Batteries in series or parallel

[Just_Askin]

Hi,
I bought 4 @ 200w panels (voc: 20.4, isc: 13.9) to be wired in 2s2p and 2 @12v 280ah batteries for my diy camper/box truck. I have not made any additional purchases (eg., charge controller, inverter, etc.) until I determine the battery configuration ( i.e., parallel or series). What are the advantages and disadvantages of each configuration?

 

[robbob2112]

How to pick a voltage



Standard Blurb

Don't spend any money, until you have planned out the entire system. An eraser is cheap, but returns can be costly.

Planning

1. Energy Audit - what do you have to power?
2. Size the inverter for your maximum instantaneous demand (including surges).
3. Size the battery for how long you want power, when the sun isn't shining.
4. Size the PV to cover the loads and recharge the battery, when the sun is shining for your area - most in the US use 4hrs or 5 hours a day of sun
5. Trying to use old equipment you already have usually costs more in design compromises than just selling it and doing it right.
6. READ the site - every question you have has probably already been asked - if you have special circumstance - start your own thread.

Design planning

1. Use drawio to design your system if the instructions didn't include a design you can use. https://www.drawio.com/
2. Tilt angle - your latitude is your year round tilt angle - in my case the 5/12 roof pitch is around 22 degrees so is a summer time tilt. My winter tilt is somewhere around 42 degrees - but they would act like a sail and tear my roof off if tilted that far.
3. Don't forget temperature when calculating panel voltage - my 335w panels mounted at 42degrees on the side of the house deliver 408w in winter at 36 degrees.... at 9 degrees it delivers 430w... The voltage increase is similar with an increase in current.

Installing

1. Use https://pvwatts.nrel.gov/pvwatts.php - put in your address and the rest to see how many hours a day of sun
2. Use this when you mount your panels to get the wind and snow loads - https://ascehazardtool.org/
3. Buy quality tool when you do - the cheap stuff is generally inferior and will make bad connections
4. Remember you are dealing with lethal current and voltage - use safety equipment
5. If you are unsure about anything ASK - there are many experts in different fields willing to answer your questions

 

[Just_Askin]

Thank you for the reply. That was useful information. I still need to decide on whether I'm going to have my batteries in series or parallel. I would like to put them in parallel because I have a number of 12v appliances I will be using. That will eliminate the need for a 24 to 12v DC converter and battery balancer. I understand the amperage will be higher and the charge controller will choose more, but to me it's a simpler system. Are there any drawbacks? I would appreciate some feedback on the pros and cons is each configuration. Thanks.

 

[Just_Askin]

I still need to decide on whether I'm going to have my batteries in series or parallel. I would like to put them in parallel because I have a number of 12v appliances I will be using. That will eliminate the need for a 24 to 12v DC converter and battery balancer. I understand the amperage will be higher and the charge controller will choose more, but to me it's a simpler system. Are there any drawbacks? I would appreciate some feedback on the pros and cons is each configuration. Thanks

 

[Backyard]

What do you have or how much is on 24v?

I would say your largest draw equipment should dictate your voltage. Everything else gets replaced, converted or adapted

 

[Supervstech]

I still need to decide on whether I'm going to have my batteries in series or parallel. I would like to put them in parallel because I have a number of 12v appliances I will be using. That will eliminate the need for a 24 to 12v DC converter and battery balancer. I understand the amperage will be higher and the charge controller will choose more, but to me it's a simpler system. Are there any drawbacks? I would appreciate some feedback on the pros and cons is each configuration. Thanks

12V in parallel limits your inverter output options, and increases your wiring costs.

List what you want to power, and we can better advise your choice.

 

[Q-Dog]

I wouldn't put BMS controlled batteries that large in series, so it looks like you are comitted to parallel unless you like returning stuff. Post what loads you want to run, you might be fine with 12 volt ... or you might be headed in the wrong direction.

 

[Just_Askin]

Here is the list of appliances I plan to run:

12v appliances (some not yet purchased): 3-4 cu. Ft refrigerator, 8 led lights, 4a water pump max 8a, maxxfan.

AC appliances (some not yet purchased): one burner cook top, toaster oven, laptop, tv, water heater, small space heater.

I'm guessing I'll be using around 120 to 150 amps on the DC circuit and around 2500 to 3000 WATTS on the AC circuit. Those are my best estimations without yet having purchased all of the items. I obviously won't be running everything at once, so that estimations is likely high.

I don't know if you saw from a previous post, I have purchased 4@ 200w solar panels and 2 @ 12v 280ah batteries, nothing else.

I hope this information helps you guys so you can help me. Thanks.

 

[robbob2112]

List voltage and wattage drawn for each item. This will help decide voltage and inverter size if needed.

 

[Supervstech]

If your loads remain what you have listed, you can stay in parallel, however, if you draw your max sustained for long, you are going to deplete your batteries very quickly.

You will want to buy the MOST efficient, lowest standby demand inverter possible.

Do not try to buy a low cost inverter for those loads, or you will fall short much faster than with better equipment.

Shop, post here for feedback and chose wisely.

 

[mikefitz]

Are there any drawbacks? I would appreciate some feedback on the pros and cons is each configuration. Thanks

Up to around 2500 to 3000 watt inverter, stay with a 12v system, over 3000 watts consider 24 a 24 volt system. If considering a 24 volt system use 24v lithium batteries, using 12v lithium batteries in series will cause issues. A 12v systen is easier to charge via vehicle alternator and DC to DC charger.
Although to are considering an 2500 watt inverter it's probable the power use will be mostly in the 1500 watt region.

one burner cook top, toaster oven, laptop, tv, water heater, small space heater.

You batteries store when full 7kW, the solar 800 watts will produce under ideal conditions, 4kW per day, realistically perhaps 3kW.
The water heater and space heater are huge consumers so will need management.

Useful additional units, battery monitor, Victron Smart shunt or BMV 712, DC to DC charger, Victron Orion XS.
Need a 60 amp MPPT for 800 watts of solar in a 12v system.

 

[Just_Askin]

Thank you all for your help. The battery issue has been resolved. We're going with 2 @ 12v 280ah batteries in parallel.

Now it's time to look at other equipment like a 50-70ish amp charge controller, a 2000 watt inverter, shore power 12v battery charger, and DC - DC battery charger from my truck's battery/alternator.

From what I've read Vectron appears to be popular and reliable, but I haven't found that they make everything I've listed above.

I want to first focus on purchasing the charge controller and inverter and then we can look at some of the smaller items.
Here is a Vectron inverter, but it's only 1200 watts https://a.co/d/hY09cz9 I'm looking at another brand that's bigger and has additional surge amperage https://a.co/d/cgWfBg6

Here is a charge controller I found on Amazon, but I don't know if it's big enough 100v 50a https://a.co/d/2rFCF05
Here is a bigger one at 150v 70a https://a.co/d/9ep90NI is 150v too high?
FYI: I am placing my panels in 2s2p configuration. The voc is 20.4 and isc is 13.9.

Please let me know what you think of these. I am also open to your suggestions related to size and brand. If you have something in mind that you think will meet my needs and can provide a link to the product, I would greatly appreciate it. Thanks again for all your help.