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PV and battery

Pocster

By Pocster
in Photovoltaics (PV)

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Pocster Advanced Member

Pocster

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Hey all!

 

I know everyone thinks Tesla when they see the title but plenty of other companies are doing this like LG.

Has anyone actually got PV linked to a 'modern' battery system - would be really interested to hear how they are getting on?

 

Cheers

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ProDave Advanced Member

ProDave

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I shall watch this topic very carefully as it's close to my heart.

 

I strongly suspect by the time I have an EPC and the cash to buy solar PV panels, the FIT will no longer exist (it's already at a rate hardly worth paying the "MCS premium" for)

 

In that case I am now thinking of DIY installed non FIT solar PV so that means ensuring near 100% self usage.  So battery storage seems pretty essential.

 

Two things bug me about packaged systems, firstly the battery life, and secondly, the details of how it operates.

 

I am strongly minded to build a DIY system so I can program the algorithm about when and how it decides to charge and discharge the batteries, and have the ability to tweak that to suit our needs. But also, I really want to use some "fit and forget" batteries which keeps pointing towards NiFe (WWII submarine battery technology) but to buy them new they are expensive, something i am hoping will change.
 

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sussexlogs Regular Member

sussexlogs

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1 hour ago, pocster said:

Hey all!

 

I know everyone thinks Tesla when they see the title but plenty of other companies are doing this like LG.

Has anyone actually got PV linked to a 'modern' battery system - would be really interested to hear how they are getting on?

 

Cheers

Im  off grid 24 2v batterys = 1000ah

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readiescards Regular Member

readiescards

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On 18/01/2017 at 10:09, Nickfromwales said:

@readiescards has ventured down this path ;). He's going off grid. 

Maybe some leads / links paul ? :)

 

As @Nickfromwales says yes I'm going off-grid.  I've spent at least 18months investigating this option and asking a zillion questions of many potential suppliers and been to various green energy shows.  In that 18 months things have changed in the battery world. Lots of research money going into batteries so what is best today might be old hat tomorrow, potentially a lot of space and weight. My thoughts on batteries:


* Lithium - the new 2170 Lithium cell from the Tesla gigafactory and Samsung and others I think will reduce Lithium storage costs considerable in the future as they come online.  This is to be in the Tesla Powerwall 2.  Tesla say the Powerwall2 is suitable for off-grid and comes with a 10 year warranty. Only trouble is it needs an extra 'backup' module that they have not yet finished designing (due late Spring 2017).  Lithium has the advantage of a faster rate of charge than lead acid - so when the sun is shinning you get to gather more. Lithium costs more but is supposed to have 3 times the life of lead acid some claim.  Lots of companies entering this market Sonnen from Germany being another.
* Aquion salt water batteries - they told me they expect to release a newer model in next few months. The current one version 2 has a better charge/discharge rate over version 1 (version 1 still for sale in UK though) but still not very good so you need tonnes of them.
* Redflow ZBM - interesting option but not in common use in UK so decided to keep away from 
* NiFe batteries - much longer life than Lead Acid
* Gel sealed for life lead acid - supposedly less life than non-sealed 
* lead acid - Rolls seem the most recommended - might need water monitoring, has a scrap value too

 

I'm ether going for bleeding edge Tesla Powerwall2 or tried and tested lead acid Rolls with a Victron Quattro or Multiplus invertor/charge controller - got to make that decision in next couple of months! I'll have 8.8kWpe and of course a shitty old dirty (to quote @Nickfromwales ) diesel generator, LPG gas cooker & oven and an electric kettle for sunny days only.

 

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ProDave Advanced Member

ProDave

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Have you costed "pence per KWh" at battery renewal time?  I.e how much it costs to replace a complete battery stack, compared to how many KWh of (free solar pv) power it has stored and delivered to you?

 

This is my main sticking point that any battery with a life of less than say 10 years ends up as rather expensive "free" electricity. Which is why I am leaning heavily towards NiFe

 

What sort of costs and how many suppliers did you find for NiFe?
 

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jack Advanced Member

jack

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28 minutes ago, readiescards said:

Only one supplier suggested NiFe so I didn't go further into it. Very happy to hear any knowledge you have of them

 

Lots of research going into these over the last few years, although they're very old tech - think of them as the Edison battery rather than the Tesla Powerwall!  

 

They're best known for copping loads of abuse, happily suffering through deep discharge, being long-lived and cheap to maintain (just top up the water), and having relative benign chemistry.  I think one problem is that they don't have great power density, so there's been no interest in them for powering portable appliances and cars, for example.

 

I looked into this a couple of years ago when I was naive enough to think that offgrid could be made to work in a suburban setting with a wife and kids who can't/won't ever turn off a light in the house!  Very interesting tech, although perhaps the economics of NiMH now makes it a non-starter.

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Jeremy Harris Advanced Member

Jeremy Harris

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I worked with NiFe cells for years, ex-WWII era aircraft starting batteries, from ground start trollies.  Nice to be able to mention them - mention them over on another forum and you get thrown off pretty quickly, as I found!

 

The life of NiFe cells is phenomenal.  I was working with very much abused cells that were, at best, made some time in the 1950's.  They were still going strong in the early 90's, when we stopped using them and hadn't lost any capacity at all in that time, as far as we could tell.

 

The downsides are that they take up a lot of space for a given energy capacity, as their energy density is poor.  They have a relatively wide voltage change (in percentage terms) from fully charged to fully discharged.  They use a strong alkali as the electrolyte, that is not pleasant to handle.

 

The big advantage if that they would undoubtedly last a lifetime, perhaps with one washout after 30 years or so and a refill with fresh electrolyte.  That means that the battery replacement cost can be, to all intents and purposes, removed from the balance sheet, as it's very unlikely that anyone would live long enough for the batteries to reach end-of life.

 

They used to be quite cheap, when Edison were still making them, with the NiFe brand name, but I believe Exide bought the rights and stopped production, most probably because the last thing a battery manufacturer wants to produce are batteries that never need replacing!

 

There are some manufactures in China making them, plus a firm in North America (can't recall whether they are in the Northern US or Canada).  They are relatively easy to DIY, and there are some that have made their own cells and they work as well as the purchased ones.  If anyone has source of the old telephone exchange glass accumulator cases then they form an ideal case for making NiFe cells.

 

As Dave says, the killer with any battery off-grid system is the cell replacement cost.  They all cost more per kWh than mains electricity, with the possible exception of NiFe cells, but they aren't that easy to get hold of.

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ProDave Advanced Member

ProDave

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These are about the only ones I can find for sale. http://www.ebay.co.uk/itm/12V-bank-Nickel-Iron-NiFe-Battery-400ah-10-x-1-2V-cell-/292003393183?var=&hash=item43fcc22e9f:m:m3iaFCECxzgoMsUm4Ksm4bw


 


 

That example is 10 400Ah cells so a total of 4.8KWh of storage. (Not sure what that translates to as actual usable storage) for about £2000  They list several packages of different sizes.  Shame they are the wrong end of the country to me so no easy way to collect and avoid the high transport costs.


 

The rest of the parts to make a DIY system are much cheaper, I would probably make my own charger, buy a couple of cheap Chinese grid tied inverters from ebay and control it all with an arduino.


 

So given you might get say 3KWh of real usable storage, at a total price to build it of no more than £3000, that's £1000 per KWh of storage for a system that should last a lifetime with no battery replacement costs.

 

Is it viable?

 

Well say I could use all 3KWh every day (unlikely but it makes the maths simple) in a year, I would be able to use 1095KWh of otherwise "wasted" solar PV, lets round that down to 1000KWh per year.  Assuming I pay 15p per KWh, that has the potential to save me £150 per year in electricity costs. So that is still going to take 20 years of use, to pay back it's capital costs. So it's marginal to say the least. But at least after it has paid for itself, the batteries would keep on going.


 

What is the typical cost per KWh of storage, for the present commercial packaged offerings?

 

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