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Nersa approves 9.4% electricity price hike


viper_za

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Based on prices on sustainable website (Which is not the cheapest) the Willard 2V batteries cost as follows:

RT11: 337AH,2V@2,400 Cycles at 50% DOD = R3.12/KW

RT25: 808AH,2V@2,400 Cycles at 50% DOD = R2.42/KW

I have seen places advertising it at 15% cheaper.

At 15% cheaper it will almost be in line with the IND23 on cost per KW. The nice thing however is that it Cycle life is a bit lower (Still high) which reduces the initial capital that you need to put on the table.

 

 

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You are right Louw ... kyk ne, daar is nie 'n MANIER wat ek sulke gelde ooit sal uitle vir batterye nie. 

Load verus wants - I will want tablets instead of Pc's. :D

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Here goes my 2 cents

Iv been looking at a 24v bank of the Torjan T105RE. 4 batteries at R9 984.80

My calculations go as follows: 225ah X 24v X 50% x 1750 cycles. = 4725KwH From the bank. Devided by the R9 940.80 Is R2.10/ KwH.

But here is the difference, I currently use 2.7KwH from Eskom and 1.4 Kwh direct from the panels. That makes my cost of power R1.38/Kwh. Now I'm working it this way because i have already paid for my setup, and it was never intended to make me money, but more of a hobby. I'm currently paying R1.87/KwH before the increase. 

By this calculation, I'll be making money, and I;m happy. Anyone see any flaws in my calculations.

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Yes, I have that graph also, my supplier said nope, recommends 1600 cycles.

I have a feeling it is more like 3672kWh, using 1600 and then subtracting losses for a average of entire system operating is only +-85%.

That is panels, wires, MPPT, switching from DC to AC and inverter itself ... nothing runs 100% efficiently.

Average rule of thumb :
Solar panels 81% efficient
Charge Contollers 95% efficient
Lead Acid Batts 80% efficient

I never liked solar calcs, until my system taught me that what you see, ain't what you gonna get, for as you, buildt my system for fun, till it became.
 

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2 things that I have always wondered about when it comes to batteries:

 

Question 1:

Has anyone ever used their batteries till they are dead due to use, not misuse?

It will be interesting to see actual cycle performance vs indication from manufacturer.

Question 2:

How much capacity does a battery have left after it has done all its cycles according to the spec sheet? I.e. Once the T105RE has done its 1600 cycles at 50%, does it still have 50%/80% capacity left?. And is it the same for all makes of batteries?

 

 

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Louw, good questions. I know the guys with the forklifts, take them to morsdood. There are though some batts that can still be used for a while, sometimes, for you need to swap the entire bank.

I would like to believe that if you keep the load proper, keep an average of say 30-40%, sometimes below 50%, you should get maybe 10-15 years if you care for the batts.

The guys off-grid get that.

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The reason for using 50% in my calculations, is that this is where you get the best bang for buck. If you go down to 80% DoD, the number of cycles drop significantly, but if you only go down to 30% DoD the number of cycles does not increase by the same amount. If you just work out the cost per Kwh, you actually get the lowest number around 50%. So it is a bit of a balancing game, if you cycle your batteries only lightly, it actually costs more per kwh over the lifetime of the battery. The same goes for cycling them too deeply.

I think one thing is for sure though: Most of us are so careful with our batteries that we probably don't cycle them deep enough to get the calculated "low" cost per kwh. We probably should look at the 30% cycle life calculation before we declare that lead acids are winning.

So where does that put us, 2018? I can't wait... :-)

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Ja, after reading here and elsewhere re. not USING the batteries, I have made a change and started to do that. 

Fri and Sat evenings more than other evenings.

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7 minutes ago, plonkster said:

The reason for using 50% in my calculations, is that this is where you get the best bang for buck. If you go down to 80% DoD, the number of cycles drop significantly, but if you only go down to 30% DoD the number of cycles does not increase by the same amount. If you just work out the cost per Kwh, you actually get the lowest number around 50%. So it is a bit of a balancing game, if you cycle your batteries only lightly, it actually costs more per kwh over the lifetime of the battery. The same goes for cycling them too deeply.

I think one thing is for sure though: Most of us are so careful with our batteries that we probably don't cycle them deep enough to get the calculated "low" cost per kwh. We probably should look at the 30% cycle life calculation before we declare that lead acids are winning.

So where does that put us, 2018? I can't wait... :-)

Am I doing my calculations wrong then?

Lets work on round number for batts 20k

30% DOD

225ah x 48v x 70%  x 2600cycles = 19 656Kwh = R1.01

50% DOD

225ah x 48 x 50% x 1600cycles = 8640Kwh =  R2.31

 

 

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18 minutes ago, viper_za said:

Am I doing my calculations wrong then?

Lets work on round number for batts 20k

30% DOD

225ah x 48v x 70%  x 2600cycles = 19 656Kwh = R1.01

30% DoD means you only get to use the top 30%.

225ah * 48V * 0.3 * 2600 = 8424Kwh => R2.36.

Same numbers at 50%:

225ah * 48V * 0.5 * 1600 = 8640Kwh => R2.30.

Same at 70%:

225ah * 48V * 0.7 * 1200 = 9072Kwh => R2.19.

In this case it actually improves the harder you work them, but for most batteries there is a drop-off point where you kill them too fast :-)

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15 minutes ago, The Terrible Triplett said:

20% DOD is the best level for most batteries.

Trojans claim 4000 cycles are 20% DOD ... +-10 years.

225ah * 48V * 0.2 * 4000 = 8640Kwh => R2.30.

That's actually on par with the 50% cost. Seems it's pretty linear for this particular battery. Okay guys, I stand corrected then. It seems that the variation in cost isn't that extreme.

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6 minutes ago, plonkster said:

225ah * 48V * 0.2 * 4000 = 8640Kwh => R2.30.

That's actually on par with the 50% cost. Seems it's pretty linear for this particular battery. Okay guys, I stand corrected then. It seems that the variation in cost isn't that extreme.

So I can do what I want with these just depends on how long I want to keep them ;)

 

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Keep them watered, check the levels, swap them around every few months, keep them charged only run them down to 100% DOD if you have no choice, only if you have to.

Or so I am told.

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I KNOW some will disagree with me, but no matter. 

My Trojans water is crystal clear. 6 months later, I noticed the cells where the pos and neg connections are made, turn murky sometimes. Perfectly normal, from supplier and verified by Torjan.

They said, I quote:
The brownish coloration in the electrolyte does not necessarily indicate that there is something wrong with the battery. The brown color comes from minute particles of the positive plate active material has washed off the plates and has collected in the electrolyte. This is very noticeable when the battery has gassed during charge. If the battery was allowed to sit for a period of time with no agitation, then the particles would fall to the bottom and the electrolyte would clear up.

 

But then I started asking, why not the rest, seeing the current is the same everywhere? No one answered sensibly.

So every 3-6 months, I reshuffle the batts, insides ones outside and turn around top to bottom so that in the end all the poles will have been connected to pos and neg of inverter and controllers.

Same time I do some maintenance en al daai goeters i.e check that all is still tight, water levels IF THE BATTS ARE FULL etc etc etc. julle ken mos al daai goeters.

But in case someone does not know yet, see attached.

Any case, I swap them around, to be fair to all poles.

Trojan_Battery Maintenance.pdf

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On 3/9/2016 at 2:38 PM, plonkster said:

The reason for using 50% in my calculations, is that this is where you get the best bang for buck. If you go down to 80% DoD, the number of cycles drop significantly, but if you only go down to 30% DoD the number of cycles does not increase by the same amount. If you just work out the cost per Kwh, you actually get the lowest number around 50%. So it is a bit of a balancing game, if you cycle your batteries only lightly, it actually costs more per kwh over the lifetime of the battery. The same goes for cycling them too deeply.

I think one thing is for sure though: Most of us are so careful with our batteries that we probably don't cycle them deep enough to get the calculated "low" cost per kwh. We probably should look at the 30% cycle life calculation before we declare that lead acids are winning.

So where does that put us, 2018? I can't wait... :-)

The problem is that you'll hardly ever run your batteries at the sweet spot. 

Let's use the figures from your next quote:

 

Quote

30% DoD means you only get to use the top 30%.

225ah * 48V * 0.3 * 2600 = 8424Kwh => R2.36.

Same numbers at 50%:

225ah * 48V * 0.5 * 1600 = 8640Kwh => R2.30.

Same at 70%:

225ah * 48V * 0.7 * 1200 = 9072Kwh => R2.19

Let's say you need to run the batteries for 19 hours (5 hours day light), with the figures above you can:

  1. run 443.37w/hour load
  2. run 454.74w/hr
  3. run 477.48w/hr

 

That's quite a fine balance to keep, in order to stick to the 50% DOD or 70% if you want to. At this exact moment, my inverter reports 2.62Kw - we're watching TV and I'm making coffee. 10 minutes later and it will drop to 620W (assuming the kettle is 100% efficient, it'e 11years old). Later on, when we switch off the TV and lights it will drop to about 300W-250W

There's no historical data so I can't see if it stays stable @ say 250W during the night but I have a suspicion it may drop a little bit since the ambient air around the fridge and freezer drops and they use a little less power as well. I want to take a wild guess that the LED flood lights also use a little less (perhaps 1W?) power when it's cooler around them?

My battery bank is 244Ah but I have no idea how many cycles the batteries can give since I can't get a datasheet on the internet, and thus I don't know what I'm paying / saving per KW. 

 

The point I'm trying to make though is that although it's nice to calculate these figures on paper, it's quite difficult in reality to stick to it. 

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I agree.

Want to add that what is not calculated here often, are losses, temp and age of the batteries. Without those figures, the straight forward calcs look optimistic. Trust me, it bites you in the end for at the end of the day, the maths do work out if all factors are taken into consideration. You can be safe'ish.

By adding a monitoring system you are forewarned of earlier than expected battery failure due to overuse and that goes back to what I have said here a few times: Keeping need versus wants in mind, what is the load you want powered, and for how long? It impacts 100% on the batteries in the end.

Solar is all about balance. Looking at 300w estimate versus actual watts used can be quite a SURPRISE(!!!) in the end. Somewhere someone said they have a +-250w Pc to monitor the system ... not the best way to do it in my opinion. It cost +-R4500pa to run it off Eskom 24 hours a day ... and a truck load MORE expensive if on batteries.

Get a BMV 702 monitor. With any software you do get, you will need it. At least you can immediately get an idea what is going on with the batteries, whilst looking for software.

So, my 2 cents, batteries and their water levels / SOC / cell volts / cells gravity are the only things in the entire system you really need to watch with a hawks eye because the panels work or they don't, the inverter works or trips but batteries , they are silently lurking spare retirement fund killers, if not coaxed out into the open. :D

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