One battery bank or several smaller in parallel?

[rabbit_39]

So assuming the calculations are done correctly, one of the systems that we came up with requires 2000Ah batteries x 48VDC. Of course we would need several charge controllers and pv arrays to charge that.

The question now is, would it be better to have several smaller battery banks wired in parallel for output (but fed by their own individual pv arrays and charge controller) or a single large battery bank fed by the same as above individual pv arrays and charge controllers wired in parallel into the single battery bank?

Thank you very much. We're getting conflicting answers from the battery guys and from the solar charge controller guys (Outback and Schneider).

Andre S

[westbranch]

what are the conflicting recommendations?

I guess it all depends.....on what they want to sell you,.... but more specifically how it works for you.

A few more details would help.

HTH

[rabbit_39]

The system is for a communication network device that runs 24 hours/day. But the load depends on the amount of "chatter" on the network. Max power is 1500Watts and the expected usage breakdown is:
1500W x 12hours = 18kwh
1200W x 6hours = 7.2kwh
900W x 3 hours = 2.7kwh
400W x 3 hours = 1.2kwh
TOTAL = 29.1kwh/day

So about 30kWh/day.

The arrays we're planning are 3500Wp PV panels x 3 (in an area that gets average insolation of 5hours according to the NASA data).

The battery companies are saying we should use several banks of smaller capacity batteries.

The solar charge controller companies are saying we can use a single bank (charge controller output in parallel) or several banks (charge controller output into their own respective banks and the output of the battery banks are wired in parallel to serve the loads).

What are the pros and cons of each system? I would think there would be less losses if I use a single battery bank.

Thank you,

[westbranch]

IMHO think Redundancy, if one fails there would be at least 1 , or more backups to keep things running.

big banks are harder to manhandle etc.
small banks have more (duplicated) issues with connections, wiring and more spares
multiple banks can discharge a differing rates.

Is that NASA data for December?

BB and others are far more knowledgeable than I so they will probably be on tomorrow.

HTH

Can you be a bit more detailed on the 30Kwh, those numbers don't quite add up

[rabbit_39]

Yes, that NASA data is for worst month of the year (which is in January for this location in Indonesia). I assume that's what you're getting at?

I added the total kwh/day to be 29.1kwh/day that I rounded up to 30kWh. Am I missing something?

Thanks for the input

[westbranch]

yes you want to use the worst month, at least as a starting point.

Hmmm Indonesia, you will have warm temps so there will be a temp derating for the PV's due to temps above 25 C. this in addition to general system derating, PV to battery.

I was just thinking out loud after adding to 29 too. rounding... yup
the other point I see is the 24 hour demand mapped (graphed) out to visualize the max and min usage, then seeing which configuration(s) will work for you, demand vs 1 or more Batt banks.
HTH

[rabbit_39]

The demand will be higher during the day, night usage is about 40-50% of that 30kwh. Perhaps I'd do better with a 1500Ah and increasing the PV panels. Hmmm I'll have to see if I have the space for it. The space is 15m x 10m with a 5mx5m tower and I'll have to use up all that room I think. Which means I'll have to make sure the sides that will get shaded by the tower be their own array. Nuts! grrrrrr!!! Oh well, will have to see what I can figure out.

Yes, average PV temp here is quite high, all year round. But it does get made up by having sunshine everyday (just about). It's a rare day that we get dark and cloudy throughout the day. Just looking at rough data, I get twice the daily energy here than in Portland, OR.

[westbranch]

I found that taking site pics with the sun at your back, at 15 minute intervals, was an eye opener regarding shadows. best if you use a tripod, load them into power point and just watch the show, amazing what you will 'see'...

you haven't mentioned battery voltage, any preferences? the load/capacity will have a determining influence.

[rabbit_39]

It will be 48VDC for something this size. Plus some of the equipment are 48VDC input already.

The loads will really be mostly the communication gear (1400W max) and the rest are small things like:
- tower aircraft lights (I may use a solar powered unit with built in battery)
- outside lights (about 30W LED lights total)
- exhaust fans (about 50W)

[niel]

don't forget about those pesky cloudy/rainy days i'm sure you get. you must account for the worst case you can expect to continuously need to run (days of autonomy) without the sun and a generator would be a good backup to this too even though gasoline is high priced. continuity is crucial for you.

this same line of thinking goes for the pvs as well for you may need to up the pv capacity to bring the batteries up faster due to weather or other unforeseen event interrupting power production with controllers, inverters, and even battery failures are possible. the efficiencies also need to be compensated for.

this is not a small undertaking.