Help sizing charge controller

[cmutwiwa]

Thanks guys, I guess I will have to go with a 24v system and follow the guidelines given above.

[cmutwiwa]

Thanks Sunking, I think that answers my question, now I know its smart to go 24v considering my panels wattage and that I need atleast 400Ah battery bank and a 60Amp MPPT controller...
One last question, whats the maximum size of inverter can I use in my setup, I know this will depend mostly on my load, but whats the limit for my setup?

[cmutwiwa]

Thank you Sunking for the detailed reply.
As I'm not willing to throw away any of my panels and I can see that a 12v system might end up more costly for me, let me say that I'm flexible and am willing to go 24v, I understand that this will need me to get an inverter so as to use AC power on my appliances.
The question is, will two 12v 150 Ah AGM batteries in series be ideal and how much in Amperage for the MPPT controller will I need?

[Sunking]

At 12 volts and 800 watts of panels you have no room for growth with a 60 amp controller. Additionally 12 volt systems are more expensive than 24 and 48 volt systems. In Kenya you have excellent conditions with a minimum 5 Sun Hour day. With 795 watts of panels you can easily harvest 3 kWh of usable power in a day, and that would require a 12 volt 1000 AH battery. With a 12 volt 200 AH battery you need to loose 2 panels and use a 20 amp minimum controller with no place or room to grow.

Smart money is to go with 24 volts. Initially you would only need a 30 amp controller at 24 volts, but that would leave you no room for future growth. Smart money initially is a 60 or 80 Amp Controller with a 24 volt 400 AH minimum battery. With that you can use up to 2.4 kWh per day or 5 times more than what Sensij just told you, and what you planned.

You do not want or need an AGM battery. They cost twice as much and only last half as long as a FLA battery making them 400% higher cost. With a 24 volt 400 AH battery you can use up to 2 to 2.2 kWh per day. AGM has applications in solar but they need to be justified for the expense. Some justifications are:

• Extremely cold climates where temps drop to -40.
• Mobile applications where spills are unacceptable.
• Very high charge and discharge rates are encountered.

As Mike said you went about this the wrong way, and if you are married to 12 volts, maximum power at 12 volts is 1000 watts with an 80 amp controller. Th eproper way to design is to determine your daily watt hour usage. Batteries have minimum and maximum charge requirements. With 800 watts of panels, dictates minimum and maximum charge controller and battery requirements. with 800 watts of panels operating at 12 volt battery minimum requirements are a 60 amp controller and a 12 volt 500 AH FLA battery or 250 AH AGM battery and both those batteries cost the same. Consequently with 800 watts of panels and a 60 amp controller would be the maximum a 60 amp controller can handle, so no room for growth.

You are trapping yourself because you went about this the wrong way. You bought panels and hoped it would work out.

[Mike90250]

your 3 panels would give you 56 amps into a 12V battery, or 28a into a 24v battery - using a good quality MPPT controller, and well aimed, un-shaded panels.

It's your choice, you say you have an investment in 12V appliances already, so maybe in your case, it's a reason to stick with 12V.

For 12V, 400ah of battery would be a good match for the panel size. But this is backwards, you generally size the battery to run your loads for 3 or 4 days, and then configure solar to provide proper charging to the batteries. If you run 400ah of batteries flat every night, they will not last very long and seldom be properly charged.

[cmutwiwa]

Thanks Sensij for the quick reply,
No, I dont intend on getting FLA batteries, I can get a 200 Ah AGM battery to start with, then upgrade later if need be. Will that still work with the 40 A MPPT controller?

My aim is to make maximum use of the panels I have and
I've been going through earlier posts here and I read experts NOT recommending 12v system, so considering the panels I already have, I'm I better off going 24v system with an inverter or should I stick to my 12v system without an inverter? Which best way would you recommend?

[sensij]

If the 150 Ah are FLA, a 20 A charge controller is about as much as you can use. More than that, and you would be at risk of overcharging your batteries, especially since you have so much PV wattage available (60 A at STC, assuming good orientation) of the panels.

If the 150 Ah are AGM, a 40 A charge controller would be good.

In either case you are still over-paneled, so you would need to make sure your mppt controller will properly limit the output current to the controllers rating. Some very inexpensive models may not.

If you can go up to 230 Ah FLA, you can get a 30 A controller.

[cmutwiwa]

Hey guys, very informative post.
I live in Kenya and I'm working on almost the same system but mine will be a 12V system (most of my appliances are 12V) or would you advice otherwise? . For now I only got the panels, three (3) 265w panels, I'm thinking of going with 150AH batteries...however, I'm not sure which is the best size MPPT in amperage I should use. The panels specs are:
Pmax - 265w
Vmp - 31.4v
Imp - 8.44A
Voc - 38.6v
Isc - 9.03A
Maximum system voltage - 1000VDC
maximum series fuse rating - 15A

Regards.