morningstar sunsaver 15

Re: morningstar sunsaver 15

There are several "issues" when sizing panels.

As "solarix" says, first is Vmp of the panel... for charging a 12 volt battery bank with an MPPT charge controller (like this one), you need a minimum of Vmp=17.5 volts or so; and for a 24 volt bank you need ~35 volts Vmp minimum (voltage maximum power). Many "24 volt panels" may have Vmp=24 volts--which is not high enough to charge a 24 volt battery bank.

Second is the maximum output current... MPPT controllers naturally limit their output current to rated maximum--so you can put more solar panels on the output and not damage anything (as long as Vmp/Imp/Voc meet controller's intput specs.). If you put "a lot" of solar panels on the input, the controller will simply limit its output to 15 amps maximum.

The maximum "cost effective array" calculation (you can go larger, but you will "lose" more power). For 12 volt battery bank with 15 amp MPPT controller:

• 15 amps * 14.5 volts bat charging * 1/0.77 panel+controller derating = 282 watt rough maximum "cost effective" array

For a 24 volt battery bank:

• 15 amps * 29.0 volts bat charging * 1/0.77 panel+controller derating = 565 watt rough maximum "cost effective" array

Again, these are "round numbers" and being "off" by 10-20% is not the end of the world either.

Solar panels will tend to produce less than rated power in hot climates/weather and produce near or over rated power in sub freezing weather.

The 0.77 derating is a typical value that works pretty well for most people (and is fairly conservative--you may "beat" the number by a few points).

-Bill

PS: Just to be sure, we are talking about this "Sunsaver"?

Morningstar SunSaver 15 Amp MPPT Solar Charge Controller