Solar System Performance

Re: Solar System Performance

Can you tell us more about the solar panels? Vmp and Imp ratings?

Also, you say you have the panels in series--More than likely, you intended to type that you have the panels in parallel (adding current, not adding voltage).

Next, assuming the Vmp is ~30 volts (pretty common), and you have the panels in parallel (Imp should be around 7.33 amps), the problem is the C60 charge controller and the Vmp=30 volt panels on a 24 volt battery bank.

The Vmp voltage of a solar panel is a "marketing" specification. A panel under full sun in a hot climate can have Vmp at operating temperature in the range of 24 VDC--Which is not high enough voltage to charge a 24 volt battery bank. For a C60 charge controller (PWM type), you ideally would have a Vmp-array-stc in the 35-40 volt range--Which you cannot do with these panels.

So, you have two options, one is to get another PWM charge controller rated for higher voltages (like a C40) and put two panels in series and 5 strings in parallel from Vmp-array-stc ~60 volts which would give you an Imp-array rating of ~36.7 amps. It will work, but your array will only operate at ~58% efficiency compared to a "properly" configured system. The C60 would not work here because the array voltage is too high.

Your other choice is to get an MPPT (maximum power point tracking) charge controller and configure the array to 2 panels in series, then 5 strings in parallel. The correct MPPT charge controller will take the high voltage/low current of the array and efficiently "down convert" to lower voltage/higher current need by the battery bank. This is the "correct" design for you situation (and the array will operate at 100% of its capability). You will have to decide if the extra money for the "proper" MPPT charge controller is worth it for your installation (and your available cash).

This is a very common mistake in the "solar industry". People call these "24 volt" panels--And they technically are--However, a "24 volt" panel for charging a 24 volt battery bank as a Vmp-stc (standard test conditions) rated for ~35-40 volts when all the "deratings" are taken into account. These panels were designed for use with Grid Tied solar power systems. The panels work fine for their intended application because GT systems can take a wide range of input voltage (Vmp-array) is typically in the 200-400 volt range--So they put a whole bunch of panels in series to make everything work.

PWM (Pulse Width Moduation) charge controllers are an "older" and "less expensive" type of charge controller that need the "exact" solar panel input voltage to work properly and efficiently when connected to the appropriate voltage battery bank. Too low of Vmp-array, and the batteries will simply not get very much charging current (your present problem). And too high of Vmp-array can damage some "24 volt" charge controller and/or is simply not very efficient.

An MPPT (Maximum Power Point Tracking) charge controller has a "buck mode switching power supply" internally which sort of behaves like an AC Variable Transformer and can efficiently change the high voltage of the array to low voltage of the battery bank--at ~95% conversion efficiency (power is conserved during the conversion). However, these type of charge controllers are much more expensive (around 3-5x more costly) than a "cheap" PWM charge controller. There are cheaper Asian MPPT charge controllers out there--But it is sort of hit or miss if those type of controller work well or not (and many are cheap PWM type charge controllers simply labeled "MPPT").

Another "nice thing" with MPPT charge controllers is you can have high Vmp-array voltages (3 panels in series for your panels) and use much smaller diameter copper wire from the array to the charge controller (save can mount solar array much farther away from the battery bank). For any charge controller, you need to keep the charge controller close to the battery bank with short+heavy cables (for a 24 volt battery bank, you only want ~0.1 to 0.2 volt drop on the battery cables for best controller operation).

Here are some MPPT type charge controllers that will work for your needs--However, you may find some European or Asian models easier to buy locally. Ideally, you need a 60 amp @ 24 volt minimum charge controller for your 2,200 watt array:

Midnite Classic (you need the standard 150 VDC model)
MorningStar (some new high Vmp-array voltage units, put 5 panels in series, two parallel strings)
Outback
Schneider/Xantrex standard array voltage
Schneider/Xantrex high array voltage

Feel free to ask more questions--Solar and MPPT charge controllers are a complex subject--And doing it 1/2 a world away in English (for you if not your native language or an engineer/electrician) is not easy either.

-Bill