battery bank ?

[geogentry]

Yes I agree 700wH per day is a reasonable output guesstimate for 200W rated panels. But optimistic to say enough to replace 40-50AH average daily usage if that's the only charge source and you're trying to get the bank back to 100% full.

Charge efficiencies greatly decrease as SoC gets higher.

I would hope that the person using a solar system did not run the system in a manner that relied only on the batteries when using power.  I believe the intent is for the batteries to be a reserve when solar energy is not available.  If someone is using the majority of the solar during the day and draining the batteries at night then they either need to learn power management or get a vastly larger system.  Even if they only used a portion of the solar during the day and drained the batteries at night it would be very difficult to get back to full charge as you said.

The efficiency would drop as most good chargers reduce the current flow to the batteries as they approach full charge because of of the increase in internal resistance of the battery as the battery approaches full charge.  If they don't there is a very real chance that the batteries will be damaged.

 

[John61CT]

Those not interested in techie details just ignore the following, but some may be interested.

Charge Efficiency Factor is independent of acceptance rate, a low acceptance rate doesn't imply low charge efficiency.

Charge efficiency = amp hours stored per amp hour input

Acceptance rate = max amps in at a specific charge voltage.

CEF varies per model battery; Trojan for example recommends starting with 89% for their T-105, and Peukert exponent of 1.24 

CEF does not stay constant across the SoC curve, and changes with age as well.

Look here for more https://marinehowto.com/programming-a-battery-monitor/
search for "coulombic efficiency"

Also a good PDF from Sandia labs here http://www.cruisersforum.com/forums/attachment.php?attachmentid=160687&d=1513634784

 

[MrAlvinDude]

So, I wonder how much of those last entries about W and Wh and Ah made enough sense to the original poster, to give any practically useful insights, and made his day and choices feel easier to make?

I hope it is okay that I have taken the liberty to summarize a few details from this thread.

Original question:
- what size battery to get to fit a 200W solar panel kit?
- would 2 x 100 Ah be good?
- is more or less Ah better?

Other comments: I would be powering
- a computer,
- cell phone,
- crock pot or
- maybe sometimes a pressure cooker
- and a vent fan

Other notes from the discussion
- I always planned on having propane stove, I don't know how to live without one
- will be basing everything (or most things) off 12 volt

- what size inverter would be good?
- some mention about a microwave own


- some mention about how much energy is realistic to be collected on an average day from 200W of solar panels.

Daily energy being equivalent of 700W. It was discussed how this can be expressed, so it is both easy to understand, for novices and experienced folks alike. So it could perhaps be expressed as 700W spread out over a day, or 700Wh, or about 58Ah (@12V).

I wonder how understandable all of these numbers are to the original poster anyway?
Or if further examples of how these numbers  translates into daily practices, limits and options, would help the original poster closer to understanding of
- will 2 x 100Ah batteries be good? Or woulds bigger or smaller battery bank be better?


Notes about batteries:
- 122Ah battery option at walmart for $86
- smaller battery bank (less than 200Ah)  is no the advisable way to go

Notes about microwave:
- then a bigger bank (bigger than 200Ah) is advisable to consider.
- an inverter big enough to run the microwave is needed (typically minimum 2000W)

Notes about,
-  the balancing act between: incoming energy, stored energy, used energy,
- and being able to recharge batteries once the energy has been used, and especially in winter (or other days with less than average sun).
- planning for only using 20% of the energy reserve in the batteries, is advisable, as it gives longer battery life

Notes about:
- the wisdom in using daytime sun/energy, during the day
- and only using smaller amounts of energy when there is no sun, and energy has to be drawn from the batteries.



Remembering what the original questions were, what kind of advice would you give the original poster?
And how would you word that advice, so it (in your opinion) makes as much sense as possible to the original poster?


I hope I have not offended anyone with this summarizing post, as this is definitely not my intention. My hope is, the summary will be able to help the original poster have some of those AHA moments, where stuff that were previously not so easy to see clearly, becomes clear. And in a couple of weeks (or so) possibly becomes second nature, and easy to use in everyday van life.
Okay?

 

[Bob2]

New B challenge in entering a post.  Please disregard and look to my question.  Thanks!

 

[Bob2]

I have a related question to battery use and types. I have typically seen where people install even numbers of batteries. In my 5th wheel, I have two 12v Marine & RV, Deep Cycle batteries. I have room to add a third in the battery bay. Is there a reason I should not add a third to add to my power storage capabilities?

Thanks!!!
Bob2

 

[MrAlvinDude]

I have a related question to battery use and types.  I have typically seen where people install even numbers of batteries.  In my 5th wheel, I have two 12v Marine & RV, Deep Cycle batteries.  I have room to add a third in the battery bay.  Is there a reason I should not add a third to add to my power storage capabilities?

Thanks!!!
Bob2

To add a new battery to existing batteries is not optimal, as the weakest battery(ies) will set the standard for all of the batteries in a battery bank. In practical terms, this will result in the new battery typically going dead at the same time as the old ones does. 


When that is said, then there is no reason (that I know of) to either use odd or even numbers of batteries, so long as they are all connected in parallel.

 

[geogentry]

Remembering what the original questions were, what kind of advice would you give the original poster?
And how would you word that advice, so it (in your opinion) makes as much sense as possible to the original poster?

You are correct.  The thread did wander too far afield to be of any use to the original poster.
I think in my first post - somewhere around number 12 in the thread I tried to answer his question.

If he uses 2 x 100w panels he will get 700 watt total for the day and will need a 250 Ah battry.  And he should get an inverter that will handle more current so that he does not have to upgrade in the future if/when he upgrades his solar system.

He then talked about using 3 x 330 watt panels.
This would give him just short of 3500 watts of power requiring him to put a battery bank together to hold 1200 Ah.  The same applies to the inverter although he may not be upgrading beyond this point.

Both of these solutions would allow him to have the respective power to use for two days with no sun.

If he is going to be using a computer that consumes 228 watts of power then the larger system would be the one to use. The smaller system would severely limit his time on the larger computer. And since he is going to be using it for gaming IMO a couple hours of gaming is not going to be enough for him. The larger system would easily allow for typical round of gaming on the more involved games with power left to do other minor tasks.

I hope I have not offended anyone with this summarizing post, as this is definitely not my intention. My hope is, the summary will be able to help the original poster have some of those AHA moments, where stuff that were previously not so easy to see clearly, becomes clear. And in a couple of weeks (or so) possibly becomes second nature, and easy to use in everyday van life.
Okay?

You did not offend me in the least.  You made a very valid point.  I find it all too easy to get carried away in such discussions and lost sight of the original objective which was to help the Original Poster.
Thanks

 

[John61CT]

I have a related question to battery use and types. I have typically seen where people install even numbers of batteries. In my 5th wheel, I have two 12v Marine & RV, Deep Cycle batteries. I have room to add a third in the battery bay. Is there a reason I should not add a third to add to my power storage capabilities?

Thanks!!!
Bob2

No problem, but generally not a good idea to add new batts to an old bank, the new one will get pulled down very shortened life.

But if they're only at say 20% or less of their expected lifespan, I wouldn't worry about it.

 

[Weight]

With our most common 12 volt lead acid chemistry systems. Using 6 volt golf cart batteries, two are needed for 12 volts. So banks are built by pairs. 12 volt batteries can be any number, odd or even. This thread did go Amtrak on the OP.

 

[highdesertranger]

for us it's best to keep it at 4 maximum. yes you can have any number(6v must be even numbers) but after 4 things start to get complicated. highdesertranger

 

[joshuafarmer]

thanks for all your info, I have been looking more into the mppt charger and I know its more reliable/efficient but what is the difference and should I get the 200 watt renogy kit with the pwm charger that has the ability to go up to 400 watts of panel or just build my own kit starting with like a 30 or 40 amp/watt mppt charger and just build around that idk if that would cost more or not but right know that would seem to be the best option.

 

[DLTooley]

thanks for all your info, I have been looking more into the mppt charger and I know its more reliable/efficient but what is the difference and should I get the 200 watt renogy kit with the pwm charger that has the ability to go up to 400 watts of panel or just build my own kit starting with like a 30 or 40 amp/watt mppt charger and just build around that idk if that would cost more or not but right know that would seem to be the best option.

I'd use the Renogy kit as a baseline comparison and then price an alternative, say putting it together with an MPPT controller.  Upgrade paths on any system are somewhat constrained, like for example the battery questions above.

It is typical for threads like this to get into the actual recommended practice, the digression is actually worthwhile if you read regularly.

I read the manuals on the Victron, Renogy, and Morningstar MPPT's.  I like the Victron as it sets the absorption phase based on actual consumption, not an estimated time.  This is critical for me as my use varies widely and any estimated setting would be either too low or too high all of the time.

The Victron is only 10 amps, but it does have a higher voltage rating so the upgrade path is putting panels in series.  As I understand it this requires panels of the same size mounted consistently.

I recently upgraded my solar panel.  I've kept the old one as a portable supplement I use when camped, and puts me at that 10 amp limit.  As such my upgrade path with a Victron will require an upgraded vehicle, which works for me.

 

[John61CT]

thanks for all your info, I have been looking more into the mppt charger and I know its more reliable/efficient but what is the difference and should I get the 200 watt renogy kit with the pwm charger that has the ability to go up to 400 watts of panel or just build my own kit starting with like a 30 or 40 amp/watt mppt charger and just build around that idk if that would cost more or not but right know that would seem to be the best option.

Many people whose opinion I respect say the cheap SC included in the Renogy kit is just fine for most people.

In your case I'd be inclined to agree, as long as the effectove price (compared to buying the panels alone) is under $50, **and** voltage setpoints and Absorb Hold times are adjustable.

For me personally, I would want to spend $100-150 on one or more lower-amp Victron MPPT and find a space-efficient high-voltage single panel that optimizes that SC output, likely around $350 total for 200+W actual SC output in good conditions.