On-grid domestic battery storage

Martyn1981

Latest battery news. Immersun yet to wake up, but monthly stored leccy growing with generation. Note the small warning on data.

Firstly - these data now come with a health warning - February has seen a few outages in the PowerVault data portal, and in exploring that, the tech guys have also noticed some inconsistencies in the data that has been logged to date, so I'm not 100% confident of the numbers in terms of kWh "saved" - they could be too high, or too low, so we'll just have to take it as it is for now.

Anyway - Feb

Imported 210kWh
Generated 83.43kWh (2nd worst Feb since install!!)
Battery discharge - (warning!) - 53kWh
ImmerSUN diversion - 3kWh (in Feb 2016 this was 22kWh - so the greedy battery has stolen all of that!)

So, the Battery has probably saved at least £7 this month in imported electricity avoided, quite a gain over January (if true!).

Either way, gotta love batteries!

shavy65

[QUOTE=Imported 210kWh
Generated 83.43kWh (2nd worst Feb since install!!)
Battery discharge - (warning!) - 53kWh
ImmerSUN diversion - 3kWh (in Feb 2016 this was 22kWh - so the greedy battery has stolen all of that!)[/QUOTE]

Would you happen to know his Import figure for Feb 2016? The comparison between 16`/17` may be of interest.

Cheers.

Martyn1981

shavy65 wrote: »

Would you happen to know his Import figure for Feb 2016? The comparison between 16`/17` may be of interest.

Cheers.

Hiya Shavy. It was 220kWh in Feb 2016, so he said:-

Imported 220kWh. Difficult to compare directly of course - but with less generation (Generated 119kWh in Feb 2016 vs 83kWh this Feb), we imported 10kWh less juice.

Too tight I suppose to draw any conclusions, but appears(?) to be going in the right direction, especially given the big generation difference.

I suspect March will start to show significant differences, and see more action from the Immersun too.

Edit: Actually, perhaps we can draw some conclusions. Assuming the batts had spare capacity, which seems reasonable looking at the months generation, then had the PV generated that 'missing' 36kWh, the batts probably would have caught most of it, leading to a 40kWh reduction, which would have been about a 20% reduction. Gut feeling is that 20% is significant enough to call successful and unlikely to be a normal fluctuation. But I'm showing impatience, Mch onwards will be more clear I'm sure. M.

Alan_Brown

I'm interested in the idea of going off grid during the summer months (June, July, august) by adding a further 3 kw to our existing 4kw of solar and obviously a battery array. I just can't see how you calculate how big the batteries should be for the size of solar you have installed. I saw that Mart mentioned 5kw of storage for his 4kw array and wondered how he arrived at that figure?

Martyn1981

Alan_Brown wrote: »

I'm interested in the idea of going off grid during the summer months (June, July, august) by adding a further 3 kw to our existing 4kw of solar and obviously a battery array. I just can't see how you calculate how big the batteries should be for the size of solar you have installed. I saw that Mart mentioned 5kw of storage for his 4kw array and wondered how he arrived at that figure?

Hello Alan. If you have a look at an earlier post you'll find some of the information:

Martyn1981 wrote: »

Hiya.

But basically, you need to think through your import and available export for the year. I broke mine down into summer, winter and spring/autumn. Then looked for where the limit is.

Summer was import limited.
Winter was export limited.
Spring/Autumn was 'goldilocks' with import covered by export.

So that gave me an economical on-drid battery figure of 4kWh useable.

Lots of important caveats in that last paragraph. That's not off-grid, that's the sensible amount of storage based on the ability to use grid leccy at any time, so simply not rational to build in any additional capacity, due to diminishing returns as you go bigger.

Have a think and a play, and then chat, as those figures for myself, are just a working theory. Also note FFU 6 post #46 which explains how 4kWh of useable storage, can supply 5kWh of leccy across the day (micro cycles of charge and discharge, particularly during cloudy weather).

What do you think?

Martyn1981

Over 50,000 solar storage systems are now installed in Germany

The increase in new installations was mainly due to a 40% drop in prices over the past three years. German solar association Bundesverbands Solarwirtschaft expects their number will double to 100,000 in 2018.

nobby1963

Morning all,
Just noticed an email from EDF this morning....


Sunplug - get smarter with solar storage

Install the latest li-ion home battery for £3,999 (inc VAT) and start saving on your energy bills.

Haven't got time to digest it at the moment but seems to be promoting a new LG battery storage system.

Cheers
Nobby.

Exiled_Tyke

nobby1963 wrote: »

Morning all,
Just noticed an email from EDF this morning....


Sunplug - get smarter with solar storage

Install the latest li-ion home battery for £3,999 (inc VAT) and start saving on your energy bills.

Haven't got time to digest it at the moment but seems to be promoting a new LG battery storage system.

Cheers
Nobby.

The price appears to be for a 3.3Kwh battery (which can discharge at 2.5Kw) together with an inverter (does this make is less efficient than systems which link into the existing inverter Marty?). Unfortunately I cannot find anything else out about the battery itself - crucially expected cycles. Still it looks like a step in the right direction.

Martyn1981

Exiled_Tyke wrote: »

The price appears to be for a 3.3Kwh battery (which can discharge at 2.5Kw) together with an inverter (does this make is less efficient than systems which link into the existing inverter Marty?). Unfortunately I cannot find anything else out about the battery itself - crucially expected cycles. Still it looks like a step in the right direction.

I did try to register an interest (as I'm an EDF customer) but failed to pass the 'can you enter your details correctly' stage, as they didn't like my phone number. I'm 'showing an interest' in most offerings just in case a DNO trial pops up, though I'm not holding my breath as WPD (my DNO) are concentrating on commercial trials. Doh! Just realised I probably shouldn't have left a space ..... but I digress.

Yep, noticed that they replace the inverter. So, here are the issues. To add a battery directly to the PV/inverter, the inverter needs to be battery friendly, some these days are, so folk can plan ahead for a retro-fit.

This is what's known as a DC system, as the inverter directs excess generation directly to the batts from the PV, so no inverter losses. It only changes it from DC to AC when you need it / discharge it.

A battery system that's not linked to the PV, is known as an AC system, as it takes the excess after the inverter has changed it from DC to AC (with losses), then changes it back to DC (losses), and stores it till you need it, then changes it back (losses).

The Tesla PowerWall II DC model is rated at 92% efficient, whereas the DC model is 'only' rated at 89%. [Edit: Tesla are dropping the DC model from their Aussie launch as the market seems more interested in retro-fit, plus the AC model has a built in inverter so makes a nice package, M.]

But an AC system gives you more choice and importantly for early FiTers, means all losses are after the TGM, not before. EG, a 90% efficient DC system that redirects 11kWh, then discharges 10kWh, will 'cost' you 1kWh at the TGM. Not significant for the latest installs, but worth considering for higher FiT rates as you'll be losing about 100kWh for every 1,000kWh that goes through the battery.

The battery is the LG Chem model, and you can find some info in the CleanTechnica list (post #1) or in their comparison they now do, here look for the RESU model.

Here's a shop link, but not a recommendation, just for ideas on prices and spec sheets.

Frustrating to see these prices when Elon's offering Australia batts at $250/kWh ..... before packs, inverters, install etc etc, but still!

Martyn1981

Exiled_Tyke wrote: »

Unfortunately I cannot find anything else out about the battery itself - crucially expected cycles. Still it looks like a step in the right direction.

Forgot to mention this, but I think it needs its own post as this is so important. That battery appears to come with a 6,000 cycle and 10yr warranty.

TBH, I'm making most of this up as I go along, trying to figure out what 'a good battery' is. My gut feeling is that the economics need to improve a lot, but regardless, we'll still need at least 10yrs to have any hope of making the investment viable, so I think 10yrs is a minimum, and 5,000+ cycles even better.

Looking at the CleanTechnica list, the cycles, warranties, life expectancies etc seem to vary not only in length but description too, so hopefully we'll see some sort of standardisation as the years progress.