Batteries for proper off-griddedness.

[MarkH]

I don't know what the extent of knowledge on here is for this sort of thing (probably deep and wide) but all opinions appreciated as always...

 

We're properly off-grid as far as electricity goes. The quote for connection was well over £20k eight years ago, the nearest juice-poles are half a mile away and coming off the back of a few years living off all of the grids on a sailing boat it made sense for us to remain un-connected - we were familiar with the demands and had got used to a low-consumption boat-based existence. Our current P.V. array is only 1kW but together with a small wind turbine it easily keeps up with our demands living in a caravan. Once we're in the house the array will increase to 4kW and I don't anticipate problems with juice abundance.

 

The fly in the ointment is the battery bank. We currently have a 345ah, 48V bank of flooded, deep-cycle lead-acid batteries made by Crown. Despite regular equalisation and diligent maintenance we've had two fail in two years necessitating a eight hour round trip for a replacement in the first instance and in the second recent case the purchase of a new battery - £170. I'm contemplating replacing the bank with something more robust, reliable and if possible lower maintenance.

 

I've thought about AGM, about lithium and about NiFe... I'm wondering if anyone has any opinions or even better - real world experience - of living with a bank?

 

 

 

 

 

[Nickfromwales]

@readiescards is in a similar 'boat' to you . 

Im not sure how far along he is with his 'offgriddyness' but he'll see the nudge and hopefully update accordingly . 

[ProDave]

This is a topic I will watch carefully.

 

I will be wanting battery storage, because by the time I get any solar PV panels there will either be no FIT or it won't be worth bothering with, so battery storage to ensure near 100% self usage will be essential.

 

What I have seen so far, with the life of batteries and cost of replacing, the "free" stored energy ends up costing not far short of retail prices when you factor in battery replacement.

 

I am leaning towards NiFe for the very long life, and hoping by the time I am needing them, there will be more of a market and the price will have fallen.

[Crofter]

This may not work for the OP, but is it feasible to use an electric vehicle as a battery bank? Obviously you would need a small bank that stayed at the house, but in theory when the car is home, the people are home too. Lots of usage patterns that would prevent this from working (e.g. if you always get home after a long commute with a flat battery in the evening) but equally for some people it may work out. And the battery bank on wheels would be taxpayer subsidised...

[readiescards]

Still 'going' offgrid but not yet made the final leap of faith on the battery decision.

 

The Tesla Powerwall2 looked very interesting but although Tesla are installing the PW2 now they are not fully off-grid ready (i.e. no generator control I think) for a few more months.  

 

I too have been looking at the NiFe (from Bimble Solar - don't know any other suppliers) and it really appeals given what it promises.  I called on the Low Carbon Trust at Brighton who have a NiFe set and they seemed really pleased with their battery bank.

 

Sorry can't offer more than that atm contact me in 6 months!

 

 

[SteamyTea]

49 minutes ago, ProDave said:

I am leaning towards NiFe

I think our Jeremy is the man who knows about these @JSHarris

 

4 kWp of PV is not much, and if self installing should not cost much.  You may find that adding more modules and putting the juice into your DHW is pretty effective and cheap to do.

There was a programme on the radio the other day about Lithium, I think it explained that even though lead was a better material, lithium had the better power density figure, not that it matters a toss for static installations.

I think it was this programme:

http://www.bbc.co.uk/programmes/b08pdzxq

 

When you have spent all our cash on batteries, and you run out of power, you can use the lithium salts to cheer yourselves up

[billt]

I have a project to go off grid (because I can, not because I need to). The initial plan was to use 24 100Ah fork lift batteries as the cheapest option, but a lot more research changed my mind and I decided to use LiFEPO4 batteries instead. They seem to be more expensive per kWh, but in fact the cost in terms of real capacity is similar. When I did my calculations cheap FLA fork lift batteries would have been about £6,600 for a 48V pack with a notional capacity of 48kWh; I choose to use 400Ah LiFePo4 batteries with a cost of about £7,000 for a nominal capacity of 19kWh. In real life, in order get a long life out of the FLA cells you can't discharge them less than 50% which reduces the capacity to about 24kWh. The LiFEPO4 batteries can be run down to 20% without ill effect, which gives a capacity of about 15kWh for my example. Over the expected battery lifetime the costs per kWh were very similar.

 

Having decided that the lifetime costs were similar the LiFEPO4 batteries have overwhelming advantages.

 

They're much lighter and easier to handle, which was an issue for me as the chosen location is difficult to access.

They are much more efficient - charge/discharge efficiency is over 90% FLA is of the order of 80%.

They have low self discharge.

They are low maintenance - no hazardous electrolyte to check and top up, no hydrogen to ventilate.

They have simpler charge requirements, you don't need to do equalisation charges etc. Although some sort of battery monitoring system is essential in order to ensure that they don't get overcharged.

Peukert effect (or equivalent) is virtually non existent. You can discharge at very high rates without significant loss of capacity.

 

I wouldn't consider NiFE. They are very expensive and difficult to get hold of, but mainly they are appallingly inefficient, about 65%.

 

There are a couple of useful discussions https://www.photovoltaikforum.com/speichersysteme-offgrid-f108/nissan-leaf-battery-in-an-sunny-island-setup--t102414.html discusses using Nissan leaf batteries in a Sunny Island system.

 

This enormous thread http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html discusses real life use of LiFEPO4 batteries in off grid situations (boats) and has some useful information about how to ensure a good lifetime, unfortunately there's a lot of dross in there as well.

 

 

[Jeremy Harris]

I've had a set of LiFePO₄ cells in my electric motorcycle for several years now, and am about to swap them out for new cells, as they have lost a fair bit of capacity.  The problem I've found is that all lithium chemistry cells degrade with age to some degree, with the older LiFEPO₄ chemistry cells losing a 2% - 3% percent or more per calendar year of useful capacity.  The majority of cell development investment has been in different lithium chemistries, much of it coming from the Tesla/Panasonic partnership, I believe.  The cycle life of LiFePO4 was claimed to be very good when I bought them, but it is extremely dependent on depth of discharge for each cycle.  Running the cells down to 80% SOC gives around 1000 to 2000 cycles, whereas only running them down to 50% SOC increases this to well over 10,000 cycles, for example.  In practice, ten years is about the maximum usable life of LiFePO₄ I reckon, when combining the loss of capacity from age and the loss of capacity from cycling.  The cells in my motorcycle have managed a bit over 7 years, and are now at around 60% of their original capacity.  I'm not replacing them with LiFePO₄, mainly because of the impact of the additional weight and size, but also because LiCoO₂ cells are now safer than they were and have a longer calendar life, and it seems that calendar life is at least as significant as cycle life in this application.  When managed carefully, with attention paid to maintaining SOC between about 30% and 95% all the time, then the newer LiCoO2 cells have a cycle life that is as good as LiFePO₄, plus they have a calendar life that's around 50% longer.  I've a set of older LiCoO₂ cells in an electric bicycle that are also around 7 years old, and they are still at around 90% capacity (but they haven't been cycled that much, maybe 600 to 800 shallow cycles).

 

NiFe cell efficiency depends very much on the usage pattern, but I used them for around 20 years or so, running high speed cameras.  In practice they managed around 80% to 85% when managed properly, and that was with cells that were manufactured before I was born - they were around 30 years old when we rescued them from some old ground power units.  They were still at full capacity when we stopped using them, and by then they were over 50 years old.  I'm not convinced that round-trip efficiency is that big an issue for home storage, as the losses only really kick in when the cells are given a full charge to 100% SOC.  If charged to 95% SOC the round trip efficiency is as good as lead acid, but charging them in this way does mean using cell-level battery management, as is the case for all lithium chemistry cells, if they are to have a long life.  The main problems with NiFe is the relatively large voltage change between fully charged and fully discharged, which isn't really an issue with modern control systems, and the strong alkali electrolyte, which can be a bit unpleasant to work with.

Edited June 2, 2017 by JSHarris

[billt]

Round trip efficiency might not all that much if you are grid connected and just trying to stop exporting, but it is significant if you are off grid - every joule saved counts.

[Jeremy Harris]

I agree, but it's worth looking carefully at the whole system round trip efficiency in that case, especially a system that is in use 24/7.  In practice, all battery systems have a poorer round trip efficiency than the battery performance would indicate, as a lot of the losses are outside the battery chemistry itself, in inverters, chargers, battery management systems, load dumps etc.  The majority of off-grid systems using renewable sources need a maximum generation capacity that is significantly greater than the average usage capacity, which means that, in practice, there will often be times where generation capability is being dumped or not being used.  The energy waste from such controls may well exceed the battery round trip efficiency loss over a whole year.

 

I'm also sure that a carefully designed cell-level, battery management system would reduce the NiFe cell round trip loss by a lot, as most of it comes from the old practice of just leaving all the cells in a pack on charge in order to balance the battery, allowing the higher terminal voltage cells to just gas off whilst the lower terminal voltage cells catch up.  They tolerate this, in the same way as lead acid cells do, but it's not at all efficient, particularly given the greater cell voltage differential that occurs with NiFe battery packs.  Just using a BMS like that used with lithium chemistry cells, where the charge current bypasses fully charged cells, would give a very significant round-trip efficiency improvement, and I suspect the only reason this hasn't been looked at that closely in the past is because of the history surrounding the commercial use of NiFe cells, and in particular the takeover of the original company by a large lead acid battery manufacturer (Exide) 40 odd years ago. 

 

The big advantage of NiFe cells is that they are a once in a lifetime investment, and to some degree that offsets some of the disadvantages.  The only chemistry that may come close to this sort of very long life are the newer redox flow battery systems, but they haven't been around long enough to really prove themselves.  The underlying chemistry of these should give a life that's comparable to that of NiFe cells, I think.

[readiescards]

I also think lithium batteries will fall in price substantially as the gigafactories come online with the electric car take off. So a cheap FLA solution for a few years before swapping technology might be a good way to go. 

[Jeremy Harris]

Right now, a good quality FLA pack will almost certainly outlast any lithium chemistry cells, IF they are looked after well and are run within a limited range of state of charge (SOC).  Something like a big Rolls pack, or a high quality fork lift pack, run between 95% SOC and 50% SOC will probably last around 15 years, if regularly monitored and watered. At their end-of-life they will probably still deliver around 80% of their usable capacity, but will start to have other problems, like individual cell partial failure, which makes maintenance a pain.

 

Lithium may well improve, but I have a strong suspicion that ion transfer storage has an inherent issue with calendar life.  This probably isn't an issue for vehicles, which is where most of the R&D investment is going, but is for domestic energy storage.  My personal view is that, as domestic energy storage starts to grow, redox flow batteries will get more development.  The potential is there for redox flow batteries to have a calendar life of decades, as, in theory, it's only the electrolyte that should degrade.  Whether this becomes reality depends on whether there is enough of a market for domestic storage.  Companies like Tesla, may well test and develop that market, as a way of reducing the cost of their main product line, vehicle batteries. 

[MarkH]

19 hours ago, JSHarris said:

Right now, a good quality FLA pack...

 

Thanks everyone.

 

That seems to be the bottom line - that for now at least FLA is the way to go. If increased home storage happens - and it seems likely - maybe NiFe or flow batteries or something will become a consideration. It seems the wisest move is to hold off, wait and see.

 

I'm not sure why I've lost two batteries in two years (with a single cell failure each time), maybe Crown batteries are prone to failure (supplier says not) or maybe my setup is lacking somewhere. Buying a new battery at £200+ every year is a nuisance though. 

[Temp]

http://energystorage.cleantechnology-business-review.com/news/renault-and-powervault-team-up-to-turn-ev-batteries-into-home-storage-5832805

 

French automaker Renault has partnered with UK energy storage firm Powervault to reuse batteries from electric vehicles in home energy storage products.The move will see the cost of a lithium battery-based Powervault home storage unit drop by 30 per cent to around £3,000 fully installed, which it says will help bring energy storage to the "tipping point" of mass market rollout  continues..

 

Powervault also announced a 12-month trial of 50 units in homes fitted with solar panels across the UK, to assess the technical performance of the batteries and gauge consumer response to home energy storage. The trial will be a mix of M&S Energy customers, social housing tenants and schools in the South East, Powervault said.

 

According to Renault, the batteries used will be around 10 years old, and will have a further 10 years of additional life in them as part of a Powervault system. Powervault said it expects to sell 30,000 of the Renault units by 2020 - equal to 15,000 car batteries.

 

 

[MarkH]

Just to update this - a few years down the line. My 345ah@48V flooded lead acid bank has done the job for over 5 years now but a very busy recent work period and various other factors have contributed to some shoddy maintenance and FLA doesn't like that. They need tending and every bit of neglect takes it's toll. Anyway - the bank of twelve 115ah FLAs is now a bank of eight battered, prematurely aged sulphated hulks. 

 

I'm probably going with lithium - Pylontech. The price has come down, the warranties are long, they play well with Victron kit and will do what they're supposed to without me having to mess around with sulphuric acid once a month. 

[readiescards]

Nice to re-visit this topic.

In the end I bit the bullet and paid the £24k + other costs to get connected.  In 2017 I just felt the Lithium batteries technology and price point was not in my favour.  Now, end of 2020, I think it would be much more viable to go off grid - though I've not kept abreast of the offgrid technology - as the Lithium battery price has dropped.  Having paid out such a huge amount to connect I won't be going off grid though - I need to use a lot of electric to justify the connection!

 

Oh and when we had the house valued 2018 the surveyor thought not having an electric connection would knock £26k of the value, irrespective of any investment in batteries, as very few people would want a non-mains house

 

Edited November 28, 2020 by readiescards

[Dan F]

5 minutes ago, readiescards said:

Nice to re-visit this topic.

In the end I bit the bullet and paid the £24k + other costs to get connected.  In 2017 I just felt the Lithium batteries technology and price point was not in my favour.  Now, end of 2020, I think it would be much more viable to go off grid - though I've not kept abreast of the offgrid technology - as the Lithium battery price has dropped.  Having paid out such a huge amount to connect I won't be going off grid though - I need to use a lot of electric to justify the connection!

 

What would you do in winter? Run a generator? wind turbine? 

[readiescards]

I was running a second hand diesel generator alongside my 8.8kV PV setup, the original plan being that generator would kick in to charge the battery bank after a few days of dullness.

 

My (2017) research into wind turbines suggested they needed to be high/large to be effective and a potential large consumer level wind turbine would need to be taken down if the winds got extreme!

[Nickfromwales]

5 hours ago, readiescards said:

 

I was running a second hand diesel generator alongside my 8.8kV PV setup, the original plan being that generator would kick in to charge the battery bank after a few days of dullness.

 

And for the generator to have a wet cooling system, so that it could be connected to a 2-3000L buffer tank to store ‘waste’ heat from the generator and use it for DHW uplift / space heating direct feed for preheat etc. 
Off grid means waste nothing. 

[Gone West]

7 hours ago, Nickfromwales said:

And for the generator to have a wet cooling system, so that it could be connected to a 2-3000L buffer tank to store ‘waste’ heat from the generator

Thought that was called a CHP system.

[SteamyTea]

6 minutes ago, PeterStarck said:

Thought that was called a CHP system.

Yes, and the efficiency would be a lot better.

Don't know if you can get still get them easily, and then convert them to some flavour of 'bottled' gas.

They do have limited electrical power output, usually around a kW.  So are of limited use in reality.

 

[Gone West]

It appears this lot do a 5.5kWe.

[Crofter]

LiFePO4 does seem to be getting tantalisingly cheap now.

I need to install a large battery bank in my boat, the conventional route would be 4x225Ah 6v FLA, which would cost £600+. The actual useable capacity (50-85% SOC) would be about £3.80/Ah.

If you buy from the likes of AliExpress/Alibaba, you can now get 4x280Ah lithium cells for about £340 delivered. Assuming 80% useable capacity, that's just £1.50/Ah.

Of course it's all the associated parts of the system that make the cost mount up. And it's a real steep learning curve trying to work out where to place the smart parts of the system. but I do wonder if a lot of the perceived wisdom about lithium systems derives from the days when the cells were hideously expensive, and it made sense to invest in shiny blue boxes to keep them safe.With the actual cells becoming so cheap, I wonder if we can afford to take a different approach these days.

[SteamyTea]

20 minutes ago, Crofter said:

LiFePO4

How well do they cope if they get in contact with seawater?

I seem to remember that lithium, sodium and chlorine can quickly become a mess, but then I am not a chemist.

[DamonHD]

3 hours ago, Crofter said:

LiFePO4 does seem to be getting tantalisingly cheap now.

I need to install a large battery bank in my boat, the conventional route would be 4x225Ah 6v FLA, which would cost £600+. The actual useable capacity (50-85% SOC) would be about £3.80/Ah.

If you buy from the likes of AliExpress/Alibaba, you can now get 4x280Ah lithium cells for about £340 delivered. Assuming 80% useable capacity, that's just £1.50/Ah.

Of course it's all the associated parts of the system that make the cost mount up. And it's a real steep learning curve trying to work out where to place the smart parts of the system. but I do wonder if a lot of the perceived wisdom about lithium systems derives from the days when the cells were hideously expensive, and it made sense to invest in shiny blue boxes to keep them safe.With the actual cells becoming so cheap, I wonder if we can afford to take a different approach these days.

 

Come and have a read over at fieldlines.com where people do indeed play a little fast and loose, but without generally setting fire to anything.

 

However, you aren't going to want to build an inter-seasonal store out of Li batteries to carry energy into the winter when you're cold because there's less solar insolation...

 

I priced up an (optimistic, no-space-heat, Vanadium redox) interseasonal battery for my house which is quite low use, and it was something like £250k and sould have needed a basement dug for it.  Note that we generate enough from PV to cover all our electricity (and space-heat with heat pump) use over a year, ie we're already net zero on that.

 

Rgds

 

Damon