What size charge controller fo I need and should I wire my solar panels in parallel or series?

[bmtrirow]

I have a 24V system with 550AH of battery and 4-200W solar panels. I'm planning to wire 2 pairs in parallel and then the pairs in series with each other. Is that best?

Also what size charge controller do I need for this system? Thanks for your help!

 

[Craig]

We would need to know the open circuit voltage and the amp rating of the panels to help with configuration.
If you do not plan on using more than the 4 panels you currently have then you need a charge controller than can handle 800 watts at 24 volts or at minimum 40 amps which is the nearest round number i got by dividing your 800 watts generated solar power by 24 volts.

I am a bit concerned though that you may need more solar to keep your batteries charged if you use all that capacity often. as you have it now it would take 16 hours of ure sunlight to charge your batteries fully if they were empty. Depending on your planned usage this could be important.

 

[bmtrirow]

Thank you Craig! I may get more solar panels, but I am using this set up in a van and have limited space for them. I don't expect to use the entire battery bank each day, I will probably only use 1/3, but I like having the extra as backup. I will also connect to my alternator and have a charger for shore power to help top the batteries off.

 

[Ped]

May I ask what youre planning to power? Thats a boat load of draw for such a small system. About 7,000 watts a day if my math is right. At 20a from alternator youre looking at idling your engine 4-8 hrs every morning depending on the time of year. As a comparison in my van I use about 1.5kw running all 120vac 16" fan 24hrs, dorm fridge, TV for 12hrs, and various chargers.

Sorry if youre aware of all this. Some people might not so you never know.

 

[bmtrirow]

I appreciate the comment, maybe I'm thinking about this wrong. Below are my power needs assumptions (pretty conservative, I don't think I'll actually use this much). I'm still figuring out exactly which appliance to purchase. Also, I know there will be some loss when converting from 24V to 12V which I haven't baked in yet.

Unit		Consumption (Watts)		Volts		Usage (hours)		Total (Watts)		Total (Amps)
Lights (6)		30		12		8		240		20
Charging		200		110		2		400		4
Fans (2)		200		12		12		2,400		200
Water Pump (2)		140		12		2		280		23
Electric Oven		1,800		110		1		1,800		16
Refrigerator		16		12		24		374		31
Induction Burner		1,800		110		1		1,800		16
UV Lights		130		12		1.5		195		16
Total								7,489		327

 

[Ped]

Oh yeah youre way off on some of those. My 16" fan pulls ~24w on low and about 36w on high. And everything is in 12v for a 24v system so needs to be divided by 2. Forgets watts, focus only on amps for this.

LED lights are like 250 milliamps..nowhere near 30w. Water pump wont even register. Consider it 1-2a @ 24v MAX.

an 1800w toaster oven is huge (mine is 600w) but only pulls that on toast. On broil or bake its only half that. You really baking 1hr a day? Thats a ton.

Your fridge will probably average more like 40a year round. 20 in winter and 60a on suumer. Probably more like 15/55 it just depends where you are and how much you use it. Its 120v right? Dont buy 12v fridges if youre running an inverter anyway its a waste of money.

Your inverter will consume around 1-1.5a as well depending on size.

Because youre limited in roof space, not usong lifepo4, and not carrying a generator I highly advise against an induction burner. Just do propane on a small tank. At this rate it would be cheaper for you to go lifepo4 and/or get a small 800w generator ($200) and battery charger instead of relying on your engine.

 

[bmtrirow]

Thank you for the advice, that's really helpful. I don't own the appliances yet so I was making guesses. I'll adjust my assumptions.

 

[Ped]

Im assuming youre talking ~18v panels as you never clarified.

Like I said dont bother with the 12v fridges. Theyre no more efficient. Its just running an inverter is another 20-30a extra. If youre running one already its a waste of money. Been through this a ton.

Realistically if you do away with certain redundancies and adjust the numbers to real world youre doing about the same as me. Around 1.5kw give or take with that setup. Which would be about 7-8hr recharge time. Fine for summer but winter will need a small generator and charger setup as it will require way too much engine idle. At least 2 hrs a day for the cooler months. Thats hard on an engine.

By the time you buy all that and the gas you will burn in a year a 200ah/24v lifepo4 (shun bin - $1500) is just as cheap if not cheaper, and frankly a 100ah @ 24v would do fine (1.5-2 day reserve with zero sun, realistically 4-5 days with reduced panel output). That would be a fraction of the size and 450lbs+ less weight. Which IS significant in a van already loaded down for camping. Youre 400w/24v system (real world 4.2-4.6kw) will be perfect for it without needing even the alternator virtually ever.