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

[12VoltInstalls]

Inflation is nothing more than a tax

It’s more like interest paid to central banks

government will keep inflating, it allows them to print more. pay back less than they borrowed or promised to the SS recipients

 

[Hedges]

One thing we have to watch when trying to calculate ROI is that unlike many investments, this equipment doesn't return principal at end of the term, so can't compare cash flow to interest/dividends/rent. Purchase price is sunk cost.

Lithium batteries could carry a disposal cost in the end.
Lead-acid could have a scrap value.


Inflation and the printing presses, chicken and egg.

Almost two decades ago, I didn't think PV would get cheaper due to energy content. I didn't think inverters would get cheaper because Moore's Law doesn't apply to power electronics. (Smaller digital IC geometries consume less power and run faster for more computational ability, while increasing die per wafer. Power devices need area and are limited in power handling by thermal path. PV needs area to capture light.)
However, PV dropped from $5/watt to $0.50/watt or less. Inverters from $1/watt to $0.25/watt (for same brand, comparable quality and performance. Other brands cheaper.)

One inconvenience of PV investment is it needs to be right-sized. It is OK up to where it offsets self-consumption. Much less return if generating surplus and trying sell it. Maybe if we implement zero-export by using surplus to mine Bitcoin, crack H2O into H2, transmute Pb into Au.

I would like to be able to store summer surplus for consumption during winter cold. Perhaps hydrogenation of vegetable/mineral oil. Seriously. It appears hydrogen can be cost-effectively stored when bonded to another chemical. Later use can be as fuel for burning or powering an engine, either in its new form or after cracking to release the hydrogen, or for a fuel cell. Each has its plusses and minuses. There is efficiency loss, recovery vs. consumption of oil feedstock, need to scrub gas sufficiently, poisoning of fuel cell, coking up of a diesel engine. Cost vs. simplicity.


"government will keep inflating, it allows them to print more. pay back less than they borrowed or promised to the SS recipients"

That's why there is a "separate but unequal" retirement plan for federal employees.
My modest proposal: Pool the assets of Social Security and FERS.

 

[Ozark Tinkering]

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.

That made me flashback to that same period while I was working out in San Diego. I encountered another electrician I'll call Jim who was in his early 50s and he had just recently commissioned his new rooftop grid tied system. Like you he had taken advantage of that CEC program and I want to say he had something in the neighborhood of 10kw in solar on his roof. You can probably tell me what a 10kw sma grid-tie system was worth back then but I'm sure it was plenty.
Like me, Jim had plenty of heavy industrial construction experience as he also had spent several years on the road building powerhouses and had purchased a home with a mostly flat roof in the Lemon Grove area of San Diego, many years earlier. He designed his own rooftop rack out of unistrut and being there on the coast he used hotdip galvanized and installed the entire system on his own. It passed San Diego inspection 1st try. I think their insolation rating is something like 6.5
I think his personal goal was to prepay for as much of everything as he could so he wouldn't need money in the future. If he's still alive today I bet he's glad he did it since SDG&E currently accepts a premium (over $.50) for their power.

 

[12VoltInstalls]

didn't think inverters would get cheaper because Moore's Law doesn't apply to power electronics. (Smaller digital IC geometries consume less power and run faster for more computational ability, while increasing die per wafer. Power devices need area and are limited in power handling by thermal path. PV needs area to capture light.)

There’s actually a book out discussing the hidden inflation of the last two decades due to the free fall of the cost of production in the same time period. I mean to buy it- can’t recall the title.
We’ve reduced worldwide starvation numbers dramatically and globally health conditions have improved some. But with fake money and central banks we haven’t “come as far” as we should have due to those factors imho.

Solar anything shouldn’t be going up in price at this point. Everyone from Vietnam to Thailand to SKorea are so efficient now that things solar should be way cheaper than they are. Solar components are inexpensive in many aspects, but not affordable for the masses no matter how they derive their electricity.

 

[Ozark Tinkering]

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.

How I Squeezed the Most Out of a Stimulus Check and Created Passive Income:
In 2020 my wife and I received a total of $3600 in federal stimulus. Our income is otherwise stable and reliable so we just added it to our savings. Toward the end of the year we were comfortable in pulling the trigger on a $12,800 5.1kw grid-tie system for the roof so we took the leap. We paid cash and our portion ended up being $9200 with the $3600 stimulus making up the rest. We commissioned it in Jan. of '21 and took a 26% tax credit on it to the tune of $3328. That brought down our real out of pocket to $5872.
During the 1st year it produced about 6.5mwh that in my case works out to an average of around $54 a month.
I'm no accountant but that looks to me to be somewhere around 9% annual return on the money I have parked on my roof?

 

[jberger]

If you are looking at enough battery storage for 2-3 days, then a single day should only be 30% DoD.
I think only discharging 30-60% should probably increase the lifecycle of the cells to match some of the larger projections of 6000-8000 cycles. Lowering the discharge rate also helps with the projected lifespan of the associated equipment, especially the BMS.

When I look at the 100% DoD charts, from any of the manufacturers, the total cycles is much less, so I think it's another datapoint that absolutely needs to be considered when trying to make the comparisons.

So when I'm looking at the numbers, I tend to look at it terms of hours/days of capacity, and seeing what my current dollars can buy.

 

[Ozark Tinkering]

One thing we have to watch when trying to calculate ROI is that unlike many investments, this equipment doesn't return principal at end of the term, so can't compare cash flow to interest/dividends/rent. Purchase price is sunk cost.

Lithium batteries could carry a disposal cost in the end.
Lead-acid could have a scrap value.


Inflation and the printing presses, chicken and egg.

Almost two decades ago, I didn't think PV would get cheaper due to energy content. I didn't think inverters would get cheaper because Moore's Law doesn't apply to power electronics. (Smaller digital IC geometries consume less power and run faster for more computational ability, while increasing die per wafer. Power devices need area and are limited in power handling by thermal path. PV needs area to capture light.)
However, PV dropped from $5/watt to $0.50/watt or less. Inverters from $1/watt to $0.25/watt (for same brand, comparable quality and performance. Other brands cheaper.)

One inconvenience of PV investment is it needs to be right-sized. It is OK up to where it offsets self-consumption. Much less return if generating surplus and trying sell it. Maybe if we implement zero-export by using surplus to mine Bitcoin, crack H2O into H2, transmute Pb into Au.

I would like to be able to store summer surplus for consumption during winter cold. Perhaps hydrogenation of vegetable/mineral oil. Seriously. It appears hydrogen can be cost-effectively stored when bonded to another chemical. Later use can be as fuel for burning or powering an engine, either in its new form or after cracking to release the hydrogen, or for a fuel cell. Each has its plusses and minuses. There is efficiency loss, recovery vs. consumption of oil feedstock, need to scrub gas sufficiently, poisoning of fuel cell, coking up of a diesel engine. Cost vs. simplicity.


"government will keep inflating, it allows them to print more. pay back less than they borrowed or promised to the SS recipients"

That's why there is a "separate but unequal" retirement plan for federal employees.
My modest proposal: Pool the assets of Social Security and FERS.

How I Squeezed the Most Out of a Stimulus Check and Created Passive Income:
In 2020 my wife and I received a total of $3600 in federal stimulus. Our income is otherwise stable and reliable so we just added it to our savings. Toward the end of the year we were comfortable in pulling the trigger on a $12,800 5.1kw grid-tie system for the roof so we took the leap. We paid cash and our portion ended up being $9200 with the $3600 stimulus making up the rest. We commissioned it in Jan. of '21 and took a 26% tax credit on it to the tune of $3328. That brought down our real out of pocket to $5872.
During the 1st year it produced about 6.5mwh that in my case works out to an average of around $54 a month.
I'm no accountant but that looks to me to be somewhere around 9% annual return on the money I have parked on my roof?

Then to top it off when the $2400 stimulus money showed up in 2021 we put in another $600 and for $3k had a dozen or so hardwood trees removed that were blocking full sun from our panels. Also a 26% credit to the tune of $780.
Oops... made $$$ on that one got a 2 year supply of nice oak firewood and a 5ton pile of wood chips for composting!

 

[12VoltInstalls]

when the $2400 stimulus money showed up in 2021 we put in another $600 and for $3k had a dozen or so hardwood trees removed that were blocking full sun from our panels.

But don’t forget we’re paying for that fake money right now ?

 

[Hedges]

You can probably tell me what a 10kw sma grid-tie system was worth back then but I'm sure it was plenty.

I just did

How I Squeezed the Most Out of a Stimulus Check and Created Passive Income:
In 2020 my wife and I received a total of $3600 in federal stimulus. Our income is otherwise stable and reliable so we just added it to our savings. Toward the end of the year we were comfortable in pulling the trigger on a $12,800 5.1kw grid-tie system for the roof so we took the leap. We paid cash and our portion ended up being $9200 with the $3600 stimulus making up the rest. We commissioned it in Jan. of '21 and took a 26% tax credit on it to the tune of $3328. That brought down our real out of pocket to $5872.
During the 1st year it produced about 6.5mwh that in my case works out to an average of around $54 a month.
I'm no accountant but that looks to me to be somewhere around 9% annual return on the money I have parked on my roof?

I think that $684/month is 11% cash flow on your net $5872 out of pocket, 6.8% on the $9472 including stimulus check (which you could have put in a frothy stock market or 0.01% passbook account.)

If it lasts for ever, that cash flow percentage is as good as an interest rate.
If the system gets torn off your roof in a hurricane one year later, you're out 89% to 93% of your investment.

Unlike say a T-bill, you don't get principal returned in the end. So not all of that cash flow is same as interest. Over 20 years, you'll get 220% on out-of-pocket or 137% on the cash you could have had. You get the cash back plus 37% returned, 1.84% per year. Probably about what some interest bearing investments offer? Or maybe not right now. At times in the past decade I've received 2% +/- on 5 year CDs, but they're probably 1% today.

Your panels should last 25, maybe 40 years. Inverters may need replacing at some point.

< 2% doesn't seem impressive; somebody please double-check my initial check of 'Tinker's math.

The return after 30 years operation with one inverter replacement probably looks much better.
Also if by some remote possibility the utility does raise electric rates in that time, or even in the next 20 years.

"$12,800 5.1kw grid-tie system"
$2.51/watt. Not bad for turnkey installed (in the U.S., somehow Australia is much cheaper).
But materials are about $1/watt, so the $1.51/watt in labor, overhead, markup is why it isn't the slam dunk my DIY numbers show.

 

[Hedges]

Then to top it off when the $2400 stimulus money showed up in 2021 we put in another $600 and for $3k had a dozen or so hardwood trees removed that were blocking full sun from our panels. Also a 26% credit to the tune of $780.
Oops... made $$$ on that one got a 2 year supply of nice oak firewood and a 5ton pile of wood chips for composting!

Congratulations, you now have a larger carbon debt to repay
You've both released CO2 and removed a sequestration system.

 

[Ozark Tinkering]

Congratulations, you now have a larger carbon debt to repay
You've both released CO2 an removed a sequestration system.

But...but...my enphase app says I have already saved 117 trees???

 

[Ozark Tinkering]

I just did

That's what I figured.

After Jim got his system dialed in somehow he finagled a reverse mortgage loan on his house and I never heard of him out on the road again. Never heard how he fared in the end with his reverse mortgage, but he definitely was on the leading edge of grid-tie solar in the early 2000s.

@Hedges I tip my hat to you sir, for being right there with him.

 

[svetz]

Assume $120 per cell for 280 Ah 3.4V = 952 Wh

Dang! Good price on cells! Best I've seen was around $0.156/wh. Are those new/grade A?
3.4? Shouldn't that be 3.2V and 896 wh?

One needs to compare solar with batteries and solar without.

As the thread's about finding the price point at which it makes sense to abandon the grid/utility, having your own generation is a given.

Then batteries become almost an impossible proposition if the objective is saving money.

Based on what @Hedges said (cells at $0.134/wh), then from the math (see #36 & #39) it looks like you can break even in a decade with 3d autonomy & generator assuming 2% inflation if your total bill now is $.15/kWh. But if you go 2d autonomy and a generator it gets better. If they last longer than a decade it gets better. So, it doesn't need to drop much more to make it a "savings" proposition. The LTO looks like they're already a savings proposition, but the low power density means they'll take up a lot more space.

 

[Hedges]

Dang! Good price on cells! Best I've seen was around $0.156/wh. Are those new/grade A?
3.4? Shouldn't that be 3.2V and 896 wh?

They swore these were grade A!
(Really, only what I read here and remember. Any errors < 10% I consider in the noise, beyond what can count on my fingers.)

I seem to recall $80 to $120 for 280 Ah. But lots of pain and suffering from stripped shallow threads in dead-soft aluminum.

 

[eXodus]

Europe energy prices just tripled in the last 6 months.

One kWh is now 43 cents Euro.
The 4500kwh from my solar array is suddenly worth almost 2000 euro a year. (system had payback already a few years ago)

A battery went from payback in 15 years to payback in less then 4.

Do not assume that energy from the grid stays cheap my friends.

Guess I go battery shopping

 

[upnorthandpersonal]

One kWh is now 43 cents Euro.

Germany?

 

[Zwy]

It’s more like interest paid to central banks

Nope, it's a hidden tax. Devaluing a nation's currency allows the gov to print more.

 

[BMcL]

Europe energy prices just tripled in the last 6 months.

One kWh is now 43 cents Euro.
The 4500kwh from my solar array is suddenly worth almost 2000 euro a year. (system had payback already a few years ago)

A battery went from payback in 15 years to payback in less then 4.

Do not assume that energy from the grid stays cheap my friends.

Guess I go battery shopping

Agree, I didn't put much weight on the payback from savings when I purchased my system.
It's priceless when the grid is down, and America is very vulnerable to an attack on the grid.

 

[Ozark Tinkering]

Nope, it's a hidden tax. Devaluing a nation's currency allows the gov to print more.

When you get a cost of living raise it can put you into an even higher tax bracket, so the raise ends up being taxed at a higher rate and the taxman gets a raise too.

 

[wattmatters]

It's a little misleading

I think perhaps rather than focus on numbers per se, it might help if we work towards an agreed process for calculating the per kWh cost which anyone can use and plug in the values for the variables applicable in their individual case.

I have ideas but I think it would help to pull together the list of variables in the equation, e.g.:
- total purchase costs
- installation/commissioning costs
- maintenance costs
- capacity utilisation (average daily energy throughput divided by the battery capacity)
- expected degradation of capacity
- time frame for the system to be operational (will you be there 5 years, 10 years, 20?)
etc, etc

When we know what all the relevant variables are, then perhaps a more robust methodology can be developed to provide each use case a more reliable number with which they can compare to alternatives such as staying on grid.

The value of backup is different for everyone, so it wasn't included in the calculations

This is a tricky issue and I don't think we can just hand wave it away.

The grid does include the cost of redundancy in how it operates.

So if we are talking about a completely off-grid scenario, surely it will need some form of redundancy built in? Each user case will be different in why that redundancy is required, be it for periods of poor insolation, or anticipated maintenance etc, and what form that redundancy would take (be it alternative sources of energy to keep everything running through to "I don't care if I'm off line for two weeks waiting for a replacement doodad").

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.

OK, that's one way to calculate it.

My question though is how much energy will actually be cycled through the battery? Because it is the actual total energy throughput which matters, not the battery's capacity.

Unfortunately, these calculations assume solar panels+battery or nothing. One needs to compare solar with batteries and solar without. Then batteries become almost an impossible proposition if the objective is saving money.

When looking at a grid-tied scenario, definitely. In a totally off-grid scenario then batteries are kinda non-optional.

Cycle battery once per day for 10 years, 55,600 kWh from 3650 cycles (approximate lifespan)

The total energy a battery is capable of cycling though, and what you actually end up cycling through it are two completely different things.

Back to my question above, how much energy will actually be cycled through the battery over a given period of time?

e.g.:

Let's say you do your energy audit and recognise that to manage through periods of poor insolation, and/or times of year where daily consumption is seasonally much higher the battery needs to be (say) 3x your average daily consumption.

That's great. Except for large parts of the year you won't use the full capacity of the battery every day. Indeed the capacity utilisation for a battery scoped for off-grid needs may well be quite low, 30-40% perhaps.

So while a battery might be XkWh in capacity, on average over a year (or decade) you may actually only use 35% of the capacity each day. There will be days you use it all, and days you barely draw down on it. What that capacity utilisation ratio is will be individually variable, but I would be very surprised if it is unity or higher for an off-grid scenario.

In my opinion the battery cost per kWh should be based on the actual energy throughput for your expected use case.

I'll give an example, in this case it involves grid-tied batteries but the same principle applies to off-grid.

A couple of years ago I surveyed a dozen or so owners of Tesla Powerall 2s. Most had the one battery (13.5kWh useable), and one had two of them. I asked them for the total energy throughput for a full year for their battery, and calculated the daily average. It turned out the average capacity utilisation was ~60% of actual capacity, with none above 80%, some under 50%. So the energy throughput cost per kWh was somewhat higher than based on one full cycle per day.

Now being grid tied systems, if the battery is fully discharged well it's no big deal, the grid keeps the lights on. But if you expect to be fully off-grid, well the likelihood is the battery size required would be much larger than what makes financial sense for a grid tied solution.