Solar PV battery options

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.

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.

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.

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

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

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

Looks straightforward. Thanks. Must check the pricing.

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.

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

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.

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.

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.

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. :-)

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!