Oops, I think I made a boo-boo there.

MPPT (and generally) solar controllers are rated for maximum output current. Remembering that Power=Voltage*Current, if you have 2x battery bank voltage (24 volts vs 12 volts), the "power" (wattage) would be double...

For example, (using their numbers), 400 Watts @ 30 amps:

• P=V*I
• V=P/I= 400 Watts / 30 amps = 13.33 Volts battery charging voltage (12 volt bus)
• V= 800 Watts / 30 Amps = 26.67 Volts battery charging voltage (24 volt bus)

This is all approximate, because battery charging voltage runs from ~10.5 volts to ~15 Volts... So actual charging power varies too.

Nominally, assuming this is a good quality & well designed MPPT solar charge controller, our calculation for the maximum "cost effective" array would be (if 24 volt battery bank):

• 30 Amps charging current * 29.0 volts charging * 1/0.77 solar panel+controller derating = 1,130 Watt (std or marketing numbers) array

Now, there is the working voltage for the array... If 75 Volt Vmp panels, then the Imp-array would be around:

• 800 Watts / 75 Volts Vmp = ~10.67 Amp Imp array (manual's specifications)
• 1,130 Watts / 75 volts Vmp = 15.07 Amp Imp array ("our" deratings")

MPPT charge controllers efficiently take high voltage & low current, and efficiently down convert to low voltage & high current needed to charge the battery bank.

Most MPPT charge controllers will accept an "over sized" array and will never output more than their rated output current (long term, there are possiblities of outputting more than rated current during short periods of time, such as when doing MPPT "sweeps").

The 0.77 derating factor is based on the fact that companies use room temperature for cell temperature when defining test conditions. However, while the test condition is ~25C, real panels run +20C or hotter (i.e., 45C) under full sun, hot ambient, low wind conditions). This causes the Vmp-array (in real life) to drop a lot. To as low as ~81% of the panels Vmp-std rating).

For most installations (unless sub zero conditions), they will rarely output more than ~77% of their rated power (another 5% loss for controller efficiency, dusty panels, etc.).

Note that if you are in sub zero (F) conditions, then panel Voc (voltage open circuit) does rise--Leading to an issue that needs to be checked--The Voc-cold for your local conditions (Caribbean island, vs Alaskan mountain range) could exceed the controller's Vpanel-max input rating (100 VDC?). Thin film panels have different temperature factors vs crystalline silicon panels. Details matter here.

I don't know anything about this brand, so following their specifications/limits is always a good place to start.

-Bill

For an MPPT type charge controller (which are more expensive than PWM type)--A 100 VDC max input (and Vmp~30-60+ volts for 12/24 volt battery banks) is about standard.

To a degree, it is a tradeoff between "expensive" MPPT charge controller and "cheap" GT/non-standard panels, vs a "cheap" PWM controller and more "expensive" Vmp=18 or Vmp=36 volt panels).

There is a problem in that some(?) PWM charge controllers are labeled MPPT "branded"--Obviously not good. And even some cheap MPPT controllers can have issues with not working correctly... So it is a bit of a gamble.

Generally, large systems (say >800 Watts) tend to favor MPPT controller + "GT" non-standard panels. And smaller system (less than ~400 Watts, tend to favor PWM controllers with Vmp~18 volt "battery voltage" friendly panels).

And why I suggest that folks 1) look at their loads closely--Solar power is not cheap, 2) do several paper system designs to get the basics, and 3) start to pick and price actual hardware and possibly go back to earlier steps if too expensive, does not work, etc.. And lastly 4) buy hardware.

-Bill

Since Vmp for your 140 Watt panels is ~62.3 volts... For a 12 or 24 volt battery bank, you need an MPPT controller to get even a fraction of the "true" panel(s') output power... PWM controllers are Array current in = Battery current charging:

Vmp~62.3 volts, 2.25 Amps, then for a 12 or 24 volt battery bank, the charging energy for 10 panels in parallel series (assuming a generic PWM controller would not burn out with the high Voc from your panels):

• 10 parallel panels * 2.25 Amps Imp = 22.5 Amps (PWM "perfect solar day/angle" harvest current)
• 22.5 amps * 14.75 volts charging (12 volt flooded cell Lead Acid Batteries) = 332 Watts "ideal day peak" (12 volt bank)
• 22.5 amps * 29.5 volts charging (24 volts) = 664 Watts "ideal peak" (24 volt bank)

With a MPPT charge controller, roughly, the harvest on an "ideal-nominal day/time" would be:

• 1,400 Watts Pmp * 0.77 typical panel derating = 1,078 Watts (panel derating and MPPT losses)
• 1,078 Watts / 14.75 volts charging = 73.1 amps charging (MPPT @ 12 volt bank)
• 1,078 Watts / 29.5 volts charging = 36.5 amps charging (MPPT @ 24 volt bank)

Thin film panels are a bit different vs Crystalline Silicon panels--But the above is "close enough for government work).

-Bill

Note, on my post #9... I made a typo, assuming your panels are all in parallel (not series).

Actual array configuration does depend on the MPPT solar charger you eventually purchase.

Your region (guessing on IP address) is not great for solar (Antwerp Belgium, fixed array, facing south):

http://www.solarelectricityhandbook.com/solar-irradiance.html

Antwerp
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 39° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
1.38	2.20	3.03	3.83	4.49	4.29
Jul	Aug	Sep	Oct	Nov	Dec
4.29	4.23	3.29	2.38	1.50	1.07

Realistically, "good sun" is 3 or more hours per day... That gives you decent harvest from February through September. An example of a 1,400 Watt solar array (correctly connected with an MPPT solar charge controller would be):

• 1,400 Watts * 0.52 off grid system with AC inverter typical efficiency * 3.0 hours of sun per day (long term average) = 2,184 WH per day

Depending on the cost of power--Say $0.30 per kWH (higher US rate):

• 2.184 kWH per day * $0.30 per kWH = $0.66 per day

That is assuming you use 100% of your harvested energy per (March) day--Which you generally do not... You have to decide the cost of the system (emergency backup power outside of winter, summer cabin, etc.) vs the value to you.

And yes, while government subsidies have really made solar panels cheap (mostly built overseas these days), Grid Tied solar, and green energy programs in general, have been on the back of subsidies paid by taxes and higher energy bills--With the subsidies pretty much going to the green energy companies that lobbied for the subsidies.

In the USA, off grid homes usually do not get any subsidies, or smaller ones such as "no state sales tax" on solar components (5%-9% typical US state sales tax, but it does vary from 0% to 10%+).

-Bill