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Domestic Batteries for on-grid solar

Domestic Batteries for on-grid solar

RE: Domestic Batteries for on-grid solar

Coming in with no context w.r.t. to the blog, but the results didn't necessarily ring alarm bells in some sense
> The blogger was apparently expecting much better capacity degradation performance than actually measured -- I don't know whether that expectation was necessarily justified -- many of the batteries seemingly were on track to meet the specified end-of-life (EOL) capacity of 60%
> Given the nature of the accelerated testing and whether such conditions didn't cause excessive degradation, the capacity results weren't necessarily alarming
> Note that accelerated life typically requires lots of units tested just to figure out what the acceleration factor is in the first place

> I would separate the "failures" from the capacity question in an engineering discussion -- one major issue is that a 10-yr lifetime requires roughly a mean time between failure of 95 years to achieve a 90% reliability
> That's not necessarily unachievable, but given the accelerated life conditions, it's not clear to me whether those conditions were excessively harsh. We've (the royal one) obviously have achieved reliabilities on that order in satellites and other hardware
> Note that acceleration factors for battery might result in a different acceleration factor for the electronics, etc., so one has to be very precise about what the true results were and how to interpret them

> The bigger issue was that some of these companies were too small to necessarily have done all the engineering and design to make everything work
> Accelerated life testing is where we find out whether our design assumptions were correct and to fix them if they weren't -- unfortunately, if the company goes belly up, then the lesson is never learned and no corrective actions will have taken place

TTFN (ta ta for now)
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RE: Domestic Batteries for on-grid solar

Well now you've got me wondering what the usage profile for an on-grid battery looks like. i suppose that is very dependent on how the controller/smart meter is programmed.


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Domestic Batteries for on-grid solar

My guess is that the usage profile would depend largely on the time of use rates for utility power.
No point in cycling the battery if there is no monetary gain as a result.

RE: Domestic Batteries for on-grid solar

My electricity provider claims the average electricity usage for a 2 occupant house is 17 kWh a day, at this time of year (winter) a 5kW solar system gives about half that.


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Domestic Batteries for on-grid solar

I have a BYD H box.

That hard cycling of any battery is going to kill it.

The way I have mine set up is it starts charging at about 10 am and then its done by lunch and it does it an C0.6 but the BYD BMS looks after it. Then hours later when the sun goes down it discharges.

I would have thought the charging/discharge electronics would be sitting at max 24 h using this testing profile. Same with the battery chemistry.

I might change the charging release time so it gets a slow charge as the sun comes up.

RE: Domestic Batteries for on-grid solar

Does the hard cycling exceed the ratings of the battery? Perhaps we need better standardization of the definitions of capacity.

RE: Domestic Batteries for on-grid solar

There is its in kWh but the USA solar lot tend to use amp hours. Which is mainly linked to the utter panic when you start talking about triple figure voltages so a lot especially DIY run at around 48V.

The charge and discharge, is done with a C value. So using my battery as an example which is a 6.4 kWh its C value its charging is 0.6C so the max it will accept is 3.7 kW. Discharge it can do 1C so 6.4kW I think it can also do 1.2C for a period.

Again this isn't generally used in the USA they talk about amps.

I have had a look at my battery's paper work and no it won't be exceeded. But the carrier is that it comes with a BMS which has temp probes to the cells and does vary the charge and discharge rates with battery charge level and temperature. Between 10% and 90% its the book figures but outside that it changes things.

RE: Domestic Batteries for on-grid solar


Again this isn't generally used in the USA they talk about amps

That's exactly the problem, there isn't a standardized definition. KWh is really the only number that matters. Ah is used because batteries tend to operate at lower voltages than the system so you can call out a higher Ah to give an inflated capacity number.

And when you have battery systems that don't tolerate deep cycling such as lead acid you really need to divide your capacity by 2 or more.

RE: Domestic Batteries for on-grid solar

There is in the rest of the world.

But you do seem to have a hardcore that doesn't want to play the game.

They also want everyone else to follow US electrical regulations. Enphase were trying to lobby the EU to go for a standardised safety and limitations for domestic solar which would have made microinverters and optimisers be pretty much mandatory.

Thankfully the Austrian and German inverter manufactures put that nonsense to rest.

RE: Domestic Batteries for on-grid solar

AGM lead acids you should only use 50%, according to the standard blurb. If you look at the DoD vs number of cycles curve it doesn't really cost much more per kWh over the life of an AGM battery whether you use 80% DoD or 50%.

and here's someone who's run the numbers


The danger of course with using 80% routinely is that one day you leave the pump running overnight and then everything shuts down. (Ahem)


Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: Domestic Batteries for on-grid solar

It seems to be only off grid that run 12/48V home made battery gear which use wet battery's in europe.


When I went through the options 3 years ago LIPo4Fe had clear advantages on all fronts apart from temperature window and charge rate.

That is my limitations. I have stuck mine in a constant 20 deg cellar. I get 95% discharge off a 6.4 kWh high voltage battery.

Most of the big names are NMC. Which I suspect in 5 years time there will be lots of noise as they start needing replaced as a lot of people seem to have it in their heads that they are going to get 15-20 years out of them. If they fail just after the 10 year warranty is up then they will be lucky to recuperate the investment.

If you did a spread sheet with life cycles, capacity, cost LiPo4Fe clearly came out on top but then they had the highest up front cost until Tesla power wall came along and China started producing 12V wet replacements in Lipo4Fe. But the 12 V ones are a bit dodgy because they each have an internal BMS and things can happen if you try and charge them in series. The solar battery industry world wide is miss selling rather wildly. When you add in the DIY battery packs some of which are disasters waiting to happen they whole thing is a bit of mess.

My hybrid inverter had 2 compatible at the time one NCA the other the BYD liPo4Fe and i wasn't going to go AC couples. 3 years on more by luck than judgement it looks like I went for the best option.

RE: Domestic Batteries for on-grid solar

The worst part is that the people selling these things, can't even answer my first five questions.
Not that I am counting the number of questions. Just that they have no technical depth to answer.
I also seem to have to explain to people, over and over, that car batteries are not storage batteries.

RE: Domestic Batteries for on-grid solar

Don't forget Greg that a lead acid battery is always losing capacity so today's 50% cycle could be tomorrow's 80%.

RE: Domestic Batteries for on-grid solar

I bought mine of a company called mg solar in Germany.

Must admit he was very knowledgeable on all of the solar stuff. And also persuaded me to go for 6.4 kWh not bigger. And he was right if I had gone bigger it would never have paid itself off.

I put 1200 kWh through my battery every year which is 400 euro. I bought it for 4200 euro. Next size up would have been 5500 euro

RE: Domestic Batteries for on-grid solar

The wet lead acid battery bank is almost a cult religion.

The amount of heavy duty wire they use and chargers etc.

Then there is the regular maint required. The weight of them and the volume they take up.

I can't see how they can be cost effective. Especially if you take labour into account. Distilled battery water isn't cheap to boot.

RE: Domestic Batteries for on-grid solar

Them flooded cell lead-acid batteries are what keeps the lights on...

I’ll see your silver lining and raise you two black clouds. - Protection Operations

RE: Domestic Batteries for on-grid solar

FLA has a lot of advantages. They aren't prone to fire, number one. They may sound like an environmental disaster in a box, but the lead is very recyclable and acids aren't particularly difficult to neutralize and dispose of.

RE: Domestic Batteries for on-grid solar

I don't have a problem with fla for stuff that they are good at. But the solar charging and discharge profiles don't really suit them.

Energy density is also an issue.

It's the amount of time and effort and tlc that the people who have relatively problem free time with them with solar go through.

They need to be almost a family pet, checked on, fed, pampered occasionally.

I have logged onto my BMS once in 3 years and 500 cycles.

I still think high currents play a large part in them dying quickly and heat. Mine max out put is 11 amps. Some of the DIY banks are pumping 200 amps plus with round circle losses over 30%. Mine is 4%.

The ones we tend to use in Europe are 100v plus voltage and set output current. So if you increase the capacity the voltage goes up. They say its more efficient if the voltage is above you single phase as voltage.

I think Tesla is 275V same as mine. But if I went for the max number of modules roughly the same capacity as a powerwall2 it would be over 550V. The powerwalls cause issues because they are over 16amps. And I don't like the no right or way to alter settings feature on them. Apparently they lock out if the internet drops out for a period of time.

RE: Domestic Batteries for on-grid solar

That would be a problem as the internet here goes out for almost every heavy rain or snow.

RE: Domestic Batteries for on-grid solar

It's not instantaneous. Its 10 days plus or something like that. One of its features is power cut islanding.

I only know what you see in the solar groups. Wrong chemistry, way to expensive and no control over what it does was my issue so didn't progress to in depth feature research.

RE: Domestic Batteries for on-grid solar

Flooded lead acid batteries go bad over time due to the lead particles building up under the plates, causing individual cell loss.

The acid itself doesn't go bad and can be reused.
Submarine, LA batteries have acid circulation pumps to pump the acid through coolers to reduce the temperature, back in the day.

Back in the day, the battery would be drained, with all the lead particulates, and quickly refilled with acid and recharged.
As long as the plates were more of less intact, the battery may have reduced capacity but still works.

Battery life is extended if overcharging is avoided.

The mesh pad designs, are not as robust. but more data is required.

RE: Domestic Batteries for on-grid solar

So you could get a longer life if the battery jar was deeper than the plates. Sort of wondered why the old battery jars were so deep. But I have never seen one working, just the jars at farm auctions.

RE: Domestic Batteries for on-grid solar

I think they call them trash racks, where there is space at the bottom of the cell for the plate material that is shed during every cycle. Also noticeable when the material builds up it pushes the plate and terminals up and out of the casing. For this reason there's always some space allowed for in the terminal for growth.

A former employer had a nice cutaway profile of a battery that showed all the components, it was quite impressive.

EDMS Australia

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