Cornwall and Batteries....;)

[Cornish Dragon]

Hi Guys,
Just finished a fairly stressful 10 pv systems in 9 working days....
2 of which are mine..... planned in fact for March next year,
many thanks to the Greenest Gov ever...
Now that I won't be getting my next three systems MCS
done, I want to concentrate on developing my 12 volt and
battery back ups capacity .....
Of which I know very little .....
IS there any one near South East Cornwall, Bodmin Moor way
on the Forum. Are able to offer vegetables, general building,
a mini digger,  holidays and even money (£ or euros!) for
any knowledge you have.....
Also has anyone had any experience of the SMA lithium
Battery Packs ?
CU
CD

[Outtasight]

Can`t find any mention of SMA lithium battery systems but do know of a Victron one that is supposed to be available soon (at the usual inflated price).

I`m going to try and convert to LiFePO4 batteries this year as my lead acids are on their last legs.  You can get really massive cells from a distributor in Prague (search for GWL and Winston Battery).

They start at 20Ah and go up to 7000Ah.  You`d need deep pockets though.  But in theory the investment pays as they are good for 5,000 cycles at 70% DoD.

Contrary to BMS sellers claims, you can use these cells without a complex and expensive battery management system provided you use cells big enough and set conservative charging Voltages.  At least that`s what the guy on EVTv claims - he`s built several cars that do not use a BMS to balance the cells.  Just operates the pack in the 20% to 80% charge range to avoid overcharge and overdischarge.  Ideal solar batteries never reach empty or full so this simplifies things.  And this partial charge state is exactly what lead acid batteries hate the most.

The normal low voltage cut-out on a inverter will be too low for lithium cells so I`ll have to use a programmable Low Voltage Disconnect (LVD) on my charge controller to shut the inverter down before the cells are damaged, but other than that, it should work.

You need four 3.2V cells for a nominal 12V system and eight cells for a 24V system.

I`m nowhere near Cornwall but happy to help with info.

What are you planning?

[Jeremy]

The guy on EVtv has it wrong, I'm afraid.  There was a lengthy debate on the ES forum about just how wrong he was and how little he understood about lithium battery chemistry, particularly the red herring of "bottom balancing".  All lithium cells will last longer if charge voltage limited, in fact if you limit the cell voltage to slightly less than that needed for full capacity you can get a significant increase in calendar life (and calendar life is the big issue with lithium chemistries, as they lose capacity with time even if kept at the perfect cell terminal voltage and never cycled).   Even the  best lithium iron phophate cells lose about 5 to 10% capacity per year from age related degradation and this starts from the date of manufacture.  My own big LiFePO4 pack in my electric boat is now three years old, has maybe 200 charge/discharge cycles (with a good battery management system and modest DoD each cycle) and is now at about 85% of it's original capacity.

Cell level charge control is very easy to implement and there are several commercial systems that aren't complex or costly.  Cell level discharge control can also be very simple to do as well, as long as you have a means by which the battery can be disconnected from the load without using a lot of parasitic power when turned on.

For a domestic energy storage system I'm not convinced that lithium chemistry is the way to go (yet).  It's optimised for low weight and volume with high capacity and discharge capability, so good for vehicles, but suffers from a relatively short calendar life and the need for careful cell level monitoring.  As space and weight are less of an issue for an off-grid domestic system, but battery life is probably one of the most important factors, how about looking at NiFe cells?  These easily last for a few decades, with little or no drop in capacity.  They are very robust and need little in the way of cell-level management, just maximum continuous charge current control and occasional topping up.  They are available in large capacities, either new or sometimes second hand from old battery backup systems, and although not cheap they are a very good investment, as they will almost certainly last out the rest of your lifetime.

[biff]

yo! outtasight,
               welcome back.we all missed your intresting posts.
                                                                biff

[Mike McMillan]

My 17 year old single cell varta wet cells are starting to loose their shine,, they came off a yacht and have given me 3 years of excellent service. My experience with AGM batteries on yachts has convinced me that wet cells are still the way to go. I am looking at Rolls or maybe Varta again. Unless someone else can come up with a better solution.

Mike McMillan

Off grid,  IOW

[Cornish Dragon]

Thank you Guys for your posts and advice
Some times I wonder if I live in an strange Cornish
world of my own 
However I did attended a major technical seminar where
SMA was present in Bristol....They gave out brochures
with a these big (black?) cube batteries say 750 mm
cube and a new auto power management controller
and said they sold them in Germany as domestic
power failure systems. Since then I can't find them !

Thanks Outtasight will look into the Victron ones..
And i am looking forward to a visit from Jon /
Other-power at the weekend to see if he can straighten
me out 
CU
CD

[billi]

 You perhaps mean the   SMA Sunny back up systems    and  poor battery

[billi]

CD  , if you would explain your (UPS) idea and your  installed PV a bit more  detailed , we will come up with ideas

[Cornish Dragon]

Hi Billi.........
Thank you for the offer..
I am in the very early stages with this so please just some pointer......
I am fortunate about 1995 I paid (lots then ! even more now!) to have
a single phase but 44kva transformer upgrade  with four separate
meters here on the Estate.
This turns out very useful 16 years later as if the "government"
had not sh@t on me I was going to do four lots of pv 3.5 to 4 kws.
so I would have 4 sets by April next year.
Instead I now have one and that is currently east and under performing
installed before the 12 th Dec deadline. Now with the legal crape
surrounding  the FIT I am installing a second set due South hoping
for an extension till April at full fit rate... !
I want to end up with the ability to run off grid four or more chest
freezers and essential lighting possibly on a continuous basis in the
face of cataclysmic mains grid failure 
Plus it would be good to run one of the swimming pools on a
12volt inline water heater direct without an inverter on the cheapest
panels I can find...   currently running on 90 tubes and oil !
This is an over view so any thought you guys have would be welcome
Thank you

CD

[knighty]

CD... if you have mains power you're better off sticking with that

every cheap batteries etc.. will end up costing you more than the mains power

do all 4 grid connections come in at the same place ?

if they do, at least 2 of them must be on the same phase

so you could have 1 of them changed over to E7 power... and the other as normal...

then use the normal one during the day and the E7 power at night....

you could use a timer to switch between each one automatically... and because they're on the same phase you can join them together before you just before the change over so you always have power / no need to reset clocks etc...


do you want batteries because you have a lot of power cuts ?



for the pool... even with cheap non-msc PV panels you'll get a lot more heat for your money with evacuated tubes !

[billi]

    Knighty     , about 3-4 years ago , i was pretty sure that PV and a heatpump  would outperform  in winter   , anything else delivered from the sun from  solar thermal

Today  i know


The point is , as far as i can see ,is  to get a clever system in place , not like others that just switch on the immersion !

So instead of just dumping into hot water , a battery is needed  as a back up  ore even more to provide electricity to the place at night

Sure Batteries seems od ,

[knighty]

  Knighty     , about 3-4 years ago , i was pretty sure that PV and a heatpump  would outperform  in winter   , anything else delivered from the sun from  solar thermal
Today  i know

maybe for each square meter of roof space.... but does the pv and heat pump still win out on a cost base ?

if a 4kw PV system and a 4kw heat pump set you back £10,000 and give you say 10kw of heat on average ?
(totally guessing the numbers)

for £10,000 you could install 10 lots of 30x58mm tubes... with low temperature pool water I bet they give a lot more than 1kw each ?

[billi]

Knighty

 10 thousand  GBP buys me a 10 kw PV all incl  excl labour   with non  Msc panels ( Ivan  has seconds for 100 GBP for 170-180 Watt modules )   so about 9000 kwh of electricity  per year ....

An additional heat source for the pool is  needed in both heating cases ....

There is an  advantage electricity has over heat  , 

If we play with these 10 kw PV   and  use it for an (half) off grid idea  and ad  3500 GBP  for a 30-40 kwh Battery   etc     ( 6000 Panels , 1200 Charge controller , 3000   for a 5 kw Off grid inverter ) and only cycle the battery by 30-40 %   ,  she should last 15 years

But that is all theory only     and not sure if thats any good for CD .....



Billi

[knighty]

Knighty
10 thousand  GBP buys me a 10 kw PV all incl  excl labour   with non  Msc panels ( Ivan  has seconds for 100 GBP for 170-180 Watt modules )   so about 9000 kwh of electricity  per year ....
An additional heat source for the pool is  needed in both heating cases ....
There is an  advantage electricity has over heat  , 
If we play with these 10 kw PV   and  use it for an (half) off grid idea  and ad  3500 GBP  for a 30-40 kwh Battery   etc     ( 6000 Panels , 1200 Charge controller , 3000   for a 5 kw Off grid inverter ) and only cycle the battery by 30-40 %   ,  she should last 15 years
But that is all theory only     and not sure if thats any good for CD .....
Billi

billi... I understand where you're coming from

but if all the power generated is going into pool heat then I still thinkthe evacuated tubes will win for £/kw heat

[Cornish Dragon]

Thank you guys....
interesting points Billi and knightly both indeed
It boils down to two things.....
NOW getting the lowest fuel bills from the dastardly
energy providers .
FUTURE for me is envisaged as a world without main
power or oil or at best intermittent power and I will
expect  to lay in as much provision as possible.....

The 90 tubes have done a great job when the
sun is out... Has been clicking in and out today 
They have halved the old LPG heating costs and
now a good saving on the oil boiler too

I knew about Ivans panels and with the batteries
I could use these in both the NOW and FUTURE
situations....
may need to talk more with you both.....
Many thanks..

CD
ps just putting in another 3.5kw of PV in the hope
the govoprats loose their court case....