New user

Re: New user

Again, since you asked--My two cents worth:

getravi wrote: »

Reason for not going with 600volt MPPT controller:
1. Cost

Very reasonable decision point. 600 VDC controllers usually only make sense if the wire runs are very long from array to controller or you already have a 600 VDC array for your GT Inverter and want to "slap" a charge controller in with a transfer switch so you can choose to use GT Solar or backup battery bank in an emergency (utility down)--A 600 VDC controller + smaller battery bank for backup power is starting to sound interesting to me. Not cheap, but add a smaller 2kWatt Outback inverter + my little Honda eu2000i--Compelling (except for the costs).

2. wanted to avoid high voltage

600 VDC is not really high voltage (from an NEC point of view). All wiring we use for 120/240 VAC is rated for 600 VAC (fuses/breakers are another issue).

3. wanted redundancy

Understand your desire.... After designing various larger computer systems with redundancy for telephony and networking systems--I would choose to go with non-redundant and simply buy a spare to put on the shelf. Redundancy, "properly done" is expensive, can be an energy waster, and gets more and more complex as you design for fault isolation, self diagnosis, and more hardware to get around issues caused by the redundant design.

4. The cost of a single morningstar 600volt mppt controller that outputs 48v is about $1200. Although, the string's Voc is 600 vDC, the max input PV power is still 3200 watts. I would still need 3 of these controllers for my 10KW array. Below are the reasons I went with my decision:
a) three 600 volt controllers is $3600 versus cost of same three conrollers but in 150 Voc @ $400/piece = $1200. Even including additional wiring , its much much cheaper!
b) parallel wiring allows me easier trouble shooting and or eliminating in groups of 3 panels at a time.
c) if I used the 600 volt system, I would have 1 string of 12 panels. A break in the line or panel affects all of them.

We always suggest doing several paper designs first, then making a choice. I have no issues with your choices (as discussed in this post). Cost is always a major issue--And when you need to parallel charge controllers because your charging requirements exceed the output of any single controller--It is simply a requirement to parallel.

so, where is the reliability issue?

Parallel solar panels are "different" because they are current sources. They are a "natural" to parallel load sharing.

Batteries (voltage sources) have problems because they do not share current "very well".

As far as the batteries, all batteries are protected by breakers as are all equipment loads.

Sounds good... As a check, look at each hot wire (usually +) that leaves the battery bank and goes to a load/source. Pretend (in your mind) that you short to the -/return load. How much current from all power sources (battery, battery chargers, etc.) can feed current down that wire to the short (note, you have have 50 amps from one side of the wire and 10 amps from the other--Evaluate each "side" of the short circuit--I.e., 50 amps from left and 10 amps from right--You don't need to sum the current to 60 amps total and review wire gauge).

With multiple power systems (battery strings, multiple chargers, etc.)--You can sometimes get surprised how it all can add up and exceed the wire rating.

As far as the system not having run at full load, that is absolutely not true. The system was designed to be run with atmost 1 string of batteries with 100% load and full PV production. It has been tested and confirmed with ammeters.

You don't have your system in your Signature Line--What is a string of batteries (AH and voltage of string and/or bank). What type of battery (flooded cell, AGM, etc.)? And what do you consider "full power" (charging and discharging)?

It sounds like (as I recall) you really only pull "full power" in the middle of the day--So your available current for loads is Bank+Solar Charge controllers. And if that works well for you--That is great. You could have some "micro cycling" issues with the battery bank (single phase AC inverters do not draw "DC" flat rate current... They actually draw a Sine Squared 120 HZ (if 60 Hz inverter, or 100 Hz if 50 Hz inverter) current wave form. Basically, for a part of the cycle, the inverter draws near zero current and part of the cycle the inverter draws sqrt(2)*RMS-Wattage. So, the battery bank needs to behave both as a battery and like a "capacitor" during this current profile. You don't really want the battery to drop below ~12.7 volts (12 volt bank) to ensure that you are not "charging/discharging" the battery 100-120 per second. And obviously, the battery has to be able to accept all the charging current from the array when the inverter is at the zero current part of the cycle.

I don't mind the criticism, but it most of us here at my work are wondering how others are doing their calculations.

For most people--They want power on demand. So the power system (batteries+inverter+charger+panels) needs to not only charge when the sun is up, but supply "needed power" when the sun is down and when the storm clouds roll in.

That is the most conservative way to design the system... But it may not be the most cost effective for you.

-Bill