Solar power, can it be done DIY?

[ThaiFig]

5 hours to charge at .2C from sunshine is doable, but the 8 following hours of absorbtion would require power from the grid, defeating the purpose...  I'd want to be able to more or less immediately follow the charging session with a .2C discharge to continue to function without resorting to the grid. Still, the idea of having a battery that almost duplicated the capabilities of a Lifepo4 battery at the price of a lead acid battery is intriguing. It's not something I would have considered, even though I know Lifepo4 batteries are likely to be obsolete by the time they reach the end of their useful life, having been replaced with a newer tech.  So thanks for bringing them to my attention.  How do you utilize them?  Charge at a higher rate at the expense of future longetivity?

[Muhendis]

11 hours ago, ThaiFig said:

Interesting. Victron apparently has some as well.  Here's what they had to say about them:

 

Yeah.

Not just victron but just about every battery company is climbing onto that particular bandwagon.

When I got my batteries last year, there were very few choices but now you can find pages of companies advertising them.

 

At 77kg each, mine are heavy but since the intention is to leave them in situ I have no problem with that.

The same as older style lead acids, I still target 30% DoD which will give them an estimated 11+ year life.

Given the choice I went for the Gel type batteries. They have a design life of 20 years whereas AGM's and other VRLA types only have 15 years.

What is meant by design life is standby use not daily cycling.

 

Are they easy to DIY?

Absolutely.

If you can change a car battery you can do your own Lead carbon installation.

[lom]

How does it affect the lifetime of lead-carbon batteries if you only have an hour or two of absorption time before starting to discharge them?

[Muhendis]

14 hours ago, ThaiFig said:

5 hours to charge at .2C from sunshine is doable, but the 8 following hours of absorbtion would require power from the grid, defeating the purpose...  I'd want to be able to more or less immediately follow the charging session with a .2C discharge to continue to function without resorting to the grid. Still, the idea of having a battery that almost duplicated the capabilities of a Lifepo4 battery at the price of a lead acid battery is intriguing. It's not something I would have considered, even though I know Lifepo4 batteries are likely to be obsolete by the time they reach the end of their useful life, having been replaced with a newer tech.  So thanks for bringing them to my attention.  How do you utilize them?  Charge at a higher rate at the expense of future longetivity?

Firstly the lead carbon batteries will charge as fast as your solar installation can manage. My somewhat knackered solar panels feed up to 45 Amps into the battery which is 750Ah and the battery is often full before lunch. Speed of charge depends what other machines I have running. I do woodwork. 

My charge controllers know what state of charge the batteries are at and they modify the CC/CV profile accordingly. When the batteries are full charging ceases. 

There is no effect on longevity although the first initial charge cycle needs to be a bit gentle and kept below 60 Amps per battery. After that they will take everything you can throw at them.

The thing about lead carbon batteries is that they act like a capacitor and so don't have the charge limitations of lead acid batteries.

14 hours ago, ThaiFig said:

but the 8 following hours of absorbtion would require power from the grid

This does not make sense to me.

Once the batteries are full they no longer require charging so whatever is available from your solar panels can be used for whatever you want this includes trickle charging if necessary.

Why do you think you would need power from the grid?

14 hours ago, ThaiFig said:

I'd want to be able to more or less immediately follow the charging session with a .2C discharge to continue to function without resorting to the grid.

As long as you have a decent bit of sunshine on your panels, resorting to the grid shouldn't come into it.

Your batteries are for when the sun don't shine which, surprisingly, happens for almost 12 hours every day.

[Muhendis]

2 hours ago, lom said:

How does it affect the lifetime of lead-carbon batteries if you only have an hour or two of absorption time before starting to discharge them?

A lead acid battery will suffer from sulfation if it is only partially charged.

Lead carbon batteries, on the other hand, will not suffer from sulfation to anything like the same extent.

Charge cycles for lead carbon are the same as for lead acid ie there is a constant current phase followed by a constant voltage phase more commonly referred to as CC/CV

CC mode pumps current into the battery and monitors the battery voltage. When a certain voltage is achieved, usually 90%, the charger will switch to  CV (sometimes referred to as the absorption stage) mode and monitor current flowing into the battery.

When this current reaches a very low value charging is complete and stops.

This process can be ridiculously fast with lead carbon batteries.

[ThaiFig]

13 minutes ago, Muhendis said:

Firstly the lead carbon batteries will charge as fast as your solar installation can manage. My somewhat knackered solar panels feed up to 45 Amps into the battery which is 750Ah and the battery is often full before lunch.

 

When the batteries are full charging ceases. 

 

There is no effect on longevity although the first initial charge cycle needs to be a bit gentle and kept below 60 Amps per battery. After that they will take everything you can throw at them.

 

The thing about lead carbon batteries is that they act like a capacitor and so don't have the charge limitations of lead acid batteries.

This does not make sense to me.

 

Why do you think you would need power from the grid?

 

In your case charging ceases when target voltage is reached.  But the longevity claims I've seen so far are with .2C charge rates. If you slow charge a battery at that rate, voltage will rise to the final level but the battery won't be full, it needs to be held to that final voltage till current drops to zero or thereabouts. This absorption period for lead acid is several hours. (Set the cutoff voltage too low with Lifepo4  and it will also require a lengthy absorption  time). With your high rate of charge, you won't need that absorption time but I'm thinking your batteries will take a major longevity hit instead. Have you seen any data to support your belief that high C charge rates don't wear out your batteries faster?  Just because you CAN do something doesn't always mean you SHOULD 😉. 

[ThaiFig]

45 Amps into a 750 Ah battery would take 16 hrs to deliver that much energy.  .2C would be 150 amps. So you aren't rapid charging them after all, quite the opposite. So forget my last comments about longevity.  If they reach a full state after only a few hours at 45 amps, they either don't really hold 750 Ah or, more likely,  you aren't draining them very much overnight.

[Muhendis]

2 minutes ago, ThaiFig said:

45 Amps into a 750 Ah battery would take 16 hrs to deliver that much energy.  .2C would be 150 amps. So you aren't rapid charging them after all, quite the opposite. So forget my last comments about longevity.  If they reach a full state after only a few hours at 45 amps, they either don't really hold 750 Ah or, more likely,  you aren't draining them very much overnight.

Please note my earlier comments re. 30% DoD

 

3 minutes ago, ThaiFig said:

you aren't draining them very much overnight.

Well done you have won the top prise.

The less they are discharged, the longer they will live.

Having said that my solar panels are well over 10 years old and I do have other things to do with whatever power they can give as well as charge batteries.

I will be getting some shiny new panels in the near future.

[ThaiFig]

OK, I understand now. The advantage that lifepo4 holds is that you can routinely run them with 90% DoD on a daily basis. With a single charge/discharge cycle daily, they will die of old age before they use up their cycles.   If you limit yourself to 30% DoD on your carbon batteries, you end up with 3 of them for every lifepo4 (plus BMS) you are substituting.  So in my case  they would have to be 1/3 the cost of the same capacity lifepo4 battery/BMS combo to make economical sense. Perhaps that's the case, I don't know. Even if that's not true now, it could be in the future.  Now that you've introduced them to me, I'll definitely keep them in mind for my next install.  For this one, I've already started assembling the parts for a lifepo4 48 volt system.

 

BTW - I'm seeing multiple promotions of Tier 1 550 watt panels for around 3000฿ online. Could be a good time to upgrade 😀 

[Muhendis]

38 minutes ago, ThaiFig said:

Just because you CAN do something doesn't always mean you SHOULD

You sound like my wife 

You are quite right about normal lead acid batteries but I am talking about lead carbon batteries 

Please note I have already mentioned they need a gentle charge the first time around.

After that they can be charged similarly to a capacitor which is what they are in some respects.

48 minutes ago, ThaiFig said:

This absorption period for lead acid is several hours.

Agreed 

This is referred to as charge acceptance

But I am not talking about lead acid.

Charge acceptance for a lead carbon battery is similar to a LiFePO4 which is much much better than lead acid.

This is due to the capacitive effect of the additional carbon/graphene rather than the chemical change in the lead/lead sulphate of the lead acid battery.

 

If you try to charge a lead acid battery too quickly it will cook and enjoy a slightly more violent but shorter life.

 

[Muhendis]

2 minutes ago, ThaiFig said:

BTW - I'm seeing multiple promotions of Tier 1 550 watt panels for around 3000฿ online. Could be a good time to upgrade

Thanks.

Already on it but I am looking at 340W for preference because they are smaller for manhandling and less of a problem if one is not so good.