All the prices are from actual published figures and more useful just as a comparison between different energy sources as they relate to wholesale on gigawatt quantities.
At what price does LFP storage make it possible to go off-grid?
- Thread starter svetz
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I'd agree with the previous comments regarding keeping your grid tie. While not as "pure" setup as being totally self sufficient, I think you will find it great;y reduces your costs (mostly by reducing the size of battery bank you'll need). You can still setup many inverters to use your generated power first then switch over to the grid (as well as recharging the batts at lower night rates, if that applies for you).
You can play with the cost numbers, but a one day battery bank along with enough PV to meet typical daily need might be an interesting design point to calc the costs/payback with.
You can play with the cost numbers, but a one day battery bank along with enough PV to meet typical daily need might be an interesting design point to calc the costs/payback with.
Hedges
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My estimates, cost per kWh cycled through a battery over anticipated life:
AGM $0.50/kWh
FLA $0.25/kWh
Lithium (big name) $0.50k/kWh
DIY LiFePO4 $0.05/kWh
Off-brand and recycled batteries might approach DIY cost.
Compare to PV panels and grid-tie inverters $0.025/kWh (together with all materials for DIY install $0.05/kWh total) amortized over first 10 years.
Half that over 20 years, or a bit more than half if inverter needs replacement.
PG&E rates $0.26 to $0.42/kWh for some plans
their EV schedule, $0.16 to $0.59/kWh
Electric Vehicles
With the number of electric vehicles in California growing every day, PG&E is committed to low electric vehicle rates, and home charging for electric cars in California.
www.pge.com
Obviously only cheaper batteries compete with grid. I can't come out ahead spending $0.50/kWh for a battery to store power worth $0.16 for use when rates are $0.59/kWh
schmism
Solar Addict
That math makes no sense to me. (and this is frequently a topic you like to bash)
lets say 27kwh of DIY battery cost $4000. per your above numbers you save $0.43 for each peak hour you shave. Lets say you conservatively shave 5 peak hrs a day 4000/.43=9300/5hrs per day = 1860 days to pay off. or 5 years. Less if you consider the non peak hrs you might be off grid.
If your shaving peak hours the math says it ALWAYS pays to have 10-12hrs of daily battery.
wattmatters
Solar Wizard
What are the assumptions for this number?
svetz
Works in theory! Practice? That's something else
I suspect it's LFP cells at < $182.5/kWh installed & expected to last a decade ($182.5 / 365d /10y = $0.05/kWh/cycle ).
It's a little misleading as you'd need ~2d autonomy to reduce the DoD to where you could get a decade's worth of cycles ... so more like 10¢.
That's what we're doing, playing with the numbers to see where it makes sense to go off-grid based on your grid bill. It's not about independence, it's about costs/payback.
For my case of $.15/kWh (low compared to a lot of folks) it looks like for LFP with a 10-year calendar life, 3-day autonomy, & a generator, assuming 2% inflation and less than 2% on investments, that break-even number is ~$140/kWh purchase price of LFP. See post #36 for math.
But, if LTOs can calendar age for two decades, then at current prices it looks like we're there for break-even costs and incredibly worthwhile if they can age to 30 or 40 years. See post #39.
I'm not wild about LTOs due to the power density, but solid-state batteries will fix that and most think mass production is less than 5 years off.
There's also talk about a federal ESS tax rebate similar to what Massachusetts is already doing. Knock 25% off the price and that $140 for LFP goes to $186. So, for LFP ESS it'll be a while until it's worthwhile for me.
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One thing that I didn't see brought up is the old "two is one, one is none" mantra.
If you have an existing grid connection, I wouldn't cut it off regardless of numbers.
I would use it as a backup to the main solar power system as if one of them goes down, hopefully the other can be used as a backup.
If you have an existing grid connection, I wouldn't cut it off regardless of numbers.
I would use it as a backup to the main solar power system as if one of them goes down, hopefully the other can be used as a backup.
svetz
Works in theory! Practice? That's something else
Lithium-titanate battery - Wikipedia https://en.wikipedia.org/wiki/Lithium-titanate_battery
The calculations after the OP generally use 3 days autonomy and a generator. So, four is three?
Never say never is also an old mantra.
The value of backup is different for everyone, so it wasn't included in the calculations as to what the ESS price point was to where it made more sense to be off-grid than on-grid.
For example, my DIY LiFePO4 cost per kWh is ~$136 (including BMS, bus bars, fuses). Assuming 2500 cycles only, you get $0.054 per kWh cycled.
Ozark Tinkering
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That's pretty much where I am right now. I am grid-tied with 5kw of Enphase micro inverter system and ideally I would like to install another 5-7.5kw to that system. After a year of production along with some heavy weatherizing of my home I can see where if I were to go that far for the most part my utility bill would be the minimum hookup charge.
I've used a gas generator I converted to propane about 12 years ago and it gets me through those outages but not without it being a huge pain in the butt. The last outage was that storm that blew through a couple of weeks ago and power was out for just over 48 hours. I can continue to use that generator but I'd rather not. It produces really dirty power and I could replace it with an inverter generator that also has a block heater and electric start but I figure if I'm going to do that I might as well go ahead and get started with a small solar/batt/inverter system so I can begin to reduce my dependence on propane.
Ever try pulling the rope on a portable generator when it's 5ºf outside? Yeah...no. Not at my age anyway. That's pretty much my weather conditions when the power goes out here. That's really what is motivating me to move on a battery system charged with solar.
Zwy
Solar Wizard
Solid state is not happening in less than 5 years, if ever.
They have been trying for years, it's not scale able.
Sodium? Yes.
Ozark Tinkering
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My understanding was that solid state batteries for EVs will be hitting the market relatively soon?
First EVs with solid state batteries to be demonstrated in China
State-owned Dongfeng Motor delivers 50 electric cars with solid-state batteries for demonstration in China.
thedriven.io
RV10flyer
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$23K in my 120 kWh bank. I guess one could blow that on a jacked up 4wd $80-90K truck or bass boat or RV or 8 vacations. I’ll enjoy my 22.2 kw solar system every minute of the day and especially when I tell the power company I don’t need them anymore in a month or so. It may take 20+ years of my present power bills to pay for. I’ve built my own house, garage and airplane. I enjoy this kind of “work” and fun.
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12VoltInstalls
life passes by too quickly to not live in freedom
In a two-dimensional way, yes.
Three non-hardware factors are in play as well- both obvious and not always obvious.
Location: even if grid is available, the cost offset in whatever time-vision the consumer envisions is sometimes not relevant. The value over time may justify the upfront
Situation: if solar enables a normal or somewhat normal existence that is otherwise presently out of reach, logistically difficult, or circumstantially unfeasible the cost of batteries may not be a deterrent
Backstage economics: there are financial considerations for individual households that not everyone calculates for. The increasing cost of grid power over, say, a ten-year period is a kind of cost offset some folks factor for; if financing the solar at low to no interest- now that we have inflation again- over a ten-year period the consumer will be paying less than market value because they will be paying yesterday’s dollars with lesser-value obtained dollars (wages ‘gust’ with inflation generally); the sustainable lifespan of a singular solar purchase can cost less by half over 20 years + and the long-term economic benefit is desirable to them.
Saving money often has some form of a cost and certain subsets of people understand that intrinsically- usually it’s second-generation small business owners or certain first generation immigrants that think that way from my observations.
So the straight-up math isn’t 100% of the factors.
Hedges
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Pretty much.
Assume $120 per cell for 280 Ah 3.4V = 952 Wh
$500 REC BMS (I would use with my Sunny Island)
16 cells + BMS for $2420, 15232 Wh
Cycle battery once per day for 10 years, 55,600 kWh from 3650 cycles (approximate lifespan)
$2420/55600 = $0.044/kWh
Cells may have claimed 2000 cycles, 4000, maybe 6000 (equivalent 100% cycle, but cycled less? Actual 100% cycles?)
Anyway, I don't think its supposed to be only 3650 cycles to 50%, should get 80% DoD and a few more years.
I'm not considering 2 days autonomy, not thinking autonomy at all, just grid connected and storing power at Noon to consume at 6:00 PM when rates are high.
In other words, DIY batteries for approximately a nickel per kWh do make sense when the spread in utility rates between off-peak and peak is $0.40/kWh. Or, if you don't have net metering and rates are $0.45/kWh because you can roll your own power for about $0.025 to $0.050 while the sun shines, store to use when sun unavailable.
Last time I price out name-brand batteries (LG RESU) I came up with $0.50/kWh over their cycle life. That matches about the highest cost of power from PG&E, so doesn't make sense.
Hedges
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Yes, quick payback for these DIY battery prices.
More or fewer hours of battery doesn't figure into calculation of payback time (or of whether you save/lose money.) Only into total cost and savings/loss. (Except if your goal is to avoid a "demand charge", which doesn't appear to be in consumer utility schedules where I am.)
Our peak rates (for one rate schedule) are 4:00 PM to 9:00 PM, so greatest savings from having a battery able to deliver the power I consume during those particular 5 hours. Larger bank would let me shave consumption during mid-priced mid-peak, less savings. Or, get more years before cycle life used up, meaning pay today for anticipated savings I won't enjoy until 11 years from now. I think it is more profitable to drive a car (or a battery) into the ground in less time, get my money's worth sooner.
27 kWh of battery for $4000, $148 purchase price per kWh.
Assume 4000 cycles lifespan, 11 years of one deep cycle per day. You might do 80% to 90% avoiding knees, but I'll assume 100%.
$148/kWh capacity / 4000 cycles to end of life = $0.037/kWh
Yes, this is why I say DIY LiFePO4 makes financial sense. I can make power for $0.025 to $0.050/kWh, store it for $0.037/kWh
That is much less than our lowest rate of $0.16/kWh, so could store power during the day to charge an EV at night (which is what that rate schedule is for).
Even better to charge from PV (or grid) at Noon, assuming typical rate schedule of $0.26/kWh off peak. Consume at 6:00 PM when rate is $0.42/kWh.
Commercial LiFePO4 if $0.50/kWh of cycle life loses money. Break-even when price = spread of utility rates.
Hedges
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If you can finance at 0% interest during a decade of 8% inflation, when prices double and buying power of dollar falls in half, you win. It does for most investments, if you can get that spread.
We've already seen the dollar do that in about a decade since 2008 (depending on who's inflation figures you believe - the price of an iPad, or steak, lumber, tires and other commodities.)
Back about 2003 to 2005 I placed this bet and spent $100,000 for grid-tied PV producing all my power. CEC rebate gave me back $50,000. The power probably amortized out to $0.20/kWh by now.
Some of the power I used for electric heat, since I had surplus. Would have been cheaper to just burn natural gas.
As you might imagine, if I had forgone solar and put the same $50k in the S&P 500 I'd be way ahead.
Today when I can DIY grid-tie PV for $1/W using commercial rack mounts, approach $0.50/W by cheaping out on hardware (even more with bottom of the barrel used panels), net-metering is a slam dunk. Too bad it is going away.
PV + DIY batteries in a zero-export system look like a winner in the new landscape where net metering isn't one for one any more. But only if the batteries reach anticipated life. I think break-even occurs at around 25% of anticipated lifespan.
Zwy
Solar Wizard
That is a semi SSB. Still has some liquid. https://carnewschina.com/2022/01/24...explained-when-its-coming-to-mass-production/My understanding was that solid state batteries for EVs will be hitting the market relatively soon?
First EVs with solid state batteries to be demonstrated in China
State-owned Dongfeng Motor delivers 50 electric cars with solid-state batteries for demonstration in China.
Zwy
Solar Wizard
I look at this as a place to park my money and get a decent return on it. Money Market doesn't pay squat, inflation is high, electric rates are increasing and won't get cheaper. Stock market carries huge risk right now, I started investing before the Dot Com bust so I've been thru a few drawdowns over the years where the increase in value was lost and took a long time to earn back. Not that I don't have money in equities or commodities, I just don't like all eggs in one basket. I have the money, I just need to put it somewhere to get a return on it.
I look at this as a risk free investment for the most part, you just can't get that return elsewhere. The tax advantage is icing on the cake. Not just the tax credit for solar, the average homeowner pays income tax on the money they earned to pay the electric bill in their home. Bottom line is more disposable net income in today's dollar. Inflation is nothing more than a tax, if you think things will get lower in price, you are kidding yourself. Having a big balance in a checking or savings account, even under your mattress, is costing you whatever the inflation rate is. The government will keep inflating, it allows them to print more.
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