What is wrong?

Re: What is wrong?

The six panels in series will run MPP at about 100 vdc. The worse case Voc should be less then 140 vdc.

At full sun MPP would be 100 vdc @ 7 amps = 700 watts. You will average much less then this.

At peak noon, the 700 watts will go through charge controller with its efficiency loss.

From the specs for the Midnight controller it is not easy to interpret the conversion loss. It appears they are optimized for a 70 vdc PV system. If I assume their peak efficiency is 92%, then from the graphs the PV input power is 1500 watts in their diagram. At 100 vdc panel the efficiency drops to 89%. This is probably a pretty good number for you to use.

That means at peak power input of 700 watts you will deliver 625 watts to the battery.

At 13.8 vdc that would be a charge current of 45 amps at peak illumination. If you want to get to 90 amps at peak you need to double your panel quantity with another six series string.

With your present panels you will deliver about 80 kWH/mo. in summer and 70 kWH's in winter months. Assuming you are not on the rainy side of the island.

Re: What is wrong?

boukman wrote: »

That was quick! I assume that the six panel would add up to 72 VDC

A "12 volt" panel will produce about 17 volts, so six in series will produce about 100 volts. On the specification sheet someplace there will be a number like:

Voltage at Max Power (Vmpp) 17.something


Pay careful attention to wire sizes so you don't lose too much power by using too small wires.

Keith

Re: What is wrong?

boukman wrote: »

Thanks for your quick shots. How do I optimize my panel to get top efficiency from CC? I mean should I buy 6 more 12 V or 3 more 24 V, with concern for correct charging current for the batteries

I would lean towards two parallel strings of six panels, if you can get another six with the same or similar characteristics.

Doing this with a 12 volt battery configuration will be harder than using 24 or 48 volts. Assuming you end up with 6 volt, 225 amp hour Trojan T105s, you are going to need six or 8 batteries to support 3-4 KWHs a day. Batteries are a lot more complicated than one might expect, so doing one string of 8 batteries will work better than doing two strings of 4 batteries or 3 strings of 2 batteries.

Two more variables to keep in mind is when your power use occurs and what your peaks are. For example, if much of your power use is in the afternoons, then most of the time a smaller system might work because you can use power directly from the panels and not from the batteries. However, if you have to start and run something like a pump, you may need a bigger system because of the starting surge.

Where in Haiti are you?

Keith