Schneider charger

MPPT charge controllers are "rated" by their output current... i.e., 60 Amp maximum here. The output power depends on the voltage of the "load" (battery bank). For example, say your bank "sees" these voltages at different times of the day (starting out with a low battery to fully charged then to float):

• 60 Amps * 24 volts (low battery) = 1440 Watts
• 60 Amps * 27.2 volts (battery getting charged in full sun) = 1,632 Watts
• 60 Amps * 29.6 volts (battery at setpoint voltage. From bulk to absorb) = 1,776 Watts
• Battery will go from 60 amps down below 1% rate of charge (400 AH bank.. from 60 amps to 4 amps)
• 60 Amps * 27.2 volts (battery in "float"+loads from AC inverter, etc.) = 1,632 Watts

The MPPT controller is sort of like an automatic transmission for a car... It "matches" the solar array output to the current/voltage needs of your battery bank. Obviously, if you have less sun, the Watts from the solar array is less, and the charging current to your battery bank is less.

For your 6 panels * 260 Watts, the typical maximum wattage from the array would be:

• 6 panels * 260 Watts = 1,560 Watt array (standard conditions rating)

More or less, by the time you take real conditions into account, the typical maximum available array wattage (in full sun, warm day, hot panels, real charge controller) is closer to 77% maximum of rated value (some folks like 75% max).

• 1,560 Watt array * 0.77 real world panel+controller deratings = 1,201 Watts "available" from array

And the maximum current from the controller would be (note, this is roughly the best you will see on clear/sunny/cool days, clean solar array, charging a discharged battery bank):

• 1,201 Watt array * 1/24 volts (low battery voltage) = 50 Amps current
• 1,201 Watt array * 1/29.6 volts (charging setpoint) = 40.6 Amps current

And since MPPT controllers can be "over paneled" (they will safely limit their output current to "rated current"), you can "justify" an array of:

• 60 Amps * 29 volts charging (nominal) * 1/0.77 panel+controller deratings =2,260 Watt array "cost effective" Maximum
  

What McGivor says... Heat (and thermal cycling) is an enemy of electronics (and batteries, and just about anything else). He lives in a hot climate (Thailand) and would probably prefer to run his equipment at 80% of maximum ratings (or less) so they run cooler. There is something to be said for derating your system components--But it does cost you too--Larger equipment running at less than rated power.

And just to give you an idea... A very handy engineering rule of thumb. For every 10C (or 18F) increase in temperature, your devices will last 1/2 as long (or "age" 2x factor). Running your electronics cool, good ventilation, mounted away from sun/sources of heat, all good...

Typical solar power electronics, plan on a ~10+ year life, and possible repairs at 5+ years. Note that most electronics are "repairable" by the factory about 5 years after purchase/end of product life (support for firmware, components, etc.).

Not saying your stuff will die at 10.0 years--But you should have money in the bank for repairs (and battery bank replacement)--It is just a question of when, not if--Stuff will eventually fail. Off Grid Solar power is expensive.

-Bill