Upgrading from 400w to 800w - wiring issues

[sensij]

That makes sense. I may go the MPPPT route for no, rewiring will be kinda of a b*tch so I'll save that for next long weekend.

Do you have an opinion on wiring size? I know 10 gauge isn't rated for 60 amps.

If you want to carry 60 A, you'll need to go to at least 6 awg, maybe heavier if your run is more than 10 ft.

Sunking's comments on "wasting your money" need to be qualified by more details of your installation. For example, in San Diego, with a south facing, 18.5 deg tilt system in early May on a clear day, my 3.1 kW grid tie system produces this:
energy.JPG



If you use that same production ratio on a 400 W, 600 W, and 800 W array with a 30 A mppt charge controller on a 12 V battery, assuming equivalent efficiency, you curves would look something like this:

demo.JPG


You get a lot of payoff for going from 400 W to 600 W, not so much going from 600 W to 800 W. However, the full 800 W is super valuable on the cloudy days when you need it most, since you'd be unlikely to clip at all. If your location isn't as sunny in general, or if your panels are not optimally oriented, your production curves would be lower than what I've shown here, and again, the 800 W starts to become more valuable.

[Sunking]

How would that work exactly? If I kept the 800w 12v setup how would it only deliver 30 amps with an MPPT when it delivered 45 to the PWM?

It means you wasted your money buying more panels. A MPPT 30 amp controller would clip off the 400 watts of panels you just added. A 45 amp controler would clip off 200 watts.

[muskogeezeke]

The mppt functionality gives the controller the ability to adjust the voltage at which the panels operate. By increasing the the apparent load on the panels, the 45 A is reduced to 30 A because the panels are operating at a less optimal point on their IV curve.

With a 500 Ah, 12 V battery, you would be better off with a 60 A charge controller... the battery can take it (assuming FLA or AGM). If you can rewire the battery to 24 V, and wire the panels as SunEagle suggested, you can stick with a 24 V, 30 A mppt charge controller.

That makes sense. I may go the MPPPT route for no, rewiring will be kinda of a b*tch so I'll save that for next long weekend.

Do you have an opinion on wiring size? I know 10 gauge isn't rated for 60 amps.

[muskogeezeke]

If you went to a 24volt system then 800w would deliver 30amps.

Copy that, just making sure I understood. Thanks!

[sensij]

How would that work exactly? If I kept the 800w 12v setup how would it only deliver 30 amps with an MPPT when it delivered 45 to the PWM?

The mppt functionality gives the controller the ability to adjust the voltage at which the panels operate. By increasing the the apparent load on the panels, the 45 A is reduced to 30 A because the panels are operating at a less optimal point on their IV curve.

With a 500 Ah, 12 V battery, you would be better off with a 60 A charge controller... the battery can take it (assuming FLA or AGM). If you can rewire the battery to 24 V, and wire the panels as SunEagle suggested, you can stick with a 24 V, 30 A mppt charge controller (or PWM for that matter, if you are so over-paneled at this point that you don't need mppt).

[SunEagle]

How would that work exactly? If I kept the 800w 12v setup how would it only deliver 30 amps with an MPPT when it delivered 45 to the PWM?

If you went to a 24volt system then 800w would deliver 30amps.

[muskogeezeke]

To be clear I meant you first wire 4 of the panels in series and then do the same for the next set of 4. You then wire those 2 sets of 4 in parallel.

I believe you said you have the first 4 wired in parallel. That is is ok for a PWM charge controller but you end up losing about 33% of the total wattage for charging. Using an MPPT CC allows you to get more wattage out of the panels as well as keeps the wire size down due to the series wiring.

Gotcha. Would that not make it 24v?

[muskogeezeke]

A 30 A mppt charge controller will allow you to keep your existing wiring, without causing the amperage problems you saw with your PWM controller. On sunny days, the controller should be running at its max 30 A for several hours. What is your battery capacity? A higher amp CC could get you more charging energy, but is not a good idea if your battery can't handle the additional current.

Edit: I agree with littleharbor that it might be worth exploring rewiring the battery to a 24 V configuration.

How would that work exactly? If I kept the 800w 12v setup how would it only deliver 30 amps with an MPPT when it delivered 45 to the PWM?

[SunEagle]

Thanks sun eagle. I currently have them wired as two groups of four. Controller was showing 45A under full sun. What about wiring size? I currently have 500AH battery bank.

To be clear I meant you first wire 4 of the panels in series and then do the same for the next set of 4. You then wire those 2 sets of 4 in parallel.

I believe you said you have the first 4 wired in parallel. That is is ok for a PWM charge controller but you end up losing about 33% of the total wattage for charging. Using an MPPT CC allows you to get more wattage out of the panels as well as keeps the wire size down due to the series wiring.

[muskogeezeke]

Thanks sun eagle. I currently have them wired as two groups of four. Controller was showing 45A under full sun. What about wiring size? I currently have 500AH battery bank.

[sensij]

A 30 A mppt charge controller will allow you to keep your existing wiring, without causing the amperage problems you saw with your PWM controller. On sunny days, the controller should be running at its max 30 A for several hours. What is your battery capacity? A higher amp CC could get you more charging energy, but is not a good idea if your battery can't handle the additional current.

Edit: I agree with littleharbor that it might be worth exploring rewiring the battery to a 24 V configuration.

[littleharbor]

Might also consider going with 24 volt system. You would be able to keep your 30 amp controller, that is if it will do 24 volt charging too. Most will.

[SunEagle]

Well with 800 watts of panels charging a12volt battery you will need at least a 60amp CC. Also to get the full output of that 800w you should go to an MPPT type.

Depending on the panel Voc you might be able to wire them into two groups of 4. But you have to be careful not to exceed the maximum DC voltage input for that CC.

I guess my next question is that now you have 800 watt of panels are you planning on increasing your battery system Ah rating?

[muskogeezeke]

Hey all,

Hoping I could get some help. I have been running an off the grid cabin for about a year on a 400w 12v system. I puchased an additional four 100w panels and installed them in parrelall. Was loving the performance, until the spring got here and my amperage spiked, causing issues with my 30A charge controller. My mistake, did not take this into account.

What do I need to make the 800w system work? I believe I need a 50A charge controller, but will this requring replacing my wires (currently using 10 AWG)?

I'd appreciate any help I can could get, thanks!