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At what price does LFP storage make it possible to go off-grid?

svetz

Works in theory! Practice? That's something else
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Sunday morning with a cup of coffee and like many of you thinking about my bills. The power bill specifically and wondering what the price point per kWh needs to be to consider going off-grid. Let's tempt the calculator gods....

The electricity portion of my monthly power bill says the rate is $.0638/kWh.

But, the actual cost from everything else on the bill divided by the usage puts me at ~$0.15/kWh currently.
To keep the math simple, let's assume I use 50 kWh/d on average year-round and have an insolation of 5.

Over the next 20 years at 50 kWh/d, the sum of the utility bills will be $83,594 at 3% inflation or $74,731 at 2% inflation, or $66,991 at 1% inflation.

With an insolation of 5, to get 50 kWh/d I'd want a 10kW array, assuming a DIY cost of $1/W, that's $10,000. Leaving ~$64,731 for the battery at 2% inflation.

At a max of 50 kWh/d 2 days of autonomy is 100 kWh of energy storage.

So, assuming all that to be true, once battery prices fall below $64,731/100 kWh = $647/kWh the system would break even in 20 years at 2% inflation. At $323/kWh, the system would pay itself back in 10 years.

The Chins on Amazon is under $300/kWh, so are we there? Should DIYers start going off-grid?

The advert for the Chins claims 2,000 cycles. 20 years of cycling is 7,300 cycles.

Battleborn says 3k to 5k cycles. We know it has to do with the depth of discharge
as shown to the right.

Let's say the chart is correct. If we had 3d autonomy (150 kWh), the average usage
would be 33% DoD which should get us to 8,000 cycles or >20 years.

So $64,731 / 150 kWh = $431 kWh for a 20 year payback at 2% inflation, or $215/kWh
for a 10 year payback. If you don't care about payback it seems like we might be there,
the Chins has a payback under 14 years at 2% inflation.
blog-img-lfp-battery.png

Side note: If you have a good net-metering agreement, you'll probably never want to go off-grid....just increase the size of your PV to zero-out the bill...

What do you think?

Update:
Thread recap in post: #190

Update: Example spreadsheet at
https://docs.google.com/spreadsheets/d/14AMvgJr2mxrx2NPxqzGxOkh3kuu4hjsc4KaJWOOP72o
 
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My one concern is that the 150 kWh battery will age out before 20 years - I think the 10 years of battle born is probably at or just over/under the real lifetime.
So if you have to replace the battery bank once and the inverter/SCC once, plus add a generator (for long winter storms), I don’t think we are quite there yet. But we are getting close. Especially with higher energy rates.
 
I once read a few years ago on another forum that once price per kWh was over $0.45 it would be worth it, but that was factoring lead acid.
 
Another consideration is that your calculations assume what is (in my opinion) only a very conservative expectation on the rise of electricity costs.
At ~6 cents/kwh, you have some very inexpensive rates compared to the rest of the nation. That's the rate that I was paying here 12 years ago; now it's ~14 cents/kwh plus all the other ridiculous costs.
 
Are you including cost of money or lost opportunity for the capital expended?

If you aren't 100% disconnected from the grid then there is a standby cost for the connection (at least where I live)
 
Another consideration is that your calculations assume what is (in my opinion) only a very conservative expectation on the rise of electricity costs.
At ~6 cents/kwh, you have some very inexpensive rates compared to the rest of the nation. That's the rate that I was paying here 12 years ago; now it's ~14 cents/kwh plus all the other ridiculous costs.
It's not really 6¢/kWh, as the OP says the total cost is 15¢/kWh when you factor everything in. But, I believe the net-metering is based on "electricity costs", so it's to their benefit to minimize that number.

Are you including cost of money or lost opportunity for the capital expended?
Just comparing costs that would be paid over 20 years to the utility versus the cost of being completely off-grid (e.g., 100%, no stand-by).
 
My one concern is that the 150 kWh battery will age out before 20 years - I think the 10 years of battle born is probably at or just over/under the real lifetime.
Calendaring aging is a concern. With 2d autonomy, you should get 6000 cycles, about 4 years short (18%), but assuming they only calendar age to a decade it would halve the price point to $161.5/kWh for a 10-year payback at 2% inflation using the other numbers in the OP.

So if you have to replace the battery bank once and the inverter/SCC once, plus add a generator (for long winter storms), I don’t think we are quite there yet.
Go Enphase! 20-year warranties! ; -)
But you're right that there should be a generator and fuel added into the calculation. I ignored it as the amount was below the level of accuracy for the rest (it's all pretty loose ; -). For example, a 2kW generator running over 24 hours is just about 50 kWh/d and a 2 kW inverter generator runs about $1k. So, at 2% inflation that's $64,731 - $1,000 = $63,731 kWh; divide that by 100 kWh to $637/kWh for energy storage, so about $10 less not including fuel.
 
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Interesting rate structure your utility has...
Mine runs $.095 per kw and with fees and taxes runs $.105ish per kw. My usage has been a moving target over the years but since installing a grid-tied system I have become very aware of my usage and what it costs. My insolation rate is about 4.8. Not the best but still okay. With my grid-tied system included I'm currently averaging about 35kwh per day from my utility. For another $20k I could have enough solar on my roof to cover 100% of my needs (paying someone else to do the work) and have nothing but a minimum monthly hookup charge that seems to me could be handy to have standing by.
Having said that, I think if I was 35 years younger and starting out in the woods...again, I for sure would be looking toward total independence from the grid.
Elon says the best part is no part...I say the best watt is the watt never used.
When I began this journey into solar, my usage was off the chart. It was embarrassing how much power I was wasting. Over the last year I generated 6.5mwh with my system. I probably saved the need for kwh by twice that much by tightening up my shack.


Sunday morning with a cup of coffee and like many of you thinking about my bills. The power bill specifically and wondering what the price point per kWh needs to be to consider going off-grid. Let's tempt the calculator gods....

The electricity portion of my monthly power bill says the rate is $.0638/kWh.

But, the actual cost from everything else on the bill divided by the usage puts me at ~$0.15/kWh currently.
To keep the math simple, let's assume I use 50 kWh/d on average year-round and have an insolation of 5.
 
My peak PG&E rate is $0.50 and the peak time period is 5 to 9PM so much of the year, little solar generation can be banked at that rate.
That's what I'm talking about! Been trying to get a cousin to go solar in San Diego for a long time. My system set up where he is on the border would generate much more than it does where I am and would save him a crap ton of money at those rates. When my bill is $90 his bill for the same usage is $450. Even having battery power for peak hours would probably be a smart move.
 
There are Two ways to look at the Cost of Solar with Battery. probably more too.
1) an existing home already wired to the grid and it is added on.
2) a new home build with or without grid AND the cost of the actual Grid Connection !

Case in point, Big Power wanted $55,000 to install poles & lines + Transformer Unit. Solar was LESS THAN HALF with Batteries !

There is the Trixy part too... I dropped heavy bucks on Rolls Surette Deep Cycle Solar Batteries back in the day (April 2015), Lithium Anything was well into Ludicrous back then. So I spent $3000 for 428AH Gross / 214AH Useable ! Now considering what $3K in LFP can do today ? AND the fact that I have RETIRED the Lead (now offline going for disposal), the math equation is simple. So now I am finishing 1190AH of LFP, it cost more than the lead but now there's plenty of stored energy and good to go for the longhaul.
 
There are so many factors to the equation which are unique to each individual scenario, there is no one answer.

In many cases it may never be feasible where you are as you may not ever be able to supply or store enough energy when it's needed. Physical limitations on what can be installed are a factor. Costs might involve relocation, or changing energy supply systems as using electricity as energy may not be the best choice any more for some energy demands.

Plus you are now the grid and you are responsible for ensuring it operates at all times you need it. Add in costs for redundancy and backup, and ongoing maintenance and replacements. In some places backup (outages will happen) isn't so easy as internal combustion engines may not be permitted, or at least have some restriction (e.g. noise) on their use.

The demand side of the equation can't be ignored either and going off-grid may require significant investment. Improving thermal performance of the home, upgrading to energy efficient appliances, smart control systems and so on. It can means changes to home infrastructure (e.g. I'd probably need to swap to using a heat pump for heating water to reduce that load by 75% and that's expensive and requires extra plumbing).

As a rule of thumb in Australia, if you already have the grid then going completely off-grid makes little financial sense. Storage costs would need to be an order of magnitude lower for some to contemplate it but most will run into many of the issues above. They likely won't be able to generate enough energy with the space they have.

Other options may make more sense for some, e.g. a grid-supported system, where you are somewhere on the spectrum of partially to largely self sufficient but still use the grid for covering peak power demand and/or the low/no supply periods. The grid can still be a decent backup generator.

In Australia, financially it's better to have grid-tied solar PV without storage. Adding storage just makes the financials much worse. To begin to make sense storage needs to cost, fully installed, less than US$150/kWh, in some places a bit more, perhaps US$200/kWh. For grid tied storage installed per code here (DIY is out of the question unless you are a licensed solar electrician) it's ~ US$1,000/kWh. It's not in the ball park.

To make a grid-tied battery worthwhile from a financial POV (I already have 11kW of grid-tied solar PV) and so reduce reliance on the grid without eliminating it, it needs to have a payback <7 Years. Batteries will decline with performance and age, inverters will require replacement and so on. Maintenance costs needs to be allowed for. In our case the battery (+ inverter and installation) costs need to be under US$150/kWh before a 7 year break even can be achieved.

Fully off grid? Yikes. That would involve at least tripling our 11kW solar PV, have to field mount it and trench in cabling, and well over 100kWh/battery. We will have days > 100kWh along with poor solar PV conditions. IOW we would have to do a LOT to change the load side of the equation.

For some fun I run some numbers through my battery simulation model. This is based on my actual 5-min interval data over the past 3 and a bit years.

Here is the state of charge for my 11kW PV system assuming the battery had a max 10kW charge/discharge rate, round trip efficiency of 89%, 0% reserve capacity (IOW full capacity always available to discharge) and a total storage capacity of 100kWh:

Screen Shot 2022-01-24 at 7.37.21 am.png
Clearly there are long periods where battery sits at full/near full charge, and long periods where the battery struggles to be charged at all.

And this would be the power still required to be imported from the grid at times because neither the solar nor the battery could supply the demand. It correlates closely with the SOC chart above when the battery is at low / zero SOC:

Screen Shot 2022-01-24 at 7.37.47 am.png

As you can see, there are still plenty of occasions I'd need much larger inverter capacity and solar PV capacity, at least triple what I currently have (10kW inverter, 11kW PV).

And that's really expensive to do compared to just buying from the grid.

IOW ~80+% of the cost of going fully off-grid is servicing ~10% of the demand.
 
In California, they have the Self-Generation Incentive Program (SGIP). SGIP provides a dollar per kilowatt ($/kW) rebate for the energy storage installed. So, they'd want to add that in if they want to participate (might be reasons not to).

I think New York, Massachusetts, and Vermont have deals too, but Maryland is one of the only, if not the only, states in the country currently offering a storage-specific tax credit for its residents. The tax credit covers 30% of the cost of your storage system, up to $5,000 for residential batteries.
 
There are so many factors to the equation which are unique to each individual scenario, there is no one answer.
True Words. Everyone will be different and the reason for showing the math in the OP was so folks could look at their own numbers.

I basically started it as a rough exercise to get a feel for what the $/kWh should be for me to start thinking about going fully off-grid and doing a deeper dive into the numbers. I was fairly shocked by what I found so figured I'd post it for feedback. Like Rocketman I'm not convinced they'll calendar age 20 years, so was sort of walking away with the idea that once they fall under $180/kWh it would be time to sharpen my pencil for some serious numbers. Then @Ampster reminded us he put his ESS together for $125/kWh. So, guess it's already time to look more seriously into it.
 
Then @Ampster reminded us he put his ESS together for $125/kWh. So, guess it's already time to look more seriously into it.
In a pure sense my answer went outside the scope of the original question. Because of seasonal differences I could never purchase enough storage to carry me through the winter off grid or totally be totally self sufficient. If one was to look more seriously into the question one would have to consider the cost of energy from the grid and an alternative back up to get through seasonal differences.
 
Don't forget to plug in any tax rebates or credits into the calculation, that can often cut years off the payback schedule.

Right now, I'm at .14 per kWh for utility supplied power, but our average use per day is 108.
So we are starting with HVAC upgrades and general efficiency improvements before we add panels and batteries. If we can make a real dent in the average usage, then we can move forward with a right sized system. I'll be honest, for us, it doesn't have to be an absolute net positive calculation to make the move, it just has look good enough.
 
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