Adding Panels?

Re: Adding Panels?

Yes, it's just about that simple.

You've got twelve 64 Watt panels on a PWM controller to a 24 Volt system. Those panels would be '12 Volt' units? If so they'd be wired as strings of two giving Vmp around 35 and Imp around 3.6 and you'd have six parallel strings (hopefully with a fuse each) giving about 22 Amps maximum on a 30 Amp controller. No problem.

For 400 Amp hours of battery you'd like to see that peak current nearer to 40 Amps, so you want about 18 Amps more. Using another PWM type controller the calculation is simple: 18 Amps * 35 Volts (the Vmp for a 24 Volt system) = 630 Watts of PV. Plus or minus a bit depending on exactly what panels you go for. If you use an MPPT controller (a lot more money for such a small amount of current) the formula is like this: 18 Amps * 24 Volts / 0.77 = 561 Watts of PV.

Note that it can be hard to find 'true' 24 Volt panels with a Vmp around 35 and also that they tend to cost more per Watt than GT style panels with a Vmp around 30 (too low for proper charging) as do 12 Volt panels.

Re: Adding Panels?

stmar wrote: »

What would be some good options to get the extra 630 watts? I have not had any issues with the Prostar-30 so should I consider that for an additional controller or look at a newer technology, I think you are correct about staying with the PWM controller.

Another of the same controller is most likely to 'agree' with the first regarding battery Voltage and charging set points. Stick with what you know works.

Re: Adding Panels?

stmar wrote: »

I doubt if they make panels like I have and I am sure there are much more efficient ones out there. What panels should I research for a good compatible installation? I have very little experience shopping for panels. I will stick with the Prostar like you said.

Ah, there's the rub.
Panels aren't much more efficient now than they have been before.
The issue is that the PWM ProStar will work best with the array Vmp @ 35-ish on a 24 Volt system. This means you have to find '12 Volt' panels and put two in series to make Vmp 35 or '24 Volt' panels which actually have a Vmp around 35. The 'GT style' panels may be promoted as "24 Volt" but in reality their Vmp is around 30, or even less.

Some examples from our host to clarify (look at the specs):

12 Volt panel; Solartech 130 Watt http://www.solar-electric.com/solartech-spm130p-s-n-130-watt-multicrystalline-solar-module.html/ Note Vmp 18
24 Volt panel; Solartech 130 Watt http://www.solar-electric.com/solartech-spm130p-wp-24v-130-watt-multicrystalline-solar-module.html/ Note Vmp 34
24 Volt panel; Topoint 190 Watt http://www.solar-electric.com/solartech-spm130p-wp-24v-130-watt-multicrystalline-solar-module.html/ Note Vmp 36

GT style panel; Kyocera 220 Watt http://www.solar-electric.com/kyocera-kd220gx-lfbs-220-watt-polycrystalline-solar-panel.html/ Note Vmp 26
GT style panel; Solarworld 240 Watt http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa/solarworld-sunmodule-sw240-monocrystalline-black-solar-panel.html Note Vmp 30

Those last two will not work on a 24 Volt system with PWM type controller; their Voltage is too low to bring the batteries up to proper Absorb level when used as singles.

As you can see nothing is going to work out to an exact 630 Watts. Probably the closest you could come would be four DM Solar 158 Watt panels http://www.amazon.com/158w-Monocrystalline-Solar-Panel-Pack/dp/B007VPQP5Q Vmp 18.9 - a pair in series would be 37.8 @ 8.4 Amps so two such strings would be 16 Amps on a ProStar.

Otherwise you're looking at configurations like five of the 130 Watt 24 Volt panels in parallel (18.75 Amps) or three 190 Watts for 15 Amps or four of them for 20 Amps et cetera.