dual fuel gets me gas for 0.0388. I'm paying 0.1808 for day electricity but worked out it is cheaper with the dual fuel.

garo · 20-08-2021 10:11AM

oye has the CALB batteries for 1811.92 on the end of year sale. Still significantly more expensive than what championc, unkel and Dr. Phil paid but I am tempted. Meh gonna wait a bit longer. Too anchored to the 1400 mark.

https://www.aliexpress.com/item/4001083766967.html?spm=a2g0o.productlist.0.0.58bc67acADXd6H&algo_pvid=be5ee03b-e1df-413d-be50-28a47906118f&algo_exp_id=be5ee03b-e1df-413d-be50-28a47906118f-0&pdp_ext_f=%7B%22sku_id%22%3A%2212000021896084967%22%7D