600v max from array vs. 50v max battery bank

[neffy812]

My question is probably going to be confusing, but I'll try to word it the best I can. I'm taking a PV class right now, and my teacher was just discussing grid inter-tie systems and stand-alone systems. He explained that the panels should be connected in series, and there should be a maximum 600v coming from the array. I'm guessing that this is specifically for grid inter-tie systems, but he also explained that the battery bank in a stand-alone system should be limited to 50v. In a bi-modal system, if you have 600v coming from the array into the inverter, how do you limit the input into the charge controller to 50v? Should there be a rectifier installed to drop the voltage from 600 to 50 going into the charge controller?

[Sunking]

You are confusing two different systems of Grid Tied and Stand Alone battery system. There is a third called hybrid which I will cover in a minute.

A grid tied system voltage operates from 200 to 550 volts. There is no batteries. The 600 volt limit your instructor speaks of is a code limit, but you cannot really push that limit because of the Voc of panels in cold weather would push you over the 600 volt limit.

On Off-Grid battery systems your instructor is somewhat wrong as battery systems can operate as high as 60 volts nominal battery voltage so the battery voltage range is 12 to 60 volts and there are a few used for commercial that operate up to several hundred volt. Now with that said with residential battery systems it is quite normal to run panel voltage up to 150 Voc, and charge a 12 volt battery if you want. But typical you would run panel voltage at around 18 to 30 volts for a 12 volt system, 36 to 60 volts for a 24 volt battery, and 60 up to 130 volts for the remaining. What converts the voltage downward is the charge controller, in particular a MPPT type controller. The MPPT controller down converts voltage, and up converts current. So if you had a 1000 watt 12 volt system with panel voltage of 30 volts, at the input of the controller you would have 30 volts @ 33 amps, and 12 volts @ 80 amps on the output. I will not go into the PWM controller, I am tired.

OK I mentioned a Hybrid system which is both a grid tied and battery for emergency power. They are very expensive inverter systems. For those application there is now a 600 volt MPPT controller on the market now. That allows you to run high efficiency for grid tied systems, and at the same time down convert to battery voltages. However most all Hybrid systems operate at much lower panel voltage with a standard 150 volt MPPT controller.

[billvon]

My question is probably going to be confusing, but I'll try to word it the best I can. I'm taking a PV class right now, and my teacher was just discussing grid inter-tie systems and stand-alone systems. He explained that the panels should be connected in series, and there should be a maximum 600v coming from the array.

Yes, that's a typical system limit due to max (ground referenced) panel voltage and insulation ratings. Used mainly for grid tie systems. However the widespread adoption of high voltage MPPT controllers has led to people using higher voltages for off-grid systems as well.

I'm guessing that this is specifically for grid inter-tie systems, but he also explained that the battery bank in a stand-alone system should be limited to 50v. In a bi-modal system, if you have 600v coming from the array into the inverter, how do you limit the input into the charge controller to 50v?

You don't. The charge controller drops the 600V to 50V. (All MPPT controllers effectively drop voltage.) Right now there's only one charge controller out there that can run at 600V, and that's the XW-MPPT 80-600. 200 volts or so is more common; there are a handful of controllers that will drop 200V to 50V.

Should there be a rectifier installed to drop the voltage from 600 to 50 going into the charge controller?

Rectifiers typically only give you .5 volts or so, and they dissipate that as heat - so that's not a good way to go.

[Elkhornsun]

As mentioned a MPPT charge controller reduces the voltage output to the battery bank. Not mentioned is that the MPPT type of controller does not simply clip the voltage so 95% or more of the available output from the solar array is being provided to the battery bank subject to its rate of charge limitations. MPPT solar charge controllers are two or three stage so they can regulate the voltage level depending upon the type of battery and its level of charge to minimize charge times.