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

[wattmatters]

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.

I have multiple motivations for the solar PV and battery systems I have.

The grid tied system is solar PV only. Its primary purpose is to save us money, which it is and on schedule for ~4 year payback.

But I also wanted it to reduce our carbon emissions, which it is also doing. Embedded emissions of the system have long since been paid back and it's made a good impact on that front, primarily because our grid power is coal dominated.

On that front I have also been spending money on home efficiency improvements which have been a bit less financially rational. Earlier this week I had an insulation upgrade to one part of the house, hopefully this will reduce the energy consumption a bit. We also invested in energy efficient laundry appliances and an induction cooktop. Hard to recover the expense of these items but they are not "irrational" decisions, only if the opportunity cost means the resources were better deployed in other ways. The one item that was a wise upgrade was the pool pump (pool was already there). The replacement unit consumes ~ 1/4 of the energy of the old pump. The reduced consumption paid for the additional cost of the pump within 18 months.

Soon I will be installing a smart power diverter for the hot water heating element and removing it from our overnight off-peak circuit. This system will monitor excess power being exported to the grid and vary power delivered to the hot water element accordingly. This maximises our self consumption and somewhat reduces overall carbon emissions (our night time grid power is mostly coal power, while daytime exports are offsetting grid coal + grid renewable energy). This latter decision is not financially justifiable on its own but continues my commitment to carbon reduction related to our energy consumption.

The off-grid solar PV and battery system is for grid outage backup supply, but it doubles up as an off-grid source of energy and now runs our pool pump, so that is completely off-grid. It was also built from many repurposed items (solar PV, batteries, mounting hardware) to significantly reduce the embedded carbon costs of doing so.

If we can make a real dent in the average usage, then we can move forward with a right sized system.

It's doable if you have a strategy and keep plugging away at it. e.g. this is the daily average electrical energy consumption for our home since we moved here in 2016 (all electric home, i.e. no gas):



That's a consumption reduction of 22kWh/day. We still have more to do on this front. Heating and especially cooling are our big ticket items as shown by our energy consumption split:



Our daily average net grid energy is even better:



We are not yet net zero, but closing in.

 

[12VoltInstalls]

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.

I binged on this a number of years back. Granted, inflation was flat for a while, but what I figured out was that whether pro/con for batteries/offgrid, people published numbers that were slanted to support a position one way or the other.

Real estate has gone nuts so the cost savings of a remote property have mostly evaporated, but the high cost of solar in ?2010? would be offset fairly quickly in mortgage or cash-to-cost savings.

Since then, solar has evolved to a retail installed business, products have not dropped in price as fast as the economies of scale would suggest, the socio-political climate is sustaining pricing, and we have inflation that other than temporary economic downturns (like 2008) we haven’t seen since early in the Bill Clinton years.

In this case affordability has to involve willful myopia (can I afford this today?) while extrapolating with a 10-year and 20-year perspective. And what happens when the environmentally sensitive people discover solar batteries are hazardous and essentially not recyclable? An environmental tax that makes your battery replacement in ten years cost big bucks instead of little bucks?

 

[MrM1]

And what happens when the environmentally sensitive people discover solar batteries are hazardous and essentially not recyclable? An environmental tax that makes your battery replacement in ten years cost big bucks instead of little bucks?

Ummmmm.... I use 'em for target practice with my AR?

 

[12VoltInstalls]

Ummmmm.... I use 'em for target practice with my AR?

You meant the batteries, right?

 

[MrM1]

And what happens when the environmentally sensitive people discover solar batteries are hazardous and essentially not recyclable? An environmental tax that makes your battery replacement in ten years cost big bucks instead of little bucks?

Seriously, I ran into this when I was off loaded a bunch of junk, busted, dented, leaking cells for a seller last summer. NO ONE wanted them for disposal. I still have them sitting on a shelf outside my house wondering what to do with them. I cannot find a disposal site except maybe over in the next state. And then for a hefty fee.

 

[MrM1]

You meant the batteries, right?

Hmmmm ...


Could go either way I guess.

 

[HRTKD]

I think your inflation numbers are low. The cost of electricity from the grid is going to increase more than people want it to. The shift away from low cost feeds can only cause the end user to soak up the cost.

I checked my all-in cost of electricity and it came out to $.127/Kwh. That's more than I thought but I last checked it a couple years ago. My utility company is reporting that I use more electricity and gas than almost every one of my neighbors. We've been nursing a 20+ year old furnace along and I charge my EV every 10 days or so. I tried to put the blame on the cats, but my wife just gave me the look.

 

[Ozark Tinkering]

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.

I commented earlier that the best watt is the watt never used and it's true. I was really lazy when it came to doing my efficiency upgrades but a year ago last Nov I decided I needed to jump on a solar system while the tax rebates were still available so in a rush we got the system installed by the end of 2020. Then I went to insulating and plugging leaks in the house. We changed out every lightbulb in the house with LEDs. We also had 6 oaks and a hickory tree shading the roof in the late afternoon so they had to go. In the 1st year the system made 6.5mwh and the system itself knocked about $58 a month off my bill. Last winter we had not plugged leaks or insulated and our usage was really high because we had to augment our gas heat with portable electric heaters. This winter so far has been cold but we haven't plugged in an electric heater yet.
By doing the upgrades I probably have saved twice as many watts (too lazy to pencil it out) as I've made with my panels. Right now I'm sitting at 438kwh used from my provider and I'm on day 28 in my billing cycle. Last year in the same billing cycle (for 31 days) I used 1462kwh. The year before that it was 2168kwh. I used to think I needed 15-20kw of solar on my roof to offset my usage. Now I think I could get it down to 12kw and that would cover north of 80% of my needs but won't be heating and cooling my entire 15acres in the process.

 

[svetz]

...but my wife just gave me the look.

Oh yeah, been there...

I think your inflation numbers are low....

Figured it would give me the worst-case scenario and that everyone would have their own comfort numbers anyway. Fortunately, not hard to calculate.

 

[sunshine]

To keep the math simple

I try and keep a running cost of various energy supply sources from any news snippets devoid of any agenda-
Solar $0.03kwhr
Coal $0.07kwhr
Gas $0.12kwhr
Nuclear $0.24kwhr
Battery $0.40Kwhr + add one of the above
Grid Supply $0.20Kwhr+ any above + taxes + any agendas +.....

 

[wattmatters]

I try and keep a running cost of various energy supply sources from any news snippets devoid of any agenda-
Solar $0.03kwhr
Coal $0.07kwhr
Gas $0.12kwhr
Nuclear $0.24kwhr
Battery $0.40Kwhr + add one of the above

That's energy supply cost at the source presumably, and not the cost involved in delivering the energy, which is partly common grid, partly grid specific to the generation source.

In the Australian grid, the energy delivery cost from grid sources is ~2/3rds of the total bill.

 

[curiouscarbon]

Seriously, I ran into this when I was off loaded a bunch of junk, busted, dented, leaking cells for a seller last summer. NO ONE wanted them for disposal. I still have them sitting on a shelf outside my house wondering what to do with them. I cannot find a disposal site except maybe over in the next state. And then for a hefty fee.

there's some amount of valuable material in most batteries, but extracting it requires energy and resources to extract and also transport it to the extraction machine, which i gather is expensive and rare, so it costs a bunch to recycle :/ maybe this perspective is totally confused

also transporting is even worse on recycle side because its still heavy and now potentially leaking unfriendly materials

after i gave up on the regular watering maintenance on a small FLA build in garage, it took a while to find an easy way to recycle them. they got the last laugh, belching electrolyte on the floor and requiring cleanup, because charger didn't know any better. set that up years ago and haven't looked back since decommissioning it and focusing on LFP

 

[toms]

Everyone has a different perspective. It would have cost over $250,000AUD to get mains power connected to my house.

Not a difficult decision to make.

 

[sunshine]

In the Australian grid, the energy delivery cost from grid sources is ~2/3rds of the total bill

I edited to include delivery costs as you suggest.

 

[wattmatters]

Everyone has a different perspective. It would have cost over $250,000AUD to get mains power connected to my house.

Not a difficult decision to make.

How much extra to move to a house with the grid?

 

[svetz]

...
Solar $0.03kwhr...
Battery $0.40Kwhr + add one of the above...

Not sure what that 40¢/kWh on the battery is.... let's see....

Is Solar really 3¢/kWh?
I've heard on these forums that folks down under can get solar installed for $0.50/W and in the U.S. a frugal DIYer can get under $1/W installed. With an average insolation of 4 that 1W of PV solar will generate over 20 years: 20x365x4x1/1000 w/kWh =29.2 kWh.

So yes! With the $1/W installed that's 1 / 29.2 = 3.4¢/kWh (and for those at $0.50/W installed that would be 1.7¢/kWh).

How much is ESS per kW solar currently?
The Chins battery in the OP is 35.4¢/Wh. Assuming a 1 day autonomy, every 1 W of solar with an insolation of 4 needs 4Wh of energy storage.
So, assuming an installed Chins cost of $0.36/Wh that's 4x $0.36=$1.44/W of PV per day autonomy (e.g., $4.32/W for 3 days).


Break-Even Battery $ Calculation
Let's say your total power bill is $0.15/kWh (use your actual costs) and that PV solar is 3.4¢/kWh (use the math above to get your actual numbers). Then....

($0.15 - $0.034) = 11.6¢/kWh available for energy storage to break-even.​

The value of 11.6¢ over a decade is 10 yr 365d/y x 11.6¢ = $423.4, so that's what is available for battery after solar assuming no inflation. At 2% inflation it would be $527, at 3% it would be $580, at 4% $638. That's per kWh of power over a decade.

That $423.4 needs to cover the autonomy, so a 3d autonomy is $423.4 / 3 = $141/kWh storage. ($211 for 2d autonomy).
At 2% inflation it's $527 / 3= $176/kWh.

So, if storage is under $141/kWh installed, then with the assumptions above you'd break even on the cost in 10 years with no inflation. At 2% inflation it would be $176. Obviously there's a lot of ways to slice it, for example using a generator to back-fill 2d of autonomy at 2% inflation might $243/kWh.

Saving Money?
The $141/kWh would be a bad deal overall as the money invested elsewhere would be worth more in 10 years. The 10y T-bond hit an all-time low of 0.54% for 2020, but if you assume 1.75%, then to break even the ESS would need to be under $120/kWh. Everybody has their own idea as to investment rates, so this can vary widely.

Are we there yet?
Obviously it depends on your consumption, costs, predictions for inflation and investment returns, and thoughts on the calendar life of your ESS..

 

[MrM1]

Are we there yet?
Obviously it depends on your consumption, costs, predictions for inflation and investment returns, and thoughts on the calendar life of your ESS..

And the AHJ! Don't forget the AHJ.

 

[schmism]

Several other things to consider. How often do you loose power? We have avoided 4 power outages between an hr and 4 hrs in the past year with my battery backup critical loads system.

if your in a major metropolitan area you are unlikely to be able to remove the meter from your property. said another way, most cities these days have ordiances saying you can not live in a house that is 100% off grid. So your always stuck with a meter fee. There are stories about some utilities cranking up meter fees when the usage bill plumits to nearly zero. (from a nominal $20/mo to almost $100/mo)

 

[svetz]

LTO cells don't form that pesky layer on the anode so don't calendar age as quickly. The average number of cycles is 20,000 (54 years).
How young do you need to be for them to make sense?

Let's say your total power bill is $0.15/kWh (use your actual costs) and that PV solar is 3.4¢/kWh (use the math above to get your actual numbers). Then....
The value of 11.6¢ over a decade is 10 yr 365d/y x 11.6¢ = $423.4, so that's what is available for battery after solar assuming no inflation. At 2% inflation it would be $527, at 3% it would be $580, at 4% $638. That's per kWh of power over a decade.

$42.34/kWh/y now vs sum after	2% Inflation	3% Inflation	4% Inflation
20 Years	$1049	$1171	$1311
30 Years	$1752	$2074	$2469
40 Years	$2608	$3288	$4184

These LTO cells are $323.00/kWh currently. For 3d autonomy about $1000/kW of PV in today's cost.

Solid-state batteries are expected to have around 10,000 cycles and have a greater power density so they'll have a smaller footprint than LTO.

 

[svetz]

Several other things to consider. How often do you loose power? We have avoided 4 power outages between an hr and 4 hrs in the past year with my battery backup critical loads system.

It's about on-grid vs. off-grid economics, not backup. The premise is the actual power cost of the bill compared to the costs of delivering that power. Having backup power is a definite plus, but hasn't been mentioned in the numbers as it's a very different value for everyone.

if your in a major metropolitan area you are unlikely to be able to remove the meter from your property. said another way, most cities these days have ordiances saying you can not live in a house that is 100% off grid. So your always stuck with a meter fee.

With all due respect, I suspect this is an urban legend or what the utility wants you to believe. A reference would help here.

There are stories about some utilities cranking up meter fees when the usage bill plumits to nearly zero. (from a nominal $20/mo to almost $100/mo)

Very true!
If people started disconnecting from the grid to save money it would push the burden of supporting the grid onto the "poor". I have every confidence that politicians would not do the sensible thing (e.g., give the "poor" their own systems) and would instead create a new tax on everyone to keep an old and inefficient monopoly going.