'no sell' hybrid roof top solar with batteries

[Hedges]

I know this is a bit dated, but this calc for the value of the battery is not correct.

The value of the battery is:
X = Price you pay for grid power
Y = Price you get paid for backfeeding the grid
K = KWh per month that you will consume at night that you backfed
(X - Y) * K = Value.
(until you either outrun the extra power produced during the day or outrun the total amount of power used when the panels aren't producing)

When I'm paying 12 cents and getting 4 back, my batteries pay for themselves pretty quickly.

Saving your PV generated power in batteries and using it later saves you $0.08/kWh
I think you'll go broke quickly that way.
What is the amortized cost of a battery to provide storage of one kWh? My math said $0.50/kWh the first time I did it.
That was the purchase cost of commercial lithium batteries (or AGM batteries) at the time (2 years ago), divide by kWh capacity, divide by cycle life.

I think instead of buying a battery, I could save money by paying the utility company $0.08/kWh to store it for me.
If I don't want to pay in cash, I can pay them two additional kWh to store my kWh.

I can make a kWh for $0.05/kWh (amortized over 10 years), so it would cost me $0.15 to get a kWh for later use, a loss of $0.03 if utility rate is $0.12/kWh.
But over 20 years, costs me $0.025 or $0.03/kWh (depending on whether inverter needs replacement), so building 3x the PV array I actually need would give me power for later at cost of $0.075 or $0.09/kWh. That saves money, vs. batteries losing money.

 

[timselectric]

In my case. The cost savings of buying 3 non grid tied AOI's, pays for the batteries. And in 7 years, I will have recouped 100% of my investment. With 3 days of battery backup.

 

[Surferdudemi]

Saving your PV generated power in batteries and using it later saves you $0.08/kWh
I think you'll go broke quickly that way.
What is the amortized cost of a battery to provide storage of one kWh? My math said $0.50/kWh the first time I did it.
That was the purchase cost of commercial lithium batteries (or AGM batteries) at the time (2 years ago), divide by kWh capacity, divide by cycle life.

I think instead of buying a battery, I could save money by paying the utility company $0.08/kWh to store it for me.
If I don't want to pay in cash, I can pay them two additional kWh to store my kWh.

I can make a kWh for $0.05/kWh (amortized over 10 years), so it would cost me $0.15 to get a kWh for later use, a loss of $0.03 if utility rate is $0.12/kWh.
But over 20 years, costs me $0.025 or $0.03/kWh (depending on whether inverter needs replacement), so building 3x the PV array I actually need would give me power for later at cost of $0.075 or $0.09/kWh. That saves money, vs. batteries losing money.

I think the math has changed with LiFePO4 batteries. For the batteries alone, assuming you use 60% of capacity per charge and get 4000 cycles, you're looking at about $0.07 / kWH. If you've already got the hybrid inverter-based solar system installed, you would still save money (excluding the cost of capital). If you use 70% or 80% of the battery capacity per charge, you're even farther ahead. And this ignores the benefit of having a large UPS for your critical loads when the power goes out for a day or two.

 

[Surferdudemi]

That scenario is becoming increasingly costly, in the US. Net metering, is going the way of the doe doe bird. The power company's doesn't want to be our batteries. And, has no need of our production, in the middle of the day.

Based upon the time-of-day rates I'm paying, the power company DOES want my power from 11 am to 7 pm. It's about a $0.10 differential.

 

[Zwy]

Saving your PV generated power in batteries and using it later saves you $0.08/kWh
I think you'll go broke quickly that way.
What is the amortized cost of a battery to provide storage of one kWh? My math said $0.50/kWh the first time I did it.
That was the purchase cost of commercial lithium batteries (or AGM batteries) at the time (2 years ago), divide by kWh capacity, divide by cycle life.

48 cells, 280Ah at $125 each at the low end and $150 each at the high end. Show me the cost amortized using your math because I'm coming up with way different numbers than you. One other factor is how much of the battery capacity is used, per day......

What are you using for cycle life? 6000 cycles divided by 365 days is over 16 years.

I think instead of buying a battery, I could save money by paying the utility company $0.08/kWh to store it for me.
If I don't want to pay in cash, I can pay them two additional kWh to store my kWh.

I can make a kWh for $0.05/kWh (amortized over 10 years), so it would cost me $0.15 to get a kWh for later use, a loss of $0.03 if utility rate is $0.12/kWh.
But over 20 years, costs me $0.025 or $0.03/kWh (depending on whether inverter needs replacement), so building 3x the PV array I actually need would give me power for later at cost of $0.075 or $0.09/kWh. That saves money, vs. batteries losing money.

 

[Zwy]

I look at it this way, with 3 48V 280Ah batteries, the cost is average of $6600 with cells between $125 and $150 cost. 6000 cycles (my house will use less than the full capacity of the bank), comes to $1.10 per cycle cost. If I use 30Kwh per day from the batteries (not counting any PV), that comes to $0.036 per Kwh.

 

[Hedges]

I think the math has changed with LiFePO4 batteries. For the batteries alone, assuming you use 60% of capacity per charge and get 4000 cycles, you're looking at about $0.07 / kWH. If you've already got the hybrid inverter-based solar system installed, you would still save money (excluding the cost of capital). If you use 70% or 80% of the battery capacity per charge, you're even farther ahead. And this ignores the benefit of having a large UPS for your critical loads when the power goes out for a day or two.

I agree, LiFePO4 cells for DIY I came up with around $0.05/kWh. That was something like 3000 cycles 100% DoD or equivalent.
Important thing is to do the math, otherwise people buy expensive batteries costing $0.20 to $0.50/kWh and think it will save them money.

Wild card is actual cycle life achieved.
A test of dozens of commercial batteries found only 5% of them reached expected cycle life (Sony, and one or two others.) The rest failed, were either repaired or abandoned.
So my suggestion if considering a big, expensive system would be don't count on getting more than 25% of battery life; try to break even by then.
At least with DIY, you have a better chance of repairing it. Any assembled battery, expect vendor to have vanished from the face of the earth during anticipated lifetime.

 

[Surferdudemi]

48 cells, 280Ah at $125 each at the low end and $150 each at the high end. Show me the cost amortized using your math because I'm coming up with way different numbers than you. One other factor is how much of the battery capacity is used, per day......

What are you using for cycle life? 6000 cycles divided by 365 days is over 16 years.

Here's a quick worksheet with the NPV. You can change the hurdle rate (cost of capital or RoR for alternate investment), cycle life, electricity cost differential, etc. It's in ODS format, which you can use with LibreOffice, Excel, or Google Sheets. Had to ZIP because ODS is not an allowed format.

 

[Ellis Redding]

I agree, LiFePO4 cells for DIY I came up with around $0.05/kWh. That was something like 3000 cycles 100% DoD or equivalent.
Important thing is to do the math, otherwise people buy expensive batteries costing $0.20 to $0.50/kWh and think it will save them money.

Wild card is actual cycle life achieved.
A test of dozens of commercial batteries found only 5% of them reached expected cycle life (Sony, and one or two others.) The rest failed, were either repaired or abandoned.
So my suggestion if considering a big, expensive system would be don't count on getting more than 25% of battery life; try to break even by then.
At least with DIY, you have a better chance of repairing it. Any assembled battery, expect vendor to have vanished from the face of the earth during anticipated lifetime.

This is why I would consider something like a Growatt over a lot of other ones that need proprietary batteries. Sure the system without batteries is competitive but then they require a battery that's 10x what it should be.

 

[Ellis Redding]

Here's a quick worksheet with the NPV. You can change the hurdle rate (cost of capital or RoR for alternate investment), cycle life, electricity cost differential, etc. It's in ODS format, which you can use with LibreOffice, Excel, or Google Sheets. Had to ZIP because ODS is not an allowed format.

8 year payback, if I'm reading that right.

 

[crossy]

This is why I would consider something like a Growatt over a lot of other ones that need proprietary batteries. Sure the system without batteries is competitive but then they require a battery that's 10x what it should be.

Yeah, a mate has a Huawei system. Originally designed as grid-tie the electricity authority has taken so long to install his export meter (his existing meter is non-reverse) that he decided to add batteries. Huawei use high-voltage (read $$$) packs which are almost unobtainable as "pattern" units. so now he's waiting for the batteries, 6 months and counting.

He's not (quite) at the point of ripping out his Huawei inverters, but he's not happy at giving a significant chuink of energy to the supply authority every day for free.

We are using 200Ah ex-golf cart LiFePO4 cells, half the price of new they are performing pretty well, well enough that I'm getting another pack.

 

[schmism]

Saving your PV generated power in batteries and using it later saves you $0.08/kWh
I think you'll go broke quickly that way.

The $/kWh you listed is fairly hard to debate. The facts kinda say it is what it is.

However for me there is a divide by zero issue when the grid goes down and I don't notice because I have a battery backup running critical loads. I've sailed through my third such event in the year my system has been operational. It was one of the reasons why I chose to go with a battery backup system and not a grid-sell back option.

Mines not perfect, still undergoing tweeks to get better performance out of it, but I wouldnt build it any other way.

 

[timselectric]

Based upon the time-of-day rates I'm paying, the power company DOES want my power from 11 am to 7 pm. It's about a $0.10 differential.

You're one of the lucky few, left.

 

[Zwy]

Here's a quick worksheet with the NPV. You can change the hurdle rate (cost of capital or RoR for alternate investment), cycle life, electricity cost differential, etc. It's in ODS format, which you can use with LibreOffice, Excel, or Google Sheets. Had to ZIP because ODS is not an allowed format.

It's locked in read only mode for me.

 

[crossy]

It's locked in read only mode for me.

It worked OK for me, extract the .ods from the .zip file and open with Excel (I have Office 2016 pro-plus if that matters).

It does initially open as read-only (all "foreign" files do), just click on the "enable editing" box