Jump to content


Popular Content

Showing content with the highest reputation on 24/01/2018 in all areas

  1. 6 points
    Chris Hobson

    Lithium batteries

    I have been asked to start a lithium batteries thread. Unlike lead acid my lithium experience is limited to the last month which hardly qualifies me as someone to start something like this. I however do like information catalogued so that I can refer back to it easily so on that basis I plough ahead and hope this thread develops into a resource with many contributors. I will use lead acid batteries (LA) as a reference point and assume that folk are familiar with them. What is Lithium? It is the 3rd lightest element and those of you who were the chemistry teacher nemesis at school will know it is highly reactive in both water and air and is usually stored in a hydrocarbon solvent. It readily sheds its 3rd electron and therefore its highly reactive nature. Lithium ion batteries are all similar in that their cathodes have a matrix of some lithium containing compounds and the lithium ion since it is so small moves in and out of this matrix allowing charge and discharge of the cell. There are numerous flavours of lithium ion but I think in the solar industry lithium iron phosphate (LiFePO4) has the biggest potential. Lithium iron phosphate (often called lithium ferrous phosphate to prevent the lithium ion/lithium iron confusion) is more stable and therefore safer than the other lithium ion batteries, has a greater cycle life and greater heat tolerance. Since it is charged to 3.65V rather than the more common 4.2V it has a lower specific energy not a huge problem with our stationary modules. Thermal runaway with LiFePO4 only happens >250°C whereas other lithium ion variants this temperature is a lot lower. There is a LA versus Lithium debate and this post is not about continuing the debate but to understand the beast one must make comparison to what is familiar. LiFePO4 batteries are like an AGM or Gel battery in that they are not vented – there is no giving off of gas. LiFePo4 batteries have a high charge and discharge rate and do not require a long tapered absorb and float phase. The sudden drop in charging from 30A to <2A is a clear indicator that the batteries are fully charged. My batteries in fact discharge slightly to balance the cells. Like LA batteries in theory LiFePO4 batteries should last forever but in our imperfect world LiFePO4 suffer from a process akin to sulphation. The electrolyte of LiFePO4 batteries contains LiFePO4 dissolved in an organic solvent. This precipitates out as a Li2CO3 layer on the cathode, reducing the availability of the active LiFePO4. This process is irreversible and speed up at elevated temperatures (>50°C). There is a fair amount of R&D to slow down this process. Unlike sulphation this is a process triggered by charging and LiFePO4 do not suffer from storage partially discharged like LAs do from sulphation. LiFePO4 batteries achieve nearly all their charging at about 3.3V/cell and the jump in SOC is from roughly 30% at 3.2V/cell to 90% and over at 3.3V. Since LiFePO4 batteries do not suffer from sulphation and overcharging has a negative influence on battery life some manufacturers cheat and do not fully charge the batteries thereby extending battery life for a small loss of capacity, a sensible trade off in my opinion. The biggest advantage to me besides the longevity of LiFePO4 batteries is the ability to “grow” your battery bank as the need arises. With LAs there is a problem with combining batteries of differing ages into a single bank. With LiFePO4 due to the Battery Management System (BMS) modules of differing vintages can successfully accommodated within a single battery bank. Thus one can grow one’s bank as the need arises or finances allow. I hope @plonkster, @Coulomb, @weber, @PurePower and others will add to this and correct any errors in my post making it a useful resource.
  2. 2 points

    Desalination Plant

    Off I go to Emirates airlines cargo tomorrow to pick up the unit at 145kg's of it. I am not on here often so to answer a few questions / remarks i have seen......@ebrsa - I have a tank that brine waste goes to and that then returns to the sea when full, but besides that i also have a borehole and the waste from that can go free of charge to the builders for cement mixing. I will post some pics when all in place. It will have from the borehole two x primary FRP pressure vessels with auto backwash, then to 4500lt holding tanks, from there it enters the desalinator thru that and its 7 stage RO system & UV, where the pure water goes to a 2200lt holding pressure pump tank to my home and a tap on the pavement for surplus for neighbors. the salt water holding tank and fresh water holding tanks supplying the desal unit will be controlled by electronic soloid valves, so i can switch at any point. I might be able to add the big blue 5 stage filter on the borehole line if the test results are ok from the lab and thereby bypass the desal on that line..... more to come. Got my first order of 44 of these units on the weekend.....
  3. 1 point

    Current Water Affairs.

    No no no... they didn't call him wrong. They called him racist. I've long found that a little amusing... I mean, for engineering personalities like my own, you kinda sorta care about being right about the facts, and then you worry about how to say it without being insensitive. These guys could care less about the wounded man lying next to the road to Jericho, they are upset that the Priest said something bad about Samaria. Yes, I worry about that too. I hope it won't come to that.
  4. 1 point

    Current Water Affairs.

    The idiots in central government must start doing their jobs. If not, when this mess reaches crisis point, only replacing rubber bullets with sharp points will bring some semblance of law and order. I have lived long enough to remember the times when it came to that. And still those who slavishly follow the utterances of the braindamaged media thinks Pres. Trump has it wrong when he allegedly called African and other countries s**thole countries. Personally I would say, if he did actually said that, he sure hit the nail on the head. Or are folk still to brainwashed to understand the potential tsunami we are approaching with every passing day. So I think @Mike has it right with the steps he is taking. Solutions to the water scarcity problem is the only issue we in the Western Cape should collectively focus on, including the 60% in CoCT who are selfishly and stupidly not reducing their consumption.
  5. 1 point

    Wind Turbines

    I want to divert from water a bit (sorry @TTT ) so here goes... @Mike - how is the WIND turbine doing - in use or just there for show(off) purposes...
  6. 0 points

    Current Water Affairs.

    a lot of chickens running around without heads.... your local members of whatever political party just want points. if we the people have to sit around and wait .....then you have already lost the battle. the water issue started before the Eskom debacle, i was told by a client 7 years ago to be prepared for this event......sad thing is he worked for Dept Water & sanitation....