No magic smoke, but no $ savings because I played with AC charging.

[millsan1]

Not a magic smoke post, but a newbie error I made, hope to educate other newbies.

I went live with Solar and Batteries in November of 23.

I had several thoughts in my head, re batteries.

1 - It's cool to run off batteries
2 - I need to fully cycle batteries, to keep them healthy

1 is correct, 2 is not so much, at least with Lithium Iron Phosphate.

So I ran off batteries as much as possible. When they got low, because December and January solar sucked, I would charge them back up with grid.

Then I run off batteries.

Well, stupid me, neglected to take conversion losses into account, so while it was fun, I wasted $ and my electric bills really didn't change, somewhat due to charging new EVs, but also related to all that back and forth with the batteries.

I really want my batteries for UPS of the house. I have 12 LIfePower4s, connected to my 18 KPV set up for whole home backup. 50% SOC would carry me for more than a day, in case of an outage and no solar.

So that is where I have my settings now, 50% when on grid, let the system do its thing. NO more playing with charging, discharging, percentages, etc.

 

[BentleyJ]

The scenario you describe is called Self Consumption and can yield savings but only in States like CA where Time of Use charges can be 3 to 4 times the off peak rates. In this case, the efficiency losses are more than compensated by the savings of not using utility power during peak times.

 

[millsan1]

The scenario you describe is called Self Consumption and can yield savings but only in States like CA where Time of Use charges can be 3 to 4 times the off peak rates. In this case, the efficiency losses are more than compensated by the savings of not using utility power during peak times.

Yeah, my power is flat rate, same all the time.

 

[webbbn]

You really need a Phd to understand my electric bill, but, if you ignore all the fixed taxes, fees, and surcharges, they pay me 1/2 the rate for excess that I sell back than they charge me when it flows the other way, so I try to capture as much as I can when the suns shining (which is fortunately most of the time in southern AZ), and drain the battery as much as I can at night.

I suspect it's going to be even worse in the summer when peak rates go much higher, since they don't seem to distinguish between peak and off-peak for sell-back.

 

[Oldphile]

I have 1:1 net metering unless I overproduce for the month. The overproduction earns about a 60% credit. When I get my batteries in the next few weeks, I'm planning to cycle them twice a week, just so I can verify their capability. Like @millsan1 there's actually a financial loss to deploying the batteries. I bought batteries for grid outages.

 

[JBertok]

A few factors to consider related to outages:
- Outages are more likely during bad weather where PV isn't productive.
- In an emergency, your power consumption metrics won't look like the daily usual because you'll be in an emergency conservation mindset and only powering just the essentials - refrigerator/freezer(s), internet router, lights, and maybe some heat if it's freezing out.
- Having even a small generator with a charger connected directly to the batteries would make it possible to draw down more of your storage and offset more of your draw from the grid. The idea here is that it's cheaper to keep a reserve of gasoline than it is to keep a reserve of power in high-dollar batteries. In theory, the savings from more daily self-consumption discharge from the batteries can offset the cost of the generator and chargeverter over time.

 

[1201]

I learned this the hard way too. Now if I use the grid I just use it as a passthrough to the loads and disable battery charging. I don't mind my battery sitting at 25% soc waiting for a sunny day.

 

[millsan1]

A few factors to consider related to outages:
- Outages are more likely during bad weather where PV isn't productive.
- In an emergency, your power consumption metrics won't look like the daily usual because you'll be in an emergency conservation mindset and only powering just the essentials - refrigerator/freezer(s), internet router, lights, and maybe some heat if it's freezing out.
- Having even a small generator with a charger connected directly to the batteries would make it possible to draw down more of your storage and offset more of your draw from the grid. The idea here is that it's cheaper to keep a reserve of gasoline than it is to keep a reserve of power in high-dollar batteries. In theory, the savings from more daily self-consumption discharge from the batteries can offset the cost of the generator and chargeverter over time.

Yeah my choice of batteries was 50% convenience, 25% cool factor, 25% tin foil hat SHTF.

 

[rpdom]

Yeah, charging batteries on a flat rate isn't worth it other than to prevent the batteries from over discharging. Now, on a nice TOU tariff like I've got, where overnight rates are usually below my export rate, it is definitely worth doing.

 

[JWLV]

You should avoid fully cycling LFP batteries as it could shorten its life.

Where did you get the idea that cycling a LFP battery is good for battery health?

 

[akitawpo]

LFP from SS are guaranteed for more than 6000 cycles which comes close to 17 years cycling them up to 20% DOD. Almost every manufacturer of LFP is close to this life expectancy or even more. If I spend thousands of dollars on batteries which are guaranteed for more than 17 years of continuous use, you can be sure I will use them every day. It is also very well stated that keeping LFP on high SOC for long periods can be worse than cycling them. I have been on auto-consumption for the past 3 years, no degradation on mi LFPs and have been cycling them daily. When it comes to LFP BMSs will die before you get to degrading the cells, keeping in mind to use the recommended charge / discharge rates or recommendations.

 

[robbob2112]

Everything I've read says cycle them periodically, like once a month minimum. And do a DOD of around 50% when you do. And pretty much all the mfg say for long term storage do it at 50% DOD. They also warn to never go below 10% which I treat as never go below 20%.

They aren't lead acid where you want them stored or kept near 100% with a trickle charger.

 

[Quattrohead]

You should avoid fully cycling LFP batteries as it could shorten its life.

Where did you get the idea that cycling a LFP battery is good for battery health?

For real ?

 

[JWLV]

OP said fully cycle. To me that means from 100% down to 0% DOD and back to 100%. That would be a full cycle. Doing that frequently would be bad and should be avoided. Many of you said 50%, 25%, or 20%. I wouldn’t even call that cycling. That is perfectly fine and nothing wrong with that. 0% is what I do not advise.

Perhaps my definition of a cycle is different than everyone else’s.

 

[ksmithaz1]

So if you can cycle your batteries from 100 to 0 and back 5000 times or from 80 to 20 and back 7000 times which nets the best result?

 

[JRH]

So if you can cycle your batteries from 100 to 0 and back 5000 times or from 80 to 20 and back 7000 times which nets the best result?

I think 5000 …as at the rate of tech advances very few of us ( if alive in 14-19 years ) will probably still be using the gear we own today… look at what we all used and payed a lot for 15 to 20 years ago for the cool stuff…giant tvs, laptops, solar panels ,i pods, dvd players etc…….now look at the price or if they even still make them.

I don’t disagree with being easy on them , but sooner than we think, there will be new gear and todays stuff will likely go the way of camaras , blackberrys ,and the dvd player.

Tech stuff generally just doesn’t last a long time…

I say use em up while you can , if you can outlive them…aging degradation and new better stuff will get them before cycling them deep or cycling them often…

Jus my opinion …

J.

 

[millsan1]

OP said fully cycle. To me that means from 100% down to 0% DOD and back to 100%. That would be a full cycle. Doing that frequently would be bad and should be avoided. Many of you said 50%, 25%, or 20%. I wouldn’t even call that cycling. That is perfectly fine and nothing wrong with that. 0% is what I do not advise.

Perhaps my definition of a cycle is different than everyone else’s.

Sorry grammar my am bad.

Fully cycle is somewhere around 100 to somewhere around 20 in my mind.

 

[ksmithaz1]

I think 5000 …as at the rate of tech advances very few of us ( if alive in 14-19 years ) will probably still be using the gear we own today… look at what we all used and payed a lot for 15 to 20 years ago for the cool stuff…giant tvs, laptops, solar panels ,i pods, dvd players etc…….now look at the price or if they even still make them.

I don’t disagree with being easy on them , but sooner than we think, there will be new gear and todays stuff will likely go the way of camaras , blackberrys ,and the dvd player.

Tech stuff generally just doesn’t last a long time…

I say use em up while you can , if you can outlive them…aging degradation and new better stuff will get them before cycling them deep or cycling them often…

Jus my opinion …

J.

Double trouble here. What you state above, AND, when you look at the total energy exchange 100-0-100 @ 5000 vs 80-20-80 @ 7000 you actually pushed more total energy thru the storage with the former than the latter. So if you are going to have to replace at some point anyway if you purchase less storage up front but exercise it more you end up saving money. At the expense of having to replace the components sooner. . . Which are likely to be much better by the time you get around to it!

 

[JRH]

Double trouble here. What you state above, AND, when you look at the total energy exchange 100-0-100 @ 5000 vs 80-20-80 @ 7000 you actually pushed more total energy thru the storage with the former than the latter. So if you are going to have to replace at some point anyway if you purchase less storage up front but exercise it more you end up saving money. At the expense of having to replace the components sooner. . . Which are likely to be much better by the time you get around to it!

Exactly ……. I submit the following….

 

[ksmithaz1]

One of my problems with "% charging" is if you are not supposed to go below 20%, then you mis-calibrated. Whatever was 20 needs to be zero (0). My amplifier goes all the way to 11. Yours only goes to 10. Meh. I'm not in "Spinal Tap" I don't need to go to 11 . The battery 0-100% should be calculated to optimize total energy thruput on the device. I would like to see a rating as above: 0-100 @ 6000 full cycles. This should be whatever the point is that maximized total energy in/out. Compressing the charge range is going to buy you some cycles, should that be more important you adjust from the optimal point as appropriate. Also the statistical data to date that I've seen seems to indicate charging to 100% does not seem to be destructive, but dipping down the bottom has a much greater effect. YMMV.

I think we are still learning all this stuff.