New solar panels or top up with trustworthy generator

turbochen

Active Member
Joined
Dec 10, 2008
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52
A bit two minded about this

I have converted to as green as possible in my house, All LED, cooking with Gas.. etc and my monthly electricity bill is roughly +-R1000 rand, the only big electricity user is most like the geyser

my question as following

I am planning to install 5KVA backup system with Luxpower inverter and Greenrich 5kw battery, ( still deciding on UP5000 vs WM5000, both seem identical from the spec sheet )

I currently have a 5.5kw generator that I have been using during load shedding without much issues. I am now comtemplating whether is I should install 6X450w panels or if I just use generator to top up in the situation where Eskom becomes unavailable to charge the battery ,

any suggestion ? is it even worthwhile to consider fork out extra capital for solar panels taking into the consideration of my monthly electricity bill of +-R1000?
 
In my opinion, if you are doing the back up system regardless, the extension to solar panels will likely be worth it, even at that level of monthly spend.

The panels is the part of the system that gives you pay back.
So calculate what the cost of the panels and installation will be and compare anticipated generation will be. This will give you an idea of your bill savings and you can calculate pay back.
Also factor in the cost of fuel to top batteries.

R1000 per month makes less sense from a payback perspective if you are sizing the entire system on that cost, I was in that position and the energy independence was the swing factor for me.
 
Adding the panels to the system is likely not a huge jump in cost comparer to the system as a whole, and as mentioned it gives you actual financial return. Since you're putting the system in anyway, it's probably worth adding a bit more to generate your own power.

Keep the generator for when you have a cloudy week with no electricity either.
 
Having a backup system without solar panels means that you will be using eskom to charge the batteries if they are flat, so you will pay additionally after loadshedding to charge the batteries... alternatively charging from generator using fuel to charge also at an additional cost...

With solar not only will you be charging the battery off solar but most likely will run your house during daylight hours without Eskom so definately a greater saving, given in your case the return on investment will be much longer, but you will definately have a return on investment
 
Backup power is a dead loss expense

You already have that

The solar expense will take about 2years to roi
You don't have to go big

ie size the panel quantity on usage


And then start earning back what you spent on batteries and inverter the next few years

If you you don't have big enough batteries to carry you overnight, just get panels to just cover the base load/day time usage ,it will help preserve the batteries too

ie cycle once a day with night time shedding not while sun is shining

It is the difference of 4.5 years vs 13 too go through 5000 (generalisation salt) cycles of the battery
 
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Thanks for all the feedbacks, I truly appreciate it,

I am new to the whole thing, with regarding to the cycle thing, @leon.davibe can you elaborate more? Is it the setting on the luxpower inverter or ?
 
Thanks for all the feedbacks, I truly appreciate it,

I am new to the whole thing, with regarding to the cycle thing, @leon.davibe can you elaborate more? Is it the setting on the luxpower inverter or ?
Cycling meaning using the battery

Load shedding is what is causing the cycling

ie every time you discharge and recharge it is a cycle


Any battery has a an amount of cycles it is good for

The lithiums tend to have 80% of their capacity left after x amount of cycles

How deep you use the batteries determines how many cycles it takes to get to that 80%

ie according to manufacturers

Some might say you can get 2000 cycles if cycling the battery 100% everytime
ie if you only have one 5kwh battery and use all of it every loadshedding

And say you may get 5000 cycles if cycling 80%
So lets say you never use all 5kw but only 4kw



By adding panels while the sun is shining the load will be carried by what the panels produce and thus can save 2 cycles per day

Since the batteries are left mostly full maybe will just assist if there is a bit of clouds and production dips below load

You just cycle the battery once with the night time load shedsing

And will also save electricity not just the batteries

I am still on phase 1 only backup power , panels waiting on the budget, soon
 
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Cycling meaning using the battery

Load shedding is what is causing the cycling

ie every time you discharge and recharge it is a cycle


Any battery has a an amount of cycles it is good for

The lithiums tend to have 80% of their capacity left after x amount of cycles

How deep you use the batteries determines how many cycles it takes to get to that 80%

ie according to manufacturers

Some might say you can get 2000 cycles if cycling the battery 100% everytime
ie if you only have one 5kwh battery and use all of it every loadshedding

And say you may get 5000 cycles if cycling 80%
So lets say you never use all 5kw but only 4kw



By adding panels while the sun is shining the load will be carried by what the panels produce and thus can save 2 cycles per day

Since the batteries are left mostly full maybe will just assist if there is a bit of clouds and production dips below load

You just cycle the battery once with the night time load shedsing

And will also save electricity not just the batteries

I am still on phase 1 only backup power , panels waiting on the budget, soon
A perfect explanation... the only thing I would add is to reduce battery memory the batteries need to go through a full discharge-charge cycle (down to 10% and back up to 100%) at least once every 90 days, otherwise it ends up like your cellphone that doesn't hold charge anymore because you have only cycled it between 75% and 100% for 2 years.
 
A perfect explanation... the only thing I would add is to reduce battery memory the batteries need to go through a full discharge-charge cycle (down to 10% and back up to 100%) at least once every 90 days, otherwise it ends up like your cellphone that doesn't hold charge anymore because you have only cycled it between 75% and 100% for 2 years.
I know this use to be a thing on the ni-cd and other chemistries

To be honest i haven't read to much on the topic just had it that the lithium isn't prone to this (salt)

And since we have load shedding we do it anyway without it being on the to-do list :)

It is however a good idea to cycle it like you said ,once in a while as that is the only way to pick up if you have problems,ie bad cells and for the shunt to sync to what is available thanks to degradation
 
A perfect explanation... the only thing I would add is to reduce battery memory the batteries need to go through a full discharge-charge cycle (down to 10% and back up to 100%) at least once every 90 days, otherwise it ends up like your cellphone that doesn't hold charge anymore because you have only cycled it between 75% and 100% for 2 years.
There's no memory effect on lithium batteries
 
A perfect explanation... the only thing I would add is to reduce battery memory the batteries need to go through a full discharge-charge cycle (down to 10% and back up to 100%) at least once every 90 days, otherwise it ends up like your cellphone that doesn't hold charge anymore because you have only cycled it between 75% and 100% for 2 years.

Lithium doesn't have memory that you have to "reset" and Cellphones don't use LiFePO4 they normally use NMC or Polly that only have 800-1000 cycles to 80% capacity on them

LiFePO4 takes about 3000+ cycles to hit that 80% mark.
 
Yea the nmc in your phone doesn't have a memory effect the chemistry is just capable of less cycles than LFP

some say 800-1000 cycles

But the rules of thumb is sometimes bad


As the battery industry is constantly changing and making changes to these chemistries for quicker charging etc

So often we have outdated info on internet
 
Cycling meaning using the battery

Load shedding is what is causing the cycling

ie every time you discharge and recharge it is a cycle


Any battery has a an amount of cycles it is good for

The lithiums tend to have 80% of their capacity left after x amount of cycles

How deep you use the batteries determines how many cycles it takes to get to that 80%

ie according to manufacturers

Some might say you can get 2000 cycles if cycling the battery 100% everytime
ie if you only have one 5kwh battery and use all of it every loadshedding

And say you may get 5000 cycles if cycling 80%
So lets say you never use all 5kw but only 4kw



By adding panels while the sun is shining the load will be carried by what the panels produce and thus can save 2 cycles per day

Since the batteries are left mostly full maybe will just assist if there is a bit of clouds and production dips below load

You just cycle the battery once with the night time load shedsing

And will also save electricity not just the batteries

I am still on phase 1 only backup power , panels waiting on the budget, soon

Just to add, a Cycle count = full use.

Partial charge-discharge does not count as a full

so 2 x 50% = 1 Cycle
or 5 x 20% = 1 Cycle

eg:

1681457054621.png
Source
 
very interesting info related to DOD and cycles

Both Dyness and Greenrich has >6000 cycles and Greenrich seems to use the latest batterytech ( based on googling )

any recommendation on which one to go for ?
 
Just to add, a Cycle count = full use.

Partial charge-discharge does not count as a full

so 2 x 50% = 1 Cycle
or 5 x 20% = 1 Cycle

eg:

View attachment 1508155
Source
Yea agreed implementing this in real life not always that easy

ie actually keeping a lifep04 battery in that 20-80 window isn't an easy task(or other in mix in flat portion)

So you have to at least once every now and again visit either top or bottom for the shunt to get a grip on reality

Not discharging to deep is easy at least if the shunt recently made a visit to the top you can trust it to determine 20% or whatever you prefer
 
Yea agreed implementing this in real life not always that easy

ie actually keeping a lifep04 battery in that 20-80 window isn't an easy task(or other in mix in flat portion)

So you have to at least once every now and again visit either top or bottom for the shunt to get a grip on reality

Actually very easy if you have a proper inverter and large capacity.

Just did so for my MD.
 
very interesting info related to DOD and cycles

Both Dyness and Greenrich has >6000 cycles and Greenrich seems to use the latest batterytech ( based on googling )

any recommendation on which one to go for ?
Often if the promise very high cycle count they don't allow you to go to zero ie you can never use 100% of the battery the reserve tank is to preserve cells not possible to be used ie bms cuts off as if empty
 
Actually very easy if you have a proper inverter and large capacity.

Just did so for my MD.
Yea you can cover the only discharge to x deep portion

But can't keep it in the section in the middle ie never visit top or bottom to get the most cycles

Cause what the shunt thinks is reality vs what the battery soc is drifts apart over time

Now naturally this is sorted by itself upon visiting the bottom which inevitably happens it is just how long it takes to get there
Nobody knows how long that string is you find the end when you do


Edit: and when this happens to know nothing is wrong
It is just calibration time again
 
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Cause what the shunt thinks is reality vs what the battery soc is drifts apart over time

Now naturally this is sorted by itself upon visiting the bottom which inevitably happens it is just how long it takes to get there
Nobody knows how long that string is you find the end when you do

That's why you use proper batteries have proper BMS and COMs
It reports the charge capacity directly to the inverter and the inverter can be set accordingly.

MD's Inverter + batteries alone cost R160K

ie: we leaving the kids toyz world, and deal with proper equipment.
 
The problem i have is this if i have to choose which to use as my calibration 3.65v or 2.2v

I would choose the top never the bottom

I don't know how many bms are configured this badly
I know my shoto is

Now yes the pack voltage is different ,that will be triggered first most likely so cell low voltage doesn't come into play , but if cells drifted one can get that abuse
 
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