Economics of power walls

Hi,

Just to introduce my initial perspective:

I have been contemplating a battery setup for an existing grid tied system for quite some time now. Looking about for what would be the most cost effective energy storage. I have looked at off the shelf LiFePO4 batteries with their own BMS. Obviously insanelyover priced. However 18650s do not seem to stack particularlywell against large lead acid batteries, if you look just purely at price per watt hour.

However taking into considerations Lithium batteries are more suited to greater depth of discharge then things get a little interesting. Most lead acid batteries should really not be discharged below 50% depth of discharge. However taking into account how often you would require that depth of discharge, say just every now and again, when there are a few cloudy days in a row. Does Lithium really still work out cheaper, given that Lithium batteries do actually have a fairly definite number of charge cycles.

I work in IT, and I see a lot of dead laptop batteries (obviously I have been keeping an salvaging the good cells. A lot of these batteries are less than 3 years old.

Ok, so the questions:

Should I use new cells, or is it worth the effort of assembling packs of used cells? (Both labor and safety spring to mind here)

Secondly how many charge cycles are you getting out of your packs?

Hopefully this will help me answer my questions about weather to go lithium or lead acid.

I did further add a poll for those who wish to vote.

It's a great question to ask.
Do you have $ amounts to sharefor comparison?

I was fortunate to pick up my LiFe prismatics rediculously cheap, probably couldn't afford them at cost.
But I will say they are AWESOME!

Have you looked at large prismatic LiFe cells? But then you have to factor in a bms system.

Good topic

Your question is like "How long is a string"

It all depends on where you live and for what price you get the battereies and how expensive are the grid electrics. In my area batteries are hardly worth it as of yet. Its like 15+ years unless you get them cheap and you do do the job yourself.

But I use LiFe mostly but have also laptop cells. All based on the total cost per kWh in the end.

Cycles depend on type of cell and type of use. All from 50 to 10 000 cycles. Cycles depend on for instance the DOD you use. If you go between 80 and 60% on life you can get 10 000 cycles easy before they degraded to much meanwhile perhaps 80% DOD you get 2500 cycles...

And in the end will you go to 80% left or 60% left or even less in terms of total capaciy untill you say they are used and need to be switched out?

Wattsup said:

It's a great question to ask.
Do you have $ amounts to sharefor comparison?

I was fortunate to pick up my LiFe prismatics rediculously cheap, probably couldn't afford them at cost.
But I will say they are AWESOME!

Have you looked at large prismatic LiFe cells? But then you have to factor in a bms system.

Good topic

Click to expand...

Well I get my Lead Acid batteries from a wholesaler. So I can get them much cheaper than most. I also don't pay freight (big expense for heavy batteries). So for me they do work out cheaper.

That said I am accumulating a reasonable quantity of 'dead' laptop batteries. I have the equipment to test and charge them. I am considering building a small power wall for lights and small draw appliances (phone chargers, fans etc.) This should make a good pilot project.

It becomes a complex equation, evaluating charge cycles, capacity, and cost. Especially given the enormous difference in battery capacity. I have good reason to believe that I would get a decent life out of VRLA lead acid batteries, even with the occasional 50% depth of discharge. That said, apparently not fully charging Lithium batteriescan multiply their life by a factor of 10.http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

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daromer said:

Your question is like "How long is a string"

It all depends on where you live and for what price you get the battereies and how expensive are the grid electrics. In my area batteries are hardly worth it as of yet. Its like 15+ years unless you get them cheap and you do do the job yourself.

But I use LiFe mostly but have also laptop cells. All based on the total cost per kWh in the end.

Cycles depend on type of cell and type of use. All from 50 to 10 000 cycles. Cycles depend on for instance the DOD you use. If you go between 80 and 60% on life you can get 10 000 cycles easy before they degraded to much meanwhile perhaps 80% DOD you get 2500 cycles...

And in the end will you go to 80% left or 60% left or even less in terms of total capaciy untill you say they are used and need to be switched out?

Click to expand...

Something that does interest me, is running Lithium batteries, it is easy to replace just a couple of cells. Unlike lead acid, it is easy to measure an exact cell capacity. So much like harvesting laptop batteries, DIYpower walls that are no longer performing could be dismantled and cells checked and harvested.

used 18650s by the pound are cheaper than lead acid.
figure usable power in price per kw.
li-co you ger 100% usable
life you get 80% usable
lead acid you get 50% usable

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Korishan said:

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Click to expand...

You indeed are correct. If you read my previous post. Not only is lithium predictable but salvageable too.

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Geek said:

Korishan said:

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Click to expand...

You indeed are correct. If you read my previous post. Not only is lithium predictable but salvageable too.

Click to expand...

I do not want to be labeled as a nay sayer. For want of better words. I understand batteries and chemistry. To be straight up bms needs to be used on lead acid as much as lithium. I shall be sending som pm to some of the more experienced users of lithium batteries for my piolet project.

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Geek said:

Korishan said:

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Click to expand...

You indeed are correct. If you read my previous post. Not only is lithium predictable but salvageable too.

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Geek said:

Korishan said:

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Click to expand...

You indeed are correct. If you read my previous post. Not only is lithium predictable but salvageable too.

Click to expand...

I do not want to be labeled as a nay sayer. For want of better words. I understand batteries and chemistry. To be straight up bms needs to be used on lead acid as much as lithium. I shall be sending som pm to some of the more experienced users of lithium batteries for my piolet project.

Click to expand...

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I need the time to salvage and test the cells I have. I currently have 20kg of laptop batteries

Korishan said:

another thing to consider is that lithium is far easier to upgrade than lead acid. If you want to add capacity, you can add any size pack in parallel to an existing unit and you're good to go. With LA, it's a little harder due to weight and bulkiness.

Click to expand...

The pioint you make is very valid. Assuming understanding of the bettery technology, battery management and a sound understanding of electronics. I was expecting this thread to spark (pun intended) some debate. I don't mean to be a fly in the ointment so to speak. I have many things to learn before I assemble even the smallest battery bank (power wall) I shall be acquiring some cheap ebay balance setups to suit my needs. I have done alot of research (ie read and searched these forums) and found this most inspiring.