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Hi, my name is... and... How much Rand per W of electricity?


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Jacques and I live and work in Waterfall, KZN.

I've done a few Mecer + lead acid load shedding DB installations and now taking a big step towards solar and larger inverters and its scary and exciting and I'm thrilled to introduce myself and HELLO EVERYBODY!¬†ūüĎč

So I was wondering about using batteries as a way to not only have a storage of energy but as a way to offset electricity cost.
Currently I am paying R2.0866 per kW of hourly usage or converted R0.002c per watt of electricity used in an hour.

An AM-2 Hubble Lithium Ion battery sells for R26 000 @ 3000 cycles used at 100% DoD.

Consider the calculations below:

5.5kW = 5500W
5500W * 3000 cycles = 16 500 000 watts per full lifetime of one battery.
R26 000 / 16 500 000 = R0.00157 cents per watt. That is 24.5% cheaper than Ethekwini's tarrif. At 6000 cycles (50% DoD,) we have twice the amount of cycles, therefore twice the amount of savings. Almost 50% cheaper!!

We know that tarrifs  have been on the rise. Unless municipalities pull thumb or already pulling thumb and considering sourcing electricity independent of Eskom we can have hope. Another source of hope is that individual sources of power production have passed legislation to self-generate from 1MW to 100MW and I remember recently reading in an ethekwini newspaper that bi-directional meters are being highlighted to being rolled out where you can sell power back to the grid.

We really can save the earth by taking these small steps away from coal/fossil fuel burning to harvesting natural sunlight energy.

Edited by jacquesretief
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On average, every day I use 15kW of power. That's R936 per month.

If I were somehow able to keep a 5kW battery fully charged, I would be able to deplete it 3 times a day and cover my full electricity use per day.

That means, I would use 3 cycles per day. This is an easy one: This means that I would have a 1000 day battery.

Just under 3 years of lifetime use.

Instead of paying the municipality I could buy a new battery every 27 months (R936 electricity bill * 27 months). Which means that I save R5000 a year, which I could put that towards more batteries to get to that maximum cycle life of 6000.

I'm loving this¬†ūüėć

Edited by jacquesretief
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You are not considering the power you save during the day generated by you solar panels. You would have to add that in to your calculation.

In my case, since I've installed my system, 2 X 5 KVA growatt inverters + 12 X 410 W panels  + 1 5,1 Kw/H LI battery I've been saving an average of +_ R800 / month.

Ok I've to consider we are in summer, I presume in the winter months , June, July and August  I may not be able to save as much.

And the main factor, no more darkness during load shedding.

 

Edited by Antonio de Sa
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You will not be able to charge your battery 3 times a day.

In my case so far with good planning my battery is usually fully charged by about 11:00,  I've been able to use my 3 KW geyser from about 10 in the morning by about 12 the water is hot and enough for 3 people to shower, in the evening the wife does all the cooking using an electric stove and the battery usually last until +_ 10  keeping at 20% DOD 

See my consumption/ power generated in the last 30 Days.

432 KW/ H generated by my PV and 142 KW/H grid power. 

image.thumb.png.4ba055b7ff0aaae0ce1e8f49df1835d5.png

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A few corrections.  Not to nitpick but some of your terminology and calculations will confuse some.   Remember that  kWh is a measure of energy, whilst kW is a measure of power.  If you have a geyser that has a power rating of 2kW that you run for 3 hours, you will have consumed 6kWh of energy.

 

4 hours ago, jacquesretief said:

Currently I am paying R2.0866 per kW or converted 2c per watt of electricity used.

Clearly you mean kWh, not kW.  But, it would be 0.2c per Wh, not 2.

 

4 hours ago, jacquesretief said:

At 6000 cycles (above 50% DoD,) we have twice the amount of cycles, therefore twice the amount of savings. Almost 50% cheaper!!

Actually, 6000 cycles at 50% DOD will yield exactly the same energy as 3000 at 100% DOD.

 

3 hours ago, jacquesretief said:

If I were somehow able to keep a 5kW battery fully charged, I would be able to deplete it 3 times a day and cover my full electricity use per day.

That means, I would use 3 cycles per day. This is an easy one: This means that I would have a 1000 day battery.

There is normally no good reason to cycle your battery several times in one day - once it is full you will simply use your input power (grid or PV) to power your loads, keeping the battery full.  Discharging the batteries whilst you PV exceeds your loads makes no sense at all.

 

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2 hours ago, Calvin said:

A few corrections.  Not to nitpick but some of your terminology and calculations will confuse some.   Remember that  kWh is a measure of energy, whilst kW is a measure of power.  If you have a geyser that has a power rating of 2kW that you run for 3 hours, you will have consumed 6kWh of energy.

 

Clearly you mean kWh, not kW.  But, it would be 0.2c per Wh, not 2.

 

Actually, 6000 cycles at 50% DOD will yield exactly the same energy as 3000 at 100% DOD.

 

There is normally no good reason to cycle your battery several times in one day - once it is full you will simply use your input power (grid or PV) to power your loads, keeping the battery full.  Discharging the batteries whilst you PV exceeds your loads makes no sense at all.

 

Thank you for the feedback, I have made the critical corrections. I realized this mistake of '2c' instead of 0.2c whilst talking to my neighbour about the same thing.

Why will 6000 cycles at 50% Dod yield exactly the same energy at 3000 @ 100%?

Maybe I have my concepts confused and my understandings are incomplete: is one cycle of energy the maximum capacity of the battery fully once depleted?
Is 50% DoD of the rated battery capacity depleted half of a cycle? If I used 2.5kW of power in an hour of a brand new battery, I would have used 5999.5 cycles?
However, if I continued to use the brand new battery to 0%, I would have used one cycle, leaving it with 5998 cycles remaining?

Please note everyone that I do not have panels nor inverters nor batteries and is purely hypothetical and one needs to approach this thread abstractly, not practical. However the calculations and formula proving that lithium ion batteries alone is cheaper than paying for and using grid electricity remains true. 

As an installer, who, depending on my customer, may wish to expand with solar panels at a later stage while reserving basically a lifelong access to lithium ion battery thus offsetting the negative side affects of load shedding.

Panels as glorious as they are, I did not create this thread to promote their use, or not.

 

Edited by jacquesretief
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40 minutes ago, jacquesretief said:

Why will 6000 cycles at 50% Dod yield exactly the same energy at 3000 @ 100%?

If the battery is rated 5.5kWh that means you can take out 5.5kWh if you discharge it from 100% to 0% SOC and will "use" 1 cycle.  If you do that 3000 times you will have taken out 16500kWh.

If you discharge it from 100% to 50% SOC you will take out 2.75kWh and use half a cycle.  If you do that 6000 times you will also have taken out 16500kWh.

48 minutes ago, jacquesretief said:

However the calculations and formula proving that lithium ion batteries alone is cheaper than paying for and using grid electricity remains true.

Correct.  But you cannot use them alone - they need to be charged, and inverters are required to generate the AC.  In practice PV panels and inverters have finite lifespans, so the effective cost of using them is not zero.

 

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27 minutes ago, jacquesretief said:

If I used 2.5kW of power in an hour of a brand new battery, I would have used 5999.5 cycles?
However, if I continued to use the brand new battery to 0%, I would have used one cycle, leaving it with 5998 cycles remaining?

Your reasoning makes sense, Also you need to consider if you were to use one full cycle of 5.5KWH and let’s say the primary cost is the battery (R26000) than you need to also add the secondary cost of charging the battery back up to 100% state of charge again. One full cycle of 5.5KW to charge with either Council (5.5KW x R2.08/KWH) or PV (5.5KWH x PV cost/KWH x X) will have a secondary cost that need to be taken into consideration. Some form of payback calculation (X) need to be calculated into the cost of the PV panels and inverter over the lifetime of the system. If you oversize the PV array size with a lot your cost/KWH will go up as-well as payback will be longer. There is a big demand for that magic combination.

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@jacquesretief I am not sure how you would be cycling your battery down to 50% 3 times a day, we have one cycle of day/night in a day and during the day a solar system will generally produce more power from solar than the house will be using and will power the house and charge the batteries during the day. There may be a short period of using some power from the battery if the load is high and the sun goes behind a cloud or something but that is the exception rather than the rule.  

The way I see it, the ROI on current battery purchases is extremely long and purchase of them only really makes sense at the moment so as to avoid load shedding or if you want to go off-grid.

According to my calculations, If you are only considering how much money you are saving money that you currently pay Eskom,  it is will take more than 8 years to pay of the batteries. 

ROI on a grid-tie system is generally much shorter and usually works out at around 3-4 years depending on what your loads are and how many you are able to move to daylight hours when the power is "free"

In SA at the moment, cost of power during load shedding is considerable  and softer considerations such as convenience of not having to run around switching on generators need to be taken into account. Considering that a 6kw generator will use 2-3ltrs of petrol an hour and average load shedding is about 2.5hrs, I used a cost of R100 for fuel per load shedding. Assuming that I use the generator only once per load shedding day, we have had a total of 47 load shedding days this year, total cost would be R4700. When you start adding those number to the equation it starts making a lot more sense to ensure that you can keep your house powered over load shedding using solar power & batteries, this is not as much an issue during the day when there is loads of solar power but I used my load in the evenings, between 18:00 & 22:00, when there is no power coming from the panels, to calculate the amount of storage I needed to make it through without starting my generator.

To maximise the return on my batteries, I keep them 90% charged until 22:00 in case of load shedding and then power the house from then until the sun comes up in the morning at which point they are down to 20% and ready to be charged up during the day.  

Good news is that the price of power storage is only going one direction and that is down. The new Tesla 4680 batteries, coming online in 2022, are estimated to reduce the  battery storage costs by 40% and that is going to put a lot of pressure on the prismatic cell battery manufacturers to reduce costs on their cells. 

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@Tariq Yup, batteries still costs way to much to go totally off-grid at the moment and doesn't really make sense, as long as you have enough batteries to make it through load shedding, to buy more batteries.

Thing is that power from Eskom is only going to get more expensive and battery prices are only getting cheaper.

Based on the current energy storage cost trajectory I am guessing that easily within the next 10 years, reduced energy storage costs are going to make unnecessary to connect to Eskom. 

The Tesla 4680 battery is really going to change the playing field, 56% reduction in battery cell cost whilst increasing the amount of batteries that can be produced. Battery costs are closely following Wright's law at the moment which says that for every doubling in kw/hr produced, price is reduced by 28%, latest forecasts are for EV production to increase from 2.2 million units in 2020 to 40 million units in 2025, this is going to result in huge reduction in storage costs. The 4680 is nickel based but this will still put a lot of pressure on the LifePo4 battery manufacturers.     

 

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19 hours ago, jacquesretief said:

Instead of paying the municipality I could buy a new battery every 27 months (R936 electricity bill * 27 months). Which means that I save R5000 a year, which I could put that towards more batteries to get to that maximum cycle life of 6000.

I'm loving this¬†ūüėć

Or you can go grid tie get money back from Eskom/Council buy a few small batteries for lights ...  and smile all the way to the bank.
This year my savings more than R34000.

My opinion the way to go

 

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24 minutes ago, Erastus said:

Or you can go grid tie get money back from Eskom/Council buy a few small batteries for lights ...  and smile all the way to the bank.
This year my savings more than R34000.

How did you arrive at the R34K savings per year? That equates to approximately 1250kWh saved per month, is that correct (taking Escom power at R2.3lkWh)?

What setup do you have, installed panel, etc?

Edited by FixAMess
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@Erastus, don't you have to remain a NET consumer, meaning you cannot feed in more units than you buy, as of today for this month I have only bought 21 kWh, ok, it is higher in winter, but not worth spending R11,000 for a bi-directional meter

Edited by Tariq
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46 minutes ago, FixAMess said:

How did you arrive at the R34K savings per year? That equates to approximately 1250kWh saved per month, is that correct (taking Escom power at R2.3lkWh)?

What setup do you have, installed panel, etc?

I have 3 inverters. Solar vacuum tube geyser my koi pond of 65000 l uses a 100W pump,  The fountain uses 200W pump and my swimming pool 450W.  Some funny filters etc I have.  My complete house is on LED's and I have a gas hob. My electricity was way over R3K per month.  Now I am getting back.  Its an immediate savings of more than R4K cash per month.
My neighbor and I did a small RO water plant so we not using council water. That is NOT part of the saving. That is +/- R1K more savings.

For my lights back up I use 6 small 4.5A batteries and for the TV a larger one.

Thus my house is fully self sufficient. I had a gas geyser that I tried and wasted R5500 then I had batteries realized it is a waste of money. I used batteries for +/- 2 years and realized it always an expense so I did a few changes and today where my munic account was more than R6000 per month the only expense I have is R1850 on tax and that is paid by solar.

I can not say all savings are from the PV system as in the past I had 2 1Kwh pumps that ran 24/7 now I replaced them with a 100W pump and pump more water.

My mods worked and voila  I recon I save at least R65K per year after my changes.  For me that is quite a large sum of $

Now I have no longer any pump with a higher wattage than 750W that takes see water for my RO and my irrigation pump uses every 2nd Day 1Kw to water the garden.

With my systems one can not do name dropping with.  I have the cheapest solar panels one can get I even bought second hand ones by those that thought .... and the cheapest inverters. Its not about names and the amount of $, its about not spending and increasing the ROI.

For me it is simple do not pay the council.

Let the electronics do the working and smile all the way ...

You can never ever achieve this with batteries and/or gas geysers ....

Never ever

Edited by Erastus
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40 minutes ago, Tariq said:

@Erastus, don't you have to remain a NET consumer, meaning you cannot feed in more units than you buy, as of today for this month I have only bought 21 kWh, ok, it is higher in winter, but not worth spending R11,000 for a bi-directional meter

You can generate up to 5Mwatt now without a licenses. 

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1 hour ago, Erastus said:

Or you can go grid tie get money back from Eskom/Council buy a few small batteries for lights ...  and smile all the way to the bank.
This year my savings more than R34000.

 

20 minutes ago, Erastus said:

My electricity was way over R3K per month.  Now I am getting back.

From a press release on COCT web site (February 2021): (CoCT and Feed-in Tariff - NRS/SSEG Regulations - Energy Talk)

"‚ÄėThe feed-in tariff works when customers are net consumers of electricity over a rolling 12-month period. They must therefore consume more electricity from the network than what they put back in over the course of a year. The feed-in tariff offsets their electricity bill and, while they will never receive money from the City, the excess power that is generated back into the City‚Äôs grid, will be used to balance out their month‚Äôs bill."

The feed in tariff is about one third of the usage tariff,  so even if you export as much energy as you use you will still pay two thirds of normal price.

Last time I looked Melkbos was part of City of Cape Town.

Something does not add up...

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3 hours ago, Calvin said:

 

From a press release on COCT web site (February 2021): (CoCT and Feed-in Tariff - NRS/SSEG Regulations - Energy Talk)

"‚ÄėThe feed-in tariff works when customers are net consumers of electricity over a rolling 12-month period. They must therefore consume more electricity from the network than what they put back in over the course of a year. The feed-in tariff offsets their electricity bill and, while they will never receive money from the City, the excess power that is generated back into the City‚Äôs grid, will be used to balance out their month‚Äôs bill."

The feed in tariff is about one third of the usage tariff,  so even if you export as much energy as you use you will still pay two thirds of normal price.

Last time I looked Melkbos was part of City of Cape Town.

Something does not add up...

City of Cape Town even if they wish can not over rule rules and laws from the Parliament or Nersa.  They think they can but not possible at all.
They had that argument until the state president announced the new rulings and ,,,,

Guys the COCT is not independent they are also under law just like others.
 

   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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19 minutes ago, Erastus said:

laws from the Parliament

If I understand you correctly you are saying that there are laws or regulations that compel municipalities to allow you to be a net exporter of energy and to pay you at such a rate for the exports that they will actually owe you money.  Furthermore I understand that the COCT is actually doing this with you (giving you money back), despite publicly saying that they will not do it.

These laws / regulations appear to be a very well kept secret - I can find no reference to them.  Perhaps you would be so kind as to provide a reference to this information?  I am sure that many members here will find it very useful.

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